In the thirteenth century, nearly 100 million people in Asia died of an inexplicable infection. In the next century, another 50 to 75 million people died in Europe, as rats carried a flea that carried a bacterium that could cause the emergence of apple-sized tumors in the skin in just two days, fever in three days, darkening of the fingers and toes with gangrene in five days, and death from coughing blood in as little as a week.
Later known as the Black Plague, the disease reappeared from time to time, killing millions, for over 400 years. Even today, people sicken and sometimes die of plague in Uganda, in Kyrgyzstan, in the Western Sahara, in Mongolia, and also in over a dozen states in the USA.
Two members of family of the author of this article were infected with bubonic plague while doing environmental surveys, one at a lake in western North Carolina, and the other at a prairie dog town in Colorado, presumably after they were bitten by fleas living on rats that carry the disease. By chance of knowing an infectious disease expert who had experience in treating bubonic plague and having family members who knew to call for help, both survived—but barely. Even in the twenty-first century, rats can still transmit the deadliest infection the world has ever known. Which is one of the reasons why they are considered one of the leading pests.
But plague is not the only devastating disease that is carried by common pests. In 2008, City News Toronto ran the story of Daniel Chevrier, a one year-old boy who had developed seizures and lost his sight just a month after becoming infected with roundworms.
The Chevrier family lived in a comfortable middle-class home with a nice back yard and a dog in Hamilton, Ontario. Daniel was a healthy, active toddler throughout his first year of life, but somehow he came in contact with roundworm eggs, probably brought in by the family dog after it rolled in dirt in which raccoons had defecated, possibly as much as a year earlier. Petting the family dog transferred the parasite to the boy’s fingers, and brain and eye damage set in just a few weeks later.
Chances are that the rat in your attic does not carry plague, but even in the United States hundreds of people have been infected with plague after being bitten by fleas that lived on rats. Chances are that your family dog or cat will not bring in roundworm larvae brought to your property by raccoons, but even in metropolitan Toronto, scientists estimate, there are over 150 raccoons per square mile, 80% of them infected with not just roundworms but up to 13 different kinds of parasitic infections.
This means that a cute little raccoon can transmit not just one or two but any of 13 different diseases to your pets, your children, your spouse or yourself. Moreover, raccoons are just one of dozens of animals that can transmit diseases to people. Here is an A to Z overview of the most common zoonotic (animal-originated) diseases that can occur without appropriate pest control.
Babesiosis is a parasitic infection that usually causes only mild symptoms, such as chills, fever, and diarrhea, but that can be deadly in people whose immune systems have been compromised by chemotherapy or HIV. The disease is transmitted from mice to people by the same species of ticks that can also carry Lyme disease. A telltale sign that a rodent is infected with the disease is red urine.
Babeiosis is most common on islands just offshore from New York and Massachusetts, especially Fire Island and Nantucket. The first line of defense against the infection is setting up ultrasound deterrents wherever doors are left open, with mouse cubes or mouse traps set out in pantries.
Bovine tuberculosis is, as its name suggests, a form of tuberculosis that is most commonly found in cows. Humans, however, can also develop tuberculosis from this strain of bacteria, and humans can acquire the disease from an astonishing variety of animals including cows, mice, rats, raccoons, skunks, and badgers. Approximately 38% of New Zealand is infested with opossums that carry the disease.
Excluding rodents with ultrasound devices, mouse cubes, live capture traps, and snap traps will reduce the risk of catching this now relatively rare disease. It is also important to remember to wear cotton gloves when handling dead animals or the traps in which they are caught or killed.
Chagas disease, a condition also known as American trypanosomiasis, is disease caused by a protozoan (a one-celled animal) transmitting by “kissing bugs,” so called because the insect typically bite the face. In about 60% of people who are infected with this disease, no symptoms appear, but 20 to 40% of infectees develop serious and even life-threatening deformities of the heart and digestive system. You can read more about it at the CDC.
Kissing bugs acquire the parasite from opossums and possibly raccoons and pass it on to people. Simply keeping opossums and raccoons off your property—and certainly out of your house—will greatly reduce the risk of catching this increasingly common infection.
Cryptosporidiosis is a water-born parasitic infection that can affect both humans and animals. Typically a cryptosporidiosis infection results in a bout of diarrhea that lasts one to weeks. Most people recover if they avoid dehydration. People who have damaged immune systems, however, may develop permanent and life threatening diarrhea after being infected with the parasite.
The most common origin of cryptosporidiosis in people is exposure to untreated drinking water. Chlorine-resistant strains of the parasite may also flourish in swimming pools. Anytime animal feces falls in swimming pools, cryptosporidiosis is a remote possibility. Exclusion methods such as fences and ultrasound repellent units may keep animals out of the pool and cryptosporidiosis out of the water.
E. coli O:157 is an especially aggressive form of the common E. coli bacterium that is 100,000 times more infectious than other strains of the organism. It grows in the digestive tracts of herbivorous animals. The bacterium does not cause infections in the cows, horses, and gophers that may contract it, because it has to latch on to specialized receptor sites in the intestines to avoid being flushed away with bowel movement. Humans, however, have these receptor sites, capturing the bacterium and exposing the infected person to severe diarrhea. In some cases, the E. coli O:157 gets into the bloodstream and breaks down red blood cells. The resulting flood of protein can overwhelm the kidneys and cause death by kidney failure.
You are far more likely to get this strain of E. coli by exposure to cattle manure than any other source. If you trap a gopher, however, be sure not to handle any feces with bare hands or even with work gloves to avoid exposure to this especially infectious strain of the bacterium.
Giardia is a protozoal parasite that multiplies in the small intestine. It feeds on sugar released from digested food in the stomach, converting it into ethanol, the kind of alcohol that is in alcoholic beverages. It causes diarrhea that is so severe that it usually is accompanied by “purple burps,” along with a feeling of being more than slightly drunk. The parasite is shed in the feces of all kinds of woodland creatures and survives for months or years in its cyst form until is drunk along with untreated water.
Giardia can survive in chlorine-treated pools. Excluding all kinds of woodland animals from your pool is helpful for avoiding the disease. Both people and dogs can catch giardia by drinking water contaminated by animal feces.
Hantavirus infections are acquired by rodent bites or by handling rodent feces or urine. They are most common in dry mountainous areas, such as the Four Corners (junction of Colorado, New Mexico, Arizona, and Utah) in the southwestern United States. Hantavirus infections can result in severe damage to the kidneys or viral pneumonia, or both. There is no medication for this disease.
It is very important to make sure your home is sealed so that rodents cannot come in. Sheds and workshops should be set with traps to eliminate rats and mice, and an ultrasonic unit may be useful in your home if it is only turned on every other day. Never handle dead rodents with your bare hands, and avoid transferring rodent urine or feces from your gloves to any surface you cannot disinfect.
Leptospirosis is a disease that is acquired from urine of infected rats, raccoons, skunks, rabbits, hedgehogs, deer, and dogs. Typically an infected wild animal urinates in standing water, the family drinks the water, and then humans pick up the infection when cleaning up after the dog. Leptospirosis infections at first cause flu-like symptoms with intense headache and muscle pain, and then a week or two later there may be hepatitis, severe eye pain, blood clots, and even kidney failure. A strong indication that a human has leptospirosis is getting sick after the family dog’s eyes turn yellow.
While leptospirosis is hard to treat, it is relatively easy to prevent. Make sure your pets do not drink from standing rainwater or flood waters, or from plumbing leaks inside your home. Simply keeping your pet away from contaminated water—and not drinking it yourself—is enough to prevent the disease. If drainage issues cannot be addressed, then consider using repellents or fencing to keep animal pests off your property.
Mediterranean spotted fever is a tick-borne infection most common in countries surrounding the Mediterranean Sea but occasionally diagnosed even in North America and Australia. The condition is also known as Boutonneuse fever. A tick bite transmits the rickettsial parasite that causes the disease characterized by fever, chills, minor pain at the site of the bite but severe headache and muscle pain, joint pain, and the formation of a tache noir, an area of dead skin, a few days later. Typically a human is bitten by a tick the dog brings in from an area where there are many mice and rats.
Preventing this infection involves making sure that you never allow the grass of your lawn to grow tall, and fencing off your lawn to prevent wild animals from entering—especially during the summer. Keep Mediterranean spotted fever out of your house by keeping mice and rats out of your house with ultrasound deterrents, mouse cubes, and rat traps.
Plague is the bacterial infection that was once known as the Black Death. The bacterium Yersinia pestis lives in fleas that ride on rats. The rats themselves die of plague, but the fleas hop off to infect other rats and humans. Once infected, human-to-human transmission can occur through saliva, nasal secretions, skin to skin contact, or sex. Most forms of the plague cause fever, painful swellings under the skin all over the body, and death when the lungs fill with blood, usually in just a few days.
Plague still exists today, even in the United States, although only about 400 Americans are known ever to have developed the disease. Most commonly the family cat eats an infected rat and acquires a plague-infected flea in the process. The flea then infects a family member.
While you are extremely unlikely to be infected with plague, making sure your pets do not come in contacts with rats makes the probability of infection even lower. Make sure your pets never eat dead rats they may find on your lawn (which are far more likely to have died of rat poison than from plague) and keep rat infestations under control anywhere a pet may roam.
Rabies is an almost-always fatal infection if it is not treated promptly. The rabies virus is transmitted by a bite through infected saliva. The virus works its way through the peripheral nervous system outside the spinal cord slowly. During this time, treatment with vaccine and immune globulin can stop the disease. Once the virus reaches the spinal cord, however, it travels quickly to the brain, causing a painful and horrifying death in just a few days.
Humans most often acquire rabies from dog bites (or, in Texas and northern Mexico, bat bites), but dogs most often acquire rabies from rabid skunks (in the northern United States and Canada) or rabid raccoons (especially in the southeastern United States). Excluding skunks from your property reduces risk of your pet’s catching the disease—but timely rabies vaccination is even better. If you are bitten by a rabid animal you must seek emergency care.
In the United States, the cost of the vaccine is approximately $11,000, but the maker of the vaccine will provide it for free if you are uninsured. Because of this subsidy, however, entire counties sometimes do not have the vaccine. It is essential to get treatment quickly.
Toxoplasmosis is a bacterial infection humans most commonly catch from their cats by handling kitty litter with unprotected hands. The cats in turn catch the infection by eating rats and mice that have the disease. Most symptoms in people are mild, but mothers can transmit toxoplasmosis to their unborn children and toxoplasmosis infections during the first trimester of pregnancy often result in miscarriage. Some people who are infected with toxoplasmosis develop depression or schizophrenia.
The most effective way to prevent toxoplasmosis is to make sure your cats never eat rats. Make sure you trap rats in any location frequented by cats, and never, ever enlist the services of your cat for keeping rats under control. In a fight between a pack of rats and a cat, the cat will always lose, usually resulting in the death of the cat.
Salmonella infections originate in spoiled food. They can cause bloody diarrhea, vomiting, dehydration, and, in some cases, kidney failure.
Raccoons often dine in garbage cans where food that may have been contaminated with minor amounts of Salmonella has grown dangerous amounts of bacteria. The raccoons eat the food and spread Salmonella through their droppings, and careless handling of food knocked out of the garbage can without gloves and without washing afterward can result in infections in people. The solution is to use garbage cans with tight lids that raccoons cannot open, and to keep raccoons off your lawn and away from your home whenever possible.
Typhus is a rickettsial disease caused by lice, mites, or fleas on rats. The kind of typhus spread by rats causes extremely high fever, severe joint pain, dry cough, headache, backache, and a red rash that spreads over the entire body. Without treatment, it is often fatal. Millions of people died from typhus every year before the invention of antibiotics, but the disease still kills up to 200,000 people a year today.
Avoiding contact with rats prevents typhus. Killing rats rather than trapping rats is essential for eliminating the disease. On this site you can read more here about electronic pest control and other devices to help get rid of a problem.