Turkey coccidiosis is caused by protozoan parasites of genus Eimeria. Eimeria species are ubiquitous in intensive turkey production facilities. Seven Eimeria species have been characterised and documented in turkeys. Among the seven species, E. adenoeides, E. meleagrimitis and E. gallopavonis are considered as predominant and highly pathogenic strains of turkeys. Coccidiosis causes substantial economic losses to the turkey industry by affecting intestinal health and production performance. This manuscript describes the pathologic manifestations of these predominant Eimeria species along with diagnosis and control measures.

Coccidiosis is an economically important enteric disease of turkeys caused by the apicomplexan parasites of genus Eimeria. Eimeria species are obligate, intracellular parasites affecting the intestine of turkeys. They are ubiquitous in intensive turkey production systems (Figure 1) and the disease transmission occurs through the fecal oral route. Seven Eimeria species have been well recognised and documented in turkeys: E. adenoeides, E. gallopavonis, E. meleagrimitis, E. dispersa, E. innocua, E. meleagridis and E. subrotunda. Among these, three species, E. meleagrimitis, E. adenoeides and E. gallopavonis (Figure 2), are predominant in turkeys. These three Eimeria species are considered as highly pathogenic strains of turkeys.

In mild infection, pathological manifestations of turkey Eimeria species in the intestines are not very well pronounced and defined. Most of the time, it may go unnoticed as subclinical coccidiosis without any severe lesions or clinical signs, but may still adversely affect production performance. In cases of clinical coccidiosis, classical lesions in the intestinal tract along with morbidity and mortality are observed. Coccidiosis induces morbidity by impacting the feed intake, poor feed conversion rate (FCR), and reduced body weight gain. It may cause dehydration and blood-tinged diarrhoea along with mucous casts (Figure 3). In a 2022 US turkey industry survey, coccidiosis was ranked as the #9 disease affecting the turkeys.

Predominant and Highly Pathogenic Eimeria Species of Turkeys

Eimeria meleagrimitis

• Target region in the intestine: Duodenum and jejunum.
• Prepatent period: 4.3 days (103 hours).
• Gross lesions: Watery contents along with fibrin strands, mucoid exudate, and clots. Mild infection may cause petechiae on the mucosa. Severe infection results in the thickened intestinal wall along with formation of diphtheritic membrane, haemorrhage, and necrosis (Figure 4).

Eimeria adenoeides

• Target region in the intestine: Ceca.
• Prepatent period: 4.3 days (103 hours).
• Gross lesions: Normal cecal contents are replaced with watery cecal contents with caseous clots/ chunks or results in the formation of fragmented cecal core or solid core. Petechiae may be seen on the mucosa (Figure 5).

Eimeria gallopavonis

• Target region in the intestine: Primarily ileum, extends up to cecal neck and rectum.
• Prepatent period: 4.4 days (105 hours).
• Gross lesions: Normal intestinal contents are replaced with caseous and/or haemorrhagic exudate. Presence of white spots on the mucosa and thickened intestinal wall (Figure 6).