Screwworms are cutaneous myiases (i.e. infections with fly maggots) especially harmful for livestock. The affect mainly gazing cattle and sheep, but can attack whatever wild and domestic mammals, including horses and occasionally humans and birds as well. Dogs and cats can be affected, mainly in rural areas. They are found worldwide in tropical and subtropical regions, with a species-specific distribution.
The most relevant species are:
- Chrysomya bezziana, the Old World screwworm; occurs mainly in tropical Africa and Asia.
- Chrysomya megacephala. Occurs mainly in Africa and Asia, in the same regions as Chrysomya bezziana, but also in America where it was introduced early in the 20th century.
- Cochliomyia hominivorax, The New World screwworm. After the large-scale eradication campaigns in North America (down to to Panama) it remains very common in South America.
- Cochliomyia macellaria. Occurs in America.
Chrysomya bezziana and Cochliomyia hominivorax are obligate parasites, i.e. they cannot complete their life cycle on alternative substrates such as carrion, dung or manure, but only on their living hosts. They are also called "primary" myiases, because they are the first flies colonizing the injuries. Although they cannot pierce or otherwise damage the skin of their hosts, they deposit their eggs on minuscule injuries such as those caused by other parasites (e.g. ticks, biting flies) or on any kind of wounds that livestock can get, both occasional (through fencing, vegetation, etc.) or operational ones (e.g. after castration, dehorning, parturition, tail docking, shearing, etc.).
Chrysomya megacephala and Cochliomyia macellaria are "secondary" myiases, i.e. they deposit their eggs on injuries already infested with larvae of primary screwworms. They extend and worsen the wounds already infested with maggots.
Other species of both genus Cochliomyia and Chrysomya are facultative parasites, i.e. they can survive on carrion and/or other organic substrates. Some species are of forensic interest because they colonize cadavers and enable a quite accurate determination of the time of death.
Biology and life cycle of screwworm flies
Adults of Cochliomyia hominivorax, the New World screwworm, are medium-sized flies, about 10 mm long. Their body shows metallic greenish-bluish colors, and the eyes are red-orange. The life cycle can be completed in about 3 weeks. Adult females deposit 200 to 400 eggs on injuries of the host, even on minute ones such as insect bites. And they also are capable of laying eggs on uninjured, soft body parts (perineum, body openings, corners of the yes, etc.). Egg laying happens mostly in the afternoon and evening, which prevents exposure of hatching larvae to direct sunlight. Each female lays a total of about 3'000 eggs in her lifetime.
Larvae hatch out of the eggs within hours and start feeding on the host's tissues, progressively deepening and extending the injury. If larvae are disturbed while feeding they burrow deeper in the tissues like a screw: this is why they are called "screw"-worms. Besides digestive enzymes larvae release toxins that prevent wound healing. Open injuries become infected with secondary bacteria. Blood and pus attract other flies that worsen the wound. Larvae mature in about 1 week and reach up to 2.5 cm length. Mature maggots drop to the ground, burrow themselves in the soil and pupate within hours.
Adult flies hatch already 3 to 5 days later, depending on temperature. By unsuitable weather hatching can be delayed for several weeks. Mating occurs in the vegetation. Females mate only once and keep the sperms in a reservoir for fertilization of the eggs that are progressively produced and deposited. This specific behavior strongly supported the sterile-male release technique used to eradicate these flies in most of North America. By suitable conditions 8 to 10 generations can follow within one season. Adult flies are excellent fliers, capable of traveling up to 250 km in two weeks. Cochliomyia hominivorax prefers habitats with abundant trees and humid environments. It avoids open landscapes and arid regions.
Chrysomya bezziana, the Old World screwworm, is 6 t 12 mm long. It has a similar aspect and behavior as Cochliomyia hominivorax. It can complete its lifecycle in 2 weeks. Females deposit 100 to 200 eggs on the border of minute injuries or mucous membranes. In only 2 days larvae have invaded and liquefied the tissues around the wound. If disturbed larvae can burrow themselves into the host's tissues as deep as 15 cm. In less than a week mature maggots drop to the ground and pupate. Adults hatch in 1 to 8 weeks depending on weather conditions.
Click here to learn more about the general biology of insects.
Harm and economic loss due to screwworm flies
If wounds infested with maggots are left untreated, fly larvae fed into the animals flesh and affected animals can die in less than 2 weeks: they are actually eaten alive. If they survive, they are severely weakened and more susceptible for other diseases and parasites. The hides are strongly damaged and are downgraded at slaughter.
Cochliomyia hominivorax was considered the most damaging pest of cattle and sheep in the USA before its eradication (completed in the 1960's). Already in the 1930's damage to the livestock industry in the US was estimated at above $200 million. Thanks to the eradication program it has been eliminated from Mexico, several Caribbean Islands, Guatemala, Honduras, Costa Rica, Nicaragua and down to Panama. Nowadays it remains one of the most damaging pests in South America and parts of Central America.
Chrysomya bezziana was and remains a highly damaging pest for cattle, sheep and goats in endemic regions in tropical Asia and Africa. Regional incidence depends strongly on climatic and ecologic conditions. In favorable years regional outbreaks can become a tremendous pests for livestock.
Non chemical control and prevention of screwworm flies
The eradication of Cochliomyia hominivorax in the USA, Mexico and most of Central America is the biggest success story of biological control in veterinary medicine. It has been achieved using the sterile male technique developed by R.C. Bushland and E.F. Knipling, two North American entomologists in the 1950's. This technique has been also applied successfully to several crop pests in the USA and elsewhere. It consists in releasing billions of industrially produced male flies previously sterilized through X-radiation.
These sterile males compete successfully with natural fertile males and mate with the females, which subsequently produce no offspring. After several years releasing sterile males, natural fly populations are decimated and eventually collapse and disappear from the concerned region. Such a campaign includes an enormous logistic effort for producing and releasing the sterile males at the right places and in the right moment and quantity, and for monitoring the fly populations in vast regions where the campaign is being run.
The current eradication campaign aims at eliminating Cochliomyia hominivorax down to the Isthmus of Panama and to establish a permanent biological sterile-male barrier there to prevent its re-introduction from South America.
The same sterile-male release approach was used to successfully control an outbreak of Cochliomyia hominivorax accidentally introduced into Libya in the 1990's, which threatened to spread to the whole Old World with potential catastrophic consequences for the livestock industry.
There have been no serious attempts to eradicate Chrysomya bezziana, in the Old World using this technique.
Strictly speaking, the sterile male technique is not a "biological" control method, since biological control is usually restricted to the use of natural enemies of a pest, and sterilized males are obviously not natural enemies of the females of the same species. However, it is an excellent alternative to whatever chemical control methods since it leaves no pesticide residues in food commodities and the environment.
Learn more about biological control of flies and other insects.
Where screwworms are a pest, i.e. in South America, and tropical regions of Africa and Asia, best prevention is to avoid handling practices that cause injuries to livestock during the peaks in the fly season. This includes parturition, castration, dehorning, shearing, tail docking, etc. that attract egg laying flies to the resulting injuries.
Preventing infestations with blood sucking parasites (e.g. ticks, horn flies, stable flies, horse and deer flies, etc.) will also reduce the incidence of screwworms, because screwworm flies are also attracted to such minute wounds as those caused by these parasites.
Traps have also been used to reduce fly populations, often in combination with the sterile-male technique previously mentioned.
Click here if you are interested in medicinal plants for controlling lice and other external parasites of livestock and pets.
Chemical control and prevention of screwworm flies
Many concentrates used for periodically dipping or spraying livestock or horses against ticks and flies will usually kill established screwworm infestations as well, but only those that contain synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin, etc.) and organophosphates (e.g. chlorpyrifos, chlorfenvinphos, coumaphos, etc.), not those with amitraz. However, protection against re-infestation will last only for a few days. Pour-ons (backliners) with such parasiticides are often not suitable because they do not ensure complete coverage of the host's body.
Otherwise numerous ready-to-use dressings for direct treatment of injuries infested with maggots are available in most countries. They are used preventively for topical treatment of injured body parts after castration, dehorning, shearing, etc., as well as curatively for killing maggots already established in whatever injuries that animals can get. Such dressings are available in various formulations such as powders, lotions, ointments, creams, sprays, aerosols, etc. They contain larvicides belonging to the synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin), carbamates (e.g. carbaryl, propoxur) and organophosphates (e.g. chlorpyrifos, diazinon, trichlorfon, etc.). These dressings often contain disinfectants, painkillers, and/or wound healing chemicals as well. Such dressings for livestock or horses are sometimes approved for use on dogs and cats as well.
Systemic macrocyclic lactones (e.g. doramectin, ivermectin, moxidectin) have an excellent efficacy against screwworms. Classic injectables (i.e. containing 1% active ingredient) will cure established myiases and protect livestock for several weeks against re-infestations. They are vastly used as preventatives in livestock after management operations that bear a risk of screwworm infestation (e.g. castration, dehorning, etc.). Pour-on formulations are usually also effective against screwworms. Drench or other oral formulations are usually not effective enough.
So far there are no effective repellents to keep screwworm flies away from livestock, horses or pets.
|If available, follow more specific national or regional recommendations or regulations for screwworm control.
Resistance of screwworms to parasiticides
So far there are no reports on screwworm resistance to parasiticides.
This means that if a particular product has not achieved the expected control, it is most likely because the product is not adequate or it was not used correctly, not because screwworms have become resistant.
Screwworms ni myiases ngozi (yaani. Ugonjwa wa maggot ya kuruka ni hatari sana kwa wanyama. Mnyama huyo huathiriwa hasa na ng'ombe na kondoo, lakini anaweza kushambulia wanyama wa pori na wa kufugwa, kutia ndani farasi na mara kwa mara wanadamu na ndege. Mbwa na paka wanaweza kuathiriwa, hasa katika maeneo ya mashambani. Wao hupatikana ulimwenguni pote katika maeneo ya kitropiki na ya kitropiki, na usambazaji maalum wa spishi. Spishi muhimu zaidi ni: - Chrysomya bezziana, Old World screwworm; hutokea hasa katika kitropiki Afrika na Asia. - Chrysomya megacephala. Mti huu unapatikana hasa katika Afrika na Asia, katika mikoa sawa na Chrysomelaria bezziana, lakini pia katika Amerika ambapo ilianzishwa mapema karne ya 20. - Cochliomyia hominivorax, Mdudu wa Ulimwengu Mpya. Baada ya kampeni kubwa za kuangamiza katika Amerika Kaskazini (hadi Panama) bado ni ya kawaida sana katika Amerika Kusini. - Cochliomyia macellaria. Inatokea nchini Marekani. Chrysomya bezziana na Cochliomyia hominivorax ni vimelea vya lazima, yaani. Hawezi kukamilisha mzunguko wake wa maisha kwenye substrates mbadala kama vile carcass, mbolea au mbolea, lakini tu juu ya majeshi yao hai. Pia huitwa myiasis "ya msingi", kwa sababu wao ndio nzi wa kwanza kuanzisha makazi katika majeraha. Ingawa hawawezi kupasua au kuharibu ngozi ya mwenyeji wao, wao kuweka mayai yao juu ya majeraha madogo kama vile yale yanayosababishwa na vimelea vingine. Mnyama anaweza kuumwa na kuumwa na mbuzi au kuumwa na aina yoyote ya jeraha ambalo wanyama wanaweza kupata, mara kwa mara (kwa njia ya uzio, mimea, nk.) au operational (kwa mfano Baada ya castration, de-horning, partourition, mkia docking, shearing, nk.). Chrysomya megacephala na Cochliomyia macellaria ni "wa pili" myiases, yaani Maziwa yao huanguka kwenye vidonda vilivyojaa mabuu ya vimelea vya kwanza. Wao hupanua na kuharibu majeraha ambayo tayari yamejaa minyoo. Spishi nyingine za jamii zote mbili Cochliomyia na Chrysomya ni vimelea vya hiari, yaani. Wanaweza kuishi juu ya carcass na au substrates nyingine za kikaboni. Baadhi ya spishi hizo zinavutia wataalamu wa kitiba kwa sababu huishi kwenye maiti na hivyo kuweza kuamua kwa usahihi wakati wa kifo. Kwa mfano, kwa ndege aina ya Cochliomyia hominivorax, aina ya wadudu wa ulimwengu mpya, ni aina ya wadudu wenye ukubwa wa kati. Mwili wao una rangi ya kijani-kibichi-kibichi, na macho yao ni ya rangi ya machungwa-nyekundu. Mzunguko wa maisha unaweza kukamilika katika wiki tatu. Wanawake wazima huweka mayai 200 hadi 400 kwenye majeraha ya mwenyeji, hata kwenye majeraha madogo kama vile kuumwa na wadudu. Pia, huweza kuweka mayai kwenye sehemu laini za mwili (perineum, sehemu za mwili, pembe za mwili, na kadhalika). Kuweka mayai hutokea hasa alasiri na jioni, ambayo huzuia kuambukizwa kwa mabuu ya kuanguliwa kwa mwanga wa jua wa moja kwa moja. Kila mwanamke hutaga mayai 3,000 katika maisha yake. Larva huanguliwa kutoka kwa mayai ndani ya saa chache na kuanza kula tishu za mwenyeji, hatua kwa hatua kuimarisha na kupanua jeraha. Ikiwa mabuu hufadhaishwa wakati wa kulisha wao huchimba ndani zaidi katika tishu kama screw: hii ndiyo sababu wanaitwa "screw"-worms. Mbali na enzymes za kumeng'enya chakula, mabuu hutokeza sumu ambazo huzuia uponyaji wa majeraha. Majeraha yaliyo wazi huambukizwa na bakteria za pili. Damu na umajimaji huvutia nzi wengine ambao huharibu jeraha. Larvae kukomaa katika wiki moja na kufikia urefu wa sentimita 2.5. Nyigu wakomavu huanguka ardhini, hujichimba ndani ya udongo na kugeuka kuwa vifaranga kwa muda wa saa chache tu. Ndege wazima huanguliwa baada ya siku tatu hadi tano, kulingana na joto. Kwa sababu ya hali mbaya ya hewa, kuanguliwa kwa ndege kunaweza kucheleweshwa kwa majuma kadhaa. Kuoa hutukia katika mimea. Wanawake huoa mara moja tu na kuweka shahawa katika hifadhi ya mayai ambayo hutokezwa na kuwekwa hatua kwa hatua. Utendaji huo wa pekee ulithibitisha sana mbinu ya kuondoa nzi hao katika sehemu kubwa ya Amerika Kaskazini. Kwa hali nzuri, vizazi 8 hadi 10 vinaweza kufuatia katika msimu mmoja. Ndege wazima ni ndege wazuri sana, na wanaweza kusafiri umbali wa kilometa 250 kwa wiki mbili. Cochliomyia hominivorax hupendelea makao yenye miti mingi na mazingira yenye unyevunyevu. Yeye huepuka maeneo ya wazi na maeneo yenye ukame. Chrysomelybus bezziana ni aina ya minyoo ya ulimwengu wa zamani, ambayo ina urefu wa mita 6 hadi 12 na ina uwezo wa kupanua urefu wa mita 3 hadi 5. Ina sura na tabia sawa na Cochliomyia hominivorax. Inaweza kukamilisha mzunguko wake wa maisha katika wiki mbili. Wanawake huweka mayai 100 hadi 200 kwenye mipaka ya majeraha madogo au utando wa utando. Baada ya siku mbili tu, mabuu ya mnyama huyo yamevamia na kuyeyusha tishu zilizozunguka jeraha hilo. Mnyama huyo anaweza kuharibu larvae na kuingiza ndani ya tishu za mwenyeji kwa kina cha sentimita 15. Katika muda usiozidi juma moja, minyoo wakomavu huanguka ardhini na kugeuka kuwa vifaranga. Wanyama hao huanguliwa baada ya wiki moja hadi nane, ikitegemea hali ya hewa. Bonyeza hapa ili kujifunza zaidi kuhusu biolojia ya jumla ya wadudu. Uharibifu na hasara za kiuchumi kutokana na nzi wa screwworm: Ikiwa majeraha yaliyoambukizwa na maggot hayatibiwa, mabuu ya nzi huingia kwenye nyama ya wanyama na wanyama walioathirika wanaweza kufa kwa chini ya wiki mbili: kwa kweli wanakula hai. Ikiwa wanaokoka, wanadhoofika sana na wanakuwa na uwezekano mkubwa zaidi wa kupatwa na magonjwa mengine na vimelea. Ngozi ni vibaya sana na ni downgraded katika mauaji. Cochliomyia hominivorax ilikuwa ni wadudu wa kudumu wa wanyama wa mifugo na kondoo nchini Marekani kabla ya kuondolewa kwa ugonjwa huo. Tangu miaka ya 1930 uharibifu wa mifugo nchini Marekani ulikadiriwa kuwa zaidi ya dola milioni 200. Kwa sababu ya mpango wa kuangamiza, imeondolewa kutoka Mexico, Visiwa kadhaa vya Karibea, Guatemala, Honduras, Costa Rica, Nikaragua na chini ya Panama. Leo bado ni mojawapo ya wadudu wenye uharibifu mkubwa zaidi katika Amerika Kusini na sehemu fulani za Amerika ya Kati. Chrysomya bezziana ni wadudu wa hatari kwa mifugo, kondoo na mbuzi katika maeneo ya kitropiki ya Asia na Afrika. Mzunguko wa mkoa hutegemea sana hali ya hewa na ikolojia. Katika miaka yenye kuvutia milipuko ya magonjwa ya mkoa yaweza kuwa wadudu wakubwa sana kwa mifugo. Ugonjwa wa Cochliomyia hominivorax katika Amerika ya Kati, Mexico na sehemu kubwa ya Amerika ya Kati ni hadithi kubwa ya mafanikio ya udhibiti wa kibiolojia katika dawa ya mifugo. Imepatikana kwa kutumia mbinu ya kiume isiyo na uzazi iliyobuniwa na R.C. Bushland na E. F. Kneipping, wataalamu wawili wa wadudu wa Amerika Kaskazini katika miaka ya 1950. Mbinu hii pia imetumika kwa mafanikio kwa wadudu kadhaa wa mazao nchini Marekani na kwingineko. Ni kutolewa kwa mabilioni ya nzi wa kiume waliozalishwa kiviwanda ambao hapo awali walikuwa wamezaliwa kwa mnururisho wa X. Wanaume hao wasio na uzazi hushindana na wanaume wenye uzazi wa asili na kuoa na wanawake, ambao baadaye hawazaa watoto. Baada ya miaka kadhaa ya kuachilia nje wanaume wasio na uzazi, idadi ya nzi wa asili hupungua na hatimaye kuanguka na kutoweka kutoka eneo hilo. Kampeni hiyo inahusisha juhudi kubwa za kiufundi za kuzalisha na kuachilia ndege wa kiume wasio na uzazi katika maeneo sahihi na kwa wakati na wingi sahihi, na kwa ajili ya kufuatilia idadi ya nzi katika maeneo makubwa ambapo kampeni hiyo inaendeshwa. Kampeni ya sasa ya kuangamiza ina lengo la kuondoa Cochliomyia hominivorax chini ya Isthmus ya Panama na kuanzisha kizuizi cha kudumu cha kibiolojia cha sterili ya kiume huko kuzuia kuingizwa tena kutoka Amerika Kusini. Utaratibu huo wa kutolewa kwa viumbe wa kiume ulitumika kudhibiti kwa mafanikio mlipuko wa Cochliomyia hominivorax ulioletwa kwa bahati mbaya nchini Libya katika miaka ya 1990, ambao ulitisha kuenea kwa Ulimwengu Mzee wote na matokeo mabaya kwa sekta ya mifugo. Hakukuwa na majaribio makubwa ya kuondoa Chrysomya bezziana, katika Ulimwengu wa Kale kwa kutumia mbinu hii. Kwa kweli, mbinu ya sterilization ya kiume si mbinu ya kudhibiti ya kibiolojia, kwani kudhibiti kibiolojia kwa kawaida kunahusishwa na matumizi ya maadui wa asili wa wadudu, na wanaume waliopigwa marufuku kwa wazi si maadui wa asili wa wanawake wa spishi hiyo hiyo. Hata hivyo, ni mbadala bora kwa njia yoyote ya udhibiti wa kemikali kwani haiachi mabaki ya dawa za kuua wadudu katika bidhaa za chakula na mazingira. Jifunze zaidi kuhusu jinsi ya kudhibiti nzi na wadudu wengine. Screwworms ni wadudu wa kawaida. Katika maeneo ya kitropiki ya Afrika na Asia, kuzuia ni kuzuia mazoea ya kushughulikia ambayo husababisha majeraha kwa mifugo wakati wa kilele cha msimu wa kuruka. Hii ni pamoja na kuzaa, castration, dehorning, shearing, mkia docking, nk. Hii inawakumbusha ndege wanaozaa mayai kuwa na hatari ya kuambukizwa. Kuzuia maambukizi ya vimelea vinavyomvuta damu (kwa mfano Ticks, pembe nzi, stable nzi, farasi na deer nzi, nk.) Hii pia hupunguza uwezekano wa kuambukizwa na vimelea vya screwworm, kwa sababu vimelea vya screwworm huvutiwa na majeraha madogo kama yale yanayosababishwa na vimelea hivi. Pia mitego imetumiwa kupunguza idadi ya nzi, mara nyingi kwa kuchanganya na mbinu ya wanaume wasio na uzazi iliyotajwa hapo awali. Kwa mfano, unaweza kutumia mimea ya dawa ili kudhibiti kutu na vimelea vingine vya nje vya mifugo na wanyama. Vipimo vya kemikali vinavyotumiwa kwa mara kwa mara kuingiza au kunyunyizia mifugo au farasi dhidi ya vimelea na nzi kwa kawaida vitaua maambukizi ya vimelea vya screwworm, lakini tu wale ambao wana pyrethroids za synthetic. cypermethrin, deltamethrin, permethrin, nk.) Organophosphates (kwa mfano) Chlorpyrifos, chlorfenvinphos, coumaphos, na kadhalika Kwa sababu ya hali hii, hakuna dawa ya dawa ya amitraz. Hata hivyo, kinga dhidi ya kuambukizwa tena itaendelea kwa siku chache tu. Mara nyingi dawa hizo hazifai kwa sababu hazifai kufunika kabisa mwili wa mwenyeji. Vinginevyo, vifuniko vingi vilivyo tayari kutumiwa kwa ajili ya kutibu moja kwa moja majeraha yaliyoambukizwa na minyoo vinapatikana katika nchi nyingi. Hizi hutumiwa kwa kuzuia kwa matibabu ya sehemu za mwili zilizojeruhiwa baada ya castration, dehorning, shearing, nk, na pia kwa kuua maggot tayari imara katika majeraha yoyote ambayo wanyama wanaweza kupata. Vifaa hivyo vinapatikana katika muundo mbalimbali kama vile poda, lotions, ointments, creams, sprays, aerosols, nk. Wao ni pamoja na larvicides mali ya pyrethroids synthetic (kwa mfano Cypermethrin, deltamethrin, permethrin, carbamates (kwa mfano Karbamuti (karbamuti) na propoxyl (karbamuti) Chlorpyrifos, diazinon, trichlorfon, na kadhalika). Mara nyingi vifuniko hivyo vina dawa za kuua viini, dawa za kupunguza maumivu, na au kemikali za kuponya majeraha. Nyakati nyingine vifuniko hivyo kwa ajili ya mifugo au farasi hupendekezwa kutumiwa kwa ajili ya mbwa na paka pia. Lactone ya macrocyclic ya mfumo (kwa mfano: Doramectin, ivermectin, moxidectin) zina ufanisi bora dhidi ya vijidudu vya screw. Injection ya kawaida (kwa mfano, Dawa hii ya dawa ya kuua myocardial infarction (inayohusisha 1% ya dutu) itaponya myocardial infarction na kulinda mifugo kwa wiki kadhaa dhidi ya maambukizi ya mara kwa mara. Wao ni sana kutumika kama kuzuia katika mifugo baada ya shughuli za usimamizi kwamba kubeba hatari ya screwworm infestation (kwa mfano castration, de-horning, na kadhalika. Kwa kawaida dawa za kumwagika kwa maji pia zina matokeo dhidi ya minyoo. Dawa za kuondoa maji au dawa nyingine za mdomo kwa kawaida hazifanyi kazi vya kutosha. Kwa sasa hakuna dawa zenye matokeo za kuwazuia nzi wa kuua minyoo kutoka kwa mifugo, farasi, au wanyama-vipenzi. Ikiwa inapatikana, fuata mapendekezo au kanuni maalum za kitaifa au za kikanda kwa udhibiti wa minyoo. Upinzani wa screwworms kwa parasiticides Hadi sasa hakuna ripoti juu ya screwworms upinzani kwa parasiticides. Hii inamaanisha kwamba ikiwa bidhaa fulani haikufikia udhibiti unaotarajiwa, ni uwezekano mkubwa kwa sababu bidhaa haifai au haikutumiwa kwa usahihi, sio kwa sababu minyoo ya screw imekuwa sugu.