Veterinary Research Forum

Abstract To date, routine diagnosis of canine heartworm disease relies on detecting Dirofilaria immitis antigens in blood or the microscopic examination of blood smears. However, each method has limitations, potentially leading to life-threatening situations for infected dogs. This study aimed to determine the prevalence of filarial infection, risk factors, and appropriate detection methods in practical clinics. A total of 113 dog blood samples from two provinces in Thailand (Chonburi = 73 and Nakhon Nayok = 40) were analyzed for D. immitis infection using buffy coat smears, commercial immunochromatographic tests (SNAP 4Dx Plus), and polymerase chain reaction. Overall prevalence was 51.53% (58/113) across all methods. The positivity rates were 15.38% (12/78) for buffy coat smears, 8.00% (4/50) for SNAP 4Dx Plus, and 45.43% (51/113) for polymerase chain reaction. All positives from the test kits correlated with other methods. A significantly high prevalence was observed in dogs under 2 years old. Accessibility to pet care services in urban areas appeared to have a protective effect. Positive commercial test results could confirm D. immitis infection. However, selecting more than one diagnostic technique in clinics, including morphological examination, immunochromatography, or molecular methods, is recommended for early and more accurate detection, along with the promotion of heartworm prevention strategies.

Abstract Dirofilaria immitis is an important filarial nematode in dogs. In this study, age and sex distribution of this zoonotic nematode among dogs were investigated in northwest of Iran in Meshkin-Shahr city. Molecular characteristics of the isolates, based on cytochrome oxidase subunit 1 (COX1) gene were compared to the isolates from other areas of the world.Blood samples were collected from 91 dogs which were selected by simple classified accidental sampling. Thin and thick blood smear examinations were used to find out infectivity with D. immitis. DNA extraction was performed from adult D. immitis recovered from heart of infected dogs. The COX1 gene was amplified and sequenced. Phylogenetic analysis was carried out using sequences obtained in this study along with relevant sequences deposited in the GenBank. Phylogenetic analysis and sequence variation was performed using MEGA software in comparison with those COX1 sequences deposited in GenBank. Out of 91 dogs, 19 (20.87%) were found positive for infection with D. immitis. There was no statistically significant difference between males and females of dogs in terms of D. immitis infection. However, the rate of infection in dogs more than 2 years old was significantly higher than those with lower age. Both sequences analyzed in this study showed 100% homology to each other. Intra-species variation of these isolates with those from other areas of the world amounted to 0 to 0.50%. Phylogenetic analysis of the COX1 gene suggested that it is conserved, and can be used for study on genetic diversity and classification of filarial nematodes.