Released August 2007 - The Indian Society for Parasitology

6Agrawal and Banerjeespecies. This genetic make-up influences host range,pathogenicity and patency etc. of the parasite. Thegenetic variations in S. japonicum are wellestablished, which later led to creation of new specieslike S. mekongi, S. malayalensis and S. sinensium orstrains which differ in their snail susceptibilities(Attwood, 2001).with a variety of host species, there is all the possibilityof the existence of wide genetic variations amongsame helminthic species from different geographicalareas. However, this subject has failed to attract Indianscientists perhaps because of the complexity of subjectand requirements of more sophisticated equipments toprove genetic variations at molecular level.Attempts have been made by Dutt and Srivastava(1968)to differentiate S. nasale species/ strains whichinfect cattle and buffaloes, as only the former host wasfound to suffer clinically from nasal schistosomosis.The cross-transmission experiments revealed nodifference between S. nasale species from these twohost species. Nevertheless, no attempt was made tocompare S. nasale from different geographical areaseither from the same or different host species to recordgenetic variation.When nasal schistosomosis from differentgeographical areas was compared, indirect evidencewas obtained which suggested the existence ofdifferent parasite strains, which were found to differ intheir host susceptibility and clinical symptoms. Thus,Banerjee and Agrawal (1991)recorded the presence ofS. nasale at Jabalpur in buffaloes, whereas local cattledid not show any symptoms, though it was present incross-bred cattle where parasite was causing a mildform of the disease. In contrast, at Bhubaneswar localcattle did suffer from larger granuloma and profusewatery nasal discharge (Agrawal et al., 2003). Even S.nasale at Balaghat of Madhya Pradesh was differentfrom that of Bhubaneswar with regard to clinicalsymptoms etc. All these findings suggested geneticvariation among S. nasale belonging to differentgeographical areas.Variation in prevalence of fasciolosis, among differentdomestic animals and incrimination of different snailspecies (Choudhary, 1994) in different geographicalareas suggest that genetic factors play role in suchvariations.EPIDEMIOLOGYThe epidemiology consists of four components i.e.host, etiological agent, transmission factors andenvironment. Diagnosis, as fifth component, has beenincorporated by Agrawal (2003) as it influencesepidemiological findings to a great extent. Theepidemiological aspects of fluke infections in Indiahave been dealt with in greater details recently byAgrawal (2003), whereas details of haemonchosis inIndia have been covered by Sood (2003b). Therefore,these aspects are not discussed here.There is influx of research papers in recent pastdealing with prevalence of helminths in differentdomestic animals from different parts of the country.These works, some of which claim to be the first timework in a particular animal, helminth species orlocation or by a different technique, have notcontributed much except variation in the prevalencerates of a particular parasite in a host or in a givengeographical area. In these studies, no serious efforthas been made either to study biological behaviour ofthe helminth in nature or in different domestic animalspecies in the locality or correlating prevalence withecological changes, husbandry practices, introductionof new animals or with production traits or even withhealth condition of the animals. In the absence of thesedata, such repeated works do not add any newinformation on helminthic diseases.With regards to host, no serious attempt has been madeto identify resistant breeds of animals either for one ormore helminthic infections. However, there iscircumstantial evidence that Garole sheep ofThere are reports of buffalo-dog, camel-dog, goat-dog Sunderban area in West Bengal is resistant tostrains of Echinococcus granulosus from India but fasciolosis despite grazing in marshy land. A moreconfirmation on molecular basis is awaited (Das et al., detailed study, including experimental infection, is2003). Human susceptibility to these different strains needed for confirming the phenomenon with work forof E. granulosus has yet to be acertained.isolating-resistant gene.A new variety of helminthic population in the form ofdrug-resistant strains is emerging in different parts ofthe country, which sooner or later may replacesusceptible strains leading to a big problem. BecauseIndia is characterized by different agro-climatic zonesIndia is well known for its rich biodiversity, whereanimals are resistant to many pathogens (includinghelminths), and hence able to survive under adverseconditions. However, resistant animal breeds orresistant genes for important helminthic infections