in 1983 , odend ' hal   published a short book listing the worldwide distribution of animal viruses . it reported the classification as well as host , historical movements , and diagnostic techniques available . of the 110 viruses cited , 35 were arboviruses , those viruses that are transmitted primarily by an arthropod vector . this first attempt at mapping animal viruses provides a useful baseline for reviewing the current state of arboviruses of livestock . arboviruses are mainly classified to the virus families bunyaviridae , togaviridae , reoviridae , and flaviviridae . the majority of these virus families have a ribonucleic acid genome , with the clear exception of the asfarviridae to which african swine fever virus belongs ( table 1 ) . in table 2 an updated list of arthropod - borne virus pathogens of humans , livestock , and wildlife is provided . during recent years several pathogenic arboviruses the most well - known cases have been the movement of west nile virus from the old world to the new world   and the introduction of bluetongue virus into northern europe . this has prompted a wide range of authors to review the potential viruses that could emerge in the uk and europe and assess the risk of such emergence events in the future [ 59 ] . the cooler climate experienced in northern latitudes ( above 50 ) means that there are fewer species and less diversity among particular arthropod species and the viruses they harbour than found in subtropical and tropical regions . currently , there are few arthropod - borne diseases of livestock in europe and as a result , livestock in the uk and many areas of northern europe may be highly susceptible to many arthropod - borne viruses listed in table 2 an exception to this is the presence of louping ill virus , which is considered to be the only arbovirus of veterinary importance that is endemic within the uk . the virus has been present for hundreds of years and is restricted to moorland locations , particularly in devon , cumbria , wales , and scotland . this tick - borne virus causes fatal encephalitic disease in sheep , although it has been reported in a range of other species . a number of reports have suggested that west nile virus and two other mosquito - borne viruses had been introduced into the uk , although cases of disease in horses have not been reported . this is in clear contrast to the situation in italy where wnv has repeatedly emerged to cause neurologic disease in horses from the tuscany region . recurring outbreaks of disease have occurred in both livestock and humans suggesting the permanent establishment of this virus in the mosquito population . this has made assessment of future climate change trends essential to understanding the impact on both the ecology of the uk and risk of vector - borne disease introduction and establishment . such changes might enhance the establishment of invasive arthropod species such as the asian tiger mosquito ( aedes albopictus ) that in turn could directly import an exotic virus . it could also boost the population of indigenous vectors that could in turn increase the numbers of biting events , enhancing the likelihood of virus transmission . furthermore , increases in temperatures can shorten the extrinsic incubation period , the time between the vector taking a blood meal and becoming infectious to a new host , thus enhancing virus persistence in a new area . a wide range of routes would enable arthropod - borne viruses to translocate into a disease - free area . these can be divided into those that are part of the normal ecology and are influenced by the environment and climate that are presumably occurring all the time . avian species are known to harbour many pathogens   and certain viruses such as avian influenza and newcastle disease virus are transmitted around the globe through bird migration . for arthropod - borne viruses , virus movement can occur via transportation of the vector   or through infection of the host , particularly a viraemic animal that is subsequently fed on by an arthropod in a disease - free destination . the range of crimean - congo haemorrhagic fever appears to be increasing slowly in south - east europe associated with spread by its tick vector ( hyalomma spp . ) . bluetongue virus transmission into the uk is believed to have resulted from direct introduction of its midge vector ( culicoides spp . ) assisted by wind movements in 2007 . it is likely that movements by these routes , if they happen , are occurring continuously and can not realistically be controlled . the alternative to natural introduction is often mediated by the actions of man . again , this could occur through passive introduction of the vector through the movement of humans , livestock , or trade goods between endemic and disease - free areas or by the movement of infected livestock between countries . theoretically , these mechanisms of entry can be regulated and effort should be directed to prevention programs . a key aspect in preparing for the emergence of arthropod - borne diseases is the establishment of tests capable of detecting them . these include key features such as sensitivity of the assay and its specificity for the target virus . the assay must also be validated to provide assurance of its reliability , or at least give an indication of what might be missed . the assay under development needs to compete with existing technologies in terms of cost and speed to deliver desirable benefits to encourage adoption . some tests may be applied to surveillance for virus , in which case the test needs to be amenable to cost - effective delivery of high volumes of samples . this in turn can complement serosurveys for particular viruses or be applied to sampling arthropod vectors in order to provide early warning of potential disease incursion . for some technologies , the cost of individual tests is prohibitive for application to large numbers of samples or in resource - poor areas such as africa . in each of these areas , molecular detection techniques have been very competitive as evidenced by the numerous tests developed in recent decades . many of the assays reported in this paper provide a result considerably faster than more traditional detection methods such as virus isolation and plaque - reduction neutralization tests . genetic variability of viruses is an inherent weakness in the use of molecular detection techniques with primer - mismatch being a constant problem . this has to some extent been overcome by the wealth of sequence data now available on many of the viruses that affect livestock . here we provide an overview of those arthropod - borne viruses that cause clinical disease in livestock and lead to economic losses . it will not consider important arboviruses that cause significant human disease with no livestock involvement such as yellow fever , dengue , toscana virus , and chikungunya virus . background information on the disease caused by particular viruses is described , the main arthropod vector and the reported current geographical distribution is provided for the viruses selected . this is followed by a brief review of reported rapid molecular tests that detect specific viruses or those tests that detect virus groups that contain numbers of animal pathogens . bluetongue ( bt ) is a disease of ruminants with sheep being the most susceptible and affected species and cattle being affected to a lesser extent . asymptomatic infections have been recorded in various other species such as deer , alpaca , llamas , and goats [ 1719 ] . since the emergence of btv serotype 8 in northern the incubation period from exposure to disease is between two and fifteen days , averaging around 6 days . in sheep , disease is first characterised by a fever and salivation , which develops into a more severe form causing mucopurulent discharge from the nasal passages and oedema of face and lips . the tongue may become cyanotic hence the name bluetongue and haemorrhages can form on the coronary band . in affected cattle , crusts and erosions are visible on the nasal and oral mucosa , in or around the nostrils and lips . other signs include salivation , fever , conjunctivitis , muscle necrosis , and stiffness in limbs . btv is endemic throughout the world with the total of 24 serotypes circulating across the globe . in 2007 , a new orbivirus , toggenburg virus , was isolated from goats in switzerland and is now characterised as a tentative 25th serotype of bluetongue virus . bluetongue virus was first reported in africa when the disease was described in european merino sheep that had been introduced into the cape colony . historically , the disease has predominantly been found between latitudes 40n and 35s until 1998 when the virus entered europe and caused repeated outbreaks involving mainly five serotypes ( btv-1 , btv-2 , btv-4 , btv-9 , and btv-16 ) around the mediterranean basin affecting 12 european countries , three north african countries , and israel . in 2006 , btv-8 emerged in northern europe with outbreaks in most western european countries and as far north as denmark and southern sweden . btv-8 emerged in south - east england in 2007 and spread to locations throughout the uk . however , the uk government introduced a voluntary vaccination programme in 2008 , which controlled the disease and no further outbreaks have been reported within the uk . in 2008 , small localised outbreaks of btv serotype-6 were reported in cattle herds in the netherlands and germany . this was the second serotype to bypass southern europe and emerge directly to northern europe . the only known biological vectors of bluetongue virus are the biting midges of the culicoides genus . the most widespread vector is afro - asiatic c. imicola , which is distributed in asia , the middle east , most of africa , and in southern and eastern europe . the absence and scarce distribution of c. imicola during the bluetongue outbreaks in italy in 2000 onwards led to a search for novel vectors for virus transmission . light - trapping and rt - pcr experiments identified the c. pulicaris and c. obsoletus complex ( c. obsoletus ss . , c. chiopterus , c. dewulfi , c. scoticus ) as potential vectors . later , field studies during the 2006 outbreak in northern europe also found no c. imicola in traps , but identified c. dewulfi , c. obsoletus , and c. scoticus as possible vectors . in addition , these species have a palearctic distribution and they are known to be widespread throughout europe . the high parity rates of c. dewulfi and c. obsoletus complex observed in netherlands further supports the possibility of these species playing a role in bluetongue transmission . these observations suggest that more than one species of midge are responsible for bluetongue virus distribution . since the early 1990 's , a range of rt - pcr assays targeting different btv genome segments have been developed with a common drawback that they were only able to detect a limited number of serotypes [ 3237 ] . furthermore , most of these methods required the use of agarose gel electrophoresis for nucleic acid detection , which made them laborious and unpractical for diagnostic purposes . however , the spread of btv in northern europe has seen the reporting of a number of conventional   and real - time rt - pcr assays detecting all 24 serotypes simultaneously [ 3941 ] . these assays have been designed for diagnostic requirements ; they are all rapid , reliable , and sensitive , enabling high throughput testing , which can be applied directly to clinical samples . the genome of bluetongue virus consists of ten double - stranded rna segments coding for seven structural and three nonstructural ( ns ) proteins . several of these genome segments are highly conserved within serotypes , which make them potential targets for molecular detection . all recently published real - time rt - pcr and traditional rt - pcr assays use different btv genome segments as a target . orr and coworkers   designed an assay targeting genome segment 10 ( encodes ns3 ) using a stem - loop molecular beacon ( mb ) fluorescent probe . the probe can be used for both real - time rt - pcr detection and quantification purposes . two groups have published duplex assays using two primer sets , where one assay targets btv genome segment 7 ( encoding the main btv - specific antigen , vp7 ) and the other targets the segment 1 ( encoding the viral polymerase , vp1 ) . using genome segment 1 as a target not only allows detection of all 24 serotypes , but will also detect geographic variants within individual serotypes by differentiating the samples to eastern ( middle - east , asia , australasia ) and western ( africa , the americas ) genotypes . considering the high genetic variability through reassortment and mutations of rna viruses , it is possible that current real - time rt - pcr assays might fail to detect some strains of btv in the future . to address the problem of the genetic variability of btv , the most recent real - time rt - pcr assay is based on the primer - probe energy transfer ( priproet ) which is characterised by its tolerance towards mutations in probe region . african horse sickness virus ( ahsv ) is the causative agent of african horse sickness , a disease of equidae with a high level of mortality . horses are the most affected species whereas mules and donkeys show mild clinical signs or no signs at all , and zebras are considered a natural host and reservoir for ahsv . based on clinical and pathological findings , african horse sickness can manifest in four forms ranging from mild symptoms with no mortality to a severe disease with 95% mortality rate . the mildest form , horse sickness fever , is characterised by mild to moderate fever lasting up to 5 days and affecting most commonly the african donkey . a cardiac ( subacute ) form is recognised by long - lasting fever , oedema of the head , neck , chest , or supraorbital fossae and petechial haemorrhages in the eyes and tongue with mortality rates around 50% . the most severe manifestation with highest mortality rates is a pulmonary ( peracute ) form , which is characterised by a rapid onset of disease . death can occur without previous indication of illness or an animal can show signs of fever , depression and respiratory distress . the most commonly seen clinical presentation is a mixed ( cardiac - pulmonary ) form which can reach mortality rates as high as 70% 36 days after onset of fever . the virus is currently endemic in subtropical and tropical areas of africa below the saharan desert , which seems to provide a natural barrier against spread northwards . nine serotypes have been recognised which all have been reported in southern and eastern africa . serotypes 4 and 9 are found in western africa and are the only serotypes that have caused outbreaks outside of africa . the major outbreaks outside africa have so far occurred in the middle east , spain , and portugal . the first outbreak in 1966 started from gibraltar and was caused by serotype 9 , which resulted in 637 animals dying or being slaughtered . in 1987 , a number of subclinically infected zebras were imported into a safari park near madrid , which caused four further outbreaks between 1987 and 1990 . however , these outbreaks were due to serotype 4 of ahsv . this was the first time that a serotype other than 9 had been recorded north of the sahara desert . before the eradication of the virus in spain at the end of 1991 , the outbreaks resulted in over 1300 horses dying or being destroyed and the virus spreading into portugal , tunisia , and morocco . like bluetongue virus , african horse sickness virus is spread by biting midges of the culicoides genus . the major vector for transmission is c. imicola , but also c. bolitinis has been shown to play a role in virus spread . in 1998 , over 100 horses died in an isolated population in clarens valley in south africa and ahsv was isolated from the most locally abundant midge species , c. bolitinis , collected during light trap studies . it has been suggested that other culicoides species might be involved , especially where low - grade cycling of virus is occurring . the first rt - pcr assays for ahsv detection and serogroup identification were time consuming and labour intensive procedures which involved either restriction fragment length polymorphism ( rflp ) or dot - blot hybridisation assays [ 4749 ] . these were followed by several conventional rt - pcr assays , which still required gel - based visualisation and took between four and six hours to complete [ 5052 ] . however , a huge improvement in molecular diagnosis has occurred during recent years , resulting in numerous real - time rt - pcr assays that are able to detect , quantify , and discriminate the serotypes of ahsv in a short period of time [ 5357 ] . currently ahsv is only endemic in africa , where laboratory conditions vary and real - time rt - pcr equipment can be too costly . therefore , some studies have aimed to develop both real - time rt - pcr and conventional rt - pcr in parallel or solely improve conventional rt - pcr to provide better and faster diagnostic tools that are available in all circumstances . these studies have shown high sensitivity and specificity of both conventional and real - time rt - pcr assays for all nine serotypes . detection limit for both conventional and taqman real - time rt - pcr has been reported to be 1.2  tcid50/ml . more importantly new , improved rt - pcr assays can provide results within three hours of sample receipt . epizootic haemorrhagic fever virus ( ehdv ) causes a haemorrhagic disease in ruminants , especially in white - tailed deer in america and in cattle elsewhere . the clinical signs are often similar to those caused by bluetongue virus which complicates diagnosis . the clinical signs reported in cattle include reduction in milk production , fever , loss of appetite , weakness , excessive nasal and ocular discharge , oral ulcerations , discolouration of the udder , and oedema of hooves . ehdv-1 was first isolated in white - tailed deer in new jersey in 1955 and it is still the most important infectious disease in deer in north america . all serotypes have caused clinical disease in cattle across the globe including north america , africa ( north and south ) , australia , the island of runion , and japan . recent outbreaks have been reported around the mediterranean including morocco , algeria , israel in 2006 , and turkey in 2007 . the earliest ehdv rt - pcr assays have been based on american isolates , mainly on serotypes 1 and 2 targeting different genomic segments [ 6365 ] . since the spread of ehdv into new territories , the rt - pcr assays reported have been type - specific rather than serotype specific or even multiplex rt - pcr assays that can simultaneously detect both bluetongue and ehdv [ 66 , 67 ] . a real - time rt - pcr has been reported that detects eight serotypes of ehdv . bovine ephemeral fever virus ( befv ) causes disease in domestic cattle and water buffalo . the disease is also known by the names 3-day sickness , stiff sickness , bovine epizootic fever , lazy man 's disease , or dengue of cattle . the clinical outcome can vary from inapparent infection to death , but generally disease has four main phases . after an incubation period of between one and ten days , disease begins with a sudden fever that can be bi- ,  tri- , or polyphasic with peaks 12 to 18 hours apart . fever lasts around half a day before the infected animal may become depressed and reluctant to move . mucous discharge from the nose and profuse salivation can be observed and milk production is reduced or ceased altogether . this period of disability usually lasts between one and two days after which most animals start to recover . although mortality rates as high as 30% have been observed , in most uncomplicated cases it is less than 2% . sequelae include reduced milk production and other complications include pneumonia , mastitis , abortion in late pregnancy and temporary infertility of bulls . the bovine ephemeral fever was first recognised in zimbabwe in 1906 . the current distribution of befv includes all of africa , the middle east , asia , and australasia . the outbreaks in the middle east have occurred in saudi arabia and israel [ 72 , 73 ] . no arthropod vector has been shown to transmit the virus , but it has been isolated from culicoides midges in kenya and mosquitoes ( culicine mosquito species and anopheles bancroftii ) in australia [ 74 , 75 ] . currently , virus isolation seems to be the standard method for bovine ephemeral fever diagnosis and only two molecular diagnostic assays detecting befv have been reported . real - time rt - pcr has been developed by stram and coworkers , whereas zheng and coworkers   reported the development of reverse transcription loop - mediated isothermal amplification ( rt - lamp ) method . both assays target the g gene and are highly sensitive assays , real - time rt - pcr being able to detect 10 befv genome copies in a sample . the advantage of rt - lamp is that no specialist equipment is required as there is no requirement for thermal cycling . however , a range of specialist apparatus is now available specifically for application with rt - lamp such as lateral flow devices and turbidometers . the disease is generally asymptomatic with a transient viraemia occurring between one and six days after infection , which lasts for about six days . occasional cases of encephalomyelitis have been observed in some infected animals . the main economic impact of akabane virus results from abortions , stillbirths , and congenital abnormalities that affect pregnant animals . abnormalities vary depending on the trimester when infection occurs , although most are severely affected and euthanized shortly after birth . serological evidence indicates that the virus is present throughout africa , asia , and the northern half of australia . disease has been observed in south africa , cyprus , the middle east , and japan . ( c. brevitarsis and c. wadei ) , africa ( c. milnei and c. imicola ) , japan ( c. oxystoma ) , and a number of mosquito species including aedes vexans , culex tritaeniorhynchus and anopheles funestus . the genome of akabane virus , like other orthobunyaviruses , is segmented , consisting of a small ( s ) , medium ( m ) , and large ( l ) segments . standard rt - pcr assays have been described for detection of akabane virus that target the s segment of the virus [ 78 , 80 ] . a further development has been to incorporate detection of akabane virus with that of aino virus , a causative agent of congenital defects in cattle . this combined assay takes the format of a real - time multiplex rt - pcr that also targets the s segment . equine encephalosis virus ( eev ) causes an acute disease in horses with a high fever and depressed appetite . clinical features such as oedema are similar to those observed for ahsv and this should be considered in the diagnosis . the virus was originally isolated in south africa and seven serotypes have been reported within the country . a recent report has suggested the emergence of eev in israel . vesicular stomatitis virus ( vsv ) causes disease in cattle , horses , and pigs and is significant as it is clinically similar to foot and mouth disease ( fmd ) . the initial incubation period is between two and eight days with a fever that often goes undetected . blister - like lesions form in the mouth , on the dental pad , the tongue , the lips , the nostrils , the hooves , and the teats . oral lesions can be sufficiently painful to cause the infected animal to refuse food and weight loss can occur . infection is not fatal , although recovery from acute disease can take two weeks and ulceration can take months to heal . a range of haematophagus insects have been associated with transmission of vsv including sand flies ( diptera : psychodidae ) , black flies ( diptera : simulidae ) , mosquitoes ( diptera : culicidae ) , and culicoides midges ( diptera : ceratopogonidae ) . experimentally , only the sand fly ( lutzomyia shannoni ) and the black fly ( simulium vittatum ) have been shown to transmit the virus transovarially or to susceptible hosts . serological evidence suggests that wild mammals can be infected with vsv but as yet there is no clear wildlife reservoir for the disease . multiplex , real - time rt - pcrs have been devised to detect and differentiate different serotypes of vsv   and differentiate vsv from fmdv within the same assay . veev in particular has caused extensive epizootics in some regions of south america ( venezuala and colombia ) . eeev has been reported from the eastern usa , caribbean , south , and central america . weevin north america culex tarsalis is considered the main vector of transmission between avian species . have also been implicated in transmission to mammals . in south america aedes albifasciatus has been reported as a vector . primer sets that detect a range of alphaviruses , including eeev and veev have been described , however , this was linked to final detection using electrospray ionization mass spectrometry . japanese encephalitis virus ( jev ) is asymptomatic in adult pigs but causes abortion , still - birth , and birth defects including central nervous system defects resulting in economic loss . the main vector of jev is culex tritaeniorrhyncus , which favours breeding in rice paddies . c. gelidus complex mosquitoes enable transmission to birds which assists in maintaining the virus in the environment . a real - time rt - pcr   that targets the 3 untranslated regions has been reported with detection to 112  tcid50/ml . a multiplex real - time rt - pcr for detection of jev , yellow fever virus , west nile virus , dengue virus ( serotypes 14 ) , and st . louis encephalitis virus has been reported   with a sensitivity of 2  pfu / ml . real - time rt - lamp [ 98 , 99 ] assays have been developed for detection of jev with detection levels as low as 0.1  pfu . the incubation period ranges from one to three days followed by fever , recumbency , and haemorrhagic diarrhoea . high rates of abortion are also associated with epidemics of rift valley haemorrhagic fever ( rvhf ) , often described as abortion storms . the virus causes disease in humans ranging from uncomplicated influenza - like illness to haemorrhagic fever with liver damage and occasionally encephalitis . the virus is considered endemic throughout much of africa , although clinical disease occurs infrequently . however , sudden outbreaks with high livestock mortality occur in many regions often following flooding . the disease was first reported in east africa ( kenya and tanzania ) but is believed to have expanded its range north , west , and south , characterised by sudden epidemics . there has been a well - documented outbreak of rvhf in the arabian peninsula associated with livestock movements from east africa . are the principal virus vector for livestock and are believed to maintain the virus between epidemics although other species are capable of acting as bridge vectors enabling transmission during epidemics , such as culex spp . numerous real - time rt - pcr methods have been developed for rapid detection of rvfv [ 103106 ] . an alternative approach is the use of reverse transcription loop - mediated isothermal amplification ( rt - lamp ) technique [ 107 , 108 ] . the detection limits of rt - lamp assays are comparable to real - time rt - pcr . wesselsbron virus ( wslv ) causes infection in sheep and goats and is associated with abortion and congenital abnormalities [ 109111 ] . in adult animals , infection is usually subclinical , although in newborn animals clinical disease can result after a one to three day incubation period with fever and anorexia . infection in humans has been reported following laboratory exposure and causes a mild influenza - like illness . virus isolation and seroprevalence studies suggest that the virus is present across africa [ 112 , 113 ] . are considered the main vector for wesselsbron virus . in a recent study over 50 isolates of wslv no specific rt - pcr tests have been reported , although the wesselsbron virus genome has been published ( ncbi reference sequence : nc_012735 ) . wesselsbron virus can be detected by rt - pcr using universal flavivirus primers and sequencing . west nile virus ( wnv ) causes encephalitic disease in horses , humans and some avian species . in horses mortality rates vary and may be particularly high in the usa reaching over 55% . until recently , wnv was an old world disease present throughout africa and asia with occasional incursions into europe around the mediterranean basin . however , in 1999 , the virus emerged in the north east usa and spread throughout the americas   and has remained endemic since that time . however , a wide range of mosquito species have been shown to support virus replication and transmit virus to mammalian species . such assays usually detect between 40 and 100 genome copies , although some suggest that sensitivity can be even lower . further developments have enabled multiplexing with other arboviral diseases [ 122 , 123 ] and improved assay sensitivity   suggesting that the detection limit is 0.07 genome copies / ml . rt - lamp assays have been developed for wnv   and used to detect the virus in mosquito samples . the sensitivity limit of these assays has been reported to be approximately 0.1  pfu . african swine fever virus infects warthogs and bush pigs in africa with no clinical disease , but domestic pigs can succumb to severe infection with an incubation period of five to fifteen days . the disease can manifest in any one of four forms depending on the virulence of a strain . highly virulent strains cause peracute and acute infections with clinical signs of high fever , anorexia , diarrhoea , recumbency , and general reddening of skin or discoloration on the ventral chest and abdomen , tips of the ears or tail , and on distal limbs . the subacute form manifests as a mild illness with an intermittent fever lasting approximately one month although pregnant animals might abort . in chronic cases , low fever , pneumonia and swelling of joints morbidity rates can reach close to 100% in herds that are nave for asfv whereas mortality rates vary , but can be as high as 100% , depending on virulence of the strain . those animals that have survived acute or chronic disease can become persistently infected and act as carriers for the virus . african swine fever has been reported in africa since the 1890 's and is endemic in most parts of sub - saharan africa where transmission appears in three different forms ; a sylvatic cycle , a domestic pig cycle and a pig - tick cycle [ 128 , 129 ] . in 1958 , asfv emerged for the first time in europe in portugal before spreading to spain in 1960 , where it caused several outbreaks until the disease was finally eradicated . in 1967 , virus was detected in italy and in 1978 asf outbreaks occurred simultaneously in malta and sardinia . whereas disease was eradicated from malta and mainland italy , asf remains endemic in sardinia where it is established in free - range pigs and wild boars . in 1998 , madagascar reported the first case of african swine fever , and from the year 2000 onwards virus has continued to spread into new territories including georgia , iran , and mauritius [ 132134 ] . the georgian outbreak in 2007 demonstrated perfectly the emerging and transboundary characteristics of asfv , as within a year virus spread from georgia to several neighboring countries including armenia , azerbaijan , and the russian republic of chechnya . in the following year , virus spread to northwestern iran where it caused an outbreak in wild boar . other short - lived , sporadic outbreaks have been reported from france , belgium , netherlands , caribbean , and south america . the subclinical infection of asfv in warthogs and bush pigs is maintained by soft ticks of the genus ornithodoros . in africa , the main vector is o. moubata , whereas in southern europe asfv is transmitted by o. erraticus . o. moubata is most abundant in eastern and southern africa particularly in cameroon , central african republic , and sudan . although , ticks do play a part in virus transmission , the epidemiological role is thought to be low , especially in those areas where tick populations are small . the more likely route of virus spread is through direct oronasal contact with an infected animal or indirectly via fomites and contaminated pig feed . the most recent outbreaks in previously asfv - free areas could have been transmitted through feed products containing infected pig meat . as there is no cure or vaccine for asfv , slaughter is the only tool for control and eradication of this highly contagious virus in infected areas . therefore , fast and reliable laboratory diagnosis is required to limit the socio - economic burden of outbreaks . furthermore , highly specific , differential diagnosis of disease is necessary , as clinical signs of african swine fever may resemble those of other infections , especially classical swine fever . the current oie manual recommends taqman real - time pcr such as the assay developed by king and coworkers . as real - time pcrs are high throughput , sensitive , specific , and quick to run , recent development of these assays has focused on improvement of existing real - time assays by applying varying pcr chemistries . this has led to several modifications of real - time pcr including use of minor groove binding probes or molecular beacon assays [ 137 , 138 ] . two assays , a lamp method and a linear - after - the - exponential pcr ( late - pcr ) , have both been adapted for use in field conditions [ 139 , 140 ] . these methods could considerably shorten the time between infection and diagnosis as there is no requirement for samples to be transported to the laboratory . crimean - congo haemorrhagic fever ( cchf ) is one the most important and widespread diseases caused by tick - borne viruses . the causative agent , crimean - congo haemorrhagic fever virus does not cause disease in livestock , but vertebrates play a role in virus transmission as part of a tick - vertebrate - tick enzootic cycle . although there is no evidence of clinical disease in animals , contact with viremic animals , tick bite , or crushing ticks taken from infected animals can lead to human infection . in humans , cchf virus causes a disease with four phases : incubation , prehaemorrhagic , haemorrhagic , and convalescence phases . following the short incubation period ( 37 days ) , sudden onset of fever , headaches , myalgia , and dizziness occur [ 142 , 143 ] . a few days later , a rapidly developing haemorrhagic period occurs , with haematomas appearing on the skin and mucous membranes with mortality rates ranging from 3% to 30% . the surviving patients will go through the convalescence period lasting 9 - 10 days which can include variable symptoms such as tachycardia , temporary hair loss , poor vision , and loss of appetite . infected humans can spread cchf via close contacts resulting in community and nosocomial outbreaks [ 144148 ] . furthermore , individuals in certain occupations such as health carers , veterinarians , farmers , and abattoir workers are at increased risk of contracting crimean - congo haemorrhagic fever [ 141 , 143 , 149 ] . the geographic distribution of cchf virus is the widest amongst all tick - borne diseases . currently cchfv is endemic in africa , asia , balkan countries , and middle and far east [ 142 , 145 , 150 ] . during the last ten years , cchfv has been rapidly introduced into new , previously nonendemic areas ; especially into eastern and southeastern europe including greece and turkey [ 149 , 151153 ] . the geographical distribution of these ticks closely match the distribution of cchfv and covers southern europe , southern russia extending to southern asia , and most of africa . the host range of these ticks varies from domestic animals ( cattle , horse , sheep , and goats ) for adults to small wild animals and birds for larvae and nymphs . since the mid 1990 's several nested and real - time rt - pcr assays , which all target genomic s segment of the tripartite genome . these assays have been developed to achieve fast initial and differential laboratory diagnosis of cchfv [ 104 , 155158 ] . both the nested and real - time rt - pcr assays are comparable in terms of sensitivity , but the results can be achieved in two hours with one - step real - time rt - pcr , whereas it takes 4 - 5 hours to run nested rt - pcr without gel electrophoresis . due to the high genetic variability of cchfv isolates , the first real - time rt - pcr assay detecting cchfv was based on a sybr green method that intercalates to any double stranded dna and requires identification of the positive product using gel electrophoresis . more specific assays can be developed by designing primers and probes directed at strains of interest , for example , those circulating in geographically defined areas . strains from the balkan region have been successfully identified by using a one - step real - time rt - pcr that is based on the fluorescence resonance energy transfer ( fret ) probe technology employing the endonuclease ( 5  3 ) activity of taq polymerase enzyme . nairobi sheep disease virus ( nsdv ) causes acute haemorrhagic gastroenteritis in sheep and goats . this is a severe and fatal disease with mortality rates reaching over 90 percent in non - immune animals . the short incubation period ( 24 days ) watery to mucoid and bloody diarrhoea is seen 24 days after the onset of fever which itself can last up to 8 days . as the disease progresses nasal discharge and conjunctivitis , death often occurs in the early stages of a disease . a variant of nsdv this virus is highly pathogenic in exotic and crossbred sheep and goats causing a disease with high fever , dullness , depression , and loss of appetite . nairobi sheep disease has been reported since 1910 when it was first identified near nairobi in kenya . nsdv is now mostly enzootic in kenya with the majority of indigenous sheep and goats having protective antibodies , and outbreaks tend to occur when flocks from uninfected areas are brought into enzootic areas . in africa , the main vector for nsdv is the three - host ixodid tick rhipicephalus appendiculatus , which is found between its northern limits of southern sudan and ethiopia through eastern , central and southern africa . livestock hosts for this tick include cattle , sheep , goats , and horses . in wildlife , antelopes and buffalo the main forms of tick - borne encephalitis virus ( tbev ) found in europe and asia do not cause clinical disease in livestock although human cases are on the increase in europe . these include louping ill virus ( liv ) , spanish sheep encephalitis virus ( ssev ) , greek goat encephalitis virus ( ggev ) , and turkish tick - borne encephalitis virus ( ttev ) . of these , liv is the most studied virus as the cause of disease in sheep and red grouse . in red grouse , liv causes rapid and fatal encephalitis whereas in sheep , disease is biphasic , especially in young nonimmune animals . the initial clinical signs of louping ill include fever and weakness before animals develop neurological signs of disease . a range between 5 and 60% of infected animals develop clinical signs and death can occur between 24 and 48 hours following the development of neurological signs . during the neurological phase , the most damage is caused to the cerebellum . clinically , the second phase is characterized by cerebral ataxia , hyperexcitability , and progressive paralysis . occasionally , natural infection of louping ill has also been reported from other species such as dogs , roe and red deer , and llamas [ 170173 ] . they are much less studied , but appear to all cause disease that resembles louping ill . transmission to humans is mainly through tick bites but can occasionally result from consumption of unpasteurized milk . liv is endemic within upland areas in the uk , particularly in scotland , wales , the northwest and southwest of england . sheep infected with ssev have been reported from the basque region of spain [ 174 , 177 ] . the first isolation of ggev was made in the village of vergina in northern greece . subsequent studies have suggested that ggev circulates in the i. ricinus population in northern greece , although at low density . ttev was first reported from northwestern turkey ( anatolia ) as encephalitis in sheep and was subsequent confirmed by nucleotide analysis to be related to tick - borne encephalitis virus [ 180182 ] . both tbev and its variants are transmitted by the three - host hard tick ixodes ricinus in europe . these ticks are the most common species of ticks in northwest europe and are also known as the common sheep tick , castor bean tick or wood tick . in addition to sheep and red grouse , the hosts for i. ricinus in the uk include mountain hares , red deer , roe deer and small mammals . in the far east of europe and throughout asia , tbev is transmitted by ixodes persulcatus . the first nested one - step rt - pcr for louping ill detection this assay , which targets the envelope ( e ) and membrane ( m ) genes of the virus genome , can be used for virus identification in ticks and other species . as the e gene is the most conserved of the three liv structural genes , a one - step taqman rt - pcr assay has been developed with primers for this protein . brain and spinal cord samples were tested and detection limit of 1  pfu / ml was achieved , making this assay as sensitive as the traditional plaque assay . in recent years , real - time rt - pcr assay detecting eight different tick - borne flaviviruses ( including louping ill ) and west nile virus has been developed in the uk . the assay employs degenerate primers targeting nonstructural protein 5 and is based on incorporation of sybr green . the assay is not as sensitive as species specific assays , but makes it an ideal choice when a single virus can not be specified before testing . a recently reported assay uses one - step real - time rt - pcr with pyrosequencing which enables the rapid differentiation between tbev subtypes . although , this assay was developed to differentiate between the main tbe subtypes , it is also able to detect louping ill virus . the majority of the viruses reviewed have been thoroughly characterized and there are a wide range of molecular diagnostic tests available . these tend to be those viruses that cause the greatest impact either to livestock health or as a consequence of spillover into the human population as a zoonotic agent . new serotypes and variants emerge and techniques may require modification or augmentation in response to genetic differences . other viruses have molecular tests available , but these are not widely in use , either because many countries do not consider them necessary or do not have suitable containment facilities to handle the virus . this group includes ehfv , befv , akabane virus , the equine encephalitides , jev , rvfv , cchfv , and variants of tick - borne encephalitis virus . further effort is needed to establish molecular tests for these viruses more widely in preparation for potential outbreaks . finally , there is a small group for which no molecular diagnostic tests have been reported . the first option is to develop specific tests that detect a single virus , often at high sensitivity . the alternative is the development of assays that detect a range of related pathogens in single step . however , this approach is often less sensitive and may require further analysis to identify the exact virus involved .   currently , rapid detection methods are dominated by nucleic acid amplification methods , particularly the polymerase chain reaction . by linking nucleic acid amplification to sequencing , it is possible to rapidly identify a large number of potential pathogenic viruses [ 114 , 188 ] . this approach has been applied to detection of flaviviruses using universal primers ( , and references therein ) . new technologies such as microarray   and next generation sequencing   are being applied to the investigation of infectious viruses . however , these technologies are expensive to establish and maintain for purely diagnostic or surveillance purposes . future development is required in this area to make these technologies more accessible and affordable for use in the detection of arthropod viruses of livestock .
arthropod - borne viruses ( arboviruses ) have been responsible for some of the most explosive epidemics of emerging infectious diseases over the past decade . 
 their impact on both human and livestock populations has been dramatic . 
 the early detection either through surveillance or diagnosis of virus will be a critical feature in responding and resolving the emergence of such epidemics in the future . 
 although some of the most important emerging arboviruses are human pathogens , this paper aims to highlight those diseases that primarily affect livestock , although many are zoonotic and some occasionally cause human mortality . 
 this paper also highlights the molecular detection methods specific to each virus and identifies those emerging diseases for which a rapid detection methods are not yet developed .