January 30, 2014
US scientists develop vaccine against poultry disease coccidiosis
Scientists at the USDA''s Agricultural Research Service (ARS) have developed an alternate vaccine delivery system for new-born chicks to improve vaccination against intestinal diseases like coccidiosis.
A common and costly poultry disease, coccidiosis is caused by tiny, single-celled parasites that belong to the genus Eimeria. Infected birds spread disease by shedding oocysts, the egg like stage of the parasite. The infected birds are slower to gain weight and grow, and sometimes die.
The disease costs an estimated US$350 million in the US and more than US$3 billion worldwide each year. Until recently, coccidiosis outbreaks were mainly controlled by medicating feed with anticcocidial drugs, but the parasite''s increasing resistance to drugs prompted the development of vaccines.
Traditional poultryvaccine methods involve vaccinating chicks in trays on a conveyor with an electronic sprayer. However, some chicks may be missed by these methods and consequently have little defence against diseases.
The alternate system, developed by scientists at the Agricultural Research Service (ARS) Henry A. Wallace Beltsville Agricultural Research Centre (BARC) in Beltsville, Md., and Southwest Research Institute (SwRI) in San Antonio, Texas, involves putting low doses of live Eimeria oocysts inside gelatin beads, which are fed to birds.
Microbiologist Mark Jenkins and zoologist Ray Fetterer, in BARC''s Animal Parasitic Diseases Laboratory, examined the gelatin bead vaccine effectiveness in chicks of layer hens and broilers. One-day-old chicks were immunised by ingesting gelatin beads or with a hand-held sprayer. The group that swallowed the gelatin beads had a greater vaccine uptake than the group that received the vaccine in spray form, and was better protected against
coccidiosis.
Scientists looked at gelatin beads as an alternative vaccination method. They experimented with different formulations, sizes, and colours.
"Our primary goal was to develop a formulation that would prevent the gelatin beads from drying out when they''re put into poultry houses, where temperatures can exceed 90°F ," says Joseph Persyn, SwRI manager of microencapsulation and nanomaterials. "The beads needed to retain moisture to keep the Eimeria oocysts active and to remain pliable so the chicks would eat them." When beads dry out, they become as hard as pebbles, Persyn adds.
Scientists also examined the efficacy of vaccine beads in chickens raised similarly to those in a poultry house. Newly hatched chicks were vaccinated by either a spray method or gelatin beads. Chicks were then raised in floor-pen cages in direct contact with litter. At four weeks of age, all chicks received an experimental challenge dose of Eimeria oocysts. Chicks immunised with beads displayed significantly greater weight gain than an unvaccinated control group. Their ability to convert feed into body mass also was greatly enhanced.
The next step is to test the gelatin beads in a commercial broiler house, Jenkins says. The scientists are looking for a poultry industry partner to take the next step in evaluating the beads.
The collaboration between ARS and SwRI will continue. Research will focus on investigating methods to improve the gelatin bead formulation and the possibility of developing a vaccine delivery device that can be used in commercial poultry houses.
A patent application has been filed by ARS and SwRI scientists for their technology of incorporating Eimeria oocysts into gelatin beads.