VPA 211: General Veterinary Parasitology and Helminthology (3+1)

HOST PARASITE RELATIONSHIP

• Host parasite relationship as the term implies is the relationship between two organisms namely the host and the parasite where the parasites invariably succeed in forging a relationship to its advantage.
• Parasites upon entering their hosts through various routes may survive or die in the host. If parasites survive they develop and multiply causing infection or disease in the host.
• In evolution, there is always a tendency towards mutual adjustment between two organisms and therefore both parasite and the host forge a relationship that may either limit the infection so that parasite control is achieved without any pathological changes. Therefore, successful parasites tend to become harmless to the host.
• Majority of the parasites that survive in their hosts do not endanger their hosts, since they do not want to lose their shelter and food. However, the host tries to expel or kill the parasite by immune responses. When the host attempts to kill the parasite by immune mediated mechanisms, immunopathological lesions develop leading to disease in the animal.
• Host-Parasite relationship is a dynamic process where the host employs innate and acquired immune mechanisms to destroy the parasite.
• The nutrition status of the host and the energy resources of the host, at the start of an infection play a role in determining the ultimate outcome of the host parasite relationship. Malnutrition will impede the animal's ability to respond immunologically to the parasite.
• As parasites are large and complex, the host finds it difficult to counter the parasites by immune mediated mechanisms, resulting in responses that are not always protective.
• In addition, parasites also evade the immune responses of the host by various ways to ensure their survival and propagation. Therefore, host parasite relationship is an intricate relationship where the host attempts to destroy the parasite but the parasite does not endanger their host lest that they so lose their shelter and food.
• Host parasite relationship occurrs in a complex ecological setting where in vivo and external environments change continuously.