Population genetic analysis of Chadian Guinea worms reveals that human and non-human hosts share common parasite populations

Following almost 10 years of no reported cases, Guinea worm disease (GWD or dracunculiasis) reemerged in Chad in 2010 with peculiar epidemiological patterns and unprecedented prevalence of infection among non-human hosts, particularly domestic dogs. Since 2014, animal infections with Guinea worms have also been observed in the other three countries with endemic transmission (Ethiopia, Mali, and South Sudan), causing concern and generating interest in the parasites’ true taxonomic identity and population genetics. We present the first extensive population genetic data for Guinea worm, investigating mitochondrial and microsatellite variation in adult female worms from both human and non-human hosts in the four endemic countries to elucidate the origins of Chad’s current outbreak and possible host-specific differences between parasites. Genetic diversity of Chadian Guinea worms was considerably higher than that of the other three countries, even after controlling for sample size through rarefaction, and demographic analyses are consistent with a large, stable parasite population. Genealogical analyses eliminate the other three countries as possible sources of parasite reintroduction into Chad, and sequence divergence and distribution of genetic variation provide no evidence that parasites in human and non-human hosts are separate species or maintain isolated transmission cycles. Both among and within countries, geographic origin appears to have more influence on parasite population structure than host species. Guinea worm infection in non-human hosts has been occasionally reported throughout the history of the disease, particularly when elimination programs appear to be reaching their end goals. However, no previous reports have evaluated molecular support of the parasite species identity. Our data confirm that Guinea worms collected from non-human hosts in the remaining endemic countries of Africa are Dracunculus medinensis and that the same population of worms infects both humans and dogs in Chad. Our genetic data and the epidemiological evidence suggest that transmission in the Chadian context is currently being maintained by canine hosts

POPULATION ASSESSMENTS OF INFECTION WITH SCHISTOSOMA MANSONI: EFFECTS OF BIAS CAUSED BY THE RELATIVE SENSITIVITY OF DIAGNOSTIC TECHNIQUES (PUERTO RICO)

This study establishes the extent and relevance of bias of population estimates of prevalence, incidence, and intensity of infection with Schistosoma mansoni caused by the relative sensitivity of stool examination techniques. The population studied was Parcelas de Boqueron in Las Piedras, Puerto Rico, where the Centers for Disease Control, had undertaken a prospective community-based study of infection with S. mansoni in 1972. During each January of the succeeding years stool specimens from this population were processed according to the modified Ritchie concentration (MRC) technique. During January 1979 additional stool specimens were collected from 30 individuals selected on the basis of their mean S. mansoni egg output during previous years. Each specimen was divided into ten 1-gm aliquots and three 42-mg aliquots. The relationship of egg counts obtained with the Kato-Katz (KK) thick smear technique as a function of the mean of ten counts obtained with the MRC technique was established by means of regression analysis. Additionally, the effect of fecal sample size and egg excretion level on technique sensitivity was evaluated during a blind assessment of single stool specimen samples, using both examination methods, from 125 residents with documented S. mansoni infections. The regression equation was: Ln KK = 2.3324 + 0.6319 Ln MRC, and the coefficient of determination (r(\u272)) was 0.73. The regression equation was then utilized to correct the term \u22m\u22 for sample size in the expression P ((GREATERTHEQ) 1 egg) = 1 - e(\u27-ms), which estimates the probability P of finding at least one egg as a function of the mean S. mansoni egg output \u22m\u22 of the population and the effective stool sample size \u22s\u22 utilized by the coprological technique. This algorithm closely approximated the observed sensitivity of the KK and MRC tests when these were utilized to blindly screen a population of known parasitologic status for infection with S. mansoni. In addition, the algorithm was utilized to adjust the apparent prevalence of infection for the degree of functional sensitivity exhibited by the diagnostic test. This permitted the estimation of true prevalence of infection and, hence, a means for correcting estimates of incidence of infection.

Derived maternal genotypes_Dmedinensis

Derived maternal genotypes_Dmedinensi

Achieving the endgame: Integrated NTD case searches.

Trachoma and Guinea Worm Disease (GWD) are neglected tropical diseases (NTD) slated for elimination as a public health problem and eradication respectively by the World Health Organization. As these programs wind down, uncovering the last cases becomes an urgent priority. In 2010, Ghana Health Services, along with The Carter Center, Sightsavers, and other partners, conducted integrated case searches for both GWD and the last stage of trachoma disease, trachomatous trichiasis (TT), as well as providing surgical treatment for TT to meet elimination (and eradication targets). House to house case searches for both diseases were conducted and two case management strategies were explored: a centralized referral to services method and a Point of Care (POC) delivery method. 835 suspected TT cases were discovered in the centralized method, of which 554 accepted surgery. 482 suspected TT cases were discovered in the POC method and all TT cases accepted surgery. The cost per TT case examined was lower in the POC searches compared to the centralized searches ($19.97 in the POC searches and$20.85 in the centralized searches). Both strategies resulted in high surgical uptake for TT surgery, with average uptakes of 72.4% and 83.9% for the centralized and POC searches respectively. We present here that house to house case searches offering services at POC are feasible and a potential tool for elimination and eradication programs nearing their end