Typhus Fevers

All age groups are at risk for rickettsial infections during travel to endemic areas. Transmission is increased during outdoor activities in the spring and summer months when ticks and fleas are most active. However, infection can occur throughout the year. Because of the 5- to 14-day incubation period for most rickettsial diseases, tourists may not necessarily experience symptoms during their trip, and onset may coincide with their return home or develop within a week after returning.

The most commonly diagnosed rickettsial diseases in travelers are usually in the spotted fever or typhus groups, but travelers may acquire a wide range of rickettsioses, including emerging and newly recognized species (Table 3-18). Game hunting and traveling to southern Africa from November through April are risk factors for African tick-bite fever in travelers, which is the most frequently reported travel-associated rickettsiosis. However, Mediterranean spotted fever infections occur over an even larger region and can be quite severe.

Rickettsialpox, transmitted by house-mouse mites, circulates in 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.

Scrub typhus 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.

Fleaborne rickettsioses caused by R. typhi and R. felis 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 entering 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.

Epidemic typhus occurs 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 endemic typhus are known in the Andes regions of South America and in Burundi and Ethiopia. Sylvatic epidemic typhus cases occur only from direct contact with flying squirrels or their nesting materials and squirrel ecoparasites in the eastern United States. Tick-associated reservoirs of R. prowazekii have been described in Ethiopia, Mexico, and Brazil.

Ehrlichiosis is most commonly reported in the southeastern and south-central United States where the lonestar tick, Amblyomma americanum, and white-tailed deer are commonplace. In Europe and Asia, transmission of monocytic ehrlichiosis appears to be due primarily to Ehrlichia chaffeensis or related organisms, which may also occur in Brazil, Panama, and Africa. E. muris and Neoehrlichia mikurensis are associated with ticks of the Ixodes persulcatus complex and their rodent hosts. These agents cause human infections in the upper Midwestern United States and Europe, respectively, and probably also cause disease in other regions. E. ruminantium and a related agent from the United States have been identified as causes of human infections in South Africa and the southeastern United States. E. canis has been reported to cause human infections in Venezuela.

Human Anaplasma infections are most commonly reported in the United States but can occur more rarely in Europe and Asia. The agent occurs worldwide, corresponding with the ranges of I. persulcatus group ticks. Although nonpathogenic genetic variants are common worldwide in many vertebrate hosts, human pathogenic types are present in rodent and small-mammal reservoirs in North America and in deer (roe and red) and wild boar in Europe.

Sennetsu fever occurs in Japan, Malaysia, and possibly other parts of Asia. This disease can be contracted from eating raw infected fish.