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Live Vaccines- An Overview Dr.K.Ramya Assistant Professor, Faculty of Veterinary Microbiology, Veterinary College and Research Institute, Namakkal, Tamil Nadu Veterinary and Animal Sciences University, Chennai
Microorganisms are ubiquitously present in the environment. Most of them are harmless and often beneficial for the host however, few of them are potent infectious agents accountable for variety of diseases in different species. These infectious agents apart from causing the disease are indirectly responsible for the economic loss due to retarded growth, loss of production etc., to a lesser extent and major impact will be loss of the animal in few infections. Hence, these infectious agents are of economic significance to the farmers. The livestock and poultry are at safe disposal with the existence of abundant scientific knowledge and incessant inventions. The key advantages of these infectious diseases arethat many of them are vaccine preventable. What is a Vaccine? A vaccine is biological entity involved in triggering or boosting the bird's immune system to produce antibodies and activate the immune cells against invading microbes. Vaccine may be a whole organism (live attenuated/ killed), or a part of the organism or the products of infectious agent or the genome of the organism either mimics natural infection without any harmful outcome or interact with the immune cells for activation. Why vaccination? The objective of vaccination are to reduce the morbidity and mortality 30
associated with disease incidence, to contain the spread of infection by the herd immunity prevailing in the vaccinated population and resulting in gradual eradication of disease from the population The outcome of the vaccination is to reduce or prevent economic loss caused by the infectious diseases.. Properties of an Ideal Live Vaccine Ÿ
Safety and Efficacy
The vaccine preparation should be f re e f ro m te r a to g e n i c i t y, carcinogenicity, toxicity, cost effective, stable without requirement of cold storage. It should confer efficient protection irrespective of the age of the bird and other factors. Ÿ
Specific
The attenuated vaccine should be able to induce immunity only against the disease of interest without producing any cross reactivity with either the host or the related pathogens. Ÿ
Memory
The live attenuated vaccines are expected to induce a good immunological memory in the host upon vaccination. The vaccinated birds should effectively respond to the etiological agent upon reinfection against which vaccinated. Ÿ
Duration
An efficient live vaccine should be capable of inducing a lasting immunity without the need of frequent immunization which reduces the cost of immunization.
Live attenuated vaccine Modified live vaccines are preparations containing viable organisms with reduced virulence (ability to produce disease) mimicking natural infection by replicating in the host without producing clinical disease. During t h e c o u r s e of i n f e c t i o n , t h e organism interacts with the host and induces long lasting and superior immunity. The vaccine preparation should contain the appropriate strain or the isolate prevalent in a particular zone to confer complete protection from the disease. Attenuated vaccines or modified live vaccines can be prepared by adapting the virus to an unnatural host (tissue culture or embryonated eggs or laboratory animals) or unnatural conditions (host/ temperature) for several generations (passages). During the process, the organisms lose its virulence gradually without affecting its immunogenicity. Features of Live vaccine The salient features of live attenuated vaccines are listed below: Poultry Planner | Vol. 23 | No.09 | September - 2021
