Evaluation of L-75Se-methionine as a radioisotopic marker for studying the migration of Schistosoma mansoni schistosomula in mice

The effects of radioactive pollution on the dynamics of infectious diseases in wildlife

The interactions between infectious diseases and chemical pollution are well known and recognised as important factors in regulating the way wild animals respond to contaminant exposure. However, the impact of ionising radiation and radionuclides has often been overlooked when assessing host-pathogen interactions in polluted habitats, despite often occurring together with chemical contamination. Nevertheless, a comprehensive body of literature exists from laboratory and field studies on host-pathogen relationships under radiation exposure, and with a renewed interest in radioecology developing; an evaluation of infectious disease dynamics under these conditions would be timely. The present study assesses the impact of external ionising radiation and radionuclides on animal hosts and pathogens (viruses, bacteria, protozoans, helminths, arthropods) in laboratory studies and collates the data from field studies, including the large number of investigations undertaken after the Chernobyl accident. It is apparent that radiation exposure has substantial effects on host-pathogen relationships. Although damage to the host immune system is a major factor other variables, such as damage to host tissue barriers and inhibition of pathogen viability are also important in affecting the prevalence and intensity of parasitic diseases. Field studies indicate that the occurrence of host-pathogen associations in radioactively contaminated sites is complex with a variety of biotic and abiotic factors influencing both pathogen and host(s), resulting in changes to the dynamics of infectious diseases.

Use of 75Se tracer and autoradiographic techniques in the study of schistosomiasis

The paper provides an overview of recent studies on the use of 75Se to tag larval schistosomes and to monitor their migration and distribution patterns in naive mice and those previously exposed to cercariae. The principles and techniques of radioassay and autoradiography in studying various aspects of 75Se-labelled larval schistosomes are described. The main shortcoming of radioassay in monitoring location and movement of labelled schistosomula is that some of the label dissociates from the schistosomula and accumulates in host tissues, notably the liver. Dissociated label is indistinguishable from schistosomula-bound label making monitoring of parasite migration extremely difficult. This difficulty is overcome by compressed tissue autoradiography where labelled schistosomula can be seen as reduced silver foci on an autoradiographic film, whereas dissociated label is too diffusely distributed to produce such reduced silver foci. Furthermore, using autoradiography, quantitative information on parasite migration in normal and immunized laboratory animals can be obtained that would be impossible using traditional recovery techniques. In addition to using 75Se tracer in migration studies, the radio-isotope has potential for elucidating various aspects of schistosome transmission ecology and snail population dynamics in natural waters.

Comparison of the protective resistance induced by 60Co-irradiated cercariae and schistosomula of the WFFS and NMRI strains of Schistosoma mansoni

Mice, CBA/HT6T6 and C57BL/10, were vaccinated with 1 X 350 or 1 X 500 Schistosoma mansoni cercariae or schistosomula attenuated with 20 or 56 krad 60Co irradiation and challenged with 200 cercariae. Protective resistance against homologous strain challenge was compared using the Winches Farm Field Station (WFFS) and Naval Medical Research Institute (NMRI) strains of S. mansoni. Maximal resistance to challenge was obtained in both strains of mice with cercariae or schistosomula of either WFFS or NMRI strain attenuated with 20 krad. Protection using organisms attenuated with 56 krad was significantly lower. Since previous studies with the two parasite strains have shown that the biological effects of irradiation are similar, the difference in the immunogenicity of the 56 krad-irradiated NMRI strain in this study from earlier studies must be due either to different local conditions for irradiation or to adaptation of the NMRI strain to a new laboratory environment. This finding may have important implications for vaccination studies and investigations of the mechanisms of immunity where radiation-attenuated parasites are used.

Some problems associated with radiolabeling surface antigens on helminth parasites: a brief review

Recent developments in technology have facilitated substantial advances in the characterization of surface antigens from a wide variety of both normal and neoplastic cells. However, the immunochemistry of parasites has lagged behind. Efforts to apply conventional radiolabeling methods to helminths have not always been successful. Experimental work with Schistosoma mansoni is reviewed to illustrate common problems encountered in surface labeling studies. These findings should provide insight for the future investigation of other helminth species.

Schistosoma mansoni: quantification of skin penetration and early migration by differential external radioassay and autoradiography

Eleven gamma-emitting radionuclides (49Sc, 54Mn, 59Fe (+2 and +3), 60Co, 65Zn, 75Se (as selenomethionine, selenocystine, selenite and selenate), 109Cd, 125Sb, 133Ba, 137Cs and 203Hg) were screened as labelling agents for Schistosoma mansoni cercariae by incubation of infected Biomphalaria glabrata snails in radioactive solution according to the technique of Christensen (1977). Only [75Se]methionine yielded satisfactorily labelled cercariae. Multiple regression analysis of volume, number of cercariae and radioactivity from a series of 10 aliquots of unwashed cercarial suspensions yielded estimates of unbound and cercarial bound radioactivity that were equivalent or superior to estimates based on assay of washed cercariae and eliminated loss of cercariae. Washing of cercarial suspensions over 8 micrometers pore diameter Millipore filters was found to result in entanglement of 60-90% of the cercariae on the filter disc. Differential external radioassay, a new technique employing partial body shielding within a total body counter, permitted separate estimation of tail and body radioactivity of conscious mice previously exposed by tail immersion to 75Se-labelled cercariae, with measurements repeated as often as desired. Approximately 39% of the 75Se present in emergent cercariae was retained by schistosomula transformed in vitro but this was subject to considerable variation, especially in schistosomula transformed in vivo. Secreted or catabolized label from penetrant cercariae and schistosomula was rapidly removed from the skin by the bloodstream. Numbers of schistosomula in tail skin were directly proportional to the number of reduced silver foci counted on tail autoradiograms; only a very small fraction of tail radioactivity represented unbound ('spurious') label. Migration of schistosomula away from skin was 50% complete at 3.8-4.3 days, as determined by probit analysis of autoradiographic data.