Rocky Mountain Spotted Fever (RMSF) is a serious bacterial illness caused by the organism Rickettsia rickettsii. It is considered the most frequently reported fatal tick-borne illness in the United States and can progress rapidly if not treated promptly. Although the name suggests a connection to the western mountains, most cases are reported from the south-central and southeastern regions. Early recognition and prevention are crucial for anyone spending time outdoors.
Is Rocky Mountain Spotted Fever Contagious?
RMSF is not transmissible from person to person through typical contact, such as touching, coughing, or kissing. The bacterium Rickettsia rickettsii cannot survive independently outside of specific hosts or vectors. This means you cannot acquire RMSF by sharing food or utensils with an infected individual, nor can the bacteria be spread through the air or water. Contact with pets or livestock that may have been exposed to ticks also does not pose a direct risk of infection to humans. The only established transmission route involves a biological vector, making the disease non-contagious in the traditional sense.
How RMSF Spreads
The exclusive and primary method of RMSF transmission is through the bite of an infected tick, which acts as the biological vector for the bacteria Rickettsia rickettsii. In the United States, the American dog tick (Dermacentor variabilis) is the most commonly identified vector, particularly in the eastern and southern states, while the Rocky Mountain wood tick (Dermacentor andersoni) is the main carrier in the western mountain states. The brown dog tick (Rhipicephalus sanguineus) has also been implicated in some cases.
Transmission occurs when an infected tick attaches to a human host and begins to feed, releasing the bacteria through its saliva. The tick generally needs to be attached for a period of several hours—typically 4 to 10 hours—before the bacteria are successfully transmitted to the host. This period is necessary for the bacteria to multiply and move from the tick’s gut to its salivary glands.
Infection can also occur if bacteria from a crushed tick’s body fluids or feces enter an open cut, scratch, or mucous membrane. This secondary, non-bite route is a concern during improper tick removal. Care must be taken to avoid crushing the tick’s body during the removal process to prevent the bacteria from contacting the skin.
Recognizing the Infection
Symptoms of RMSF typically begin abruptly after an incubation period that ranges from 3 to 12 days following the infected tick bite. The onset of illness usually involves a sudden high fever and a severe headache, often accompanied by muscle pain, nausea, and vomiting. Because these initial signs are non-specific, the disease can be difficult to diagnose in its earliest stages, which is when treatment is most effective.
The characteristic rash, which gives the disease its name, may not appear until two to four days after the fever begins, or sometimes not at all. When it appears, the rash often starts on the wrists, forearms, ankles, palms, and soles of the feet before spreading inward to the trunk. The rash initially presents as small, flat, pink spots that can later become pin-point red or purple spots, known as petechiae, which signify more severe illness.
A short incubation period or a delay in the appearance of a rash is often associated with a more severe, rapidly progressing infection. Immediate medical attention is required if RMSF is suspected. Early treatment can significantly reduce the risk of organ damage, neurological deficits, or death, which can occur within 7 to 9 days of symptom onset if the illness is left untreated.
Protecting Yourself
Minimizing your exposure to ticks is the most effective strategy for preventing RMSF, especially during the warmer months when ticks are most active. When in wooded or grassy areas, wearing light-colored clothing makes it easier to spot ticks before they attach. Tucking pant legs into socks and shirts into pants helps create a physical barrier to keep ticks from crawling onto the skin.
Chemical repellents provide an additional layer of defense against tick bites. Applying an EPA-registered insect repellent containing ingredients like DEET to exposed skin is recommended. Clothing, gear, and shoes can be treated with products containing permethrin, which is designed to kill ticks on contact.
After spending time outdoors, performing thorough tick checks on yourself, children, and pets is a necessary step. If a tick is found attached, it should be removed promptly using fine-tipped tweezers by grasping the tick as close to the skin surface as possible. Pulling upward with steady, even pressure, without twisting or crushing the body, will ensure the entire tick is removed, minimizing the risk of infection.