Immunopathology of Parasitic Diseases of Animals

Mostly, parasites cause damage to the host and produce disease directly and/or indirectly due to the host reaction. Predominantly, excessive number of parasites causes disease by exploiting the nutrition of the host. Mostly, parasitic infections including helminths and protozoal infections cause production losses. Limited number of parasites cause mild depletion of nutrition without causing harm to the host or triggering effective immune responses. Some parasites escape from host immune system. Immunological molecules like granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-2 (IL-2) can enhance the multiplication and pathogenesis of Leishmania amazonensis and interferon-gamma (IFN-γ) and epithelial growth factor can promote the multiplication and pathogenesis of Trypanosoma brucei. The innate immune responses against parasites are similar to that of bacterial and viral infections. Pathogenicity is influenced by species of the parasites, host species, age and genetics of the host, breed, nutritional status, and concurrent diseases. Helminthic infestations are the main parasitic causes of eosinophilia and it induces cytokines, which are responsible for the significant inflammatory responses. The pathology and protective immunity to most of the helminths and protozoal infections are believed to be caused by T lymphocytes, B lymphocytes, mast cells and macrophages. Infections with helminth parasites induces immune effector mechanisms results in IgE antibody production, tissue and peripheral blood eosinophilia, and infiltration of inflammatory mediator–rich tissue mast cells. Further, these responses can also induce pathologic reactions, in addition to mediating the protective immunity to the helminth parasites. Fecal and blood smear examination are the simple and accurate diagnostic tests for the diagnosis of early parasitic infections.