The Plague

New Mexico has one of the highest number of mammals in the country,with 150 known species. Eighty two species of mammals are known to be hosts of fleas. We have 107 species of fleas in New Mexico. We have plenty of mammals and plenty of fleas.

Several dogs in New Mexico have been diagnosed with plague. Plague is primarily a disease of wild animals, expecially rodents. Some species are particularly susceptible. Prairie dogs, particularly Gunnison’s prairie dog, are uniformly susceptible to fatal infections of the plague, and large proportions or even entire populations have been destroyed in a single plague event.

Plague is caused by the bacterium Yersinia pestis, an is of Old World origin and throughout history has been referred to as “Black Death.” Plague was first discovered in North America from California ground squirrels in 1905 and first detected in New Mexico rodents in 1938. As of 1982, 18 species of rodents, 2 species of rabbits and 9 species of carnivores have been infected by plague in New Mexico.

Plague is spread by fleas. The normal cycle of plague transmission is between wild rodents and their fleas in nature. When fleas ingest bacteria along with blood from infected rodents, the bacteria multiply rapidly in the gut of the flea. New Mexico has a high case rate of plague. For example, during 1988-2002, a total of 112 human cases of plague were reported from 11 western states. The majority, 97 of the cases where in Arizona, California, Colorado and New Mexico and 48 of those cases were from New Mexico.

At least 33 species of fleas have tested positive for sylvatic plague in New Mexico. Many of those fleas are rare or rarely encountered because they aren’t found in close proximity to humans or are only found on a few species of rodents. One species of flea, Oropsylla montanus, (plague flea) is very common and is the primary source of plague in New Mexico. This species of flea is found on ground squirrels, pack rats, deer mice, harvest mice, rabbits, skunks and it will feed on prairie dogs, but it kills them. Carnivorous animals such as foxes and coyotes also frequently get this flea as the flea will infest them when they eat the normal host animal. People that shoot coyotes and other animals and then skin them or handle them are prone to get the plague if the animal had the plague flea. This flea is common in the East Mountains, most of Bernalillo, Sandoval and Santa Fe Counties as well as being found sporadically in other areas of the state.

So, what do you do to prevent you or your pets from getting plague fleas? First, do not let your animals chase and catch wild animals of any kind. Although plague fleas have been found on the animals I listed, they can certainly occur on other animals as well. The fleas don’t live on the host animals but will infest their nests, so fleas may not always be present on them. If you have ground squirrels nesting in your yard, the burrows will be infested by the plague fleas. I would recommend dusting the burrows with food grade diatomaceous earth, which will kill the fleas but not harm the squirrels. If you have pack rats, you should remove their nests (middens) as they will have fleas as well as ticks, mites and kissing bugs, which aren’t very friendly. Try to discourage pack rats from living near your home. If you find a dead animal, don’t touch it as any fleas on it will quickly jump off.

Never use rodenticides as when a mouse or rat dies, the fleas and any other ectoparasites will leave and they will get on the first animal they encounter, which could include your family pets. If you have an exterminator that wants to use rodenticides, just tell them no. You want the animals trapped and removed.

There is a scientific paper published by the United States Dept. of Agriculture called, “Fleas and Lice of Mammals in New Mexico”. I wrote it in conjunction with several colleagues when I was at the University of New Mexico in 2004. It is available online in pdf format. If you have any pest questions, you can contact me at askthebugman2013@gmail.com. You can also follow me on Twitter @askthebugman.