Mapping the risk for transmission of urban schistosomiasis in the Brazilian Northeast

This is an analysis of the risk of schistosomiasis transmission in the city of Recife in the Northeast of Brazil based on the number of schistosomiasis cases (Schistosoma mansoni) registered for the period 2007-2017 together with data resulting from active search of breeding sites of the Biomphalaria snail intermediate host. The analyses were performed using Kernel Density Estimation (KDE), SaTScan and Map Algebra methodology using human socio-demographic data and biotic and abiotic data from the snail breeding sites. Investigating 44 breeding sites resulted in a total of 3.800 snails, 31.8% of which were positive for S. mansoni DNA. These data were considered in relation to total of 652 schistosomiasis cases. The KDE showed two high-risk and two medium-risk clusters, while three significant clusters were identified by SaTScan. Combining these data with the Map Algebra methodology showed that all high-risk neighbourhoods had breeding sites with snails positive for S. mansoni. It was concluded that schistosomiasis transmission cannot be controlled without basic sanitation and sewage management in the presence of Biomphalaria snails. The technique of Map Algebra was found to be fundamental for the analysis and demonstration of areas with a high probability of schistosomiasis transmission.

SYBR-Green-Based Quantitative Real-Time PCR for Discriminating Between Closely Related Angiostrongylus Cantonensis and A. Malaysisensis

Background: Angiostrongylus cantonensis is a well-known pathogen causing human angiostrongyliasis eosinophilic meningitis. Humans, as accidental hosts, are infected by eating undercooked snails containing third-stage larvae. A. malaysiensis is closely related to A. cantonensis and has been described as a potential human pathogen. Recently, the two species have been reported to have overlapping distributions in the same endemic area, particularly in the Indochina region. Because of their similar morphological characteristics, misidentification often occurs, particularly of the third-stage larva in the snail intermediate host. Methods: We designed species-specific primers to mitochondrial cytochrome b, which was used as a genetic marker. SYBR-green quantitative real-time PCR (qPCR) was employed to quantitatively detect and identify the third-stage larvae and tissue debris in the cerebrospinal fluid (CSF) of a patient, and to quantify third-stage larvae in the snail Achatina fulica collected from the field.Results: The newly designed primers were highly specific and sensitive, even when using conventional PCR. SYBR green qPCR quantitatively detected around 10−4 ng of genomic DNA from one larva and facilitated the specific detection and identification of parasitic genetic material from the CSF of a patient with angiostrongyliasis. The method also estimated the number of larvae in A. fulica and revealed that the primary source of Angiostrongylus infection in the King Rama IX public park study area was A. malaysiensis; although, the two Angiostrongylus species each infected 10% of the snails. Conclusions: Our SYBR green qPCR method is a useful and inexpensive technique for parasite identification and has sufficient sensitivity and specificity to detect a single larva and simultaneously discriminate between A. cantonensis and A. malaysiensis. The number of larvae infecting or co-infecting the snail intermediate host can also be estimated. In future research, this qPCR method could be employed in a molecular survey of A. cantonensis and A. malaysiensis occurrence within intermediate and definitive hosts. The technique should also be applied in a study analyzing CSF specimens from patients with eosinophilic meningitis to assess the usefulness of the method for clinical diagnosis.

Resource fluctuations inhibit the reproduction and virulence of the human parasite Schistosoma mansoni in its snail intermediate host

Resource availability can powerfully influence host–parasite interactions. However, we currently lack a mechanistic framework to predict how resource fluctuations alter individual infection dynamics. We address this gap with experiments manipulating resource supply and starvation for a human parasite, Schistosoma mansoni , and its snail intermediate host to test a hypothesis derived from mechanistic energy budget theory: resource fluctuations should reduce schistosome reproduction and virulence by inhibiting parasite ingestion of host biomass. Low resource supply caused hosts to remain small, reproduce less and produce fewer human-infectious cercariae. Periodic starvation also inhibited cercarial production and prevented infection-induced castration. The periodic starvation experiment also revealed substantial differences in fit between two bioenergetic model variants, which differ in their representation of host starvation. Simulations using the best-fit parameters of the winning model suggest that schistosome performance substantially declines with resource fluctuations with periods greater than 7 days. These experiments strengthen mechanistic theory, which can be readily scaled up to the population level to understand key feedbacks between resources, host population dynamics, parasitism and control interventions. Integrating resources with other environmental drivers of disease in an explicit bioenergetic framework could ultimately yield mechanistic predictions for many disease systems.