Ticks have been pathogen-carrying parasites for a very, very long time.
A new discovery in a specimen of fossilized amber, roughly 15 million to 20 million years old, reveals a tick encased adjacent to mammalian blood cells infected with microbes resembling those in the order Piroplasmida. Today, related pathogens are known to cause Babesiosis and Texas cattle fever. The research was published in March in the Journal of Medical Entomology.
The finding “shows that ticks have been vectoring protozoan pathogens for millions of years and that humans and other animals infected today with piroplasmic diseases like human Babesiosis, which is considered an emerging disease, acquired the pathogens from ticks feeding on wild mammals, especially monkeys,” says George Poinar, Ph.D., author of the research paper and an entomologist at Oregon State University. “It also shows that these pathogens had millions of years to perfect their infectivity and transmissibility, which makes them so difficult to control today.”
The amber specimen comes from a collection found in the Dominican Republic. The tick, an engorged nymph of the genus Ambylomma shows two holes on its back, and the nearby blood cells are of a size that could have come only from primates on the island. (Mammals like dogs and rabbits have similar sized blood cells but do not appear in the fossil record on Hispaniola.) Poinar says the tick most likely parasitized a monkey and was then picked off by another that was grooming it and dropped in tree sap that fossilized. He called it a “one-in-a-million” find.
In examining the specimen, Poinar both analyzed the blood cells near the tick and then cracked open the amber to examine the gut contents of the tick, as well. In both places, he identified developing piroplasms in the mammalian erythrocytes.
“Aside from providing the first discovery of fossil mammalian red blood cells and the first fossil intra-erythrocytic hemoparasites, the present discovery shows that tick-piroplasm associations were already well established in the Tertiary,” Poinar says. “This discovery provides a timescale that can be used in future studies on the evolution of the Piroplasmida.”
Journal of Medical Entomology