Suburbanization Increases Echinostome Infection in Green Frogs and Snails.

An important contribution to infectious disease emergence in wildlife is environmental degradation driven by pollution, habitat fragmentation, and eutrophication. Amphibians are a wildlife group that is particularly sensitive to land use change, infectious diseases, and their interactions. Residential suburban land use is now a dominant, and increasing, form of land cover in the USA and globally, contributing to increased pollutant and nutrient loading in freshwater systems. We examined how suburbanization affects the infection of green frog (Rana clamitans) tadpoles and metamorphs by parasitic flatworms (Echinostoma spp.) through the alteration of landscapes surrounding ponds and concomitant changes in water quality. Using sixteen small ponds along a forest-suburban land use gradient, we assessed how the extent of suburban land use surrounding ponds influenced echinostome infection in both primary snail and secondary frog hosts. Our results show that the degree of suburbanization and concurrent chemical loading are positively associated with the presence and burden of echinostome infection in both host populations. This work contributes to a broader understanding of how land use mediates wildlife parasitism and shows how human activities at the household scale can have similar consequences for wildlife health as seemingly more intensive land uses like agriculture or urbanization.

Susceptibility of Biomphalaria glabrata to infection with Echinostoma paraensei: correlation with the effect of parasite secretory-excretory products on host hemocyte spreading.

Susceptibility of the snail Biomphalaria glabrata to infection with the digenetic trematode Echinostoma paraensei was correlated with the ability of secretory-excretory products (SEP) derived from sporocysts of this parasite to interfere with the spreading behavior of host hemocytes in an in vitro assay. In 15 separate experiments, the prevalence of infection achieved by miracidia was positively correlated (C.C. = 0.779, P < 0.001) with the ability of in vitro-transformed sporocysts derived from the same batches of miracidia to produce SEP that inhibited host hemocyte spreading. Under assay conditions reflecting differences in hemolymph volumes between juvenile snails (susceptible to infection) and adult snails (relatively refractory to infection), SEP had a significantly greater effect on hemocytes from juvenile snails. No significant differences in response to SEP were noted when equivalent numbers of adult and juvenile hemocytes were used in the assay. Snails of the M line strain of B. glabrata are significantly more susceptible to infection with E. paraensei than 13-16-R1 strain snails. Exposure to SEP significantly increased the number of unspread hemocytes for both strains. However, significantly more 13-16-R1 than M line hemocytes remained spread following SEP treatment. Echinostoma paraensei sporocyst SEP effects on host hemocyte spreading mirror observed patterns in both age- and strain-related susceptibility of B. glabrata to this parasite. The results suggest that the number of hemocytes available to a particular snail influences its vulnerability to infection with E. paraensei.

Low molecular weight hydrophilic chemicals that attract Echinostoma trivolvis and E. caproni cercariae.

A Petri dish bioassay was used to study chemoattraction of the cercariae of Echinostoma trivolvis and E. caproni in the presence of various bench chemicals prepared as 5 mM solutions in agar. The design compared the attraction of cercariae migrating toward the plugs impregnated with chemicals compared to unimpregnated plugs (controls). Cercariae of both species were significantly attracted to an array of amino acids and to some carbohydrates. Cercariae of E. trivolvis but not E. caproni were attracted to the peptide glutathione. Cercariae of E. trivolvis and E. caproni were repelled from valeric and butyric acids, respectively. Cercariae of E. caproni but not E. trivolvis were repelled from dextrose. Although broad specificity exists for echinostome cercarial penetration in snail intermediate hosts, results of these studies suggest that there are specific differences in cercarial chemoattractants between E. trivolvis and E. caproni.

Eating habits associated with Echinostoma malayanum infections in the Philippines.

A survey of 61 residents belonging to 12 pre-selected families (having at least one member positive for echinostomiasis malayanum) from Barangay Malibago, Echague, Isabela (northern Luzon) suggested that infections with Echinostoma malayanum follow a "familial trend". The parasite is endemic because the raw ingestion of Lymnaea (Bullastra) cumingiana, the second intermediate host in the Philippines, is a learned habit passed down from one generation to the next. A questionnaire on eating habits revealed that Lymnaea (Bullastra) cumingiana or "birabid" was usually prepared raw or half-cooked after treatment with salt or "bagoong" (salted fish paste). It was abundant in rice fields during the wet months of the year, thus implying a seasonal infection pattern since eating frequency was affected by availability. Those who ate this snail reported a long duration of indulgence with this habit. In contrast, Pila luzonica or "kuhol", the second intermediate host of E. ilocanum, is subjected to similar eating practices but is rarely ingested raw or "half-cooked". Other than snails, shrimps, fish (Tilapia sp.) and meat are also eaten raw. This suggests that the local population is potentially susceptible to other food-borne helminthiases. Extensive use of mass media and public health education is necessary to awaken the awareness of the people to the potential hazards associated with their traditional eating habits.