Subclinical Infections of Babesia and Dirofilaria in Dogs Presented to a Veterinary Teaching Hospital: Evidence for a Silent Reservoir of Infection in Sri Lanka.

Abstract

PURPOSE: Canine filariasis and babesiosis are serious vector-borne diseases, often undetected in asymptomatic dogs. This hidden prevalence complicates disease control, as subclinical carriers may continue transmission. This study determined the prevalence of asymptomatic infections and explored potential links between breed types. METHODS: Blood samples were collected from dogs brought to the Veterinary Teaching Hospital for illnesses, vaccination, sterilization, and regular health check-ups. Babesia and filarial worms were morphologically identified through Giemsa-stained thin blood smears and Modified Knott's Technique, respectively. Infections were confirmed using conventional PCR, targeting the 18S rRNA gene for babesiosis and the 5.8S-ITS2-28S region for filariasis, following bi-directional sequencing. The prevalence and infection intensity were compared among gender, age, and breed of dogs. RESULTS: Among the 160 dogs tested, 35.0% and 16.3% were positive for infections of Babesia and Dirofilaria, respectively, of which 88.0% showed no clinical signs. A higher prevalence of Babesia infection was observed in crossbred (51%) than purebred dogs (26%; Chi square test, &#x3c7;&#x2009;=&#x2009;10.318, p&#x2009;=&#x2009;0.001), as well as with filaria infection (crossbred 42%; purebred 1%; &#x3c7;&#x2009;=&#x2009;46.866, p&#x2009;<&#x2009;0.05). The intensity of Dirofilaria infection (2.14&#x2009;&#xb1;&#x2009;5.71) was higher in crossbred dogs than purebred dogs (0.03&#x2009;&#xb1;&#x2009;0.30; Mann-Whitney U test, p&#x2009;<&#x2009;0.001). Sequencing of the amplified products confirmed the presence of Babesia gibsoni and Dirofilaria repens. CONCLUSION: Asymptomatic cases of filariasis and babesiosis among dogs reveal a persistent clinical burden, with crossbred dogs acting as subclinical reservoirs. This silent transmission complicates early detection and facilitates continued spread within the domestic canine population. This highlights the importance of routine screening across all breeds to introduce preventive and control measures to curb disease persistence.