Rocky Mountain spotted fever (tick-borne typhus fever)

What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever (RMSF) is the most severe tick-borne rickettsial illness in the United States. There are 250 to 1200 cases reported annually in the US. It is a zoonotic disease caused by the bacterium Rickettsia ricketsii. In 2007, there were 27 cases reported among New York City residents (rate of 3 cases per 1,000,000 persons).

Who gets RMSF?

Anyone exposed to infected ticks can get RMSF. Nationally, the disease is reportedly most common in children under 10 years of age, but in NYC the majority of patients are middle aged. Some people who get infected never become ill. There have been reports of multiple persons in one household and or their pets becoming infected at the same time.

How is RMSF spread?

RMSF is transmitted to humans and other animals by the bite of an infected tick. Ticks can become infected by feeding on infected animal hosts, however once infected, an adult tick can pass the infection to its offspring. In the United States, east of the Rocky Mountains and along the Pacific coast, the primary vector is the American dog tick, Dermacentor variabilis. In the Rocky Mountain region, the Rocky Mountain wood tick, Dermacentor andersoni is the primary vector species. Other ticks, particularly the lone-star tick, Amblyomma americanum may occasionally transmit RMSF. Person-to-person spread of RMSF does not occur.

It usually takes several hours of attachment before an infected tick can transmit the RMSF bacteria. Tick checks should be performed at the end of any activities that occur in tick habitat. Prompt tick removal can help prevent potential infections.

For more information on ticks and pictures, see http://www.nyc.gov/html/doh/html/ehs/ehstick.shtml

Where and when does RMSF transmission occur

Most cases of RMSF occur in the southeastern and south central United States. The American dog tick can be found in all five boroughs of New York City, as well as nearly all parks and woodlands in the eastern United States. In 1996, an outbreak of RMSF occurred in New York City primarily in the region of Soundview Park in the Bronx. However, cases of RMSF have occurred in all five boroughs. Adult dog ticks will feed on people, and are most active during the spring, summer and fall. Most cases of RMSF in New York City are reported during April, May and June. However, since ticks may be active year round, disease transmission can also occur at any time of the year.

What are the symptoms of RMSF?

RMSF is characterized by the sudden onset of moderate to high fever (which can last from 2 to 3 weeks), severe headache, loss of appetite, fatigue, deep muscle pain, chills and rash. More than 50% have nausea or vomiting early on. Initially the rash is faint and is seen on the wrists or ankles. As the disease progresses, the rash becomes “spotted” and may spread rapidly to the trunk, the extremities, and the palms and soles. Rocky Mountain spotted fever should always be considered with the presence of a rash on the soles and palms. Antibodies to RMSF may not be detectable during the first week of illness. Thus, a suspect diagnosis of RMSF without the presence of a rash or supporting laboratory results should not impede the initiation of appropriate antibiotic therapy. While a history of a tick bite may aid in the diagnosis of RMSF, it may go unnoticed. Ticks may be very small and attach in concealed areas of the body. Severe complications from RMSF can include pneumonitis, encephalitis, myocarditis, hepatitis, and death. RMSF is responsible for more deaths than any other tick-borne illness in the United States. There is a case fatality rate of up to 30% in untreated patients. Approximately 612 people died (12% among children under the age of 10 years) from RMSF between 1983 and 1998.

How soon after infection do symptoms appear?

Clinical illness usually occurs 5-10 days after infection.

Does past infection with RMSF make a person immune?

Infection with Rickettsia rickettsii usually provides long-term immunity. Regardless, persons should continue to practice preventive measures to avoid other tick-borne diseases.

How is RMSF diagnosed?

RMSF is diagnosed based on clinical presentation of symptoms or a positive antibody test to the Rickettsia ricketsii bacteria. Diagnosis can also be made by taking a biopsy of the skin where the rash occurs.

What is the treatment for RMSF?

Appropriate antibiotic treatment should be initiated immediately when there is a suspicion of Rocky Mountain spotted fever on the basis of clinical and epidemiologic findings. Treatment should not be delayed until laboratory confirmation is obtained. Antibiotics such as tetracycline or doxycycline have been effective in treating this disease.

How can RMSF be prevented?

Like all tick-borne diseases, preventing tick bites is the key to preventing RMSF. When in tick infested areas (i.e., tall grass, overgrown brush), special precautions should be taken. Wear light-colored clothing, tuck pant legs into socks, and wear closed toe shoes. Use commercial insect repellent with no more than 20% - 30% DEET. Use repellents sparingly and with care, as they may cause side effects, especially in young children. Avoid application to damaged skin. When returning from outdoors it is important to check yourself, your children and your pets for ticks. Look for ticks in all joint areas, the navel, behind ears, in the hairline, and in other skin folds. Wash all skin treated with insect repellent thoroughly. Keep your lawn mowed, cut overgrown brush, and remove leaf litter to reduce tick populations.

For more information on insect repellent safety see Repellant Fact Sheet

How should a tick be removed?

• Remove attached ticks as soon as possible.
• Use tweezers to grasp the tick as close to the skin surface as possible.
• Pull up on the tick with slow, even pressure to gradually ease out the mouth parts.
• If tweezers are not available, use fingers shielded with tissue paper or rubber gloves.
• Do not handle ticks with bare hands.
• Do not use petroleum jelly, nail polish remover, or heat to remove the tick, since these methods may increase the risk of infection with a tick-borne disease.
• Do not squash or squeeze the tick during removal.
• Wash the area of the tick bite and your hands with soap and water after the tick is removed.
• When outdoors, in tick-infested areas, check every 2 to 3 hours for ticks attached to clothing or skin.

New York City residents: For more information on Rocky Mountain spotted fever, call 212-788-9830 during normal business hours (Monday-Friday, 9:00am-5:00pm). For people residing outside of New York City, please contact your state or local health department.

Information for Professionals

Compendiums and Diagnostic and Treatment Guidelines

Last updated August 2007