There has been an arms race going on, all around us, for 60,000 years – but this hasn’t involved the conventional kind of warfare seen between opposing geopolitical factions. This conflict has taken place on a nanometer scale, between viruses and our furry feline companions; specifically, the feline immunodeficiency virus (FIV) – the cat version of the human immunodeficiency virus (HIV) – has been warring with the evolutionary lineage of kittens and cats across the world for over sixty millennia, according to a study published this month in the Journal of Virology.
At least 2.5% of cats worldwide are infected with FIV, but it has been estimated to perhaps be as high as 11%. After being sexually transmitted from one cat to another, the lentivirus begins to assault the cat’s immune system, predominantly targeting a type of white blood cell called T helper cells which normally serve to coordinate immune responses. Eventually, their immune system will collapse following extensive cell death; however, cats can live for many years as carriers and transmitters of the disease without any treatment.
This isn’t to say that the cat’s immune system is entirely helpless in dealing with the infection. A protein, APOBEC3Z3, is able to provide a mitigating response to an infection; it is able to bind with the viral particles produced during the replication process, the “progeny virions.” Although this binding process cannot destroy the virus, it does inhibit its ability to replicate through the cat’s body by causing harmful mutations in its genetic material. Humans have a similar mechanism operating within their bodies when infected with HIV, which uses a human equivalent of this protein.
Eventually, the virus manages to break down APOBEC3Z3, allowing it to continue to replicate. However, this new research reveals that the domestic cat – Felis selvestris catus – appears to have evolved a backup system for this protein.
A cat’s APOBEC3Z3 protein has seven distinct variants known as haplotypes. A variant known as haplotype V appears to have been “selected” throughout the cat’s evolutionary history for tens of thousands of years, remaining in the offspring of generation after generation of the ancestors of the domestic cat right up until the present day.
This particular variant acts in tandem with the other proteins binding to FIV as it attempts to replicate. When the virus begins to successfully break down the binding proteins, haplotype V steps in and slows down the degradation process, allowing the binding process to continue for longer.
As the study points out, FIV was first isolated and defined by researchers in 1986-1987, taken from a range of cats suffering AIDS-like disorders. Although the comparison between FIV and HIV was quickly made, the date of the original evolution and emergence of FIV was still unknown. By analyzing the genetic sequence of the domestic cat and focusing on the genesis of haplotype V, the team discovered that FIV must have evolved at least 60,000 years ago, a full 50,000 years before the cat was even domesticated.