Historically, the tiny rat flea has greatly impacted civilization as carrier of the plague. The tropical or Oriental rat flea is the main carrier of the plague bacterium, Yersinia pestis. Typically feeding on the brown rat, Rattus rattus, and the black or roof rat, R. norvegicus, the rat flea also readily feeds on people.
has probably afflicted humans since before the time of Christ. The Philistines are recorded as suffering from a disease with symptoms like those of the bubonic plague. The first pandemic of record was probably in the sixth century, beginning in Egypt. During the late Middle Ages, the Black Death laid waste to Europe in another pandemic. An estimated 25 million people died in the fourteenth century. From 1664 to 1666, 70,000 Londoners dies out of a population of 450,000. Civil disorder broke out. Terrified neighbors even put plague victims to death.
What made the disease so frightening was that its cause was unknown. Only in the late 19th and early 20th centuries did a few brave researchers establish that the rat flea had to be present to spread the disease. That discovery came during the third pandemic, which began in China's Yunnan Province in the 1890s and spread to the West Coast of the U.S. and throughout the world. Deaths in the U.S. occurred in San Francisco, Los Angeles and cities farther east, such as New Orleans.
The disease is characterized by rapidly developing high fever, headache, prostration, fatigue and delirium. By the second day, lesions know as bubos (hence bubonic plague) appear in the groin and armpits. Mortality rates are high.
Cases of plague still occur in the U.S., primarily in wild rodents. In the western states, 334 cases were reported from 1970-1994.
- Found worldwide, several species of flea, including (the main vector), and carry murine typhus. Flea feces transmit murine typhus when the host human scratches his or her skin to alleviate itching caused by fleabites, allowing the pathogen to enter the body. While thousands of cases occurred each year early in the 20th century, the disease is rare in the U.S., occurring primarily in the South. Symptoms include sudden high fever, headache, nausea, coughing and a spotted rash.
- The female chigoe, jigger or sandflea bores into the skin, usually of the feet, causing extreme irritation. If Tunga penetrans is not removed, it can cause an infection, which may become gangrenous. Chigoes are found in tropical Americas and Africa and are most prevalent in people who walk barefoot.
- Annoying to some, fleabites can cause serious irritation in sensitive individuals. Bird fleas may become a problem when construction disturbs bird nests in buildings. The can also cause irritation but is now much less frequently encountered in the U.S. than cat and dog fleas.
- Young children may be at risk if they play in areas where pet excrement is present and the cat or dog has the tapeworm Dipylidium caninum. When tapeworm eggs are defecated by a cat or dog, flea larvae may feed on the excrement and ingest the eggs. The tapeworm eggs hatch in the flea's larval gut. When the flea completes its development, a cat or dog may ingest the adult flea during grooming or nipping. A child coming into close contact with a pet may ingest a tapeworm-infected adult flea from the pet.
 - The cat flea, which parasitizes both dogs and cats and can transmit a species of tapeworm to pets, is the main flea of concern to most North Americans. The less common dog flea is similar to the cat flea.
Adult cat and dog fleas remain on the host (rather than jumping on the animal only to feed), causing severe irritation and vigorous scratching. This can lead to severe coat loss and frequent visits to a veterinarian. Both flea species may transmit the tapeworm Dipylidium caninum. The tapeworm's eggs are defecated by the cat or dog and larval fleas consume the feces.
- An important poultry pest in subtropical America, the sticktight flea remains attached to a chicken, causing ulcers in which flea eggs are laid, and in heavy infestations, anemia. The sticktight flea also will attack cats, dogs, horses and humans.
- This flea-vectored disease of rabbits wiped out nearly the entire rabbit population of the United Kingdom in the 1950s, eliminating rabbit trapping as an income source for many and reducing the food source of raptorial birds and predatory animals. The disease has been deliberately introduced in Australia as a means of controlling huge infestations of rabbits.
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