Abstract
Background:
Histomonas meleagridis is the protozoan parasite responsible for histomoniasis, a severe disease in turkeys causing characteristic cecal and hepatic lesions and potentially high mortality. Chickens are generally less affected but are recognized as important reservoirs and asymptomatic carriers. Despite its global distribution, the epidemiological situation of histomoniasis in Algerian backyard poultry remains poorly documented. This is of particular concern because backyard flocks are often located near commercial poultry farms, including turkeys, and no effective treatment is currently available.

Aim:
The present study aims to investigate the prevalence and histopathological characterization of Histomonas meleagridis in backyard chicken farms in the Batna region (Eastern Algeria).

Methods:
From September 2024 to May 2025, a total of 43 backyard chickens (Gallus gallus domesticus, Linnaeus, 1758), including 17 males and 26 females, were examined. The backyard farms (n=20) were randomly selected within the study region. Within these farms, chickens presenting clinical signs suggestive of histomoniasis were submitted for diagnostic investigation and screened for Histomonas meleagridis infection using macroscopic and microscopic methods. Histomonas meleagridis positive and negative samples were subsequently evaluated using a lesion scoring system to assess the severity of caecal and hepatic lesions.

Results:
Twenty-one chickens (48.83%) from 12 farms showed macroscopic lesions typical of histomoniasis, while 18 chickens (41.86%) from 13 farms tested positive through histological analysis. Among the 43 chickens examined, 19 were infected with Heterakis gallinarum, corresponding to a prevalence of 44.18%. Coinfection with both parasites was detected in 7 birds (16.27%). Infected chickens exhibited significantly more severe lesions in the liver and caeca than uninfected birds (p < 0.05). No significant difference was found between lesions in birds infected only with Histomonas meleagridis and those coinfected with Heterakis gallinarum.

Conclusion:
This is the first report on the prevalence and histopathological characterization of Histomonas meleagridis in backyard chicken farms in Batna province, Eastern Algeria. Findings suggest that Histomonas meleagridis is the primary cause of caecal lesions, while Heterakis gallinarum does not significantly aggravate the lesions. Given the proximity of these farms to commercial poultry operations, especially turkey farms, the study highlights the pathogenic importance of Histomonas meleagridis, which could pose a serious threat to the commercial poultry industry, particularly due to the limited availability of effective treatments.

Key words: Histomonas meleagridis; Heterakis gallinarum; Backyard chickens; Parasitology; Algeria.