Coccidiosis in Poultry
What is coccidiosis?
Coccidiosis or intestinal coccidiosis in poultry is the clinical disease and accompanying array of symptoms caused by the infection of coccidian protozoa in the genus Eimeria. Depending on the level of infection and type of coccidia species, coccidiosis can be characterized by varying levels of morbidity, mortality, enteritis and a decrease in performance parameters.
How does coccidiosis impact the global poultry industry?
Coccidiosis is a major concern in poultry worldwide due to its effects on enteric health and overall flock performance. In the U.S., coccidiosis is estimated to contribute to $127 million in economic losses. Additionally, interactions from other disease pathogens, nutritional imbalances and coccidiosis can lead to further stress in birds and, as a result, an increase in the severity of other clinical disease symptoms. Therefore, due to the cost of prevention, treatment of coccidiosis and production losses, it is recognized as the disease with the greatest economic impact in poultry.
What causes coccidiosis in poultry?
Coccidiosis is caused by the apicomplexan protozoan parasite in the genus Eimeria. Eimeria are host-specific, and distinctive different forms of intestinal coccidiosis manifest in different species. In chickens, depending on the source, seven to nine species of Eimeria that can cause coccidiosis have been described. The main identified species of Eimeria are E. acervulina, E. maxima, E. tenella, E. necatrix, E. brunetti, E. preacox, E. mitis and, depending on the source, E. mivati.
The most common intestinal infections in chickens are often associated with E. acervulina, E. maxima, E. tenella, E. necatrix and E. brunetti. In turkeys, there are at least nine species of Eimeria that have been described; however, there are four recognizable species that produce disease — namely, E. adenoides, E. meleagrimitis, E. gallopavonis and E. meleagridis. Concurrent infections with two or more coccidia are common and can cause lesions and different levels of disease.
Coccidiosis infections are self-limiting, and their severity correlates to the number of oocysts ingested, as well as the type of Eimeria species. Eimeria oocysts are ubiquitous in poultry environments and can be introduced to new farms via paratenic hosts, infected equipment, litter, vermin, personnel, equipment and through other methods.
Signs and symptoms of coccidiosis
Coccidiosis symptoms can vary from mild to severe, but most infections are considered mild. However, due to the disease’s invasion and destruction of host cells, even mild infections can negatively impact the conversion of feed nutrients into meat. Clinical signs associated with coccidiosis are species-distinctive, and the severity of the infection is based on gross lesions, in addition to microscopic intestinal lesions.
- E. acervulina infections can result in mild to severe coccidiosis, and more severe infections can result in a reduction in body weight. Watery/mucoid droppings can also be observed. Pigmentation from the skin may be lost due to carotenoid and reduced xanthophyl absorption in the small intestine. Gross lesions in the intestine are usually located in the duodenum but can extend into the rest of the small intestine if the infection is severe. These lesions are characterized by white plaques.
- E. maxima is considered moderately to severely pathogenic. Symptoms can vary from mild to severe, with mortality rates of up to 30%. It can cause poor weight gain, diarrhea, ruffled feathers, loss of appetite and pale skin. E. maxima affects the mid-gut anywhere after the duodenum and past the Meckel’s diverticulum; however, heavy infections can be seen throughout the small intestine. An intestine infected with E. maxima may be edematous, flaccid and thickened and can reveal increased mucus — typically, yellow or orange in color — and blood. In more severe infections, the mucosa can slough off.
- E. tenella lesions are easier to recognize due to their type and location and due to increased mortality rates. E. tenella is considered one of the most pathogenic Eimeria spp. It is primarily found in the ceca, and in severe disease cases, there is an associated increase in morbidity, blood in the feces, weight loss, dehydration, loss of appetite, anemia and diminished skin pigmentation. Bloody cecal cores may also be seen in the ceca. Mortality associated with E. tenella may be due to toxic factors from bacteremia.
- E. brunetti is found primarily in the lower intestine after the Meckel’s diverticulum; however, in severe infections, it can be found in the upper and lower intestines, including in the ceca and cloaca. Symptoms can vary from mild to severe in heavy infections. Moderate mortality rates and reduced feed conversion may be observed. Gross lesions in the gastrointestinal tract may be present and are characterized by petechiae, watery contents, thickened mucosa, pallor and, in severe cases, erosion of the mucosal layer. Digested or coagulated blood may be observed in the feces.
- E. necatrix lesions are found in the small intestine around the same area as E. maxima lesions and are typically seen in the pullet stage and in older birds. E. necatrix is considered one of the most pathogenic Eimeria spp. Infections of E. necatrix can cause high morbidity and mortality rates of more than 25%. Additionally, decreased body weight, decreased egg production, emaciation and secondary infections can also be observed. Gross lesions in the gut are typically ballooning and involve thickened mucosa and blood. Usually, E. necatrix lesions are described as “salt-and-pepper” in appearance due to the white and black plaques seen in the mucosa.
Typical signs of coccidiosis in turkeys include depressed birds with ruffled feathers, increased watery or mucoid diarrhea, loss of appetite, bloody feces and general morbidity. Recovery is often quick, and lesions may not be as easily identifiable in turkeys as in chickens. All ages can be affected; however, mortality rates tend to be lower for older birds than younger birds.
- E. adenoides is considered the most pathogenic species of coccidia in turkeys. Birds may show reduced body weight, high morbidity and, in severe infections, high mortality rates. It is found primarily in the ceca, but in more severe infections, it can extend to the lower small intestine and cloaca. Feces may be watery with mucus casts and may also be blood-tinted. Cecal cores may be present in the ceca and the intestinal wall may be edematous-dilated, with petechial hemorrhages and mucus.
- E. meleagridis is considered one of the most pathogenic species and can cause increased morbidity and mortality rates and general depression in young birds. It is primarily observed in the upper gastrointestinal tract; however, in more severe infections, it may be observed throughout the small intestine. The feces of infected turkeys may have some blood specks, in addition to mucus. The tips of the villi may also be denuded and edematous.
Management tips to help prevent coccidiosis
The prevention of coccidiosis in poultry is key to avoid damage from infection and to mitigate any associated production losses and welfare issues.
A recommended integrated approach would be to use a combination of:
- Antiprotozoal agents (coccidiocidal vs. coccidiostatic)
- Improved animal husbandry practices
Additionally, as many in the industry decrease their use of antibiotics for management and prevention, naturally derived feed additives have become more popular — especially those derived from:
- Essential oils
These additives are most successful when used in addition to good bird-rearing management practices.
Additional tips and recommendations to help reduce the risk of coccidiosis:
- Proper animal husbandry and biosecurity practices and good pest control (e.g., preventing and eliminating pests like rodents, flies and litter beetles) are crucial, regardless of the type of production system. Additionally, cleaning and disinfection between flocks must be carried out to prevent other diseases from being introduced into the flock.
- Increased down-time and good litter management can also help with the pathogen load and, as a result, better management of coccidia challenges from flock to flock.
- Bird immunity status plays a significant role in the recovery from and level of tolerance to the disease; as such, ensuring a healthy start with good-quality chicks and mitigating any immunosuppressive causative agents, such as viruses and mycotoxin challenges, are vital.
- Providing high-quality feed ingredients and ensuring the availability of feed will also contribute to the delivery of feed additives to help mitigate coccidia infections, will diminish the secondary infections associated with coccidia cycling and will help maintain overall gut health.
Coccidia control programs should be tailored to each operation’s unique circumstances. Therefore, the plan for controlling coccidia long-term should include routine monitoring and testing to evaluate the effectiveness of each program, along with the implementation of sustainable practices.