Serum Samples from Co-Infected and Domestic Cat Field Isolates Nonspecifically Bind FIV and Other Antigens in Enzyme-Linked Immunosorbent Assays

Abstract

We evaluated enzyme-linked immunosorbent assay (ELISA) specificity for measuring seroantibody responses to two types of retroviral infections in domestic cats: feline immunodeficiency virus (FIV) and feline foamy virus (FFV). We compared the seroreactivity of specific pathogen-free (SPF) cat sera, sera from SPF cats inoculated with either FIV or FFV, and field isolates (e.g., shelter or privately owned cats). Sera from SPF cats experimentally infected with the cognate virus had significantly lower background in both FIV and FFV ELISAs compared to sera from negative field isolates. ELISA values for SPF cats exposed to either FIV or FFV tended to have higher OD values on the opposite ELISA antigen plate. FIV nonspecific background absorbance was greater than that of FFV, and 10 of 15 sera samples from FIV seronegative field samples were measured in the indeterminant range. These findings highlight that exposure to off-target pathogens elicit antibodies that may nonspecifically bind to antigens used in binding assays; therefore, validation using sera from SPF animals exposed during controlled infection results in the setting of a cutoff value that may be inappropriately low when applied to field samples. Our work also suggests that infection of domestic cats with pathogens other than FIV results in antibodies that cross-react with the FIV Gag antigen.

Seroprevalence of feline foamy virus in domestic cats in Poland

“…Many attempts have been made to find any link between FFVfca prevalence and demographic variables which could help to determine the main infection risk factors. While no consistent association with gender has been proven, greater prevalence was linked with advancing age (3,25,388), which is consistent with the studies on other FVs. Similarly to simian foamy viruses, FFVfca is mainly transmitted through close social or aggressive interactions among animals, such as grooming, licking and biting (38), which is supported by the oral mucosa having been confirmed as the main site of active FFVfca replication in domestic cats (4).…”

“…Therefore, we can suspect that there may be other factors influencing the reactivity of the sera in our ELISA assays. One possible explanation can be linked to the recent report from Moskaluk et al (25) proving that sera from a population of domestic cats negative for FIV and FFVfca showed higher reactivity to the antigens specific to both viruses than the sera of virus-negative specific pathogen-free (SPF) cats. Additionally, sera from SPF cats experimentally infected with FIV or FFVfca showed some cross-reactivity with an antigen of the other virus.…”

“…Feline foamy virus (FFVfca) was first isolated in 1969 (32) and since then it has been found to be broadly distributed worldwide in cat populations. Different studies from Europe, Australia, North and South America and Asia reported FFVfca prevalence ranging from approximately 30% to even 100% in domestic cats depending on sex, age and geographic region analysed (2,3,4,5,8,13,25,30,39). FFV-like viruses were also found in wild feline species and were detected in 35% of one such endemic to the Japanese island of Iriomote (Felis iriomotensis) and in one leopard cat species (Felis bengalensis) from Vietnam (24,29).…”

Diagnostic Accuracy of a Point-of-Care Immunoassay for Feline Immunodeficiency Virus Antibodies, Feline Leukemia Virus Antigen, and Dirofilaria immitis Antigen

“…The envelope protein gp40 (transmembrane (TM) protein) is considered the immunodominant protein in FIV infection [ 27 , 28 , 29 , 30 ]. Additionally, some anti-Gag antibodies, including those against p15 and p24, are perceived to be less specific for FIV and may be the result of infection with other viruses [ 31 ].…”