Vaccination

Authors: Jenkins, Mark

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 11/22/2019
Publication Date: 12/11/2019
Citation: Jenkins, M.C. 2019. Vaccination. In: Dubey, J.P., editor. Coccidiosis in Livestock, Poultry, Companion Animals and Humans. 1st Edition. Boca Raton, Florida: CRC Press. p. 51-58.

Interpretive Summary: A number of factors have contributed to the increased use of live Eimeria oocyst vaccines to control coccidiosis in broiler and layer chickens. Between 2010 and 2016, worldwide broiler production has increased 17% to approximately 23 billion broilers. In the same time period, the number of eggs produced has increased 12.5% to 1,350 billion eggs. This is because the relative cost of raising broilers and egg-layers is low compared to other food animal commodities which is due in part to greater efficiency of feed conversion in commercial breeds of chicken. Also, egg production can, depending on whether the eggs are for consumption (table eggs) or serve as a source of chicks for broiler replacement, exceed 250 eggs/year. The short life span of broilers (5-8 weeks depending on market) and the rapid growth rate that in 1950 required 10 weeks to produce a 1.4 kg broiler now requires only 5 weeks to produce the same size broiler has led to intensive poultry production. Depending on its size, a typical broiler house will contain up to 35,000 chickens. Typically, broilers are raised in close proximity to one another at a stocking density of ~ 0.075 m2/chick during growout which is ideal for rapid transmission of infectious agents between chickens in a poultry house. One such agent is protozoa in the genus Eimeria that replicates in the intestinal tract and thereby inhibits nutrient uptake and growth, not to mention predisposing chickens to other diseases, such as necrotic enteritis. For decades, avian coccidiosis has been controlled by adding anticoccidial drugs to feed. However, many strains of Eimeria have developed resistance to these drugs and there is increasing consumer demand for poultry raised without antibiotics. Eimeria oocyst vaccines are an excellent alternative to anticoccidial drugs and are based on the protective immunity elicted in young chicks after ingesting the vaccine. The background to vaccine design, current methods of application, and prediction for the future are presented in this review.

Technical Abstract: Avian coccidiosis is regularly listed by poultry veterinarians as the most important poultry disease affecting performance of broilers and egg-layers. Worldwide the parasitic disease costs poultry growers and companies over $ 1 billion in losses due to unrealized weight gain, poor feed conversion efficiency, and the cost of anticoccidial controls, be it drugs or live Eimeria oocyst vaccines. Increased mortalities in broilers between 2.5 – 3.5 weeks of age is most often due to necrotic enteritis associated with acute coccidiosis infection. Similar to Eimeria oocysts, Clostridium perfringens spores are capable of resisting inactivation in litter and are prevalent throughout growout. Eimeria vaccines are attractive because they can be used in rotation throughout the year in place of ionophores and synthetic chemicals, and thereby stem the inevitable anticoccidial drug resistance that occurs when these compounds are continually used. The major obstacle in use of live Eimeria vaccines is how to ensure each chick ingests a minimum dose of oocysts so that subsequent exposure to Eimeria oocysts in litter has a boosting effect rather than causing outright enteric disease. Improving vaccine delivery, reducing the carry-over of viable Eimeria oocysts during down-time (2-3 weeks) in a poultry house, and gaining an understanding of how genetic diversity affects vaccine design are just 3 of the many research areas ripe for investigation.