Editorial Note: Ehrlichia, members of the family Rickettsiaceae, are obligate, intracellular bacteria that parasitize mononuclear or polymorphonuclear leukocytes. The ability of Ehrlichia to infect and cause disease in animals is well documented (7). Canine ehrlichiosis, also known as tropical canine pancytopenia, is caused by E. canis and has an acute and chronic phase. After an incubation period of 10-14 days, dogs develop an acute febrile illness that may include depression, anorexia, lymphadenopathy, and thrombocytopenia (8). The chronic phase of the disease, which is often fatal, is characterized by pancytopenia and bone marrow hypoplasia. In the United States, serological evidence of E. canis infection has been reported among dogs in at least 34 states (9). Preliminary data suggest that human ehrlichiosis, like canine ehrlichiosis, is tickborne. Although canine ehrlichiosis is transmitted by the brown dog tick, Rhipicephalus sanguineus, this tick is probably not the main vector or reservoir involved in human transmission since it rarely bites people (10). There is no evidence that human ehrlichiosis is transmitted directly from dogs to people (2,3). Before 1986, only one Ehrlichia species, E. sennetsu, had been recognized as a human pathogen (11). Infection with E. sennetsu results in an acute febrile illness with lymphocytosis and postauricular and posterior cervical lymphadenopathy similar to mononucleosis. To date, this disease has been found only in Japan and Malaysia (7). Currently, the diagnosis of human ehrlichiosis is based on an IFA test that shows a fourfold or greater increase or decrease in antibody titer against E. canis with a minimum titer of 80. The test is a modification of the IFA test used for canine ehrlichiosis (12). Tetracycline has been shown to be effective in both the acute and chronic phases of canine ehrlichiosis (13). Human ehrlichiosis appears to respond to tetracycline administered at the same dose and schedule used for RMSF. However, insufficient data exist to recommend chloramphenicol as an alternative antibiotic. Physicians should consider the possibility of ehrlichiosis when patients have a febrile illness and a history of recent tick exposure. The diagnosis can be confirmed by testing acute- and convalescent-phase serum samples (taken 2-4 weeks apart) for E. canis antibody. Serologic testing for E. canis antibody is available at CDC. Only serum specimens submitted as pairs (i.e., acute- and convalescent-phase samples) will be accepted for testing. Specimens should be submitted to CDC through state health departments. References 1. Maeda K, Markowitz N, Hawley RC, Ristic M, Cox D, McDade JE. Human infection with Ehrlichia canis, a leukocytic rickettsia. N Engl J Med 1987;316:853-6. 2. Fishbein DB, Sawyer LA, Holland CJ, et al. Unexplained febrile illnesses after exposure to ticks: infection with an Ehrlichia? JAMA 1987;257:3100-4. 3. Fishbein DB, Taylor JP, Dawson J, et al. Human ehrlichiosis in the United States [Abstract no. 1277]. In: Program and abstracts of the Twenty-Seventh Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1987:319. 4. Rohrbach BW, Harkess JR, Ewing SA, Kudlac JF, McKee GL, Istre GR. Human ehrlichiosis, Oklahoma [Abstract no. 1278]. In: Program and abstracts of the Twenty-Seventh Interscience Conference on Antimicrobial Agents and Chemotherapy. Washington, DC: American Society for Microbiology, 1987:319. 5. Taylor JP, Betz TG, Fishbein DB, Roberts MA, Dawson J, Ristic M. Serologic evidence of possible human infection with Ehrlichia in Texas. J Infect Dis (in press). 6. Helmick CG, Bernard KW, D'Angelo LJ. Rocky Mountain spotted fever: clinical, laboratory, and epidemiological features of 262 cases. J Infect Dis 1984;150:480-8. 7. Ristic M. Pertinent characteristics of leukocytic rickettsiae of humans and animals. In: Leive L, ed. Microbiology-1986. Washington, DC: American Society for Microbiology, 1986: 182-7. 8. Kuehn NF, Gaunt SD. Clinical and hematologic findings in canine ehrlichiosis. J Am Vet Med Assoc 1985;186:355-8. 9. Keefe TJ, Holland CJ, Salyer PE, Ristic M. Distribution of Ehrlichia canis among military working dogs in the world and selected civilian dogs in the United States. J Am Vet Med Assoc 1982;181:236-8. 10. Nelson VA. Human parasitism by the brown dog tick. J Econ Entomol 1969;62:710-2. 11. Tachibana N. Sennetsu fever: the disease, diagnosis, and treatment. In: Leive L, ed. Microbiology-1986. Washington, DC: American Society for Microbiology, 1986:205-8. 12. Ristic M, Huxsoll DL, Weisiger RM, et al. Serological diagnosis of tropical canine pancytopenia by indirect immunofluorescence. Infect Immun 1972;6:226-31. 13. Amyx HL, Huxsoll DL, Zeiler DC, Hildebrandt PK. Therapeutic and prophylactic value of tetracycline in dogs infected with the agent of tropical canine pancytopenia. J Am Vet Med Assoc 1971;159:1428-32. Current Trends Recommendations for the Prevention of Malaria in Travelers Malaria continues to be an important health risk to Americans who travel to malaria-endemic areas of the world. The continued extension of chloroquineresistant Plasmodium falciparum (CRPF) in Africa, Asia, South America, and Oceania has reduced the number of effective drugs for malaria prophylaxis. In addition, some alternative drugs to chloroquine have been found to be associated with serious adverse reactions, and thus their usefulness is limited. Guidelines for prophylaxis must take into account the risk of exposure to malaria, the effectiveness and safety of antimalarial drugs, and the use of personal protective measures. Recommendations for the prevention of malaria should be revised periodically because of geographic changes in the occurrence of drug-resistant P. falciparum malaria, new information on the efficacy or toxicity of drugs used for prophylaxis, and/or the availability of new drugs. Malaria in humans is caused by one of four protozoan species of the genus Plasmodium: P. falciparum, P. vivax, P. ovale, and P. malariae. All are transmitted by the bite of an infected female Anopheles mosquito. Occasionally malaria is transmitted by blood transfusion or congenitally from mother to fetus. The disease is characterized by fever and influenza-like symptoms, which may occur at intervals and which include chills, headache, myalgia, and malaise. Malaria may be associated with anemia and jaundice, and P. falciparum infections may cause kidney failure, coma, and death. Deaths due to malaria are preventable. Malaria transmission occurs in large areas of Central and South America, subSaharan Africa, the Indian Subcontinent, Southeast Asia,* the Middle East, and Oceania. The estimated risk of acquiring malaria varies markedly from area to area. This variability is a function of the intensity of transmission in both urban and rural areas within the various regions as well as a function of the itineraries of most travelers. For example, during the period 1983-1986, 634 cases of P. falciparum among American civilians were reported to CDC. Of these, 507 (80%) were acquired in sub-Saharan Africa; 44 (7%), in Southeast Asia; and 63 (10%), in the Caribbean and South America. Of the 28 fatal infections, 21 were acquired in sub-Saharan Africa. Thus, most cases of imported malaria among American travelers were acquired in sub-Saharan Africa, despite the fact that only an estimated 90,000 Americans travel to sub-Saharan Africa each year, whereas an estimated 900,000 Americans visit Southeast Asia and South America each year. This disparity in the risk of acquiring malaria stems from the fact that travelers to Africa are at risk in most rural and many urban areas. Moreover, travelers tend to spend considerable amounts of time, including evening and nighttime hours, in rural areas where malaria risk is highest. In contrast, most travelers to Southeast Asia and South America spend most of their time in urban or resort areas where risk of exposure, if any, is limited, and they travel to rural areas only during daytime hours, when risk is limited. Drug Resistance Resistance of P. falciparum to chloroquine has been reported from all countries with P. falciparum malaria except the Dominican Republic, Haiti, Central America, the Middle East, and the following countries in West Africa: Chad, Equatorial Guinea, Guinea, Guinea-Bissau, Liberia, Senegal, and Sierra Leone. In addition, resistance to both chloroquine and pyrimethamine/sulfadoxine (Fansidar®) is widespread in Thailand, Burma, and Kampuchea. General Advice for Travelers to Malaria-Endemic Areas All travelers to malaria-endemic areas are advised to use an appropriate drug regimen and personal protection measures to prevent malaria. However, travelers must be informed that, regardless of methods employed, malaria can still be contracted. Symptoms can develop as early as 8 days after initial exposure in a malaria-endemic area and as late as several months after departure from a malarious area. Travelers should understand that malaria can be treated effectively early in the course of the disease but that delaying appropriate therapy can have serious or even fatal consequences. Individuals who have the symptoms of malaria should seek prompt medical evaluation, including thick and thin malaria smears, as soon as possible. Personal Protection Measures Because of the nocturnal feeding habits of Anopheles mosquitoes, malaria transmission occurs primarily between dusk and dawn. Travelers must be advised of the importance of measures to reduce contact with mosquitoes during those hours. Such measures include remaining in well-screened areas, using mosquito nets, and wearing clothes that cover most of the body. Additionally, travelers should be advised to purchase insect repellent for use on exposed skin before travel. The most effective *Thailand, Indonesia, Malaysia, People's Republic of China, the Philippines, Burma, Kampuchea, Vietnam, and Laos. repellents contain N,N diethylmetatoluamide (DEET), an ingredient in many commercially available insect repellents. The actual concentration of DEET varies among repellents (ranging up to 95%); the higher the concentration, the longer-lasting the repellent effect. Travelers should also be advised to purchase a pyrethrum-containing flying-insect spray to use in living and sleeping areas during evening and nighttime hours. Chemoprophylaxis Malaria chemoprophylaxis is the use of drugs to prevent the development of the disease. Preferably, malaria chemoprophylaxis should begin 1-2 weeks prior to travel to malarious areas. In addition to assuring adequate blood levels of the drug, this regimen allows any potential side effects to be evaluated and treated by the traveler's own physician. The exception is doxycycline; because of its short half-life, its use should begin 1-2 days before entering a malarious area. Chemoprophylaxis should continue during travel in malarious areas and for 4 weeks after departure from these areas. In choosing an appropriate chemoprophylactic regimen prior to travel, several factors should be considered. The travel itinerary should be reviewed in detail and compared with the information on areas of risk within a given country to determine whether the traveler will actually be at risk of acquiring malaria. The risk of acquiring CRPF malaria is another consideration. In addition, any previous allergic or other reaction to the antimalarial drug of choice and the accessibility of medical care during travel must be determined. Chemoprophylactic Regimens For travel to areas of risk where CRPF has not been reported or where only low-level or focal chloroquine resistance has been reported, once-weekly use of chloroquine alone is recommended. Chloroquine is usually well tolerated. The few individuals who experience uncomfortable side effects may tolerate the drug better by taking it with meals or in divided, twice-weekly doses. As an alternative, the related compound hydroxychloroquine may be better tolerated. (See Table 1 for recommended dosages for chloroquine and other chemoprophylactic regimens.) For travel to areas of risk where CRPF is endemic, once-weekly use of chloroquine alone is recommended. In addition, travelers to these areas (except those with histories of sulfonamide intolerance) should be given a treatment dose of FansidarR to be carried during travel and should be advised to take the FansidarR promptly in the event of a febrile illness during their travel when professional medical care is not readily available. It must be emphasized to these travelers that such presumptive self-treatment of a possible malarial infection is only a temporary measure and that prompt medical evaluation is imperative. They should be advised to continue their weekly chloroquine prophylaxis after presumptive treatment with FansidarR. (See Table 1 for recommended dosage.) Alternative Chemoprophylactic Regimens Doxycycline alone, taken daily, is an alternative regimen for short-term travel to areas with risk of CRPF. It is particularly appropriate for those individuals with a history of sulfonamide intolerance or for those, such as short-term travelers to forested areas of Thailand, Burma, and Kampuchea, who may be at risk in areas of chloroquine and FansidarR resistance. Travelers who use doxycycline should be cautioned about the possible side effects (see Adverse Reactions, page 282). Doxycycline prophylaxis can begin 1-2 days prior to travel to malarious areas. It should be continued daily during travel in malarious areas and for 4 weeks after departure from these areas. Malaria - Continued TABLE 1. Drugs used in the prophylaxis and presumptive treatment of malaria Prophylaxis Pediatric Dose >8 years of age: weight orally, once/day Presumptive Treatment for Travelers Chloroquine is not recommended for the presumptive Hydroxychloroquine is not recommended for the Tetracyclines are not recommended for the presumptive Proguanil is not recommended for the presumptive Adult Dose 3 tablets (75 mg Pediatric Dose Primaquine is only recommended for use after leaving Public Health Service. *Use of trade names is for identification only and does not imply endorsement by the U.S. Department of Health and Human Services or the |