MASTERING COCCIDIOSIS: Cocci Clinic Series – Part 1

Navigating Coccidiosis: Understanding the Life Cycle and Best Practices for Management

Written by Zamira Australia

Unveiling the Culprit: The Genesis of Coccidiosis

Coccidiosis Origins
Coccidiosis, an intestinal infection in chickens, is caused by intracellular parasites of the genus Eimeria.

Understanding the Reproduction Cycle
The reproduction cycle of Eimeria begins within intestinal cells and culminates in the excretion of infectious oocysts in chicken droppings within the litter:

Initiating the First Phase

The initial phase of the reproduction cycle initiates as chickens shed a multitude of oocysts in their faeces. The transition from internal to external environments is pivotal for parasite progression. Oxygen, humidity, and temperatures around 20 to 25 degrees Celsius are imperative for oocyst development. The litter in chicken houses provides an optimal setting for oocyst survival and advancement. The exogenous phase typically concludes within three days, yet oocysts retain their infectious potential for months in the natural poultry environment.

Triggering the Second Phase

The second phase of the coccidia reproduction cycle is triggered when a chicken consumes sporulated oocysts from contaminated litter, feed, or water. The digestive process, aided by the gizzard action and various enzymes, breaks down the outer coating of the oocyst, releasing developing progeny into the intestinal lumen.

Depending on the coccidia strains involved, the released progeny invade specific sites along the intestinal lining, multiplying within and ultimately rupturing the cell. This cycle may repeat over several generations, leading to severe infection and potential mortality in the host chicken. Coccidia infections remain localised to the intestines, with the site of infection varying among strains. Some emerging progeny may differentiate into male and female forms within the chicken intestine, resulting in the production of oocysts passed in the droppings, perpetuating the reproduction cycle. Unlike bacteria and viruses, coccidia oocysts are highly resistant to sanitation measures, capable of surviving in the chicken house and surrounding environment for extended periods. Infection primarily occurs through the ingestion of oocysts from chicken litter or the surrounding environment.

Unravelling the Spread of Coccidiosis Infection

Oocysts exhibit remarkable resilience, enduring for extended durations in hot and humid environments, although they struggle to survive in excessively hot and dry conditions. The relocation of chicken litter by various means, serves as a significant vehicle for disseminating oocysts to other farms and poultry houses.

Following a coccidiosis outbreak within a flock, surviving chickens develop a degree of immunity, offering protection against future infections for a limited period. However, this immunity is specific to the Eimeria strain responsible for the initial infection, providing no cross-protection against other strains of Eimeria.

Evaluating the General Effects of Coccidiosis

Coccidiosis infection in the intestine disrupts feed digestion and nutrient absorption, leading to decreased growth rates and impaired feed conversion efficiency. Symptoms can vary from subclinical, where chickens display no visible signs, to severe cases resulting in significant mortality. The economic impact of coccidiosis is a pressing concern for the poultry industry.

While coccidiosis is endemic among chickens and eradicating the disease entirely is impractical, various measures can be implemented to manage its impact. Improved housing and husbandry practices help reduce coccidia burdens, although they alone are insufficient to mitigate the economic strain caused by coccidiosis. The use of anticoccidial medications in feed serves as an additional tool for controlling coccidian infections.

Controlling coccidiosisAnticoccidials for Effective Management

Anticoccidials for feed medication are categorised into two groups: chemicals and ionophores. The selection criteria includes the mechanism of action, resistance development, and dosage range.

Chemical Anticoccidials: 
These compounds arrest the development cycle of coccidian multiplication at the intracellular stage. However, the prolonged use of a particular chemical anticoccidial without rotation may lead to the emergence of resistant strains.

Ionophores Anticoccidials: 
This category is particularly effective in targeting coccidia within the lumen of the intestines, with no impact on the intercellular stage of coccidia development. Ionophores also stimulate some immune response. Resistance to ionophores generally takes longer to develop, and it is often not permanent. Moreover, any loss of efficacy can often be regained following a brief withdrawal period. An approved dosage range exists for the addition of ionophores in broiler feed, with a broader safety margin for toxicity.

Combinations for Enhanced Efficacy
Combining different types of anticoccidials can enhance efficacy and minimise the risk of resistance. Potential combinations include a mix of chemicals and ionophores, offering dual mechanisms of anticoccidial action—extracellular and intracellular.

Broilers vs. Layers: Insights into Susceptibility

Broilers:
Broiler chickens are particularly vulnerable to coccidia infection during their early growth stages. At day one, they lack protective immunity, rendering them susceptible throughout their short growing cycle. Infection typically begins with a few chickens and swiftly spreads to others. Factors such as high bird density, litter accumulation on the broiler house floor, and the surrounding environment contribute to the viability and proliferation of coccidia oocysts, facilitating the faecal-oral coccidia cycle. In instances where anticoccidial-resistant strains have emerged, clinical signs of coccidiosis and mortality are often observed from three weeks of age onwards.

Layers:
The growing cycle of layers extends longer than that of broilers and maintaining low flock density can help reduce the faecal-oral infection cycle. Oocyst accumulation in layer houses occurs at a slower rate compared to broiler houses, resulting in the onset of clinical coccidiosis at a later age. Administering anticoccidial medication in feed proves effective in controlling and preventing coccidiosis incidence in layers. The primary objective is to stimulate adequate immunity among layers to prevent coccidiosis. This can be achieved by rotating layer-approved anticoccidial medications in feed for a specified period, followed by withdrawal prior to laying. The faecal-oral infection cycle enhances immunity to coccidia strains present in the poultry house litter. Effective litter management, including managing the temperature, oxygen levels, and moisture in litter to reduce oocyst survival, thus reduces unnecessary coccidia burdens. Lowering oocyst levels in the environment can enhance the efficacy of anticoccidial products.

Part 2: Decoding Coccidiacoming soon!

In Part 2 of Zamira’s Cocci Clinic Series, we’ll focus on the tell-tale signs of coccidiosis and show you how to navigate diagnosis for your farm. 


Zamira is an Australian animal health company with a mission to improve the health, wellbeing and productivity of animals through prevention, detection and treatment . Read more about us here.

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