Rocky Mountain Spotted Fever
Rocky Mountain Spotted Fever
Disease History, Characteristics, and Transmission
Introduction
Rocky Mountain spotted fever is a bacterial disease caused by Rickettsia rickettsii. This bacterium causes holes in blood vessels, which allows to blood leak into tissues and organs, causing damage to these areas. Humans become infected with Rocky Mountain spotted fever following a bite from an infected tick. Infection can also occur following contact with the blood or feces of infected ticks. Rocky Mountain spotted fever is present in most of the United States and has a yearly infection rate of about 800 cases. It is also found in some regions in South America. Similar strains of Rickettsia bacteria cause spotted fevers worldwide.
This disease usually results in fever, nausea, vomiting, headache, muscle aches, lack of appetite, diarrhea, abdominal pains, and, in some cases, a characteristic red rash. While recovery is likely for patients who receive early treatment, delayed treatment can result in complications, including death. Treatment involves a course of antibiotics for the duration of the fever. Since there is no vaccine available, the best prevention method is avoidance of ticks. This reduces the chance that a tick bite will lead to transmission of R. rickettsii.
Disease History, Characteristics, and Transmission
Rocky Mountain spotted fever was first identified as a tick-borne bacterial disease by Howard T. Ricketts (1871–1910) shortly before his death. Prior to its identification, this disease was first recognized in 1896 in the Snake River Valley of Idaho where it affected hundreds of people and was often fatal. Although it was first found in the Rocky Mountains, this disease occurs all over the United States, except for Hawaii, Vermont, Maine, and Alaska. Rocky Mountain spotted fever is a potentially fatal disease, and prior to 1940, had a mortality rate of 30%. This rate decreased to 3–5% following introduction of an effective antibiotic treatment.
WORDS TO KNOW
ACARACIDES: A chemical that kills mites and ticks is an acaracide.
TICK: A tick is any blood-sucking parasitic insect of suborder Ixodides, superfamily Ixodoidea. Ticks can transmit a number of diseases, including Lyme disease and Rocky Mountain spotted fever.
VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.
Rocky Mountain spotted fever is caused by the bacterium Rickettsia rickettsii. Infection occurs when a tick vector bites an infected animal and then bites a human. Infection can also occur if human skin is contaminated with tick blood or feces. The most common ticks to spread this infection to humans are the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermacentor andersoni). R. rickettsii lives and reproduces within cells lining blood vessels. The bacteria cause cell death, which leads to gaps forming in the surface of the blood vessel. Blood leaks through these gaps into surrounding tissue and causes tissue and organ damage. Blood leakage also causes a red rash that is present in some cases.
Various symptoms may arise over the course of a week. Initial symptoms include fever, nausea, vomiting, headache, muscle aches, and lack of appetite. A faint rash may also appear within 2–5 days after fever. Later symptoms include abdominal pain, joint pain, and diarrhea. In addition, usually around six days after the onset of fever, a red, spotted rash occurs in 35–60% of patients. Complications can arise in patients suffering severe cases when the respiratory, central nervous, gastrointestinal, and renal systems are affected. Long-term effects of Rocky Mountain spotted fever can include paralysis, amputation of limbs due to gangrene, loss of hearing and bowel or bladder control, and development of movement disorders.
Scope and Distribution
Rocky Mountain spotted fever occurs in almost all regions of the United States. It is dominant in the south-Atlantic regions, particularly in North Carolina. This fever also occurs in South America, particularly in Argentina, Brazil, Colombia, Costa Rica, Panama and, also, in Mexico. Bacterial strains (types) closely related to Rickettsia rickettsii also cause spotted fevers worldwide. The type of Rickettsia bacterium present in a region determines which type of spotted fever occurs in the area.
In the United States, the Centers for Disease control and Prevention (CDC) recorded 250–1,200 cases of Rocky Mountain spotted fever annually from 1955 to 2005. This fever predominantly occurs during warm weather when ticks are more active. The summer months in the United States, from April through to September, mark the highest levels of infection throughout the year.
All people can potentially contract Rocky Mountain spotted fever. However, males, Caucasians, and children are infected most often. Increased exposure to ticks increases the likelihood of infection. Therefore, people who live with dogs or people who reside near tick-inhabited areas, such as woodlands, are at risk of infection.
Treatment and Prevention
A course of antibiotics is used to treat Rocky Mountain spotted fever. Doxycycline is recommended by the CDC as an effective drug to eradicate this infection. However, for pregnant women, chloramphenicol should be used as an alternative to doxycycline, since doxycycline is associated with the risk for malformations of the teeth and bones in unborn children. Treatment administered immediately provides the best results. Fever usually subsides within 1–3 days following antibiotic treatment given within 4–5 days after the onset of the disease. However, recovery from fever will take longer in patients who receive treatment later, or who are suffering a severe illness.
There is no vaccine available for Rocky Mountain spotted fever. Therefore, the best prevention method is to avoid contact with ticks. This can be achieved in several ways. Areas inhabited by ticks, such as long grasslands and woodlands, may be avoided. If these areas can't be avoided, repellents on clothing or skin can help repel ticks and prevent them from biting. In addition, protective clothing, such as long-sleeved shirts, boots, and hats, can be worn to prevent ticks coming in contact with the skin. It is also important to thoroughly check the body for ticks following any activity in tick habitats. This may prevent ticks from biting, or, in the cases when ticks have already attached to the skin, will ensure early removal and reduce the chances of infection.
Large-scale prevention methods include the use of acaricides (insecticides that kill ticks) in tick-infested areas in order to reduce the number of ticks. If there are fewer ticks in an area, it is less likely that humans will be bitten.
Impacts and Issues
Rocky Mountain spotted fever is a potentially life threatening disease. Late diagnosis and delayed treatment increase the chances of complications, such as kidney failure and even death. As this disease infects approximately 800 people a year in the United States and is potentially fatal, increased awareness and reminders about prevention are recommended by the Directors of Health Promotion and Education.
This disease can be difficult to diagnose during the initial stages due to its wide range of symptoms and the fact that not all cases exhibit the characteristic red rash. This is a problem, since late diagnosis increases the chances of severe complications and possible fatalities. To address this problem, treatment is usually given before conclusive evidence confirms the disease. This approach ensures that patients with the disease receive treatment as soon as possible.
Despite prevention methods, such as the use of aracicides, the wearing of protective clothing, and the use of repellents, ticks can still come in contact with humans. When people find ticks on their bodies, removal is vital, and the earlier it is done, the less chance there is of infection. However, incorrect removal of ticks can cause complications. If the mouthparts of the tick remain in the body, infection can still occur. Furthermore, handling ticks with bare hands also increases the risk of exposure as infection can occur when blood or feces come in contact with open skin. The best technique for removing a tick involves grabbing the tick with tweezers as close to the skin as possible and pulling it away from the skin. Coating ticks with petroleum jelly or burning them with a match are not effective techniques for tick removal, despite the popularity of these methods with the general public.
See AlsoBacterial Disease; Rickettsial Disease; Zoonoses.
BIBLIOGRAPHY
Books
Mandell, G. L., J. E. Bennett, and R. Dolin. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia: Elsevier, 2004.
Periodicals
Parola, P., C. D. Paddock, and D. Raoult. “Tick-Borne Rickettsioses Around the World: Emerging Diseases Challenging Old Concepts.” Clinical Microbiology Reviews 18 (October 2005): 719–756. Also available online at <http://cmr.asm.org/cgi/content/full/18/4/719>.
Web Sites
Centers for Disease Control and Prevention. “Rocky Mountain Spotted Fever.” May 20, 2005. <http://www.cdc.gov/ncidod/dvrd/rmsf/index.htm> (accessed March 6, 2007).
Directors of Health Promotion and Education. “Rocky Mountain Spotted Fever.” <http://www.astdhpphe.org/infect/rms.html> (accessed March 6, 2007).
Illinois Department of Public Health. “Rocky Mountain Spotted Fever.” <http://www.idph.state.il.us/public/hb/hbrmsf.htm> (accessed March 6, 2007).