The cat flea (Ctenocephalides felis) can transmit diseases and parasites to humans. Flea bites can also cause allergic reactions in both pets and people. Although some people think that cat scratch disease is caused by cat fleas, the Center for Disease Control states that there is no evidence for this.
Fleas host the plague bacteria, Yersinia pestis. Cats can be contaminated by the plague bacteria after eating infected rodents or after the rodents die and transmit infected fleas to cats. The cats in turn bring the fleas into the home, where they may bite humans and transmit the disease. Don't worry too much: plague is rare in modern first-world countries, and according to the CDC, the last major outbreak in the United States occurred in 1925.
Murine typhus is caused by a bacterium carried by infected fleas from rodents to cats or humans. It is transmitted by bites from infected fleas or coming into contact with their feces. Symptoms include abdominal pain, nausea, vomiting, and an extremely high fever of 105 degrees that can last for over a week. It is rarely fatal, and is most often seen during the summer months in Texas and California.
Allergic reactions from flea bites and flea droppings are the most common problem caused by cat fleas biting humans. Flea bites often occur on the feet, ankles and legs. They can cause red, itchy welts similar to mosquito bites but smaller. Swelling, extensive itching and hives are all signs of an allergic reaction to flea bites. This can be treated with prescription or over-the-counter antihistamines, depending upon the severity of the reaction.
Tapeworms can also be transmitted to humans by the cat flea if fleas are accidentally ingested. People with weakened immune systems are more prone to worm infections, but anyone can be infected if she swallows an immature flea. Symptoms of tapeworm infections often mimic those of other diseases. Symptoms include unexplained weight loss, loss of appetite, nausea, weakness and diarrhea. Several rounds of prescription medication may be needed to rid the human body of tapeworms. The good news here is that flea bites can't cause transmission: you actually have to swallow a flea, which you probably aren't in the habit of doing. Unsurprisingly, cat tapeworm in humans is most often seen in small children, who aren't as fastidious as you about what they swallow.
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