Re-visiting the detection of porcine cysticercosis based on full carcass dissections of naturally Taenia solium infected pigs

Background

Taenia solium is a neglected zoonotic parasite. The performances of existing tools for the diagnosis of porcine cysticercosis need further assessment, and their shortcomings call for alternatives. The objective of this study was to evaluate the performance of tongue palpation and circulating antigen detection for the detection of porcine cysticercosis in naturally infected pigs of slaughter age compared to full carcass dissections (considered the gold standard). Additionally, alternative postmortem dissection procedures were investigated. A total of 68 rural pigs of slaughter age randomly selected in the Eastern Province of Zambia were dissected. Dissections were conducted on full carcasses (or half carcass in case cysticerci were already detected in the first half), including all the organs. Total cysticercus counts, location and stages were recorded and collected cysticerci were identified morphologically and molecularly. All sera were analysed with the B158/B60 antigen detecting ELISA (Ag-ELISA).

Results

Key findings were the high occurrence of T. solium infected pigs (56%) and the presence of T. solium cysticerci in the livers of 26% of infected animals. More than half of the infected carcasses contained viable cysticerci. Seven carcasses had T. hydatigena cysticerci (10%), out of which five carcasses were co-infected with T. hydatigena and T. solium; two carcasses (3%) had only T. hydatigena cysticerci. Compared to full carcass dissection, the specificity of the Ag-ELISA to detect infected carcasses was estimated at 67%, the sensitivity at 68%, increasing to 90% and 100% for the detection of carcasses with one or more viable cysticerci, and more than 10 viable cysts, respectively. Tongue palpation only detected 10% of the cases, half carcass dissection 84%.

Selective dissection of the diaphragm, tongue and heart or masseters can be considered, with an estimated sensitivity of 71%, increasing to 86% in carcasses with more than 10 cysticerci.

Conclusions

Depending on the aim of the diagnosis, a combination of Ag-ELISA and selective dissection, including investigating the presence of T. hydatigena, can be considered. Full carcass dissection should include the dissection of the liver, kidneys, spleen and lungs, and results should be interpreted carefully, as small cysticerci can easily be overlooked.

Accuracy of serological testing for the diagnosis of prevalent neurocysticercosis in outpatients with epilepsy, Eastern Cape Province, South Africa

BACKGROUND

Few studies have estimated prevalence of neurocysticercosis (NCC) among persons with epilepsy in sub-Saharan Africa. While the limitations of serological testing in identification of NCC are well known, the characteristics of persons who are misdiagnosed based on serology have not been explored. The first objective of this pilot study was to estimate the prevalence of NCC in epilepsy outpatients from an area of South Africa endemic for cysticercosis. The second objective was to estimate the accuracy of serological testing in detecting NCC in these outpatients and characterize sources of disagreement between serology and neuroimaging.

METHODOLOGY/PRINCIPAL FINDINGS

All out-patients aged 5 or older attending the epilepsy clinic of St. Elizabeth's Hospital in Lusikisiki, Eastern Cape Province, between July 2004 and April 2005 were invited to participate. Epidemiological data were collected by local study staff using a standardized questionnaire. Blood samples were tested by ELISA for antibody and antigen for Taenia solium. Four randomly chosen, consenting participants were transported each week to Mthatha for brain CT scan. The proportion of persons with epilepsy attending St. Elizabeth clinic with CT-confirmed NCC was 37% (95% CI: 27%-48%). Using CT as the gold standard, the sensitivity and specificity of antibody testing for identifying NCC were 54.5% (36.4%-71.9%) and 69.2% (52.4%-83.0%), respectively. Sensitivity improved to 78.6% (49.2%-95.3%) for those with active lesions. Sensitivity and specificity of antigen testing were considerably poorer. Compared to false negatives, true positives more often had active lesions. False positives were more likely to keep pigs and to have seizure onset within the past year than were true negatives.

CONCLUSIONS/SIGNIFICANCE

The prevalence of NCC in South African outpatients with epilepsy is similar to that observed in other countries where cysticercosis is prevalent. Errors in classification of NCC using serology alone may reflect the natural history of NCC.

The immune response in Taenia solium neurocysticercosis in pigs is associated with astrogliosis, axonal degeneration and altered blood-brain barrier permeability

Immunohistochemistry was used to examine the immuno-pathological changes and the extent of neuronal damage caused by either viable or dead Taenia solium cysticerci during porcine neurocysticercosis. Thirty pig brains with cerebral cysticercosis and 5 brains from T. solium free pigs were used in this study. Results revealed extensive astrogliosis, neuronal and mostly axonal damage in both early (grade I) and late (grades III and V) lesions as evidenced by an increased expression of glial fibrillary acidic protein (GFAP) and neurofilament protein (NFP). In many late lesions, astrocyte end-feet formed glial scars that surrounded the dead parasite. Rapid angiogenesis resulted in blood vessels lacking astrocyte end-feet suggesting loss of blood-brain barrier (BBB) hence allowing an influx of peripheral blood immune cells such as eosinophils, macrophages, CD3+ T cells, B lymphocytes and plasma cells into lesions. This study showed that porcine NCC was associated with severe nervous tissue damage, the host response of which is a collaborative effort between the local and peripheral immune responses comparable to that observed in human NCC. Results further implied that porcine NCC could be a useful model for understanding the course of NCC in human as well as provide useful information for therapeutic and/or immune strategies.

Taenia solium porcine cysticercosis: viability of cysticerci and persistency of antibodies and cysticercal antigens after treatment with oxfendazole

The aim of this study was to assess the effect of treating Taenia solium infected pigs with oxfendazole (OFZ) on viability and clearance of cysticerci and the corresponding persistence of specific antibody isotypes (IgG(total), IgG1, IgG2 and IgA) and circulating cysticercal antigen (CCA). Antibody isotypes and CCA responses were measured by antibody-ELISA (Ab-ELISA) and antigen ELISA (Ag-ELISA), respectively. Correlations were made between antibodies, CCA and the total number of cysticerci enumerated at necropsy. Forty pigs with cysticercosis were randomly allocated into two groups: Treatment group (n=20) was treated with OFZ at 30 mg/kg orally while the treatment control group (n=20) was not treated. Five uninfected pigs served as negative controls. Pigs were killed at 1, 4, 8 and 26 weeks post-treatment (wkpt). Overall, the mean total cyst count in treated pigs was 2904+/-5397 (mean+/-S.D.) while in the controls it was 6235+/-6705. Mean cyst viability was 5+/-11% (mean+/-S.D.) and 97+/-4% in treated and control pigs, respectively. Results showed that OFZ killed muscular cysticerci over a period of 4 weeks but failed to kill cerebral cysticerci. Antibodies, CCA responses and clearance of dead cysts from the meat, depended on the cyst intensity of individual pigs at time of treatment since both antibody and CCA correlated with intensity of cysticerci at necropsy (r=0.441, P=0.005; r=0.654, P<0.001), respectively. IgG1 responses were the best indicator of treatment efficacy because they were predominant in both infected treated and control pigs and disappeared early after treatment. Both Ab/Ag-ELISA failed to detect cysts in the brain. Though dead cysticerci took some time (26 wkpt) to clear from the meat, treatment of porcine cysticercosis with OFZ should, in combination with other intervention measures be considered as an important, cost-effective measure in the control of taeniosis/cysticercosis.

Prevalence of Taenia solium cysticercosis in swine from a community-based study in 21 villages of the Eastern Cape Province, South Africa

The pork tapeworm, Taenia solium, causative organism of porcine cysticercosis and human neurocysticercosis is known to occur in areas of South Africa including Eastern Cape Province but, despite increasing reports of its occurrence throughout the subregion, the prevalence is yet to be clearly established. The parasite presents a potentially serious agricultural problem and public health risk in endemic areas. The human populations considered to be at highest risk of infection with this zoonotic helminth are people living in rural areas most of whom earn their livelihood wholly or partially through livestock rearing. Here we report on initial results of a community-based study of pigs owned by resource-poor, emerging pig producers from 21 villages in the Eastern Cape Province. Lingual examination (tongue palpation) in live pigs, two enzyme-linked immunosorbent assays (ELISAs), which detect parasite antigen (B158/B60 Ag-ELISA and HP10 Ag-ELISA) and an enzyme immunotransfer blot (EITB) assay, which detects antiparasite antibody, were used to verify endemicity and estimate apparent prevalence. In the absence of a gold standard true prevalence was obtained, using a Bayesian approach, with a model that uses both available data and prior information. Results indicate that the parasite is indeed present in the study villages and that true prevalence was 64.6%. The apparent prevalences as measured by each of the four tests were: 11.9% for lingual examination, 54.8% for B158/B60 Ag-ELISA, 40.6% for HP10 Ag-ELISA and 33.3% for EITB. This base-line knowledge of the prevalence of T. solium in pigs provides information essential to the design and monitoring of sustainable and appropriate interventions for cysticercosis prevention and control.

Multi-host transmission dynamics of Schistosoma japonicum in Samar province, the Philippines

BACKGROUND

Among the 6.7 million people living in areas of the Philippines where infection with Schistosoma japonicum is considered endemic, even within small geographical areas levels of infection vary considerably. In general, the ecological drivers of this variability are not well described. Unlike other schistosomes, S. japonicum is known to infect several mammalian hosts. However, the relative contribution of different hosts to the transmission cycle is not well understood. Here, we characterize the transmission dynamics of S. japonicum using data from an extensive field study and a mathematical transmission model.

METHODS AND FINDINGS

In this study, stool samples were obtained from 5,623 humans and 5,899 potential nonhuman mammalian hosts in 50 villages in the Province of Samar, the Philippines. These data, with variable numbers of samples per individual, were adjusted for known specificities and sensitivities of the measurement techniques before being used to estimate the parameters of a mathematical transmission model, under the assumption that the dynamic transmission processes of infection and recovery were in a steady state in each village. The model was structured to allow variable rates of transmission from different mammals (humans, dogs, cats, pigs, domesticated water buffalo, and rats) to snails and from snails to mammals. First, we held transmission parameters constant for all villages and found that no combination of mammalian population size and prevalence of infectivity could explain the observed variability in prevalence of infection between villages. We then allowed either the underlying rate of transmission (a) from snails to mammals or (b) from mammals to snails to vary by village. Our data provided substantially more support for model structure (a) than for model structure (b). Fitted values for the village-level transmission intensity from snails to mammals appeared to be strongly spatially correlated, which is consistent with results from descriptive hierarchical analyses.

CONCLUSIONS

Our results suggest that the process of acquiring mammalian S. japonicum infection is more important in explaining differences in prevalence of infection between villages than the process of snails becoming infected. Also, the contribution from water buffaloes to human S. japonicum infection in the Philippines is less important than has been recently observed for bovines in China. These findings have implications for the prioritization of mitigating interventions against S. japonicum transmission.

Epidemiological studies of parasitic gastrointestinal nematodes, cestodes and coccidia infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

Between January 1999 and December 2000 faecal samples from 16264 cattle at 12 dipping sites in the highveld and nine in the lowveld communal grazing areas of Zimbabwe were examined for gastrointestinal (GI) nematode and cestodes eggs, and coccidia oocysts. Strongyle larvae were identified following culture of pooled faecal samples collected at monthly intervals. The effects of region, age, sex and season on the prevalence of GI nematodes, cestodes and coccidia were determined. Faecal egg and oocyst counts showed an overall prevalence of GI nematodes of 43%, coccidia 19.8% and cestodes 4.8%. A significantly higher prevalence of infection with GI nematodes, cestodes and coccidia was recorded in calves (P < 0.01) than in adults. Pregnant and lactating cows had significantly higher prevalences than bulls, oxen and non-lactating (dry cows) (P < 0.01). The general trend of eggs per gram (epg) of faeces and oocysts per gram (opg) of faeces was associated with the rainfall pattern in the two regions, with high epg and opg being recorded during the wet months. The most prevalent genera of GI nematodes were Cooperia, Haemonchus and Trichostrongylus in that order. Strongyloides papillosus was found exclusively in calves. Haemonchus was significantly more prevalent during the wet season than the dry season (P < 0.01). In contrast, Trichostrongylus was present in significantly (P < 0.01) higher numbers during the dry months than the wet months, while Cooperia and Oesophagostomum revealed no significant differences between the wet and dry season. These findings are discussed with reference to their relevance for strategic control of GI parasites in cattle in communal grazing areas of Zimbabwe.

Prevalence of Schistosoma japonicum infection among animals in fifty villages of Samar province, the Philippines

In the Philippines, there is a need to understand the contribution of different domestic and wild animals in transmitting Schistosoma japonicum infection to humans better. The current study describes variation in animal S. japonicum prevalence across 50 endemic villages of Samar Province, the Philippines. A total of 50 villages were selected, 25 with predominantly rain-fed farms and 25 with some irrigation system. At least 35 cats, dogs, pigs, and water buffaloes each were randomly selected and 30 rat traps were set in each village. Fecal samples were collected for up to three consecutive days for each species. The Danish Bilharziasis Laboratory method (DBL method) was used to determine S. japonicum infection status. A hierarchical logistic regression model with clustering by village and with adjustment for measurement error of the DBL method was used to estimate the prevalence of infection per village and species. Stool samples were collected from 23.4% (1189), 28.6% (1274), 36.3% (1899), and 49.4% (873) of the censused dogs, cats, pigs, and water buffaloes, respectively, and from 663 rats. The adjusted prevalence of S. japonicum infection varied greatly across villages ranging from 1.6% (95% Bayesian Credible Interval: 0.1%-10.2%) to 86.3% (65.9%-97.8%) for dogs, from 0.1% (0%-2.1%) to 21.7% (4.7%-51.2%) for cats, from 0.01% (0.0%%-1.0%) to 18.4% (7.1%-34.7%) for pigs, from less than 0.1% (0.0%-1.2%) to 72.5% (46.0%-97.4%) for water buffaloes, and from 0.7% (0.0%-9.0%) to 95.4% (77.2%-99.9%) for rats. This is the most comprehensive study of animal S. japonicum infection conducted to date. Our results show that, unlike what has been reported in China, very few water buffaloes were infected whereas rats and dogs show high prevalence proportions of infection. This, combined with significant village-to-village variation in prevalence of S. japonicum infection, suggest possible different transmission dynamics of the infection in the Province of Samar in the Philippines and China.

Research approaches for improved pro-poor control of zoonoses

BACKGROUND

Developing countries face difficulties in sustainably utilizing tools to effectively implement control measures for zoonoses. This is mainly due to dispersed and heterogeneous smallholder livestock systems, predominance of informal markets, poor infrastructure and lack of resources to deliver information, interventions, and regulations. In addition, developing countries lack an evidence base for planning and targeting control efforts. Zoonotic infections are receiving more and more international attention as diseases of neglected and impoverished communities, at the intersection between livestock production, human health, and poverty.

OBJECTIVE

To review research innovations and trends that can help identify and test targeted control strategies for zoonoses tailored to poor communities, focusing particularly on Africa.

METHODS

Review of recommendations of relevant working groups and scientific literature.

RESULTS

New and innovative research approaches promise to better capture the impact of zoonoses from a societal perspective and the perspective of poor livestock owners through more comprehensive frameworks that consider benefits of the control of zoonoses to the public health, livestock, and private sectors. It is challenging to better assure food safety in informal markets. Risk-based approaches with participatory elements provide a framework in which stakeholders can decide an appropriate level of protection to balance the needs for safe food, cheap food, and pro-poor economic growth. Appropriate information for all stakeholders and capacity-building of national and regional authorities is an important element of this process. New diagnostic tools that are accurate and easily used in developing-country health centers and markets can assist in reporting of cases, detection of patients, and testing of control strategies.

CONCLUSIONS

A research agenda on zoonoses of the livestock sector should be interdisciplinary and participatory and include intersectoral collaborations, notably between the livestock and public health sectors.

Assessment of routine inspection methods for porcine cysticercosis in Zambian village pigs

The value of tongue and meat inspection as diagnostic tools for porcine cysticercosis was assessed in 65 Zambian village pigs by comparing the results with carcass dissections. In addition, the intensity of infections, distribution and viability of cysts in infected pigs were measured. Five pigs (7.7%) were positive on tongue examination, while routine meat inspection showed 12 (18.5%) positives. However, carcass dissections detected cysticerci in 31 (47.7%) pigs. The range in number of cysticerci was 1 to 14,662 per carcass. Cysticerci were distributed throughout the carcass with the highest concentration in the heart, tongue and hind legs. In one animal 13 viable cysts were detected only in the brain. Fourteen pigs had more than 100 viable cysts, six between 2 and 100, and four had single cyst infections. Seven animals harboured only calcified cysts. These findings demonstrate the serious shortcomings of routine detection methods for porcine cysticercosis. While the specificity of tongue palpation and meat inspection was 100%, these tests failed to detect the infection in 83.9% and 61.3% of infected pigs, respectively.

Risk factors associated with porcine cysticercosis in selected districts of Eastern and Southern provinces of Zambia

To determine the risk factors associated with Taenia solium transmission in humans and pigs in the rural areas of Eastern and Southern provinces of Zambia, a questionnaire was administered in 788 households from 155 villages. Pigs were examined from 800 households. Tongue examination and enzyme-linked immunosorbent assay (Ag-ELISA) for the detection of circulating antigens of T. solium cysticerci were used to measure infection in pigs. A snowballing technique was utilised to select households with pigs. Prevalence of households with pigs infected with T. solium on tongue examination by district ranged from 12.7% to 32.1% with Ag-ELISA having a range of 30.0-51.7%. Of the total number of households visited, 18.8% and 37.6% had at least one pig positive for porcine cysticercosis on tongue examination and Ag-ELISA, respectively. Risk factors associated with T. solium infection were lack of pork inspection at slaughter (96.7%), consumption of pork with cysts (20.1%), selling of pork infected with T. solium cysticerci (18.3%), free-range husbandry system (83.2%) and absence of latrines (58.0). Free-range husbandry system (OR=1.68; 95% CI=1.36-2.07) was a significant risk factor for porcine cysticercosis in the surveyed areas. The result that pigs were mostly kept on free-range and semi-intensive husbandry systems may have permitted them to have access to eating human faeces that could be contaminated with tapeworm eggs. This study has shown that T. solium infection poses a high public health risk in the study areas and urban areas as well. We recommend that a human survey be conducted to verify the human exposure to taeniasis and/or cysticercosis in Zambia.

Epidemiological studies of Schistosoma mattheei infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of Schistosoma mattheei infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Faecal samples of cattle were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas, respectively. Patterns of distribution and seasonal fluctuations of the intermediate host-snail populations and the climatic factors influencing the distribution were also determined at monthly intervals from November 1998 to October 2000, a period of 24 months, in six dams and six streams in the highveld and nine dams in the lowveld communal grazing areas. Monthly, each site was sampled for relative snail density, the vegetation cover and type, and physical and chemical properties of the water. Mean monthly rainfall and temperature were recorded. Snails collected at the same time were individually examined for shedding of cercariae of S. mattheei and Schistosoma haematobium. A total of 16264 (5418 calves, 5461 weaners and 5385 adults) faecal samples were collected during the entire period of study and 734 (4.5%) were positive for S. mattheei eggs. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), calves compared to adult cattle (P < 0.01) and the wet season compared to the dry season (P < 0.01). Faecal egg output peaked from October/ November to March/April for both years of the study. Bulinus globosus, the snail intermediate host of S. mattheei was recorded from the study sites with the highveld having a significantly higher abundance of the snails than the lowveld (P < 0.01). Monthly densities of B. globosus did not show a clear-cut pattern although there were peaks between March/May and September/November. The mean number of snails collected was positively correlated with the water plants Nymphaea caerulea and Typha species. Overall, 2.5% of B. globosus were shedding Schistosoma cercariae. In the highveld, 2.8% of B. globosus were infected with schistosome cercariae and 1.5% in the lowveld, with the figures at individual sites ranging from 0-18.8% in the highveld and from 0-4.5% in the lowveld. The cercariae recorded here were a mixture of S. mattheei and S. haematobium since they share the same intermediate host. The transmission of Schistosoma cercariae exhibited a marked seasonal pattern, being more intensive during the hot, dry season (September/November).

Estimation of the cost of Taenia solium cysticercosis in Eastern Cape Province, South Africa

OBJECTIVES

To provide a comprehensive estimate of the societal costs of Taenia solium cysticercosis for the Eastern Cape Province (ECP), South Africa, as an objective measure of its impact in this endemic area.

METHODS

Epidemiological data on the prevalence of epilepsy, proportion of epilepsy cases due to neurocysticercosis (NCC) and consequences of cysticercosis were gathered from published and unpublished sources. Economical data were mostly obtained from governmental sources. Three methods were used for estimating productivity losses. Monte Carlo sampling was used to represent the uncertainty of the estimates with 95% Credible Intervals (95% CI). The estimation is for 1 year using a societal approach. All costs are reported in 2004 US Dollars.

RESULTS

Overall, there were an estimated 34 662 (95% CI: 17 167-54 068) NCC-associated cases of epilepsy in ECP in 2004. The overall monetary burden (in million of US Dollars) was estimated to vary from US Dollars 18.6 (95% CI: US Dollars 9.0-32.9) to US Dollars 34.2 (95% CI: US Dollars 12.8-70.0) depending on the method used to estimate productivity losses. The agricultural sector contributed an average of Dollars 5.0 million. The prevalence of epilepsy, proportion of productivity reduction and the proportion of epilepsy cases attributable to NCC had the largest impact on the overall estimates.

CONCLUSION

This preliminary estimate suggests that T. solium cysticercosis results in considerable monetary costs to a region that is already economically constrained. Because this infection is preventable, these results could guide stakeholders in deciding where to invest scarce health and agricultural resources in their countries.

Epidemiological survey of swine cysticercosis using ante-mortem and post-mortem examination tests in the southern highlands of Tanzania

Pig keeping is known to be popular in the regions of the southern highlands zone (Mbeya, Iringa and Ruvuma) of Tanzania where more than 60% of pigs under the small-scale production system are raised. However, no epidemiological surveys on porcine cysticercosis have been conducted in the zone in spite of unofficial reports indicating the disease to be a widespread problem. To estimate prevalence rates and risk factors for porcine cysticercosis in Chunya and Iringa Rural Districts and Ruvuma Region (Songea and Mbinga Districts), 722, 808 and 302 live pigs, respectively, were examined by lingually and the prevalence of swine cysticercosis was found to be 7.6%, 8.4% and 16.9% for Chunya and Iringa Rural Districts, and Ruvuma Region, respectively. Structured observations and questionnaire interviews were used to analyse pig rearing practices and household use of latrines in Chunya and Iringa Rural Districts only. The analysis of effect of pig management practices, lack of a latrine, eating undercooked pork, home slaughter and no inspection of pork and lack of knowledge of T. solium on their association to tongue positivity in pigs was done by means of a contingency table. Odds ratios (OR) with corresponding 95% confidence intervals (95% CI) and p-values were calculated. Structured questionnaire interviews identified factors associated with the disease prevalence in both Chunya and Iringa Rural Districts were free-ranging of pigs, home slaughtering of pigs and pork not being inspected. While in Chunya and Iringa Rural Districts lack of latrine and barbecuing were found a risk factor, respectively. To control the disease in the study areas of the southern highlands there is a need for significant improvements regarding the use of latrines, confinement of pigs, pork inspection and thorough cooking of pork.

Epidemiological studies of Fasciola gigantica infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of Fasciola gigantica infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Cattle faecal samples were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas respectively. Patterns of distribution and seasonal fluctuations of the intermediate host-snail populations and the climatic factors influencing the distribution were also determined by sampling at monthly intervals for a period of 24 months (November 1998 to October 2000) in six dams and six streams in the highveld and in nine dams in the lowveld communal grazing areas. Each site was sampled for relative snail density and the vegetation cover and type, physical and chemical properties of water, and mean monthly rainfall and temperature were recorded. Aquatic vegetation and grass samples 0-1 m from the edges of the snail habitats were collected monthly to determine the presence or absence of F. gigantica metacercariae. Snails collected at the same time were individually checked for the emergence of larval stages of F. gigantica. A total of 16264 (calves 5418; weaners 5461 and adults 5385) faecal samples were collected during the entire period of the study and 2500 (15.4%) of the samples were positive for F. gigantica eggs. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), for adult cattle than calves (P < 0.01) and in the wet season over the dry season (P < 0.01). Faecal egg output peaked from August/September to March/April for both years of the study. Lymnaea natalensis, the snail intermediate host of F. gigantica was recorded from the study sites with the highveld having a significantly higher abundance of the snail species than the lowveld (P < 0.01). The snail population was low between December and March and started to increase in April reaching a peak in September/October. The number of juvenile snails peaked between April and August. The mean number of snails collected was negatively correlated with rainfall and positively correlated with temperature. Mean number of snails collected was also positively correlated with Potamogeton plant species and negatively correlated with Cyperus plant species. However, none of the L. natalensis collected from the habitats were found shedding Fasciola cercariae. Metacercariae were found on herbage from the fringes of the snail habitats between February and August for both years, with most of the metacercariae concentrated on herbage 0-1 m from the banks of the habitats. Based on the findings of this study, anthelmintic treatment should be administered in December/January to control chronic and mature fasciolosis. A second treatment should be given in April/May to reduce pasture contamination and subsequently snail infection, as this is the time the snail population starts to build up. To control acute fasciolosis due to the immature liver flukes a third treatment should be given in August. The first application of molluscicides to control the snail intermediate hosts can be done in June the time when the snail is harbouring the parasite and a second application in September in order to kill new generations of infected snails

Epidemiological studies of amphistome infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe

During the period between January 1999 and December 2000, the distribution and seasonal patterns of amphistome infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Cattle faecal samples were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas, respectively. Patterns of distribution and seasonal fluctuations of intermediate host-snail populations and the climatic factors influencing the distribution were also determined by sampling at monthly intervals for a period of 24 months (November 1998 to October 2000) in six dams and six streams in the highveld and in nine dams in the lowveld communal grazing areas. Each site was sampled for relative snail density and the vegetation cover and type, physical and chemical properties of water, and mean monthly rainfall and temperature were recorded. Aquatic vegetation and grass samples 0-1 m from the edges of the snail habitats were collected monthly to determine the presence or absence of amphistome metacercariae. Snails collected at the same time were individually checked for the emergence of larval stages of amphistomes. A total of 16,264 (calves 5418, weaners 5461 and adults 5385) faecal samples were collected during the entire period of the study and 4790 (29.5%) of the samples were positive for amphistome eggs. For both regions the number of animals positive for amphistome eggs differed significantly between the 2 years, with the second year having a significantly higher prevalence (P < 0.01) than the first year. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), for adult cattle than calves (P < 0.01), and in the wet over the dry season (P < 0.01). Faecal egg output peaked from October to March in both years of the study. Bulinus tropicus, Bulinus forskalii and Biomphalaria pfeifferi were recorded from the study sites. The main intermediate host for amphistomes was B. tropicus with a prevalence of infection of 8.5%. However, amphistome cercariae were also recorded in Biom. pfeifferi and B. forskalii. Amphistome cercariae were recorded from both the highveld and lowveld areas with peak prevalence during the post-rainy season (March to May). Metacercariae were found on herbage from the fringes of the snail habitats between February and August, with most of the metacercariae concentrated on herbage 0-1 m from the edges of the habitats. Based on the epidemiological findings a control programme was devised. From this study, large burdens of immature flukes could be expected in cattle during the dry months. Since adult cattle would be resistant to the pathogenic effects of the migrating immature amphistomes the target for control would be young animals being exposed to the infection for the first time. Therefore, the first anthelmintic treatment can be administered in calves in mid June when maximum migration of immature amphistomes starting 3-4 weeks after infection in the early dry season would be expected. A second treatment could be given in late July or early August to remove potentially dangerous burdens of immature flukes acquired later in the dry season. Where resources permit, another strategy would be to treat against the mature flukes in March or April in order to reduce the number of eggs deposited on pastures and the opportunity for infection of the intermediate host snails. To reduce cercarial shedding by the intermediate host snails molluscicides can also be applied during the peak transmission periods (April/May and August/September).

Estimating sensitivity and specificity of a faecal examination method for Schistosoma japonicum infection in cats, dogs, water buffaloes, pigs, and rats in Western Samar and Sorsogon Provinces, The Philippines

Schistosoma japonicum causes a chronic parasitic disease, which persists as a major public health concern in The Philippines, the People's Republic of China and Indonesia. This infection is unique among helminthic zoonoses because it can infect humans and more than 40 other mammals. The objective of this study was to estimate the sensitivity and specificity of the Danish Bilharziasis Laboratory technique in cats, dogs, pigs, water buffaloes and rats in the Philippines. Faecal samples from each animal were collected on up to five occasions on five consecutive days in four villages of Sorsogon and Western Samar Provinces between January and July 2003. The faecal samples were analysed with the filtration and sedimentation Danish Bilharziasis Laboratory technique. Sensitivity and specificity of one, two, three, four, and five faecal samples were estimated using a Bayesian latent class approach. A total of 59, 43, 74, and 80% of the censored cats, dogs, pigs, and water buffaloes in the four villages were sampled, respectively. For all species, the sensitivity estimates when using the results of only 1 day of sampling were less than 80%. However, the sensitivity improved to at least 96% in all species when three or more faecal samples were collected on three separate days. The specificity was estimated to be above 92% across all species, even if just a single sample is used. The prevalences and 95% credible intervals of S. japonicum, adjusted for imperfect sensitivity and specificity, in cats, dogs, pigs, rats, and water buffaloes were 11.9% (6.8-18.3%), 19.9% (15.1-25.2%), 2.9% (1.1-5.2%), 31.3% (18.3-45.6%) and 6.3% (2.1-12.6%), respectively. Our results suggest that the Danish Bilharziasis Laboratory technique is valid for the detection of infection with S. japonicum in animals, and that sensitivity estimates are excellent when faecal samples are collected on at least three different days. Monitoring S. japonicum infection in animal reservoirs with a valid test could contribute to more effective public health control programmes.

Methods for assessing the burden of parasitic zoonoses: echinococcosis and cysticercosis

Cysticercosis and echinococcosis cause illness and productivity losses in human and agricultural animal populations. Recent studies suggest that these diseases have large societal impacts on endemic areas. Estimates of burden provide essential, evidence-based data for conducting cost-benefit and cost-utility analyses that will secure political will, and financial and technical resources. To evaluate the burden, the monetary and non-monetary impacts of these zoonoses on human health, agriculture and society must be considered comprehensively. In this article, we review the framework used to assess the burden of cysticercosis and echinococcosis, and the data needed to estimate the extent of the problem for societies.

Estimating and modeling the dynamics of the intensity of infection with schistosoma japonicum in villagers of leyte, Philippines. Part II: Intensity-specific transmission of S. japonicum. The schistosomiasis transmission and ecology project

A dynamic model of Schistosoma japonicum transmission is presented that incorporates effects of infection intensity, age, and sex. We use four infection intensity classes to investigate the impact of ecologic changes and public health interventions on the burden of infection within communities. Age- and sex-specific infection data from three disease-endemic villages in the Philippines are used to estimate the parameters of the model. The model gives good qualitative agreement with observed fecal egg counts adjusted for the accuracy of the Kato-Katz examination. Our results suggest that differences in infection burden between villages are caused by differences in both the infection process and the recovery process in humans. We describe the potential impact of mass treatment of all humans on the numbers with high infection. Furthermore, we show that a sudden reduction in snail population size would affect high prevalence and low prevalence communities in different ways.

A slaughter slab survey for extra-intestinal porcine helminth infections in northern Tanzania

A survey on extra-intestinal porcine helminths was conducted at three slaughter slabs that receive pigs from Mbulu, a district endemic for porcine cysticercosis in northern Tanzania. Seventy carcases of pigs between 1 and 2 years old were examined between December 1997 and March 1998. The examination involved ante-mortem lingual examination for Taenia solium cysticercosis followed by post-mortem inspection. In addition, a laboratory procedure was performed to determine whether any of these domestic pigs were infected with Trichinella species. Parasites detected were Ascaris suum (44.3%), Echinococcus granulosus (4.3%) and Taenia hydatigena (1.4%). The lack of cases of porcine cysticercosis in this study compared to previous studies suggests that pig traders are conducting their own ante-mortem lingual examinations before purchasing pigs in the rural communities where the parasite is still highly prevalent. It is concluded that improved meat inspection could prove useful in reducing the local population's risk of infection with these parasites. The results of this study have revealed the parasites of agricultral and public health importance in the targeted communities. Further epidemiological investigations are required to better determine parasite prevalence and impact in order to formulate appropriate and cost-effective strategies for control.

Risk factors for the prevalence of porcine cysticercosis in Mbulu District, Tanzania

To estimate prevalence of and risk factors for the prevalence of porcine cysticercosis in Mbulu District, Tanzania, 770 live pigs were examined by lingual examination in 21 villages. Structured observations and questionnaire interviews were used to assess pig rearing practices and household use of latrines. Associations between factors were analyzed using a Bayesian hierarchical model to obtain prevalence odds ratio (OR) and 95% Bayesian Credible Intervals (95% BCI). Prevalence was 17.4% (village-specific range 3.2-46.7%). Prevalence of porcine cysticercosis was considerably higher in pigs reared in households lacking latrines than in those reared in households that were using latrines (OR = 2.04; 95% BCI = 1.25, 3.45). About 96% of the pigs were kept under free-range conditions. This study suggests the need for further studies in order to design and implement effective prevention and control measures for porcine cysticercosis in Mbulu District, Tanzania.

A Bayesian approach for estimating values for prevalence and diagnostic test characteristics of porcine cysticercosis

Several diagnostic techniques are used to estimate the prevalence of the zoonotic tapeworm Taenia solium in pigs, but none of these tests are perfect, making interpretation of results difficult. A Bayesian approach was used to estimate values for the prevalence and diagnostic test characteristic of porcine cysticercosis by combining results of four imperfect tests. Village pigs (N = 868) slaughtered in Lusaka (Zambia), were bled, and tongue and routine meat inspected; and serum antibody and parasite antigen concentrations were determined by ELISA. A model, based on a multinomial distribution and including all possible interactions between the individual tests required 31 parameters to be estimated, but actually allowed only 15 parameters (i.e. had 15 degrees of freedom) to be estimated. Therefore, prior expert opinion on specificity and (in)-dependence of the tests was entered in the model, resulting in a reduction of the number of parameters to be estimated. The estimated prevalence of porcine cysticercosis was 0.642 (95% confidence interval 0.54-0.91). The performances of the tests were (sensitivity (se)-specificity (sp)): tongue inspection (se 0.210-sp 1.000), meat inspection (se 0.221-sp 1.000), Ab-ELISA (se 0.358-sp 0.917), Ag-ELISA (se 0.867-sp 0.947). To validate the estimates obtained from the model we performed a second study: 65 randomly purchased Zambian village pigs were bled for serum antibody and antigen determination, their tongue and meat inspected; and in addition, the carcasses were dissected for total cysticercus counts (gold standard). Cysticerci were found in 31 pigs (prevalence 0.477, 95% confidence interval 0.35-0.60), overlapping with the estimated prevalence in the first study. Sensitivity and specificity values obtained for the aforementioned tests in this study were in agreement with those estimated. A Bayesian analysis framework offers the possibility to combine prior opinion with experimental data to more accurately estimate the real prevalence of porcine cysticercosis in the absence of a gold standard.

Gastrointestinal nematodes in indigenous Zebu cattle under pastoral and nomadic management systems in the lower plain of the southern highlands of Tanzania

This study aimed to determine the prevalence and intensity of gastrointestinal nematode infections in indigenous Zebu cattle in the lower plain (lowland zone) of the southern highlands of Tanzania. Gastrointestinal tracts were randomly purchased at the Iringa regional abattoir and at Kihesa and Ipogolo slaughter slabs in different seasons of the year. The contents of the abomasum, small intestine and large intestine were processed separately to recover the worms. The results indicated that 140 out of 144 (97.2%) of the examined animals were infected. The mean (+/-SE) total worm burden was 1284 +/- 183 (range 10-12,600) worms per animal and most infected animals contained more than one nematode species. The nematode species present, their prevalence and mean burden were as follows: Haemonchus placei, 84.7%, 316; H. similis, 5.6%, 1; Oesophagostomum radiatum, 79.2%, 66; Cooperia pectinata, 55.6%, 713; C. punctata, 44.4%, 157; Bunostomum phlebotomum, 5.6%, 5; Trichuris globulosa, 5.6%, 2; and Trichostrongylus colubriformis, 1.4%, 24. The burdens were mainly composed of Cooperia pectinata (55.5%), Haemonchus placei (24.6%), Cooperia punctata (12.3%) and Oesophagostomum radiatum (5.1%). The highest burdens occurred at the end of the rainy/early dry season, while the lowest burdens were found at the end of the dry/early rainy season. There was no difference in the burdens between male and female animals. Immature cattle (< 3 years) had significantly higher worm burdens than mature cattle (p < 0.01). A poor grade for a live animal was associated with higher worm burdens only in immature cattle and then especially during the dry season (r = 0.456, p < 0.001). Anthelmintic treatments in the late rainy/early dry season and early rainy season are recommended in order to prevent outbreaks of helminthosis during the dry season and to reduce carryover of infection into the next rainy season. An additional wet season treatment is advisable in immature cattle, but may not be needed for mature cattle owing to the availability of plenty of mature, good quality pasture.

Current status of cysticercosis in Vietnam

This English review concerning the current status of cysticercosis in Vietnam has been compiled from various reports of studies conducted over the past 15 years, which have appeared in national publications in Vietnamese, in order to make the information available to the international community. Hospital surveys indicate that cysticercosis is emerging as a serious health problem in the country though most of the information comes from the Hanoi area. Many more men than women are being treated for cysticercosis with most patients being young to middle-aged adults though several juvenile cases have been seen in the south. Clinical manifestations of the disease in humans include subcutaneous nodules, epileptic seizures, severe headache, impaired vision and memory loss. Albendazole has been found to be the best drug for treating cysticercosis though it does not appear to be totally effective for curing cerebral cysts. Information concerning porcine and bovine cysticercosis is very limited and based mostly on passive surveillance at Hanoi slaughterhouses. Surveys for human taeniasis in central and northern provinces indicate a prevalence of 0.2-7.2%. However, techniques of low sensitivity were used and the results are inconclusive since it is unknown with which species of tapeworm the people were infected. In addition to Taenia solium which causes human cysticercosis, T. saginata and T. asiatica are also known to be present in Vietnam. Risk factors investigated thus far with regard to transmission of T. solium suggest that consumption of raw pork, inadequate or absent meat inspection and control, poor sanitation in some areas, and the use of untreated human waste as fertilizer for crops may play important roles in Vietnam but this remains to be validated. The evidence thus far collected suggests that a national surveillance program for cysticercosis is a great need for Vietnam. The authors recommend further research on the epidemiology and impact of cysticercosis in both human and pig hosts in order to determine whether a prevention and control program in Vietnam would be merited and cost effective.

The emergence of Taenia solium cysticercosis in Eastern and Southern Africa as a serious agricultural problem and public health risk

Pig production has increased significantly in the Eastern and Southern Africa (ESA) region during the past decade, especially in rural, resource-poor, smallholder communities. Concurrent with the increase in smallholder pig keeping and pork consumption, there have been increasing reports of porcine cysticercosis in the ESA region. This article reviews the findings concerning the presence and impact of porcine cysticercosis in seven of the ESA countries. Most of the reported findings are based on surveys utilising lingual palpation and post-mortem examination, however, some also used serological assays. In Tanzania, community-based studies on porcine cysticercosis indicate a prevalence of 17.4% in the northern highlands district of Mbulu and a prevalence range of 5.1-16.9% in the southern highlands. In Kenya recent surveys in the southwestern part of the country where smallholder pig keeping is popular indicate that 10-14% of pigs are positive for cysticercosis by lingual examination. Uganda has the most pigs in Eastern Africa, most of which are kept under smallholder conditions. Preliminary surveys in 1998 and 1999 at slaughterhouses in Kampala indicated a prevalence of porcine cysticercosis between 0.12 and 1.2%, however, a rural survey in northern Uganda in 1999 indicated 34-45% of pigs slaughtered in selected villages were infected. Additionally, a new survey of 297 pigs slaughtered in Kampala in 2002 indicated that pigs from the central region of the country were negative for cysticercosis while 33.7% of the pigs coming from the rural Lira district in the north were positive. Interestingly 8 piglet foetuses removed from an infected slaughtered sow coming from Lira district were all found to harbour cysts of T. solium providing evidence of congenital transmission of porcine cysticercosis. In Mozambique, abattoir records indicate that porcine cysticercosis is present in all provinces of the country. A serological survey on pigs in rural Tete Province found 15% of pigs positive. In Zimbabwe, a retrospective study in official abattoirs around the country from 1994 to 2001 reported a mean prevalence of 0.34% which is in contrast to a post-mortem survey in 1999, which showed that the prevalence of porcine cysticercosis in rural west Zimbabwe where smallholder pig keeping is popular was 28.6%. In Zambia, abattoir records reported porcine cysticercosis in six of the nine provinces. Routine meat inspection of 1316 pigs at a slaughter slab in Lusaka showed that 20.6% of the pigs had cysticercosis whereas serological testing of 874 pigs at the same abattoir indicated that 56.6% were found to have circulating antigens of Taenia solium. Field surveys based on lingual palpation in Southern and Eastern Provinces of Zambia revealed prevalences of 8.2-28.4 and 5.2%, respectively. South Africa has the largest number of pigs in Southern Africa and cysticercosis has been recognised as a problem in the country for many decades. There is strong evidence supporting the high prevalence of neurocysticercosis infecting humans from resource-poor areas of the country where pigs are being raised under smallholder conditions. In spite of this community-based surveys on porcine cysticercosis have never been conducted in South Africa and the last slaughterhouse survey was conducted nearly 40 years ago. The prevalences of porcine cysticercosis found in these ESA countries rank among the highest in the world and the disease is emerging as an important constraint for the nutritional and economic well being of resource-poor smallholder farming communities. The current findings suggest the widespread presence of human tapeworm carriers and thus a high risk of human cysticercosis in both rural areas and urban centres in the ESA region. More research is required in the region to assess the extent and public health and economic impact of T. solium infection in order to determine whether and what prevention and control efforts are needed.

The current status of neurocysticercosis in Eastern and Southern Africa

Some information has been documented on the epidemiology of neurocysticercosis in Eastern and Southern Africa through the monitoring of hospital-based patients with neurocysticercosis, community-based serological surveys of particular socio-economic groups of people and surveys of porcine cysticercosis. Studies have revealed that non-pork eaters have as great a chance of infection as a pork eater, the Xhosa-speaking people of the Eastern Cape Province have the highest prevalence of cysticercosis/taeniosis in South Africa probably due to the common practice of free-range pig farming and the lack of sanitation in these areas. Several studies have revealed high prevalence rates in children and interestingly, patients with active cysts suffering from epilepsy. A startling mode of transmission is where self-trained healers use Taenia segments either for benevolent (e.g. in the treatment of severe intestinal tapeworm infections) or malevolent (evil) purposes (e.g. women "poisoning" an unfaithful husband or lover by adding the contents of Taenia solium segments to beer).

Worm control practices and anthelmintic usage in traditional and dairy cattle farms in the southern highlands of Tanzania

Worm control practices and anthelmintic usage in 177 cattle farms in Iringa district in the southern highlands of Tanzania was determined through a questionnaire survey. A total of 76 traditional, 92 small-scale dairy and 9 large-scale dairy cattle farms were included in the survey. Results indicated that 87.7% traditional, 97.8% small-scale dairy and 100% large-scale farmers relied solely on the use of anthelmintics, 2.7% traditional farmers used traditional medicines while 9.6% traditional farmers had not any form of worm control practice. Worm infection was ranked the second most important constraint of productivity in cattle in the three production systems. Most farms (57.6% traditional, 35.8% small-scale dairy, 66.7% large-scale dairy) used anthelmintics with a combination of levamisole and oxyclozanide. Benzimidazoles were used only in traditional (25.4%) and small-scale dairy (32.1%) farms while nitroxynil (Trodax) was mostly used in large-scale dairy farms (33.3%). Generally, 40% of farmers treated three or four times a year and the frequency in some farms was surprisingly high for resource poor small-scale farmers. The frequency of anthelmintic treatment was mostly the same regardless of the management system. Treatments in most farms depended on availability of money and drugs and not the epidemiology of parasites. A significant proportion (46.3%, P=0.007) of farmers especially in rural areas failed to follow their pre-planned treatment schedules due to lack of money (86%) and unavailability of drugs (6.6%). Many farmers (58.9%) had used the same type of anthelmintic for four or more consecutive years and 85.3% of them would continue with the same anthelmintic. Farmers in all management systems mostly purchased anthelmintics from private veterinary drug shops and about 43% traditional and 33.3% small-scale dairy farmers mostly in rural areas obtained anthelmintics from village extension officers. Despite the fact that all farmers were aware of worm infection and the associated signs in cattle, 42.5% had poor knowledge on the source of worm infection. Small-scale dairy farmers allowed only a 1-day withdraw period for milk regardless of the type of anthelmintic used and there was no milk and slaughter clearance in traditional farms. It was concluded from this study that worm control in Iringa faces serious constrains and that education of farmers and farm hands is not adequate. Moreover, poor quality control and high price of potent anthelmintics, few extension workers, low income and low education among farmers contributed significantly to erratic worm control practices and anthelmintic usage in peri-urban and rural areas.

The prevalence of porcine cysticercosis in Eastern and Southern provinces of Zambia

The objective of this study was to determine the prevalence and importance of porcine cysticercosis in rural areas of Zambia. The study involved an abattoir survey of 1316 pigs at a slaughter slab in Lusaka and two field surveys in villages in Southern and Eastern provinces. Lingual examination of live pigs and visual inspection of their carcass as well as blood sampling for measuring circulating parasite antigen by enzyme-linked immunosorbent assay (Ag-ELISA) were used as parameters to measure infection. In the field surveys, a questionnaire was administered to every household whose pigs were examined to obtain information on pig husbandry practices and to study risk factors for the infection. Out of the 1316 pigs examined at the slaughter slab, 143 (10.9%) and 271 (20.6%) were positive by lingual examination and meat inspection, respectively. Most of the pigs were very heavily infected with predominantly live cysts. The field surveys revealed that eight (8.2%) out of 98 pigs from Southern province and eight (5.2%) out of 151 pigs from Eastern province were positive for cysticercosis by tongue palpation. Using the Ag-ELISA 20 (20.8%) and 14 (9.3%) pigs were positive in Southern and Eastern provinces, respectively. The questionnaire survey revealed poor pig husbandry practices, absence of meat inspection and control, poor knowledge of the disease and poor sanitation in the surveyed villages. The prevalence of pig cysticercosis found in this study ranks among the highest in the southern African region, in Africa and in the world. The current study suggests the presence of human tapeworm carriers and a high risk of human cysticercosis in the surveyed areas as well as in urban centres where pigs from rural areas are increasingly sold, slaughtered and consumed.

Distribution and density of cysticerci of Taenia solium by muscle groups and organs in naturally infected local finished pigs in Tanzania

The distribution and density of cysticerci of Taenia solium among distinct carcass sites was determined in 24 naturally infected finished pigs from Mbulu district, Tanzania. The heart, tongue, internal and external masseters, triceps brachii, lungs, liver, kidneys, psoas, diaphragm and brain of each pig as well as the muscles from the forelimb, hind limb, abdomen, head and thorax from one half of each pig carcass were all designated as distinct carcass sites and sliced in such a way that all fully developed cysts could be revealed and enumerated (i.e. each slice was less than 0.5 cm thick). The carcasses harboured from 76 to 80,340 cysts in total. Carcass sites which harboured the highest proportion of cysts were those of the hind and forelimbs (mean: 27.7 and 24.5%, respectively, of the total cysts in the carcass), while lower proportions were found in the tongue, heart, triceps brachii, and diaphragm (7, 3.6, 2 and 2, respectively). Relative cyst density was calculated for the different carcass sites by dividing the mean proportion of the total weight of the tissue groups into the mean proportion of cysts located in that site. The cysticerci in the examined distinct carcass sites were found in the following order of relative density: psoas muscles (10.5), internal masseter (8.1), external masseter (7.1), triceps brachii (4.9), forelimb (4.0), head muscles (3.8), tongue (3.4), hind limb (3.2), diaphragm (2.4), heart (1.9), abdominal muscles (1.3), trunk muscles (1.1), brain (1.0) and oesophagus (0.3). The proportion of cysts expected to be found at the surfaces exposed by visual examination or incision at meat inspection was calculated using an indirect method, which incorporated the area revealed by incision and visual inspection of an organ and the proportion of cysts located in the particular organ. It was estimated that 10.6% of the cysts would be located at inspected sites if regulations were followed carefully.

Experimental Schistosomiasis japonica in the pig: immunohistology of the hepatic egg granuloma

Use of the pig as an animal model in schistosomiasis research is increasing, but knowledge of the porcine immune response to schistosome infection is still very limited. We investigated the immunohistology of different maturation stages of the Schistosoma japonicum egg granuloma in pigs. Liver sections from pigs experimentally infected with S.japonicum for 9, 12 or 21 weeks were examined by immunohistochemistry using a three-step streptavidin-biotin-complex/immunoperoxidase method or a two-step alkaline phosphatase-mediated system. All granulomas showed marked expression of major histocompatibility complex (MHC) class II in epithelioid macrophages and were dominated by T lymphocytes, comprising both CD4+ and CD8+ phenotypes, with consistently higher proportions noted for CD8+ cells. B lymphocytes, as identified by expression of CD21, were confined to lymphoid nodular structures primarily associated with mature granulomas. Early and mature granulomas contained numerous immunoglobulin (Ig)G+ plasma cells. Significant differences in immunohistology related to duration of infection were not observed. The results indicate that all stages of the hepatic S.japonicum egg granuloma in the pig manifests MHC class II-dependent CD4+ T cell activity concomitant with infiltration of CD8+ T cells. B cell activity preceding the effector cell stage appears to occur in granuloma-associated lymphoid nodules, whereas antibody, mainly IgG, is produced within the granuloma.

Peri-parturient helminthosis in strains of small East African goats in Tanzania

The effect of physiological status (e.g. pregnancy and lactation) on the susceptibility to gastrointestinal nematodes was studied in the Dodoma and Kigoma strains of small East African goats in Morogoro. Forty-six pregnant does (19 Dodoma and 27 Kigoma strain) and 123 non-pregnant/dry (68 Dodoma and 55 Kigoma) from a controlled-breeding programme were used. Does were grazed on naturally contaminated pastures at Sokoine University of Agriculture for 8 months. Faecal samples and whole blood for determination of faecal egg counts (FEC), packed-cell volume (PCV) and blood eosinophils (EOS) from each animal were collected at monthly intervals from the mating period (through the gestation period) to 3 months after kidding. From kidding to 3 months after kidding, lactating does had significantly higher FEC than non-lactating/dry does. From 1 month after kidding to 3 months after kidding, lactating does had significantly lower PCV than dry does. Blood eosinophils were higher in non-lactating/dry does than lactating does but only significant at 3 months after kidding. There were no significant differences in FEC, PCV and EOS between lactating Dodoma and lactating Kigoma does. We concluded that there was no difference in peri-parturient helminthosis between Dodoma and Kigoma strains and that blood eosinophilia decreased during peri-parturient helminthosis in both strains.

An epidemiological investigation of congenital Schistosoma japonicum transmission in Hubei Province, PR China

A cohort study was conducted in Hubei Province, China, following serious flooding of the Yangtze River in the autumn of 1998 to investigate the possibility of congenital transmission of Schistosoma japonicum in humans. The cohort investigated was comprised of 205 women and their 208 infants born between 1 September and 30 December 1998. Blood and fecal samples from all the women and their infants were collected and examined for S. japonicum infection. Positive specific antibody titers were found in 14 (6.8%) of the mothers, but no fecal egg excretion was observed. All infants had negative specific antibody titers and no S. japonicum eggs were found in their feces. Hence, the present study coud not confirm congenital S. japonicum transmission in humans. Further studies are highly wanted to study the impact of prenatal exposure of S. japonicum on the offspring.

Prevalence and distribution of pig helminths in the Dongting Lake Region (Hunan Province) of the People's Republic of China

The prevalence of helminths in pigs was investigated in five rural communities situated on the embankment of Dongting Lake in Zhiyang County, Hunan Province, People's Republic of China, in an area known to be endemic for Schistosoma japonicum. The helminth prevalences identified on the basis of faecal egg count analysis were: Oesophagostomum spp. (86.7%), Ascaris suum (36.7%), Metastrongylus spp. (25.8%), Strongyloides spp. (25.8%), Trichuris suis (15.8%), Globocephalus spp. (6.7%), Gnathostoma spp. (4.2%), Schistosoma japonicum (5.0%) and Fasciola spp. (1.3%). Post mortem examinations of a small number of pigs depositing eggs of different helminth species revealed the presence of Oesophagostomum dentatum, O. quadrispinulatum, A. suum, Metastrongylus apri, M. pudendotectus, T. suis, G. hispidum and Ascarops dentata. Prevalences of all helminths, with the exception of Oesophagostomum spp., were higher in young pigs (< 8 months old) compared with adult pigs. Prevalences of trematodes were very low, especially for S. japonicum which had decreased dramatically compared with previous reports from this area of P.R. China, whereas prevalences of nematodes were generally in agreement with those reported from other Yangtze River Provinces. Results from helminth prevalence studies in pigs, conducted in other provinces of P.R. China between 1987 and 1997, are presented and discussed. It was concluded that a government helminth control programme, implemented in 1995 to control S. japonicum infection in pigs in Hunan Province, may have resulted in a greatly reduced prevalence of S. japonicum in pigs in this region.

Effects of anthelmintic treatment and feed supplementation on grazing Tuli weaner steers naturally infected with gastrointestinal nematodes

A study was carried out to determine the epidemiology of gastrointestinal nematodes in indigenous Tuli cattle and the effect of dietary protein supplementation and anthelmintic treatment on productivity in young growing cattle. Forty steers with an average age of 18 months were divided into 4 groups; 1) fenbendazole (slow release bolus) and cottonseed meal (FCSM group), 2) fenbendazole (FBZ group), 3) cottonseed meal (CSM group) and 4) control (no cottonseed meal and no fenbendazole) (control group). Performance parameters measured included worm eggs per gram of faeces (EPG), packed cell volume (PCV), albumin and live-weight gain. Results showed that faecal worm egg counts were lower and PCV was higher in the FCSM and FBZ groups than in the CSM and control groups (P < 0.01). Weight gains were higher in the CSM and FCSM groups than in the FBZ and control groups (P < 0.05). The cost benefits of anthelmintic treatment and dietary supplementation were apparent in this study. The improved growth performance of the FCSM, FBZ and CSM groups reflected a financial gain over the controls on termination of the study. The dominant genera of gastrointestinal nematodes on faecal culture, pasture larval counts and necropsy were Cooperia and Haemonchus. The incidences of Trichostrongylus, Oesophagostomum and Bunostomum were low.

Tissue responses in experimental schistosomiasis japonica in the pig: a histopathologic study of different stages of single low- or high-dose infections

The tissue responses of pigs exposed to either 100 or 2,000 Schistosoma japonicum cercariae were examined at 4, 11, 17, and 24 weeks postinfection (PI) to explore the pig as an animal model for pathologic aspects of human schistosomiasis japonica. Egg granulomas were present in the liver, intestine, and occasionally in the lungs from 11 weeks PI. There were also many free eggs and early exudative reactions to eggs in the intestine. At 11 weeks PI, pigs in the higher dose group showed marked periportal and septal fibrosis with minimal parenchymal destruction. Thereafter, lesions regressed spontaneously as the pigs underwent a self-cure. The lower dose group showed only mild lesions throughout the study. The degree of hepatic fibrosis was correlated with the density of eggs and granulomas in liver tissue. The results indicate that the pig would be particularly useful for studies of the development and resolution of schistosomal hepatic fibrosis, and also for investigations of the mechanisms behind the self-cure phenomenon.

Age-dependent occurrence of the intestinal ciliate Balantidium coli in pigs at a Danish research farm

A cross sectional study of the prevalence and intensity of Balantidium coli in pigs was carried out on a Danish research farm. The prevalence of B. coli infection increased from 57% in suckling piglets to 100% in most pig groups > or = 4 weeks old. The mean number of cysts per gram faeces (CPG) of pigs aged 12 weeks and younger were < or = 206, whereas pigs aged 28 weeks and > 52 weeks had significantly higher counts of > or = 865 CPG. Although some lactating sows had very high CPG's, no significant differences in CPG could be detected between the intensities of pregnant sows, lactating sows and empty and dry sows. No human cases of B. coli infection have been published in Denmark though it is zoonotic.

Schistosoma japonicum infection and serum and tissue concentrations of retinol and zinc in pigs

The effects of Schistosoma japonicum infection on the concentrations of zinc in serum, liver, spleen and muscle and on the concentrations of retinol in serum and liver were studied in 48 pigs. Twenty-four of the pigs were each infected by intramuscular inoculation with 2000 cercariae of S. japonicum in medium and the rest were similarly inoculated with parasite-free medium, as controls. On each of weeks 4, 11, 17 and 24 post-inoculation (PI), 12 pigs (six of which were infected) were killed. Tissue samples were collected at necropsy. Blood samples were taken prior to infection and at necropsy from all pigs, and bi-weekly from the pigs killed 24 weeks post-infection. In an analysis of variance in which serum retinol was the dependent variable, the interaction infection x time was found to be significant (P = 0.009). The main reason for this significance was that the concentration of retinol in the sera collected from infected pigs at necropsy at 11 weeks PI was significantly lower than in the control pigs killed at the same time (P = 0.02). Although, overall, infection led to higher zinc concentrations in the liver (P = 0.04) and spleen tissue (P = 0.01), it had no apparent effect on liver retinol, muscle zinc or serum zinc. However, among the pigs which were tested bi-weekly, serum zinc was consistently lower in the infected pigs than in the controls (P = 0.01). The transient declines seen in the concentrations of retinol and zinc in sera from the infected pigs were not accompanied by similar changes in the tissue concentrations, and may reflect an acute-phase response to infection. Schistosoma japonicum infection in pigs is considered a useful model of S. japonicum infection (and probably also of S. mansoni infection) in humans. Similar effects, if they occur in the human infections, may lead to misclassification of vitamin-A and zinc status in endemic populations if this status is based on serum retinol and serum zinc.

Congenital transmission of Schistosoma japonicum in pigs

Congenital transmission of Schistosoma japonicum in pigs was investigated by experimentally infecting sows at four weeks gestation (n = 3), 10 weeks gestation (n = 3), or a few weeks prior to insemination (n = 2). None of the piglets born to sows infected prior to insemination or in early pregnancy were found to be infected. However, all of the piglets (n = 26) born to sows infected at 10 weeks gestation were found to harbor schistosomes with S. japonicum eggs recovered from both their feces and livers. The findings show that congenital S. japonicum infection of pigs can occur if sows are infected during mid-to-late pregnancy and may have important implications not only for pigs but also for other mammalian hosts of schistosomes, including humans.

A new technic for counting Schistosoma japonicum eggs in pig feces

An improved laboratory method was developed for counting Schistosoma japonicum eggs in pig feces, which involves filtration, sedimentation and centrifugation, but avoids toxic chemicals. It is sensitive, allows easy differentiation from similar-sized and shaped protozoan cysts, and permits evaluation of egg viability both by direct viewing of eggs and miracidial hatching. It was found to be significantly better at recovering eggs than the modified Bell filtration technic. The sensitivity, specificity and practicality of this technic make it our method of choice for studies on porcine schistosomiasis japonica.

Schistosoma japonicum in the pig: the host-parasite relationship as influenced by the intensity and duration of experimental infection

Parasitologic, clinicopathologic, and pathologic aspects of Schistosoma japonicum infections of varying durations and intensities were studied in growing pigs injected intramuscularly with a dose of either 0, 100, 500, or 2,000 cercariae and killed at 4, 11, 17, or 24 weeks postinfection (PI). The number of viable worm pairs decreased significantly in the high dose group after 11 weeks PI but not in the lower dose groups; however, a stable population of immature worms persisted throughout the study in all dose groups. Liver egg counts also tended to decrease in the high dose group after 11 weeks but not in the other groups. Fecal egg excretion began at six weeks PI, was highest at eight weeks PI with a pronounced peak occurring only in the high dose group, and then decreased to low levels by 14 weeks PI in all groups. Egg counts from the feces as well as the liver correlated strongly with worm pair numbers during the acute phase of infection. The only clinicopathologic abnormality observed was an increase in circulating eosinophils corresponding to cercarial dose in all infected pigs by week six with peak counts occurring between six and eight weeks PI. The pigs exhibited no clinical signs of disease aside from diarrhea at the onset of patency. However, lesions were present throughout the large intestine of all infected pigs from 11 weeks PI, gradually decreasing with time. Severe liver fibrosis occurred in the 500 and 2,000 dose groups mainly at 11 weeks PI and then decreased in severity. In the liver, but not in the intestine, the severity of lesions at all time points was proportional to the cercarial dose given. The results indicate that after several weeks of patency, pigs with high intensities of S. japonicum infection are able to effectively eliminate the majority of adult worms while maintaining a stable population of immature schistosomes.

In vitro maintenance of Schistosoma japonicum and surgical transfer from donor to naïve recipient pigs

An objective of this study was to find a culture medium and a temperature range suitable for in vitro maintenance of adult Schistosoma japonicum during surgical transplantation experiments. Adult S. japonicum were cultivated in four different media (NCTC 135, NCTC 109, RPMI 1640 and 0.85% physiological saline) supplemented with 10% heat-inactivated normal pig serum (hiNPS) at either 4 degrees C, 22-25 degrees C (room temperature) or 37 degrees C. Based on survival and morphologic evaluation, NCTC 135 at room temperature was found to be the best medium/temperature combination for maintenance of worms. An additional objective was to develop a method for transplanting adult S. japonicum from experimentally infected donor pigs to naïve recipient pigs. Six Landrace/Yorkshire crossbred pigs were used as donors to supply worms for two recipient pigs. Worms for transplantation were obtained by perfusion of the mesenteric veins of the donor pigs and maintained for a maximum of 3 h in NCTC 135 + 10% hiNPS at room temperature. A total of 148 and 132 worms were surgically transferred by way of an infusion tube into caecal veins of the two recipients. Six weeks after transplantation, 14% and 36% of the transferred worms were recovered by perfusion and subsequent manual inspection of the mesenteric veins of the two recipient pigs, respectively. The successful results suggest that surgical transfer of S. japonicum worms from donor to naïve recipient pigs may be useful for future studies on population genetics, dynamics and regulation in the pig/S. japonicum model.

Recovery of Schistosoma japonicum from experimentally infected pigs by perfusion of liver and mesenteric veins

An optimized procedure for perfusion of pigs infected with Schistosoma japonicum was developed. The technique involves insertion of a perfusion influx tube into the thoracic descending aorta, clamping vessels to parts of the body which did not need to be perfused (the kidneys, hind legs, etc.) and placing a collection tube directly into the portal vein. In addition, the clamping technique allows for separate perfusion of the liver and intestinal veins. The perfusion medium was a sodium citrate buffer (40 degrees C) to which the vasodilator sodium nitroprusside was added. Furthermore, an experiment was conducted to investigate if the perfusion efficiency, measured by total worm recovery, could be increased if praziquantel was administered prior to perfusion. Twelve pigs were each infected with 1000 S. japonicum cercariae and their schistosomes were collected 11 weeks later by separate perfusion of the liver and intestinal veins. Six of these pigs were treated orally with praziquantel one hour before perfusion. In general, the vessels of the livers and intestines of all pigs were well perfused, judging by the resulting pale colour of the tissues. Worms from praziquantel treated pigs were collected within 5 min of perfusion as opposed to approximately 20 min in the non-treated pigs. More worms were collected from the livers of the praziquantel treated pigs, indicating a hepatic shift of schistosomes from the intestinal mesenteries. However, comparable numbers of worms were retained in the mesenteric veins following perfusion in the 2 groups, indicating that manual recovery of schistosomes from the intestinal mesenteries is necessary in addition to perfusion for obtaining the total worm counts. Another experiment was conducted to determine if the intensity and/or duration of infection had an effect on the number of worms collected by the perfusion technique. Seventy-two pigs were allocated into 3 groups of 24 pigs each, which were infected with either 100, 500 or 2000 cercariae per pig. The 3 groups were further divided into 4 subgroups of 6 pigs each which were perfused with our selective technique at 4, 11, 17 or 24 weeks post infection, respectively. All of the pigs received an oral praziquantel treatment prior to perfusion. The results indicated that increasing intensities and/or duration of infection resulted in trapping of schistosomes in intravascular inflammatory reactions which made it more difficult to collect the adult schistosomes by perfusion.

Schistosoma japonicum infection in the pig: the effect of a patent primary infection on a challenge infection

The response of pigs to a challenge infection of Schistosoma japonicum following a primary infection was assessed using parasitological parameters and eosinophil counts. Twenty-five Danish Landrace/Yorkshire/Duroc crossbred pigs were divided into four groups. Group A (n = 10) received a primary infection, group B (n = 5) received both a primary and challenge infection, group C (n = 5) received a challenge control infection and group D (n = 5) received no infection serving as helminth-free controls. A dose of 850 cercariae was administered by intramuscular injection at the primary infection (week 0) and challenge infection (week 12). The pigs were perfused at week 21, except for half of the group A pigs which were slaughtered at week 12. Challenge infection did not result in higher worm burdens or tissue egg counts in group B than group A at week 21 and mature/immature worm ratios were similar for the two groups. In addition, no increases in faecal egg counts or eosinophil counts were observed in group B after challenge infection. The results indicate that pigs are able to mount a very rapid and effective response to reinfection with S. japonicum following a patent primary infection resulting in prevention of establishment of challenge infection schistosomes. An anti-worm effect appears to be the main feature of this regulatory host response.