taenia solium cysticercosis is a severe zoonotic disease , which causes serious public health problems and provokes economic losses in the areas where it is endemic , particularly in developing countries ( zoli et al . , 2003 ; carabin et al . , 2006 ; praet et al . , the important findings concerning the control of t. solium cysticercosis during the past two decades were reviewed by pawlowski et al . one of the most important conclusions is that tapeworm carriers and human and porcine cysticercosis cases cluster in endemic foci . the risk factors for human cysticercosis are frequent consumption of pork , poor hygiene and having a history of taeniasis ( flisser & gyorkos , 2007 ) . although the presence of free - roaming pigs in rural areas of developing countries was identified as an important risk factor for swine cysticercosis ( sikasunge et al . , 2007 ) , this is not the only way for pigs to get access to human faeces . direct defecation of pig keepers in pig pens has been reported in the west of cameroon ( zoli et al . , 1987 ; shey - njila et al . , 2003 ) . the mayo - danay division is the most important region for pig breeding in northern cameroon . in this part of the country , pigs are kept by non - muslim people who interact with an important muslim community . pig husbandry is traditional and involves mainly local breeds which receive some domestic waste and little feed supplement ( njoya et al . , 1997 ; koussou , 1999 ) . limited data from earlier studies in northern cameroon suggested hyperendemicity of human and porcine cysticercosis ( awa et al . 2001 ) , but details are not known concerning the factors that predispose to the infection of pigs . the main objective of this study was to update data on swine cysticercosis and identify risk factors for this zoonosis in the mayo - danay division . the mayo - danay division is located in the far northern province of cameroon ( fig . 1 ) . the annual average rainfall varies from 600 to 800  mm and the wet season lasts 5 months  from may to october  while little or no rain falls during the rest of the year . there are four predominant ethnic groups : the massa , the toupouri , the mousgoum and the moussey , who are largely animistic or christian and primarily involved in crop and livestock production . 1map showing the study area ( mayo - danay division , grey shading ) in the north of cameroon ( all other cameroon districts shown as white areas ) . map showing the study area ( mayo - danay division , grey shading ) in the north of cameroon ( all other cameroon districts shown as white areas ) . a survey was conducted in mayo - danay division between june 2007 and april 2008 . a one - visit , multiple - objects survey was carried out to collect information on the pig - farming system . one hundred and fifty households , keeping 1756 pigs , were randomly sampled out of the registries kept by the authorities in the major area of pig farming . these rural areas were identified following the preliminary study carried out by assana et al . three hundred and ninety - eight ( 398 ) blood samples from pigs were collected in these surveyed households . a preliminary study had shown that the seroprevalence of pig cysticercosis in mayo - danay was 39.8% ( assana et al . , 2001 ) . assuming that a maximum sample size of 384 is required at the prevalence level of 50% ( sikasunge et al . , 2008 ) , at least 368 pigs were needed in this study according to the formula n =  zpq / l , where n is the required sample , z is the z score for confidence , p is the known prevalence , q  =  ( 1    p ) and l is the error estimation at 95% confidence ( martin et al . , 1987 ) . therefore , a sample size of 398 pigs is easily sufficient to estimate the prevalence of pig cysticercosis in mayo - danay division . serum samples collected from pigs during the survey were stored at   20c until tested . two positive serum samples from naturally infected pigs and eight negative serum samples from pigs from a local commercial pig farm without any history of cysticercosis were included as reference control sera in the enzyme - linked immunosorbent assay ( elisa ) . briefly , the sera were pre - treated using trichloroacetic acid ( tca ) and used in elisa at a final dilution of 1/4 . the monoclonal b158 was diluted at 5  g / ml in carbonate buffer ( 0.06  m , ph 9.6 ) for coating the elisa plate and the biotinylated monoclonal antibody ( moab ) b60 ( 1.25  g / ml in phosphate - buffered saline containing 0.05% tween 20 ( pbs - t20)/1% newborn calf serum ( nbcs ) ) was included as detector antibody . the incubation was carried out at 37c on a shaker for 30  min , for the coating of the first moab , and for 15  min for all subsequent steps . the chromogen / substrate solution , consisting of orthophenylene diamine ( dako , glostrup , denmark ) and h2o2 was added and incubated without shaking between 30 and 33c for 15  min . to arrest the reaction , 50  l of 4  n h2so4 was added to each well . the plates were read using an elisa reader ( multiskan rc , mtx lab systems , vienna , virginia , usa ) at 492  nm . the elisa for the detection of antibodies against t. solium cysticerci ( ab - elisa ) was based on a 14  kda antigen ( f3 antigen ) purified from t. solium cyst fluid by a two - step chromatography , as described by assana et al . the antigen ( f3 ) was diluted at 1  g / ml in a carbonate buffer ( 0.06  m , ph 9.6 ) for coating ( 1  h at 37c and overnight at 4c ) . serum samples and conjugate were blocked and incubated on a shaking plate for 1  h at 37c . pbs the wells were washed three times , and the final steps were executed as described for the ag - elisa . for both ag- and ab - elisa , the optical density ( od ) of each serum sample was compared with a series of reference negative serum samples ( n  =  8) at a probability level of p  =  0.001 to determine the cut - off , using a modified student 's t - test ( sokal & rohlf , 1981 ) . a bayesian analysis was used to estimate the true prevalence of cysticercosis in the mayo - danay division and the sensitivity ( se ) and specificity ( sp ) of both ag - elisa and ab - elisa tests using a multinomial model as described by krecek et al . briefly the results from ag - elisa and ab - elisa were combined together in a bayesian model and run in wingbugs 1.4 ( spiegelhalter et al . , 2003 ) . the prior information was obtained from previous studies on diagnosis of cysticercosis ( pouedet et al . , 2002 ; dorny et al . , 2004 ; the sensitivity and specificity of the ag - elisa were constrained to intervals ( 0.8 , 1 ) and ( 0.9 , 1 ) , respectively , whereas the sensitivity and specificity of the ab - elisa were constrained to intervals ( 0.4 , 1 ) and ( 0.5 , 1 ) . the validation of the model was based on the number of parameters ( pd ) , the deviance information criterion ( dic ) values from posterior mean of the multinomial probabilities ( dic_pr ) and from posterior mean of the parameter of the model using parent nodes ( dic_p ) and on the bayesian - p values ( bayesp ) as described by berkvens et al . ( 2007 ) . a pig that had a positive result in the ag- or ab - elisa most of the pig farmers ( 90.7% ) in the mayo - danay division kept pigs in a free - roaming system during the dry season . in the rainy season , pigs were confined in a small pig pen . from the 150 farmers interviewed , only 4.9% practised permanent indoor pig raising , whereas 13.7% allowed the pigs to roam freely during the rainy season ( since there is sometimes overlapping of various systems , the total figure exceeds 100% ) . furthermore , it revealed that 42.7% of the households keeping pigs had no latrine facilities and that 76.0% of the pig farmers declared that the members of their family used open - field defecation . the overall seroprevalence of pig cysticercosis was 24.6 and 32.2% for ag - elisa and ab - elisa , respectively . of the total of 150 households surveyed , 56.0% and 57.3% of them had at least one pig positive for porcine cysticercosis in ag - elisa and ab - elisa , respectively . there was a good correlation between the results obtained by ag - elisa and ab - elisa . two hundred and twenty - eight out of 398 sera were negative in both ag- and ab - elisa , whereas 56 out of 398 sera were positive in both tests . the estimated true prevalence using bayesian analysis was 26.6% ( 95% ci : 15.631.0% ) . forty - two sera were only positive in the ag - elisa and 72 only in the ab - elisa . the sensitivity and specificity of the ag - elisa and ab - elisa used for the diagnosis of pig cysticercosis in the mayo - danay division are presented in table 1 . table 1the true prevalence of porcine cysticercosis in mayo - danay and the sensitivity ( se ) and specificity ( sp ) of ag - elisa and ab - elisa estimated by means of bayesian analysis ( with 95% confidence intervals ) . table 2model validation based on bayesp , dic and pd used to estimate the prevalence of cysticercosis in mayo - danay division and the sensitivity and specificity of ag - elisa and ab-elisa.bayesp , bayesian - p values ; dic , deviance information criterion ; dic_pr , dic values from posterior mean of the multinomial probabilities ; dic_p , dic values from posterior mean of the parameter of the model using parent nodes . the true prevalence of porcine cysticercosis in mayo - danay and the sensitivity ( se ) and specificity ( sp ) of ag - elisa and ab - elisa estimated by means of bayesian analysis ( with 95% confidence intervals ) . model validation based on bayesp , dic and pd used to estimate the prevalence of cysticercosis in mayo - danay division and the sensitivity and specificity of ag - elisa and ab - elisa . bayesp , bayesian - p values ; dic , deviance information criterion ; dic_pr , dic values from posterior mean of the multinomial probabilities ; dic_p , dic values from posterior mean of the parameter of the model using parent nodes . the factors that were considered as significant risks for pig cysticercosis are presented in table 3 . the seroprevalence of cysticercosis in pigs was found to be associated with the pig owner 's level of knowledge about the taeniasis cysticercosis complex ( odds ratio ( or )  =  0.360 , p  <  0.05 ) and pig pen availability ( or  =  0.45 , p  <  0.05 ) . table 3univariate analysis of risk factors associated with seroprevalence of porcine cysticercosis in mayo - danay . univariate analysis of risk factors associated with seroprevalence of porcine cysticercosis in mayo - danay . in 1980 , the pig population in cameroon was estimated at more than 1,000,000 and 60% of the pigs were located in the western part of the country . after an outbreak of african swine fiver ( asf ) in 1982 ( nana - nukechap & gibbs , 1985 ) , the pig population decreased in this part of the country . since 1990 , the north of cameroon , free from asf , emerged as the main provider of pork for the city of yaound ( ndebi & ongla , 2006 ) . pigs are kept in a traditional low - input breeding system ( njoya et al . , 1997 ) , which favours infection with t. solium ( awa et al . , 1999 the results of this survey showed that 42.7% of households keeping pigs in the rural areas have no latrine facility and 76% of pig farmers use open - field defecation around the households . even when a latrine was available this did not imply that it was used by the members of the household . in fact , these latrines were built to avoid problems with the sanitary authority , which controls the availability of latrines in the villages on a regular basis . the coexistence of poor sanitary conditions and free roaming of domestic pigs ( absence of pig pens ; or  =  0.45 ; p  <  0.05 ) certainly plays an important role in the circulation of t. solium infection in the region . free roaming of pigs is known to be an important risk factor for infection of pigs with t. solium ( sikasunge et al . , 2007 ) . this is not the case in the west and north - west of cameroon where direct defecation by people in pig pens is an important factor associated with transmission of cysticercosis ( zoli et al . , 1987 ; shey - njila et al . , when answering the questionnaire , pig keepers knew and recognized pig cysticercosis through tongue examination or in pig meat , but did not know the relationship between taeniasis in humans and the presence of cysticerci in pigs . this lack of knowledge about the transmission of t. solium ( or  =  0.360 ; p  <  0.05 ) may contribute to the maintenance of a high prevalence of pig cysticercosis in the region . in an earlier epidemiological survey conducted in the mayo - danay division in 1999 , 38.9% of the pigs were found to be seropositive using an elisa for antigen detection ( assana et al . , 2001 ) . the results of the elisas in the present study ( 24.6% seropositive by ag - elisa and 32.2% by ab - elisa ) are somewhat lower but confirm that pigs are still highly exposed to t. solium cysticercosis . however , neither of the tests used for the diagnosis of cysticercosis is perfect ( dorny et al . , 2004 , the ab - elisa , using a 14  kda purified antigen ( f3 ) , is more specific but less sensitive than the ag - elisa ( assana et al . , 2007 ) . it measures the exposure of the pigs to t. solium , but this does not imply that cysticerci are present . the ag - elisa , on the other hand , detects the presence of living cysts , but cross - reacts with taenia hydatigena . the advantage of using both the ab - elisa and the ag - elisa and analysing the results in a bayesian model is that the f3 antigen used in the former test does not react with serum samples from pigs infected with t. hydatigena ( assana et al . , 2007 ) . however , the occurrence of t. hydatigena is not well known in northern cameroon and should be studied further . the seroprevalence of cysticercosis using ab - elisa was higher than when using ag - elisa . this seems to indicate that a proportion of the pigs harbour only dead cysts or have specific transient antibodies against cysticercosis ( garcia et al . , 2001 ) . in our study , 37% ( 42/114 ) of the serum samples this discrepancy might be due to the lower sensitivity of the ab - elisa or to false - positive results in ag - elisa due to cross - reaction with t. hydatigena . similar high proportions of positive sera in antigen detection found negative in antibody detection were obtained with ab - elisa using crude antigen from t. solium ( pouedet et al . , 2002 ) , crude antigen from t. crassiceps ( dorny et al . , 2004 ) and also in a recent study using an enzyme - linked immunoelectrotransfer blot assay ( eitb ) based on affinity purified glycoproteins from t. solium cysticerci ( krecek et al . , 2008 ) . in the absence of data from autopsy ( slicing of all muscles ) , which is the gold standard , it is possible to use conditional dependence between two or more imperfect tests to estimate the true prevalence of a disease and its test parameters by using a bayesian analysis ( dendukuri & joseph , 2001 ; berkvens et al . , 2006 ) . in this study , we used conditional dependence between ag - elisa and ab - elisa to estimate the true prevalence of cysticercosis in the mayo - danay division . the bayesian analysis indicated a true prevalence of 26.6% . this result is higher than the figure of 12% found by pouedet et al . the bayesian analysis of these data revealed the sensitivity and specificity of the ag - elisa to be higher than those found with the ab - elisa ( table 1 ) . however , the diagnostic characteristics of the ab - elisa using f3 antigen and the eitb , the assay most commonly used for antibody detection in the diagnosis of cysticercosis ( tsang et al . , 1989 ) , seem to be similar to those reported by krecek et al . , this study clearly shows that porcine cysticercosis is hyperendemic in mayo - danay and that the pig - farming system contributes to maintaining this high level of infection .
a survey was conducted in 150 households owning 1756 pigs in the rural areas of mayo - danay division in the north of cameroon . 
 a questionnaire survey was carried out to collect information on the pig - farming system and to identify potential risk factors for taenia solium cysticercosis infection in pigs . 
 blood samples were collected from 398 pigs with the aim of estimating the seroprevalence of t. solium cysticercosis . 
 the results showed that 90.7% of the pigs are free roaming during the dry season and that 42.7% of households keeping pigs in the rural areas have no latrine facility . 
 seventy - six per cent of the interviewed pig owners confirmed that members of the household used open - field defecation . 
 enzyme - linked immunosorbent assay ( elisa ) for antigen and antibody detection showed an apparent prevalence of cysticercosis of 24.6% and 32.2% , respectively . a bayesian approach , using the conditional dependence between the two diagnostic tests , indicated that the true seroprevalence of cysticercosis in mayo - danay was 26.6% . 
 binary logistic regression analysis indicated that a lack of knowledge of the taeniasis 
 cysticercosis complex and the absence of a pig pen in the household were associated with pig cysticercosis .