Occurrence and emerging trends of Hepatozoon canis infection in dogs in Hassan district, Karnataka

Introduction

Canine hepatozoonosis is an important tick-borne protozoan disease caused by Hepatozoon canis, an apicomplexan parasite infecting domestic and wild canids. Unlike many other tickborne pathogens, transmission occurs primarily through the ingestion of infected ticks, particularly Rhipicephalus sanguineus, rather than via tick bites (Baneth et al., 2001). [3] The disease is widely distributed across tropical and subtropical regions of the world, including several parts of India, where environmental conditions favor the proliferation of the tick vector. In India, sporadic as well as endemic occurrences of H. canis infection have been reported in different states, often associated with high tick infestation and poor management practices. However, the epidemiological pattern may vary considerably depending on geographic, climatic, and host-related factors. Clinically, canine hepatozoonosis exhibits a broad spectrum of manifestations, ranging from subclinical or asymptomatic infections to severe systemic illness. The severity of clinical signs is largely influenced by the level of parasitemia, immune status of the host, presence of concurrent infections, and overall health condition (Baneth & Weigler, 1997). [4] Common clinical signs include intermittent fever, lethargy, weight loss, anemia, lymphadenopathy, and musculoskeletal pain. In severe cases, dogs may exhibit marked debilitation and complications involving multiple organ systems. Several authors have reported the occurrence of Hepatozoon canis infection across different regions of India, including Kerala (Priya et al., 2004 [11] ; Bindu Lakshmanan et al., 2018 [5] ), Uttar Pradesh (Vijayasarathi et al., 2024) [9] , Himachal Pradesh (Devina et al., 2018 [8] ), and Tamil Nadu (Murugesan et al., 2018). [10] Despite the documented occurrence of Hepatozoon canis infection in several regions of India, reports from Karnataka remains limited (Ananda et al., 2005). [1] Furthermore, since the establishment of the Veterinary College, Hassan, in 2007, there has been no documented evidence of its occurrence in the Hassan district of Karnataka. This absence of reports may be attributed to limited surveillance, subclinical nature of infections, or under diagnosis. In this context, the present report assumes significance as it documents the recent occurrence of H. canis infection in dogs from Hassan district.

Materials and Methods Study area and sample collection

The present study was carried out at the Department of Veterinary Parasitology, Veterinary College, Hassan, Karnataka, India. The Blood samples were collected from dogs presented for clinical examination with suspected haemoprotozoan infections at Teaching Veterinary Clinical Complex, Veterinary College, Hassan. Approximately 2-3 ml of blood was aseptically collected and transferred into EDTA coated vacutainer tubes and processed immediately or stored at 4 °C and analyzed within 24 hours.

Preparation and examination of blood smears

Thin blood smears were prepared on clean, grease-free glass slides using the wedge technique. The smears were air-dried, fixed in absolute methanol for 2-3 minutes, and subsequently stained with Giemsa stain (1:10 dilution, pH 7.2) for 20-30 minutes, following standard procedures as described by Coles (1986). [6] The smears were gently rinsed with buffered water, air-dried, and examined under a light microscope under oil immersion (100×) for detection of haemoprotozoan parasites. Identification of parasites was based on morphological characteristics as described by Soulsby (1982) [12] .

Haematological analysis

Haematological parameters, including haemoglobin (Hb), total erythrocyte count (TEC), and platelet count, were estimated using standard veterinary haematological methods. The values obtained were compared with established reference ranges to assess haematological alterations, such as anaemia and thrombocytopenia, associated with haemoprotozoan infections.

Results

During a six-month period, three cases of Hepatozoon canis infection were diagnosed in dogs presented to the Teaching Veterinary Clinical Complex, Veterinary College, Hassan. The affected animals originated from three geographically distinct locations within Hassan district, indicating a wider distribution of the infection rather than a localized occurrence. Notably, no cases had been recorded in this region in previous years, suggesting a possible recent emergence or increased detection of the parasite. The diagnosis in these cases was established based on clinical presentation, haematological alterations, and confirmatory microscopic identification of the organism in Giemsa-stained peripheral blood smears. Affected dogs consistently presented with clinical signs such as high fever, inappatance, congested mucous membranes, tick infestation, dullness, depression, and recumbency. Haematological analysis revealed anaemia, indicated by decreased haemoglobin concentration and reduced total erythrocyte count, along with thrombocytopenia in all cases examined. Microscopic evaluation of Giemsa-stained blood smears showed the presence of intracytoplasmic gametocytes within neutrophils. The organisms were elongated with rounded ends, featuring a centrally located, dark-stained nucleus and pale blue cytoplasm, consistent with the characteristic morphology of Hepatozoon canis as described by Soulsby (1982). [12]

Discussion

The present study documents the recent occurrence of H. canis infection in dogs from Hassan district, Karnataka, where no cases had been recorded since 2007, suggesting a possible emerging pattern in this region. The sudden detection of three confirmed cases within a short span of six months indicates a change in epidemiological dynamics. Similar re-emergence or increased detection of H. canis infections has been reported from various parts of India, including Kerala, Uttar Pradesh, and Himachal Pradesh (Bindu Lakshmanan et al., 2018 [5] ; Vijayasarathi et al., 2024 [9] ; Devina et al., 2018 [8] ). These reports, along with the present findings, highlight the expanding distribution of the parasite across diverse geographical regions. Factors such as climate change, increased vector density, and enhanced pet mobility may have contributed to the establishment and spread of the infection in previously unaffected areas (Baneth et al., 2001). [3] The clinical signs observed in the present cases, including fever, inappatance, depression, tick infestation, and recumbency, are in agreement with earlier reports describing nonspecific but consistent manifestations of canine hepatozoonosis (Dantas-Torres, F. 2010). [7] The presence of tick infestation in all affected dogs further supports the role of R. sanguineus as a principal vector in disease transmission. Additionally, the observed haematological alterations such as anemia, thrombocytopenia, and reduced erythrocyte counts corroborate previous studies, which attribute these changes to chronic infection, bone marrow suppression, and immunemediated destruction of blood cells (Antonio et al., 2008). [2] Microscopic detection of characteristic gametocytes within neutrophils in Giemsa-stained blood smears remains a reliable and widely used diagnostic method in clinical settings. The parasitic stages observed in the present study were consistent with the classical descriptions of Hepatozoon canis (Soulsby, 1982). [12] However, it is important to note that parasitemia may be low in subclinical or early infections, potentially leading to under diagnosis. Molecular techniques such as PCR have been reported to be more sensitive and specific for confirmation of infection (Bindu lakshmanan et al., 2018 [5] and Devina et al., 2018 [8] ). The absence of reported cases over a long period followed by recent detection suggests either an emergence of infection or improved surveillance and diagnostic awareness. Urbanization, increased stray dog population, and frequent movement of pets between regions may facilitate the introduction and establishment of infected ticks in new areas. Hassan district, with its changing ecological and socio-economic landscape, may now be conducive for the survival and propagation of the vector, thereby increasing the risk of transmission.

Conclusion

This report documents the emergence of Hepatozoon canis infection in dogs in Hassan district, Karnataka. The occurrence of multiple cases within a short period indicates potential epidemiological significance and underscores the need for large-scale surveillance to assess prevalence and risk factors. Continuous monitoring, effective tick control, and increased clinical awareness are essential to limit disease spread. Further studies using molecular diagnostics and larger sample sizes are required to better understand the epidemiology and true prevalence of canine hepatozoonosis in this region.

Acknowledgement

AcknowledgementThe authors sincerely acknowledge Karnataka Veterinary, Animal and Fishery Sciences University, Bidar, and Veterinary College, Hassan for providing the infrastructure and facilities necessary to conduct this study.

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