Challenging the Clinical Paradigm of Hepatozoon canis: A Primary Pathogen Causing Clinically Significant Disease at Low Parasitaemia and a Chronic Inflammatory State.

backgroundHepatozoon canis is an important canine pathogen transmitted by the brown dog tick, Rhipicephalus sanguineus, causing a vector-borne disease with variable clinical severity. This study aimed to characterize the clinical and haematological spectrum of H. canis infection in Iranian dogs.

methodsBlood samples from 181 dogs were analysed using microscopy, PCR targeting the 18S rRNA gene and haematological profiling. Phylogenetic analysis confirmed species identity.

resultsPrevalence was 1.66% by microscopy and 6.6% by PCR, demonstrating the superior sensitivity of molecular diagnostics. The absence of tick control was a significant risk factor, increasing odds of infection 4.51-fold (p = 0.007). No significant associations were found with age, sex or source. Three clinically ill dogs exhibited fever, lethargy, weight loss, microcytic hypochromic anaemia, leukocytosis and (in high parasitaemia cases) thrombocytopenia. Notably, illness occurred even at low parasitaemia (2%). Subclinically infected dogs (n = 9) also showed significant reductions in haematocrit, haemoglobin and RBC count, alongside lymphocytosis, indicating a state of chronic subclinical inflammation and anaemia.

conclusionsThe findings confirm H. canis endemicity in south-western Iran and identify lack of tick prevention as the primary modifiable risk. This study challenges the conventional paradigm by demonstrating that H. canis can cause significant clinical disease at low parasitaemia and induces a chronic inflammatory state in subclinical infections. Consequently, H. canis should be considered a primary pathogen, necessitating increased clinical suspicion and integrated control strategies centred on effective tick prophylaxis.