Comparative Evaluation of a Point-of-Care Immunochromatographic Test SNAP 4Dx with Molecular Detection Tests for Vector-Borne Canine Pathogens in Hong Kong

Abstract

There are no comprehensive studies on the performance of commonly used point-of-care diagnostic enzyme immunoassay for common arthropod-borne canine pathogens. A comparative evaluation of an immunochromatographic test for these infections with a comprehensive polymerase chain reaction (PCR) test panel was performed on 100 pet dogs and 100 stray dogs without obvious clinical symptoms. Of the 162 positive test results from both immunochromatographic test and PCR, there was 85.2% concordance. The 24 discordant results between serology and PCR occurred in tests involving Ehrlichia canis (14) and Anaplasma platys (10), which may be related to the time of infection. No positive cases of borreliosis or rickettsiosis were detected. One important limitation of the immunochromatographic test was its lack of testing for babesiosis and hepatozoonosis. The former is the most prevalent arthropod-borne canine infection in our cohort (41%). Coinfections were found in 19% stray dogs and 6% of pet dogs with both tests (p < 0.01). Seventeen and 8 samples from stray and pet dogs, respectively, were initially positive in the PCR test for Ehrlichia. However, on sequencing of the PCR amplicon, 10 from stray and 2 from pet dogs were found to be Wolbachia sequences instead, with 100% nucleotide identity to the 16S rRNA sequence of Wolbachia endosymbiont of Dirofilaria immitis. The presence of Wolbachia DNAemia (6%) correlated well with the molecular test and immunochromatographic antigen test for D. immitis.

A Novel Dirofilaria Species Causing Human and Canine Infections in Hong Kong

“…Our previous study showed that D. immitis can be found in 10% of stray dogs in Hong Kong (34). All infected dogs also had detectable Wolbachia DNA in the blood.…”

“…Blood samples collected from the asymptomatic stray dogs were tested for antigen of D. immitis using SNAP 4Dx (IDEXX Laboratories, Westbrook, ME) as we previously described (34).…”

“…However, these features can sometimes be difficult to discern, especially in tissue sections (25). Definitive diagnosis can also be made by molecular methods in both human and animal infections (14,34).…”

It shouldn’t happen to a dog … or a veterinarian: clinical paradigms for canine vector-borne diseases

“…These are not only more convenient and generally cheaper than traditional serological techniques (e.g., immunofluorescent antibody testing), they have the important advantage in the clinical setting of empowering the veterinarian to provide immediate treatment for the pet and advice to the owner. An additional benefit of these tests, often with in-kind support provided by the manufacturers, has been an increase in the number of cross-sectional serosurveys of CVBDs around the world, which have greatly furthered our understanding of their epidemiology and geographical distribution [41,42]. Nevertheless, it should be remembered that such tests also have limitations in terms of sensitivity (e.g., acute infections prior to antibody response) and specificity (e.g., cross-reactions between organisms), and some clinically significant diseases (e.g., acute babesiosis) are still probably best diagnosed by microscopy [43,44].…”

Detection of Babesia hongkongensis sp. nov. in a Free-Roaming Felis catus Cat in Hong Kong

“…abesiosis is the commonest vectorborne canine infection in Hong Kong, with 48% and 33% of the stray and pet dogs being infected, respectively (14). Human babesiosis is usually caused by Babesia microti, B. divergens, and some newly described strains such as the WA1, EU1, -2, and -3, CA1, -2, -3, and -4, and KO1 types (9).…”