Tracking Onchocerca lupi in Northern Arizona
Wyatt Earp is a rescue dog from northern Arizona. He was adopted in 2009 in Flagstaff, AZ. In 2010, he was diagnosed with a rare eye worm called Onchocerca lupi. He was going blind because of the damage the parasites were causing his eyes. He had to have several surguries to save his vision and has been on antiparasite medication for the past 10 years to keep the infection managable. There is no cure for this parasite and only a single treatment plan (Ivermectin and Doxycycline). Wyatt's rare parasite is no longer rare in the southwestern U.S., and his story has inspired several research projects. The Wyatt Earp Project is a collaboration between Northern Arizona University and the Navajo Nation Veterinary Management Program who collect samples from dogs and cats in Northern Arizona and screens them for O. lupi.
Wyatt Earp after one of several eye surguries.
O. lupi is a vector-borne, filarial nematode that is recently emerging in the southwestern United States. It can infect dogs, cats, coyotes, and humans. It causes a disease termed onchocercosis in dogs. This disease is considered a skin and eye disease, if left untreated will cause blindness and possibly organ failure. Symptoms may not show for several years after initial infection. Symptoms include swollen eyes, eye bleeding, eye discharge, and itchy face and skin. This parasite is thought to be transmitted by a black fly; transmission cannot happen between a dog and human. There have been 12 confirmed human cases of O. lupi globally, 7 of them were in the southwestern United States. The Wyatt Earp Project aims to survey and track this parasite in Northern Arizona in order to identify hot spots where focused prevention methods could be applied.
Arizona Game and Fish collected over 800 coyote skin samples so researchers from TGen North and Northern Arizona University could look for the parasite. Prior to this study, coyotes were not known as a host species for O. lupi. Researchers found the parasite in 37 coyotes and none had physical symptoms of the parasite.
WHAT DOES THAT MEAN?
Black flies are attracted to moving water sources (such as streams and rivers) where she will take a blood meal (and infect a host) and lay her eggs. This is why Onchocerca diseases are called river blindness. It usually occurs near water sources such as rivers.
Female black flies must take blood meals in order to lay her eggs near moving water. She will bite a host (dog, coyote, cat, human, etc.) and transfer O. lupi to that animal. This is what we think is the first step of the O. lupi lifecycle. From there, she will lay her eggs in the nearby water. It is while in the black fly that the larvae mature into infectious larvae.
Currently, only canines are known to be the definitive host of O. lupi. However, there are reported cases of this parasite in humans and felines. The host must be bit by an infected fly. The larva (microfilaria) enter the bite wound and mature into adult worms. It can take years before symptoms present in the host.
Once an adult, a single adult parasite can produce up to 700 microfilaria a day, even without the presence of a male parasite. An adult worm can group upwards up 16 inches in length. Females tightly coil with a nodule anywhere in the body, but usually are in the eyes. The microfilaria produced remain sub-cutaneous and are then picked up by a new fly bite, thus completed the transimssion cycle.
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