Typhus is one of a number of diseases classified under the heading rickettsial infections. Rickettsial diseases a little strange because they exhibit characteristics of both bacteria and viruses. Rocky Mountain Spotted fever is just of the many kinds of Rickettsial infections. Rickettsial infections are vectored primarily by insects such as ticks, fleas, and lice.
Though rickettsial infections fall into three main classes, Spotted fever group, Other rickettsioses, and Typhus. We will focus on only the Typhus forms. Typhus has two strains, epidemic or sylvatic typhus and murine or endemic typhus. Though carrying the name typhus, Scrub typhus is a sub-group. Since Scrub typhus is found primarily in the Japan, the eastern Pacific rim, and as far inland as Afghanistan, it is not a real concern for American readers.
Murine typhus (Rickettsiae typhi, and Rickettsiae felis) is more common outside of the U.S. However, it is endemic (that is the infection survives without outside intervention) in southern California and Texas. It is vectored from opossums, rats, and cats to humans by fleas, thus giving the typhus the moniker “murine”.
Sylvatic typhus also known as louse-born typhus (Rickettsia prowazekii) is typically transmitted from person to person through the bites of body lice (Pediculus humanus humanus). Most infections occur during the winter when people are in close quarters and in unsanitary conditions. But the sylvatic (meaning wild) title does provide a hint where this particular typhus can be contracted. The CDC notes that Amblyomma ticks (e.g. Lone-star tick) has been associated with this infection but the likelihood is disputed. Most important for WCOs is the association that Rickettsia prowazekii has with flying squirrels. Researchers at the CDC have found that “From 1976 to 2001, a total of 39 human R. prowazekii infections were documented in persons with no reported contact with body lice or persons with lice (2–5). Nearly all of these cases were in the eastern United States, and in approximately one third of cases, contact with flying squirrels (Glaucomys spp.) or with flying squirrel nests occurred before disease onset.” While this particular article didn’t identify the species of flying squirrel, other sources state that the source is the southern flying squirrel (Glaucomys volans).
Other than humans, the flying squirrel is the only other vertebrate known to carry Rickettsia prowazekii. The challenge for researchers has been how did these people contract typhus? Interviews with patients and their associates found that exposures ranged from removing of nesting material to the handling of a single flying squirrel carcass. Though not certain, researchers theorize that infections occur through one of three possible means: 1. Dermal or mucous membrane exposure to materials contaminated by flying squirrels and their ectoparasites, 2. Direct inhalation of contaminated materials, or 3. Bites from the ectoparasites of flying squirrels. At least one (Orchopeas howardii) is known to bite humans. But at this time, no evidence exists to support that ectoparasites of flying squirrels are vectoring the disease, though researchers have found that the squirrel louse (Neohaematopinus sciuropteri) could transmit infection between southern flying squirrels and that the cat flea (Ctenocephalides felis), the gray squirrel flea (Orchopeas howardi), and the oriental rat flea (Xenopsylla cheopis) could be infected after feeding on typhus positive flying squirrels. The only thing we do know is that southern flying squirrels have tested positive for typhus antibodies. But how that infection gets to humans is still unknown.
About the Author
Stephen M. Vantassel is a certified wildlife control operator who helps individuals, businesses, and agencies resolve wildlife damage issues through training, writing, expert witness, and research. His latest books are the Wildlife Damage Inspection Handbook, 3rd edition and The Practical Guide to the Control of Feral Cats. He can be contacted at wildlifecontrolconsultant at gmail dot com.
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