Coccidiosis in turkeys is a digestive disease of importance, not only because of its direct consequences, which include diarrhea, growth retardation and worsening of the feed conversion, but also because it represents an entrance gate for other infections, such as necrotic enteritis.

This article describes the etiology of this disease in turkeys, as well as the signs and lesions that, together with lab techniques, can help us reach a diagnosis. Finally, some methods to treat and prevent coccidiosis are described.

1. ETIOLOGY

Coccidiosis in turkeys is caused by coccidia, unicellular protozoa of the genus Eimeria, which parasite the enterocytes (cells of the digestive mucosa). It is also a well-known pathogen in other poultry species, such as chickens.

There are six species of Eimeria that can infest turkeys: E. meleagridis, E. dispersa, E. gallopavonis, E. meleagrimitis, E. innocua and E. subrotunda. This species parasite different parts of the digestive tract and with different severity, for which signs and lesions observed in necropsies can help with the diagnosis.

2. LIFE CYCLE AND PATHOGENESIS

Transmission of the disease occurs via feco-oral route, when turkeys ingest infective (sporulated) oocysts. In the gut, sporozoites in the oocyst are released into the lumen and invade cells of the digestive mucosa. Inside them, several phases of asexual and sexual reproduction take place, which lead to a massive infestation and destruction of the host’s gut cells.

The damage of the gut mucosa is the cause for the clinical signs and lesions observed in animals, which include diarrhea, growth retardation and worsening of the feed conversion rate. In addition, other pathogens take advantage of the weakened mucosa and the presence of undigested feed to multiply and infect the animal. This is the case of several Clostridium species, causal agents for gangrenous dermatitis and necrotic enteritis, and the former is closely related to coccidiosis (Droual & Shivaprasad, 1994).

Once the sexual reproductive stage is completed, thousands of non-sporulated oocysts are formed, which are excreted in the feces and, after some time, sporulate and become infective to restart another cycle.

3. SIGNS AND LESIONS OF COCCIDIOSIS IN TURKEYS

Signs and lesions of coccidiosis in turkeys vary depending on the species of Eimeria involved, the number of ingested oocysts and the age and status of the animal. Severity, location and appearance of the lesions can help us reach a diagnosis, as they vary depending on the species that are present (table 1), although some of them parasite similar parts of the digestive tract.

Subclinical infestations cause growth retardation and worsening of the feed conversion; more severe cases can cause mortality.  Liquid feces and, consequently, bad litter quality and higher foot-pad lesion scores can also be observed.

Among the most common lesions in coccidiosis in turkeys, there are wall thickening and presence of watery or bloody content in the lumen. In the most severe cases, there may be ulcerations and fibrinous necrotic content. Keep in mind that, often, coccidiosis is marked by secondary infections, such as necrotic enteritis, that cause extensive and more severe lesions in the gut mucosa.

4. DIAGNOSIS

Some laboratory techniques can help us reach a diagnosis. These are always a helpful tool, but to reach a proper diagnosis, the following should also be considered:

• Clinic diagnosis: presence and severity of the diarrhea, impact on productivity.
• Lesions observed in the gut, although some of them may be unspecific: for differential diagnosis, consider mycotoxin (trichothecenes) lesions, which, unlike coccidiosis, also damage the beak, oral cavity and the gizzard corneal layer. The location of the lesions caused by coccidia can give us an idea of what Eimeria species are present.

In the lab, two main type of analyses can be conducted:

• Oocyst counting (per gram of feces) can give us an idea of the severity of the infestation, although they do not always correlate. The observation of the oocysts if helpful when describing what species are involved. Sugar or salt flotation methods can be used, and the McMaster chamber for quantification.
• Histology from mucosal scraping or intestinal samples. They can be fixed with 10% formaldehyde, embedded in paraffin wax, sliced and histological slides stained with H&E.

5. PREVENTION AND TREATMENT OF COCCIDIOSIS IN TURKEYS

Treatment

Coccidiosis in turkeys is often subclinical, so no treatment is administered unless secondary infections take place. If there are clinical signs, sulfonamide or amprolium are the most used.

Prevention

Prevention is a better tool than treatment because, many times, although no clinical signs are observed, subclinical coccidiosis worsens productivity.

There are many products, called chemical and ionophore coccidiostats, used in poultry for coccidiosis prevention but, due to the development of resistances, they have limited efficacy. Because of this, regulations of many countries around the world have banned and/or limited their use. In addition, only some of the drugs approved to prevent coccidiosis in turkeys. Shuttle/rotation programs should be applied when using coccidiostats, with products of different types and with different mechanisms of action.

Research is conducted for new solutions with a different approach, solutions that prevent coccidiosis in turkeys without creating resistances, such as vaccination and pronutrients. Chart 1 summarizes the main advantages and disadvantages of vaccinations.

Besides that, pronutrients represent a viable solution to control coccidiosis in turkeys. They are active molecules of a plant origin that stimulate cell physiology. They act as a stimulus for the target cells to start reading certain genes of their DNA related to the functioning of the organs.

The most important pronutrients for the prevention of coccidiosis are intestinal optimizers, whose target cells are the immune cells in the gut. Several field studies show that their addition to feed or drinking water, in small amounts, promote the normal functioning of the local intestinal immunity, so that the animal is able to defend itself from coccidia.

Thanks to this mechanism of action, based on the physiologic stimulation of the local immune system, these molecules do not cause the development of resistances and can completely replace coccidiostats to prevent coccidiosis in turkeys.

Another factor to consider is biosecurity. These measures include the implementation of all in/all out methodologies, exhaustive cleaning and disinfection of the facilities and depopulation between batches. The control of plagues and wild animals is of great importance, as wild birds and insects like Alphitobius can act as vectors for this parasitosis.

6. CONCLUSIONS

Coccidiosis is an important disease to consider in turkey production because, despite it is often subclinical, its control can improve productivity and decrease the prevalence of several pathologies, such as necrotic enteritis.

There are different tools to prevent this parasitosis, such as coccidiostats, vaccination or pronutrients. They should be combined with an effective biosecurity program to eliminate and prevent the entrance of coccidia in the farm.

BIBLIOGRAPHY
Droual, R., & Shivaprasad, H. L. (1994). Coccidiosis and Necrotic Enteritis in Turkeys (Vol. 38, Issue 1).
Vrba, V., & Pakandl, M. (2014). Coccidia of turkey: From isolation, characterisation and comparison to molecular phylogeny and molecular diagnostics. International Journal for Parasitology, 44(13), 985–1000.