Chapter 3Infectious Diseases Related To Travel
Rickettsial (Spotted & Typhus Fevers) & Related Infections (Anaplasmosis & Ehrlichiosis)
Marina E. Eremeeva, Gregory A. Dasch
Rickettsial infections are caused by a variety of obligate intracellular, gram-negative bacteria from the genera Rickettsia, Orientia, Ehrlichia, Neorickettsia, Neoehrlichia, and Anaplasma, belonging to the Alphaproteobacteria (Table 3-18). Rickettsia were classically divided into the typhus group and spotted fever group (SFG), although the genus has been subdivided further based on phylogenetic analysis. Orientia spp. make up the scrub typhus group.
Most rickettsial pathogens are transmitted by ectoparasites such as fleas, lice, mites, and ticks during feeding or by scratching crushed arthropods or infectious feces into the skin. Inhaling dust or inoculating conjunctiva with infectious material may also cause infection. The specific vectors that transmit each form of rickettsiae are listed in Table 3-18. Transmission of some rickettsial diseases after transfusion or organ transplantation is rare but has been reported.
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.
Table 3-18. Classification, primary vector, and reservoir occurrence of rickettsiae known to cause disease in humans
|ANTIGENIC GROUP||DISEASE||SPECIES||VECTOR||ANIMAL RESER-
|Anaplasma||Human granulocytic anaplas-
|Tick||Small mammals, rodents, and deer||Primarily United States, worldwide|
|Ehrlichia||Human monocytic ehrlichosis||Ehrlichia chaffeensis||Tick||Deer, wild and domestic dogs, domestic ruminants, and rodents||Common in United States, probably worldwide|
|Ehrlichosis||E. muris||Tick||Deer and rodents||North America, Europe, Asia|
|Ehrlichosis||E. ewingii||Tick||Deer, wild and domestic dogs, and rodents||North America, Cameroon, Korea|
|Neoehrlichia||Human neoehrlichiosis||Neoehrlichia mikurensis||Tick||Rodents||Europe, Asia|
|Fish||Japan, Malaysia, possibly other parts of Asia|
|Scrub typhus||Scrub typhus||Orientia tsutsugamushi||Larval mite (chigger)||Rodents||Asia-Pacific region from maritime Russia and China to Indonesia and North Australia to Afghanistan|
|Scrub typhus||Orientia chuto||Unknown||Unknown||Dubai|
|Spotted fever||Rickettsiosis||Rickettsia aeschliman-
|Tick||Unknown||South Africa, Morocco, Mediterranean littoral|
|African tick-bite fever||R. africae||Tick||Ruminants||Sub-Saharan Africa, West Indies|
|R. akari||Mite||House mice, wild rodents||Countries of the former Soviet Union, South Africa, Korea, Turkey, Balkan countries, North and South America|
|Queensland tick typhus||R. australis||Tick||Rodents||Australia, Tasmania|
ean spotted fever or Bouton-
|R. conorii1||Tick||Dogs, rodents||Southern Europe, southern and western Asia, Africa, India|
|Cat flea rickettsiosis||R. felis||Flea||Domestic cats, rodents, opossums||Europe, North and South America, Africa, Asia|
|Far Eastern spotted fever||R. heilong-
|Tick||Rodents||Far East of Russia, Northern China, eastern Asia|
|Aneruptive fever||R. helvetica||Tick||Rodents||Central and northern Europe, Asia|
|Flinders Island spotted fever, Thai tick typhus||R. honei, including strain "marmionii"||Tick||Rodents, reptiles||Australia, Thailand|
|Japanese spotted fever||R. japonica||Tick||Rodents||Japan|
ean spotted fever-like disease
|R. massiliae||Tick||Unknown||France, Greece, Spain, Portugal, Switzerland, Siciliy, central Africa, and Mali|
ean spotted fever-like illness
|R. monacensis||Tick||Lizards, possibly birds||Europe, North Africa|
|Maculatum infection||R. parkeri and related agents||Tick||Rodents||North and South America|
|Tickborne lymphadenopathy, Dermcentor-borne necrosis and lymphadenopathy||R. raoultii||Tick||Unknown||Europe, Asia|
|Rocky Mountain spotted fever, febre maculosa, São Paulo exanthem-
atic typhus, Minas Gerais exanthem-
atic typhus, Brazilian spotted fever
|R. rickettsii||Tick||Rodents||North, Central, and South America|
|North Asian tick typhus, Siberian tick typhus||R. sibirica||Tick||Rodents||Russia, China, Mongolia|
|R. sibirica mongolotim-
|Tick||Rodents||Southern France, Portugal, China, Africa|
opathy (TIBOLA), Dermacent-
or-borne necrosis and lymphaden-
|R. slovaca||Tick||Lagomorphs, rodents||Southern and eastern Europe, Asia|
Epidemic typhus, sylvatic typhus
Human body louse, flying squirrel ecto-
Humans, flying squirrels
Central Africa, Asia, Central, North, and South America
Tropical and subtropical areas worldwide
1Includes 4 different subspecies that can be distinguished serologically and by PCR assay and respectively are the etiologic agents of Boutonneuse fever and Mediterranean tick fever in southern Europe and Africa (R. conorii subsp. conorii), Indian tick typhus in south Asia (R. conorii subsp. indica), Israeli tick typhus in southern Europe and Middle East (R. conorii subsp. israelensis), and Astrakhan spotted fever in the North Caspian region of Russia (R. conorii subsp. caspiae).
Rickettsioses are difficult to specifically diagnose, even by physicians experienced with these diseases. Clinical presentations vary with the causative agent and patient; however, common symptoms that typically develop within 1–2 weeks of infection include fever, headache, malaise, and sometimes nausea and vomiting. Most symptoms associated with acute rickettsial infections are nonspecific. Many rickettsioses are accompanied by a maculopapular, vesicular, or petechial rash or an eschar at the site of the tick bite. African tick-bite fever should be suspected in a patient who presents with fever, headache, myalgia, and an eschar (tache noir) after recent travel to southern Africa. Mediterranean spotted fever should be suspected in patients with rash and fever after recent travel to northern Africa or the Mediterranean littoral. Scrub typhus should be suspected in patients with a fever, headache, and myalgia after recent travel to Asia; eschar, lymphadenopathy, cough, hearing difficulties, and encephalitis may also be present. Patients with typhus usually present with a severe but nonspecific febrile illness. Ehrlichiosis and anaplasmosis should be suspected in febrile patients with leukopenia and transaminitis with an exposure history. Most symptomatic rickettsial diseases cause moderate illness, but epidemic typhus and Rocky Mountain spotted fever can be severe and may be fatal in 20%–60% of untreated cases.
Diagnosis is usually based on clinical recognition and serology; the latter requires comparison of acute- to convalescent-phase serology, so is only helpful in retrospect. Etiologic agents can generally only be identified to the genus level by serologic testing. PCR and immunohistochemical analyses may also be helpful. If ehrlichiosis or anaplasmosis is suspected, a buffy coat may be examined to identify characteristic intraleukocytic morulae. Contact the CDC Rickettsial Zoonoses Branch at 404-639-1075 for further information.
Treatment of patients with possible rickettsioses should be started early and should not await confirmatory testing. Treatment usually involves doxycycline. Chloramphenicol, azithromycin, fluoroquinolones, and rifampin may be alternatives, depending on the scenario. Expert advice should be sought if these alternative agents are being considered.
No vaccine is available for preventing rickettsial infections. Antibiotics are not recommended for prophylaxis of rickettsial diseases.
Travelers should be instructed to minimize exposure to infectious arthropods (including lice, fleas, ticks, mites) and animal reservoirs, particularly dogs and cats, when traveling in endemic areas. The proper use of insect or tick repellents or insecticides and acaricides, self-examination after visits to vector-infested areas, and wearing protective clothing are ways to reduce risk. These precautions are especially important for people with underlying conditions that may compromise their immune systems, as these people may be more susceptible to severe disease. For more detailed information, see Chapter 2, Protection against Mosquitoes, Ticks, & Other Insects & Arthropods.
CDC website: www.cdc.gov/ticks
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- Roch N, Epaulard O, Pelloux I, Pavese P, Brion JP, Raoult D, et al. African tick bite fever in elderly patients: 8 cases in French tourists returning from South Africa. Clin Infect Dis. 2008 Aug 1;47(3):e28–35.
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