Schistosoma japonicum in Samar, the Philippines: infection in dogs and rats as a possible risk factor for human infection.

The role that animals play in the transmission of Schistosoma japonicum to humans in the Philippines remains uncertain and prior studies have not included several species, adjustment for misclassification error and clustering, or used a cohort design. A cohort study of 2468 people providing stool samples at 12 months following praziquantel treatment in 50 villages of Western Samar, the Philippines, was conducted. Stool samples from dogs, cats, rats, and water buffaloes were collected at baseline (2003-2004) and follow-up (2005). Latent-class hierarchical Bayesian log-binomial models adjusting for misclassification errors in diagnostic tests were used. The village-level baseline and follow-up prevalences of cat, dog, and rat S. japonicum infection were associated with the 12-month cumulative incidence of human S. japonicum infection, with similar magnitude and precision of effect, but correlation between infection levels made it difficult to divide their respective effects. The cumulative incidence ratios associated with a 1% increase in the prevalence of infection in dogs at baseline and in rats at follow-up were 1·04 [95% Bayesian credible interval (BCI) 1·02-1·07] and 1·02 (95% BCI 1·01-1·04), respectively, when both species were entered in the model. Dogs appear to play a role in human schistosomiasis infection while rats could be used as schistosomiasis sentinels.

Estimating the sensitivity and specificity of Kato-Katz stool examination technique for detection of hookworms, Ascaris lumbricoides and Trichuris trichiura infections in humans in the absence of a 'gold standard'.

The accuracy of the Kato-Katz technique in identifying individuals with soil-transmitted helminth (STH) infections is limited by day-to-day variation in helminth egg excretion, confusion with other parasites and the laboratory technicians' experience. We aimed to estimate the sensitivity and specificity of the Kato-Katz technique to detect infection with Ascaris lumbricoides, hookworm and Trichuris trichiura using a Bayesian approach in the absence of a 'gold standard'. Data were obtained from a longitudinal study conducted between January 2004 and December 2005 in Samar Province, the Philippines. Each participant provided between one and three stool samples over consecutive days. Stool samples were examined using the Kato-Katz technique and reported as positive or negative for STHs. In the presence of measurement error, the true status of each individual is considered as latent data. Using a Bayesian method, we calculated marginal posterior densities of sensitivity and specificity parameters from the product of the likelihood function of observed and latent data. A uniform prior distribution was used (beta distribution: alpha=1, beta=1). A total of 5624 individuals provided at least one stool sample. One, two and three stool samples were provided by 1582, 1893 and 2149 individuals, respectively. All STHs showed variation in test results from day to day. Sensitivity estimates of the Kato-Katz technique for one stool sample were 96.9% (95% Bayesian Credible Interval [BCI]: 96.1%, 97.6%), 65.2% (60.0%, 69.8%) and 91.4% (90.5%, 92.3%), for A. lumbricoides, hookworm and T. trichiura, respectively. Specificity estimates for one stool sample were 96.1% (95.5%, 96.7%), 93.8% (92.4%, 95.4%) and 94.4% (93.2%, 95.5%), for A. lumbricoides, hookworm and T. trichiura, respectively. Our results show that the Kato-Katz technique can perform with reasonable accuracy with one day's stool collection for A. lumbricoides and T. trichiura. Low sensitivity of the Kato-Katz for detection of hookworm infection may be related to rapid degeneration of delicate hookworm eggs with time.

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.

Population genetics of multi-host parasites--the case for molecular epidemiological studies of Schistosoma japonicum using larval stages from naturally infected hosts.

Population genetics of multi-host pathogens offers great potential for the understanding of their complex epidemiology but care must be taken to ensure that the sampling procedure does not bias estimates of population indices. The transfer of material to laboratory passage, in particular, runs the risk of bottlenecking and imposing non-random host-induced selection pressures according to the hosts used in passage. We present a novel technique allowing single-locus microsatellite genotyping of the naturally sampled larval stages, enabling unbiased population genetic studies of the multi-host zoonotic parasite Schistosoma japonicum. The utility of these larval genotyping methods for molecular epidemiological studies are illustrated in results from 3 separate data sets. In the first data set, potential loss of alleles based on the definitive host species used for laboratory maintenance was identified by comparing adult worm populations derived from mice and rabbits infected with cercarial populations originating from the same set of snails. In the second data set, bottlenecking was demonstrated by the loss of alleles in adult worms derived within a single generation of laboratory maintenance compared to their parent field-collected cercarial samples. In the final data set, comparison of miracidia and adult worms recovered from naturally infected animals demonstrated that larval analyses can provide stage-specific epidemiological information and that population genetics of schistosomes can be well described by analysis of larval stages. Our results thus advocate the use of natural life-cycle stages to obtain an accurate and ethical representation of the population genetic structure of S. japonicum and other multi-host pathogens.

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.