With the recent wet weather, the ground cover will be thick and green making it a good home for ticks. Health care providers should be on the lookout for vector-borne diseases and make sure their patients are tested appropriately. The following is a brief description of the vector-borne diseases found in Utah and their prevalence.

The most commonly reported vector-borne disease in Utah is Colorado Tick Fever (CTF). The Colorado Tick Fever virus causes the disease. The virus is maintained in a wild rodent reservoir and is transmitted to humans by the bite of the Rocky Mountain wood tick (Dermacentor andersoni). CTF is endemic to Western U.S. and Canada at elevations above 5,000 feet. For the eight-year period, 1990-1997, there were 93 reported cases of CTF in Utah residents (Table 1). The highest number of cases, twenty-three, occurred in 1993; while the lowest, four, was reported in 1996. The county of residence with the highest cumulative incidence (per 100,000) was Wasatch County (27.43) followed by Summit (6.94). Sixty-one percent of the cases were male. Ages of cases ranged from one to 90 years of age, with the mean age being 35.7 years of age (Male: 1-90 years, mean 38.7 years, Female: 3-76 years, mean 30.5 years).

Twenty-three cases of tularemia were reported in Utah for 1990-1997 (Table 1). One of these cases died. Of the cases, 87% were male. Ages of the patients ranged from two to 75 years of age with the median age being 38.2 years. Seven of the cases had an unknown exposure. Of those cases with known exposure, five were associated with deer fly bites, four because of a cat bite or scratch, three from contact with rabbits or rabbit pelts, and one from a tick bite.

Tularemia, also known as rabbit fever, can be transmitted through many different routes, including handling infected rabbits or other animals, ingestion of undercooked, infected meat, and by tick or deer fly bites. The incubation period for tularemia is about three days, with a range of two to ten days. Symptoms generally include chills, fever, malaise, and often enlarged glands. The presentation of this disease varies with the means by which it is acquired: ingestion of infected meat may cause pharyngitis and gastrointestinal symptoms; exposure through handling the meat may cause an ulcer on the hand; inhalation of infectious material causes pneumonia. Diagnosis is generally made through fourfold rise or greater in antibody titer between acute and convalescent serum specimens or by isolation of Francisella tularensis from ulcer exudate, lymph node aspirate or blood.

Utah has had four cases of plague reported during 1990 to 1997 (Table 1). The first three cases presented with bubonic plague. Bubonic plague is marked by a high fever and the characteristic bubo, or swollen lymph node, usually inguinal, sometimes axillary or cervical. There was no source confirmed for any of these cases. The 1994 case was a pneumonic plague case that was acquired from a cat. Pneumonic plague may occur as the result of secondary spread of Yersinia pestis to the lung. Primary pneumonic plague occurs as a result of inhalation of droplets expelled by an animal or human with plague pneumonia. The third form of plague is the septicemic form.

The reservoir for Yersinia pestis is wild rodents in the Western U.S. Transmission usually occurs by flea bite, though it can be transmitted through handling infected tissues of rodents or in the case of pneumonic plague, through the respiratory route. Diagnosis of plague is confirmed by culture and identification of the organism from aspirate of the bubo, from blood, or by four fold rise/fall in antibody titer. Plague is reportable immediately by telephone. Public health follow-up of cases includes identification of the source so that appropriate intervention can be made to prevent other cases. Prevention measures include avoidance of prairie dog towns, not handling or eating rodents, especially sick animals, and keeping domestic animals free of fleas.

Relapsing fever or Borrelia recurrentis (Borrelia spp.) is an uncommon illness characterized by fever episodes lasting from 3 to 6 days followed by an afebrile period of about a week. Relapses become progressively shorter and milder as the afebrile period becomes longer. A fleeting macular rash on the trunk frequently occurs. In the Western U.S. the disease is carried by a soft-bodied tick (Ornithodoros species). In the last eight years, five cases have been reported in Utah residents (Table 1).

Six cases of Rocky Mountain spotted fever (RMSF) were reported in Utah residents during the eight year period (Table 1). The disease is much more common in the south central and eastern states. Only one of the cases was known to be acquired outside of Utah. RMSF is the most serious of the tick-borne diseases.

Seventeen cases of Lyme disease have been reported in Utah residents between 1990 and 1997 (Table 1). Seventy-one percent of the cases were female and ages of the cases ranged from 2 to 68 years with a median age of 35 years. Seven cases (41%) were acquired outside of the state. The surveillance case definition used to report Lyme disease is either the presence of erythema migrans, the characteristic lesion associated with this disease, at least 5 mm in diameter; or positive serology and one of the late manifestations associated with this illness: neurologic, cardiac, or arthritic abnormalities. The incubation period for Lyme disease ranges from 3 to 32 days. Beginning symptoms include the characteristic erythema migrans, malaise, fatigue, fever, headache, stiff neck, myalgia, migratory arthralgias, or lymphadenopathy. Tick studies show that Ixodes pacificus is present in Utah, but no Borrelia burgdorferi was found in any tick or mouse studies.

The last vector-borne reportable disease to be discussed is malaria. Utah has had 30 cases of malaria reported over the past eight years (Table 1). All of the cases have been imported from outside the United States. Over one third (11) of the cases were imported from Africa, another third were imported from India (6) and Central America (6). The remaining third were imported from Indonesia (3), Philippines (1), Pakistan (1), and one with a travel history that includes several Caribbean Islands and Central America. Twenty (70%) of the cases have been male. Almost 50% of the cases were between 20 and 29 years of age.

Malaria is a parasitic disease caused by one or more of the following sporozoan parasites: Plasmodium vivax, P. malariae, P. falciparum and P. ovale. The disease is transmitted by the bite of the female Anopheles mosquito. The incubation period or time between the infective bite and the appearance of clinical symptoms is approximately 7-14 days for P. falciparum, 8-14 for P. vivax and P. ovale and 7-30 days for P. malariae. To prevent malaria, all travelers to the subtropics and tropics should check with their local health department or physician for information on malarial prophylaxis.

The State Public Health Laboratory or the Centers for Disease Control and Prevention (CDC) can test for these diseases. Physicians may call 584-8400 for further information about specimen collection and submission. Single copies of fact sheets on vector-borne diseases are available from the Bureau of Epidemiology, 538-6191.