Cloning and characterization of glutamate dehydrogenase gene of Haemonchus contortus

Gastrointestinal nematodes, causative agents of parasitic gastroenteritis, cause serious economic losses particularly to the sheep and goat industry all over the world. Among these, Haemonchus contortus (Barber's pole worm) is most important and predominant species causing anaemia and morbidity in the host. In the female parasite, the vulvar region shows variation in morphology, with two morphotypes of the parasite being described, one with button form and the other with linguiform vulvar flap. Glutamate dehydrogenase (GDH) secreted in the intestinal cells of the parasite is considered to maintain the parasite's redox balance in response to changes in tissue pH. The enzyme is also present in the excretory/secretory product (ESP) of L4 and adult parasite. Present study was carried out to clone and characterize GDH gene in both the morphotypes of female H. contortus for determining variations in the gene sequence in these two morphotypes. The cDNA was synthesized from total RNA of linguiform and button form female H. contortus and full length open reading frame (ORF) of GDH gene was PCR amplified. The GDH gene of both morphotypes was sequenced and nucleotide sequence was compared between these two morphotypes and a UK strain of H. contortus. The nucleotide sequence of Indian isolate revealed 97.9% homology between button form and linguiform morphotypes and a homology of 96.8% and 97.4%, respectively, of the button form and linguiform female H. contortus with the UK strain. The study revealed presence of closely related GDH gene of UK strain in the Indian isolate of H. contortus.