Vector-borne diseases, by nature, have complicated transmission cycles. In the simplest of cycles, an insect acquires an infectious agent (pathogen) from a reservoir host and then transfers (vectors) it to another host such as a dog, a cat, or a human. It is interesting that in this age of technology, some questions about pathogen transmission remain unanswered. In the case of flea-borne typhus, these gray areas cause confusion that result in mixed-messages about protection of public health. One thing is certain — in order to contract flea-borne typhus, a person has to have had contact with a flea. In that regard, the disease is considered 100 percent preventable — if you don’t come into contact with fleas and their feces, you won’t get the disease. As human cases of flea-borne typhus increase across the county each year, it is important to understand what pest management professionals can do to protect themselves and their customers from this potentially fatal disease.
A Mild Disease?
Perhaps the most pervasive myth associated with flea-borne typhus is that the disease has a mild presentation. Ten to 14 days after becoming infected with rickettsia bacteria from the feces of an infected flea, a person will begin to experience a wide range of symptoms, including a sustained high fever, chills, body pains, nausea, vomiting, aversion to light, severe headache, and possibly a rash that starts from the center of the body and spreads to the limbs. However, that is not always the case. In 2010, Meghan Daum, a writer for the Los Angeles Times and founder of the Facebook group “Survivors of Murine Typhus,” spent four days in a medically induced coma and nine days hospitalized before being diagnosed with flea-borne typhus. She wrote that the illness upended her life and that she still, years later, suffers from hearing loss. Her physicians were surprised she recovered so fully. Although deaths from typhus are rare, the Austin/Travis County Health and Human Services Department reported that in 2012 a resident of Austin, Texas, succumbed to the illness.
An analysis of cases reported to a public health agency in Orange County, Calif., found that 85 percent of reported cases were hospitalized for an average of six days, with some requiring hospitalization for months. Because the initial symptoms of the disease resemble flu, patients often visit their physician many times before receiving the correct diagnosis and antibiotics. As patients wait for the correct diagnosis and treatment, the illness can progress and lead to hospitalization. When correctly diagnosed and treated with doxycycline, most infections clear within a few days. The key to diagnosing the disease is to recognize that it occurs in the area. Each year, an increasing number of cases of flea-borne typhus are diagnosed in the United States. In 2011, eight states reported cases, primarily from Texas, California, and Hawaii. Pest management professionals should check with their local public health authorities to determine if cases have been reported from the area where their pest management or wildlife management activities are conducted.
In a typical flea-borne typhus transmission cycle, a flea acquires an infectious agent (pathogen) from a reservoir host and then transfers (vectors) it to another host such as a dog, cat, or human. (Chart: OCVCD)
There are plenty of reasons why so much confusion about the transmission of flea-borne typhus exists. Three facts stand out. First, there are two pathogen species that can be transmitted by multiple species of fleas that are found on a wide variety of vertebrate host animals. Second, the historical transmission cycle, called murine typhus, involves the bacterium Rickettsia typhi, transmitted by Xenopsylla cheopis fleas which are often found on Norway rats (Rattus norvegicus). This transmission cycle is still present in some areas of the United States, such as downtown Los Angeles. Third, the majority of human cases reported to state health departments are a result of the suburban cycle of flea-borne typhus, called cat flea rickettsiosis, involving the bacterium Rickettsia felis, the cat flea (Ctenocephalides felis), and it’s primary hosts, which are feral domestic cats (Felis silvestris) and Virginia opossums (Didelphis virginiana). This suburban transmission cycle is likely responsible for the 286 cases of flea-borne typhus reported in Texas, and most of the 51 confirmed cases reported from California, in 2011. It is estimated that for every case of typhus reported to health officials, four additional cases are unreported making it likely there are many more cases of this disease that go unreported.
Considering that Virginia opossums and domestic cats are found across the United States, why aren’t there more cases of this disease? One reason may be the mode of transmission. A flea bite is not sufficient to vector the bacterium that causes flea-borne typhus. Rather, humans become infected when they scratch bacteria-laden flea feces into the bite or other fresh skin wounds. Typhus bacteria can also be transmitted though inhalation of flea feces or the entry of flea feces into the mucosal lining of the eyes or stomach. Flea feces accumulate in fur of flea-infested mammals such as cats and dogs, so it’s not difficult to imagine that a person petting their flea-infested pet could inhale the feces. The primary mode of transmission is assumed to be scratching flea feces into skin wounds. Of note is that less than 30 percent of typhus patients remember having received a flea bite.
Arming yourself with up-to-date knowledge, clear training and proper procedures, will ensure that you, your colleagues, your family, and your customers receive the best available level of protection from flea-borne typhus.
Opossums are a primary host for cat fleas that can be infected with bacteria that spread flea-borne typhus (photo: OCVCD).
Protection For PMPs.
Since both forms of flea-borne typhus are spread primarily through the introduction of infective flea feces into skin wounds, service technicians must protect themselves from flea bites and from bringing fleas into their living and work spaces. Remember that fleas will leave an animal once it has died, or if the animal is weak or displaying signs of stress. When responding to a dead animal removal, be aware that hundreds of fleas may be host-seeking in the area. Long-sleeve pants and shirts treated with an approved insect repellent (like DEET) should be worn on every flea job or animal removal. All skin wounds should be covered by bandages. An N95 respirator and eye goggles should be worn when treating fleas inside homes or crawlspaces, and when trapping or removing animals from the property. Work clothing should be placed in plastic bags immediately upon removal, and stored in those bags until laundered. At home, keep all vertebrate pets on flea control.
The author is vector ecologist for the Orange County Vector Control District (OCVCD) and can be contacted at firstname.lastname@example.org.