Study Reports the First Molecular Characterization of FIV in Mainland China

A study recently published in PLoS One reported the molecular characterization of feline immunodeficiency virus (FIV) in domestic cats in mainland China. Notably, this is the first study to describe FIV subtype A in continental Asia.

FIV is a retrovirus that primarily affects male cats. It has a global distribution with an overall prevalence between 2% and 30%, depending on geographic location. Seven subtypes (A, B, C, D, E, F, U-NZenv) of FIV have been identified, with subtypes A and B being the most common; the subtypes are differentiated by sequence variations of the envelope (env) gene, a major gene in the retroviral genome. FIV subtype A, which can be found in such countries as the United States, New Zealand, and South Africa, commonly causes neurologic signs.

From April 2013 to June 2015, the study’s authors collected blood from 615 cats in five cities across four of mainland China’s provinces. Cats from one city lived in shelters; cats from the other cities presented at veterinary clinics with such symptoms as stomatitis and renal failure.

DNA was extracted from the blood samples for molecular analysis. Fluorescence resonance energy transfer polymerase chain reaction (FRET-PCR), which can differentiate FIV subtypes A—E, was conducted to detect sequences of the group-specific antigen (gag) gene, another major retroviral gene. Standard PCR was performed to detect env gene sequences from regions V1—V5 of this gene; subtypes were then differentiated using an algorithm that identified polymorphism within regions V1–V4.

The authors obtained gag and env sequences of FIV subtypes (including subtype A/B) from GenBank, an NIH-sponsored database; each sequence had a database accession number that corresponded to a specific FIV strain. The GenBank sequences were compared with the gag and env sequences identified during the study. Gag and env sequences from both sources were used to construct a phylogenetic tree.

Eight of the 615 (1.3%) cats were FIV-positive. Of these eight cats, all were male, seven exhibited clinical signs (renal failure, stomatitis, depression, feline calicivirus infection, high fever), and six were intact. The authors attributed the low prevalence rate to the cats being primarily indoor pets. The cats with clinical signs were relatively young (≤3 years old); this was unexpected given that FIV-positive cats usually stay asymptomatic for many years before displaying signs of infection.

FRET-PCR demonstrated that gag sequences from all FIV-positive cats belonged to FIV subtype A; these sequences shared 97% to 99% similarity with two GenBank FIV subtype A strains from Canada.

In the FIV-positive cats, sequences from the V1—V2 env region shared 90% to 93% similarity with two FIV subtype A strains—one each from Scotland and Japan. The V3—V5 sequences shared 94% to 95% similarity with the same FIV subtype A strain from Scotland and 94% to 96% similarity with an FIV subtype A/B strain from Australia.

For both the gag and env sequences, percentage similarities with other FIV subtypes were notably lower.

Phylogenetic analysis confirmed that the Chinese strains of FIV from the eight FIV-positive cats belonged to subtype A.

Given the study’s findings, the authors advised Chinese veterinarians to be cognizant of the possibility of FIV subtype A infection in their feline patients. They also suggested that larger studies be conducted to identify other FIV subtypes in the region and “facilitate the development of accurate diagnostic tools and control programs.” In addition, because a recent study of the Fel-O-Vax vaccine reported vaccination breakthroughs for several FIV subtypes, including subtype A, the authors believed that “further studies on the usefulness of vaccination under conditions of natural challenge are required.”

Dr. Pendergrass received her doctorate in veterinary medicine from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, LLC.