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In-Clinic Canine IgG Antibody Titer Test Comparative Study: Results from Five Clinics
Salomon, K., de Lange, T., Calis, A...
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Abstract
This study was carried out in order to study the performance of three in-clinic test kits for the detection of protective plasma IgG antibody titers against canine Adenovirus (CAV), canine Parvovirus type 2 CPV-2) and canine Distemper Virus (CDV). Plasma samples from 46 adult vaccinated dogs were tested for the presence of protective IgG antibodies using three commercial in-clinic test kits; Canine VacciCheck (Biogal, Israel), RapidStatus Titer Test (Biotech Laboratories USA) and FASTest CDV-CPV Ab (Megacor, Austria). The accuracy of the three in-clinic test kits was evaluated against two respective gold standards tests, serum Virus Neutralization (for CAV and CDV) and Hemagglutination Inhibition (for CPV) assays, performed at the Animal Health Diagnostic Center in Cornell University, New York. The gold standard tests determined that all 46 dogs had protective serum IgG antibodies against CPV-2, 45 against CDV and 44 against CAV. Sensitivity calculations revealed that both VacciCheck and FASTest demonstrated equally good results while RapidStatus generated less accurate results when compared to the gold standards. CPV-2 sensitivity evaluations of VacciCheck, FASTest and RapidSTATUS were 98%, 98% and 78% respectively. The CDV sensitivities of VacciCheck, FASTest and RapidSTATUS were 100%, 100% and 60% respectively and the CAV sensitivities of VacciCheck and RapidSTATUS were 98% and 57% respectively. The FASTest does not test for CAV.
Keywords: In-Clinic Titer Testing; Accuracy; Canine Core Vaccination.
Introduction
According to the World Small Animal Veterinary Association (WSAVA) and the American Animal Hospital Association (AAHA) Vaccination Guidelines, canine core vaccines are highly effective in protecting the majority of dogs against infection by the canine distemper virus (CDV), canine adeno-virus (CAV) and canine parvovirus type 2 (CPV-2) (1, 2, 3). The guidelines recommend that adult dogs be revaccinated with these core vaccines no more than every 3 years. Although this interval is recommended, many studies have shown that the modified attenuated virus vaccines confer protection for a period considerably longer than 3 years. The presence of plasma IgG antibody against CDV, CAV and CPV and the associated conferred protection against infection have been confirmed by numerous studies (4, 5, 6, 7, 8). These studies concluded that, when properly administrated, core vaccine protocols lead to a long-lived persistence of vaccine-induced protective antibodies and consequently, immune protection for more than 3 years after the last administration.
Positive titer serological tests can generally be attributed to an undetected subclinical exposure, maternally derived antibodies (MDA), or vaccination generated antibodies.
Core vaccine IgG antibodies circulating in the blood are commonly quantified in reference laboratories while semi-quantitative evaluations can be performed with a few commercial in-clinic assay kits (9). Quantitative IgG assays can be useful in determining the presence of MDAs, providing information that may be useful to determine the best time to begin core vaccination. Lack of seropositivity 4 weeks after completion of the puppy series at approximately 16 weeks of age, usually indicates the absence of protective immunity and justifies revaccination (10, 11, 12). Failure to mount an immune response following additional vaccination is a strong indicator that the puppy may be incapable of developing protective immunity. Infection following immunization can be associated with vaccine factors resulting in inadequate antigenic stimulation or host factors, owing to an inadequate immune response to an adequate antigen challenge. Vaccine factors may arise from fault in manufacturing, failure of the end user to adhere to expiry of the shelf-life, inadequate cold chain maintenance during transport and storage or incorrect vaccination technique. Host factors include, in addition to interference by MDAs, genetic mutations leading to immune deficiency syndromes (10). Antibody tests can be used to demonstrate the duration of immunity (DOI) following vaccination with core vaccines and spare the dogs unnecessary and possibly detrimental revaccination (12, 13, 14).
There is a positive correlation between CDV, CAV and CPV seropositivity and immune protection against infection with these diseases. Both guidelines mentioned previously advocate the use of serological testing in place of automatic yearly revaccination. The WSAVA guidelines specify that the presence of IgG antibody (regardless of the titer) indicates protective immunity and immunological memory (1, 2). Negative test results in fully vaccinated dogs, on the other hand, could indicate that the titers are below the limit of detection for the test or that there is a complete lack of protective antibodies in the sample tested. In rare cases, dogs that have been tested to have a low titer or be seronegative may be in fact immune and are still capable of generating a significant anamnestic response to vaccina- tion (14). Such animals are not easily identified, therefore the guidelines recommend that an animal with a negative result, regardless of the test used, should be considered as having no protective antibody and potentially susceptible to infection.
The gold standard serological tests used to determine IgG antibody titers generated from core vaccine antigens were the Virus Neutralization (VN) test for CDV and CAV and the Haemagglutination Inhibition (HI) test for CPV (15, 16, 17). These tests can be performed only in specialized diagnostic laboratories. Accurate and affordable in-clinic test kits are marketed in several different configurations ranging from lateral flow to ELISA and Solid Phase Dot Blot. Some of these point-of-care (POC) kits have been validated against the gold standard tests and are defined as semi-quantitative since they generate results in numerical values which correlate positively with the gold standard tests (9). These test kits can rapidly determine the presence of serum IgG antibody against canine core vaccine antigens within 10-23 minutes, providing valuable in-clinic information.
The aim of the present study was to evaluate and compare the performance of 3 different titer kits in an in-clinic setting and to compare the results with the gold standard tests performed at the Animal Health Diagnostic Center in Cornell University, New York. Five different veterinary clinics tested three different POC titer test kits using samples collected from vaccinated adult client-owned dogs received in their clinics. [...]
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