We all know that fleas and ticks are horrible critters whose bites cause our dogs and cats a great deal of discomfort. But what makes them much more than just a nuisance is the serious diseases they can spread, which — if left untreated — can sometimes be fatal. In most cases, these flea and tick-borne diseases tend to be found in particular regions of the country, so it’s important to know if you live in one of these areas. Here are five diseases spread by fleas and ticks that you need to be aware of, along with the parts of the country where they’re most commonly found. 1) Lyme Disease Lyme borreliosis is the most commonly reported insect-borne disease in the country according to the U.S. Centers for Disease Control and Prevention (CDC), and both animals and humans can contract it. Caused by a bacteria called Borrelia burgdorferi, the disease got its name in the mid-1970s when several cases were diagnosed in the town of Lyme, Connecticut. The most common carrier of Lyme disease is the deer tick, which is generally found in forests or grassy, marshy areas near bodies of water in regions of the country including southern New England, the eastern Mid-Atlantic states, the upper Midwest (particularly Wisconsin and Minnesota) and the West Coast, especially northern California. The symptoms of Lyme disease often don’t appear until months after a pet has been infected. Once they do appear, they include fever, loss of appetite, lameness, joint swelling and decreased activity — and some animals also experience kidney problems. Infected horses can also develop neurologic disease, eye problems, and dermatitis. Pets who are diagnosed with Lyme disease are generally treated with antibiotics and anti-inflammatories. Unfortunately, once contracted, there is no cure for the disease — which is why prevention is so crucial. If you live in an area where Lyme disease is present, be sure to speak to your vet about the right preventative medications to keep your pet safe from the ticks who carry it. 2) Rocky Mountain Spotted Fever Spread through both ticks and mosquitoes, Rocky Mountain spotted fever (RMSF) is also caused by a bacteria — this one called Rickettsia rickettsii — and can also infect both pets and humans. Once in the bloodstream, the bacteria damages tiny blood vessels, resulting in inflammation that causes small hemorrhages that look like spots. What makes the disease so dangerous is the fact that this bleeding can also occur on organs including the heart, brain, and kidneys, causing what can be life-threatening damage. Though its name suggests that the disease is localized in the Rocky Mountain range, that isn’t actually so. While the first cases were found there, helping to give the disease its name, only a small percentage of them are contracted there currently. In fact, the CDC says that “RMSF cases occur throughout the United States, but are most commonly reported from North Carolina, Tennessee, Missouri, Arkansas, and Oklahoma.” Symptoms of RMSF in pets look similar to those of Lyme disease and include fever, nausea, vomiting, lack of appetite and muscle pain. And, like Lyme disease, the symptoms often don’t materialize until well after infection. Once diagnosed, RMSF is generally treated with antibiotics. But again, prevention is the best defense, which is why it’s so important to keep your pet on the preventative medication recommended by your veterinarian year-round. 3) Murine Typhus While Lyme disease and Rocky Mountain Spotted Fever tend to affect dogs more than cats because of the environments where they thrive, Murine typhus — a flea-borne illness — tends to affect cats more often because rats are the main carrier of the flea that transmits the bacteria carrying it. The bacteria, Rickettsia typhi, thrives in hot, humid areas with large rat populations in states including California, Texas, and Hawaii. This disease can also be contracted by humans, and symptoms include fever, nausea and body aches. Again, antibiotics are the most common treatment for Murine typhus, and keeping your pet on a regular regiment of the flea preventative prescribed by your vet is the best way to keep your pets from contracting it in the first place. 4) Canine Anaplasmosis Yet another tick-born illness is canine anaplasmosis. And, once again, the bacteria that causes it has a rather menacing sounding Latin name: anaplasma phagocytophilum. As with Lyme disease, the deer tick is the main culprit, which means it’s most commonly found in all the same regions of the U.S. The most common symptoms are quite the same, too — fever, lethargy, joint pain, lameness and loss of appetite. Other less common symptoms include vomiting, diarrhea, coughing, labored breathing, bruising and nosebleeds. And while the name suggests only dogs are susceptible, the disease has actually been reported in numerous animals. Just like the other diseases on the list, antibiotics are used to treat canine anaplasmosis, and — yet again — prevention with regular doses of a prescribed parasite preventative is the best medicine. 5) Mycoplasma Haemofelis The last disease on our list — mycoplasma haemofelis — is cat-specific (though recent evidence suggests that it can be contracted in humans, especially those with weakened immune systems) and transmitted through flea, tick and mosquito bites. Unlike the other disease we’ve discussed, however, the bacteria that causes it isn’t confined to one specific region of the U.S. The disease affects cats when the bacteria attaches to their red blood cells, causing their immune systems to treat the cells as foreign invaders and start attacking them. In turn, the loss of healthy red blood cells can result in fever and Feline Infectious Anemia, with symptoms including pale gums, lethargy, loss of appetite, shortness of breath and rapid breathing. Antibiotics are once again the most common treatment, though in severe cases, cats with the disease may need a blood transfusion to bring their red blood cell counts back to a safe level. Steroids are also used in some cases. And, once more, the best course of action is preventing the infection with a veterinarian-prescribed parasiticide in the first place — especially since fleas carrying this disease can be found all over the country. Hopefully, two themes have emerged from this list of diseases spread by parasites. First, most of them have the same (or similar) symptoms, which is why it’s important to see your veterinarian for a proper diagnosis as soon as they develop. And second, a regular course of preventative meds will help go a long way toward keeping your pet from contracting them in the first place!