Typhus epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]
Overview
Epidemiology and Demographics
Age
- All age groups are at risk for rickettsial infections during travel to endemic areas.
Gender
- The typhus group of infections has no sexual predilection.
Geographic distrubution
- Both short and long-term travelers are at risk for infection.
- Transmission is increased during outdoor activities in the spring and summer months when ticks and fleas are most active.
- The most commonly diagnosed rickettsial diseases in travelers are usually in the spotted fever or typhus groups, travelers may acquire a wide range of rickettsioses, including emerging and newly recognized species.
- Tickborne spotted fever rickettsioses are the most frequently reported travel-associated rickettsial infections.
- Game hunting and traveling to southern Africa from November through April are risk factors for African tick-bite fever, and this consistently remains the most commonly reported rickettsial infection acquired during travel.
- Mediterranean spotted fever infections are less commonly reported but occur over an even larger region, including (but not limited to) much of Europe, Africa, India, and the Middle East.
- Rocky Mountain spotted fever (also known as Brazilian spotted fever, as well as other local names) is reported throughout much of the Western Hemisphere, including Canada, the United States, Mexico, and various countries in Central and South America.
- Contact with dogs (in both rural and urban settings) and outdoor activities such as hiking, hunting, fishing, and camping increase the risk of infection.
- Scrub typhus, which is transmitted by mites encountered in high grass and brush, is endemic in northern Japan, Southeast Asia, the western Pacific Islands, eastern Australia, China, maritime areas and several parts of south-central Russia, India, and Sri Lanka.
- More than 1 million cases occur annually.
- Most travel-acquired cases of scrub typhus occur during visits to rural areas in endemic countries for activities such as camping, hiking, or rafting, but urban cases have also been described.
- R. typhi and R. felis, which are transmitted by fleas, are widely distributed, especially throughout the tropics and subtropics and in port cities and coastal regions with rodents.
- Humans exposed to flea-infested cats, dogs, and peridomestic animals while traveling in endemic regions, or who enter or sleep in areas infested with rodents, are at most risk for fleaborne rickettsioses.
- Murine typhus has been reported among travelers returning from Asia, Africa, and the Mediterranean Basin and has also been reported from Hawaii, California, and Texas in the United States.
- R. akari, the causative agent of rickettsialpox, is transmitted by house-mouse mites, and circulates in mainly urban centers in Ukraine, South Africa, Korea, the Balkan states, and the United States.
- Outbreaks of rickettsialpox most often occur after contact with infected rodents and their mites, especially during natural die-offs or exterminations of infected rodents that cause the mites to seek out new hosts, including humans.
- The agent may spill over and occasionally be found in other wild rodent populations.
- Epidemic typhus is rarely reported among tourists but can occur in communities and refugee populations where body lice are prevalent. *Outbreaks often occur during the colder months when infested clothing is not laundered.
- Travelers at most risk for epidemic typhus include those who may work with or visit areas with large homeless populations, impoverished areas, refugee camps, and regions that have recently experienced war or natural disasters.
- Active foci of epidemic typhus are known in the Andes regions of South America and some parts of Africa (including but not limited to Burundi, Ethiopia, and Rwanda).
- Louseborne epidemic typhus does not regularly occur in the United States, but a zoonotic reservoir occurs in the southern flying squirrel, and sporadic sylvatic epidemic typhus cases are reported.
- Tick-associated reservoirs of R. prowazekii have been described in Ethiopia, Mexico, and Brazil, but documented human cases are rare.
- Ehrlichiosis and anaplasmosis are tickborne infections most commonly reported in the United States.
- A variety of species are implicated in infection, but E. chaffeensis and A. phagocytophilum are most common. Infections with various Ehrlichia and Anaplasma spp. have also been reported in Europe, Asia, and South America.
- Neoehrlichia mikurensis is a tickborne pathogen that occurs in Europe and Asia. Sennetsu fever, caused by Neorickettsia sennetsu, occurs in Japan, Malaysia, and possibly other parts of Asia. This disease can be contracted from eating raw infected fish.