Designing strategies for the control of coccidiosis in chickens on poultry farms using modern diagnostic tools
Sonja Frölich, Jacqueline Farhat, Michael Wallach
The iThree Institute and the School of Medical and Molecular Biosciences, University of Technology, Sydney, Sydney, New South Wales, Australia
Abstract: Coccidiosis is caused by the intracellular protozoan parasite Eimeria and is a major worldwide problem in the poultry industry today. The current strategies to control the disease still rely heavily on anticoccidial drugs and on the use of shuttle programs to periodically introduce attenuated live parasites onto poultry farms. Recently, because of the improved performance of broiler chickens, farmers are able to raise chickens for market within a period of only 5–6 weeks. This short growth period enables the development of strategies for coccidiosis control either by ensuring an even exposure of chickens to parasites in the litter, inducing immunity against reinfection, or by keeping parasite numbers below a threshold level wherein only subclinical infections will occur. Therefore, the development and use of new diagnostic tools to precisely identify the Eimeria species and strain and to measure the number of oocysts in the feces and litter can be very helpful in predicting exposure and designing strategies for the control of coccidiosis in the field. The purpose of this study was to describe recently developed methods of diagnosis in terms of their sensitivity and usefulness, describe ways in which litter oocyst numbers can be quantitated, and start to develop an analytical tool that can be used for designing strategies for the control of coccidiosis. A multiplex polymerase chain reaction–based assay has been developed that enables the identification of all seven Eimeria species in a single reaction tube. Previous reports have shown it is possible to detect one oocyst using a polymerase chain reaction–based assay; however, other reports have found that under both laboratory and field conditions the minimal level of sensitivity is only 20 oocysts. In addition, the present authors’ studies have found that when using spiked mixed samples, the level of detection of a contaminating Eimeria species is only 5%. Therefore, it is imperative that a new method be developed with a tenfold higher level of sensitivity for field-testing. Once this test is developed and validated, it can be used to monitor the litter and assess the parameters (climate, hygiene, breed of chicken, etc) that govern coccidial outbreaks on farms.
Keywords: Eimeria, multiplex PCR, sequence-characterized amplified regions (SCARs), chronic enteritis, poultry management
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