Rocky Mountain Spotted Fever

Rocky Mountain Spotted Fever (RMSF) is a vector-borne disease. 

It is transmitted to humans by an infected tick.  The infective bacterial agent is Rickettsia Rickettsii and the ticks have acquired the organism from an infected animal.  Humans are infected when the tick takes a blood meal.

The American dog tick is the primary vector in the USA.

It is a disease of the western hemisphere (USA, Canada, Mexico, Panama, Costa Rica, Argentina, Brazil and Colombia). Most USA states are affected with the highest number of cases occurring in Oklahoma, Tennessee, Arkansas, Maryland, Virginia and North and South Carolina.  It is a notifiable disease in America and between 250 and 1200 notifications occur annually.  

It is unusual to find the responsible tick and testing for the disease can be difficult.  If there is a suspicion of RMSV, appropriate antibiotic treatment is usually started as soon as possible.

Deaths do occur. A fatal outcome is associated with older age and a delayed diagnosis (more than 5 days from disease symptom onset).

Travellers are at low risk for RMSF. Those most at risk include hikers, campers, and those involved in outdoor work. 

Two main factors determine the risk of tick habitation in a particular area.  These are vegetation and climate. This makes it possible for local authorities to warn visitors of the possibility of tick habitation in a particular area.  

Most case notifications occur between April and September, the warmer months of the year.

The brown dog tick is well known as a vector in Mexico. Humans are often infected through their contact with dogs, and this is often the case in children.

Occasionally an advisory is issued by the Centre for Disease Control (CDC) for travel to a particular region. In December 2023 an advisory was issued for Tecata, Mexico after 5 people were confirmed with RMSF over a 5-month period. Three died from the disease.

If forewarned, then the visitor can reduce their exposure to ticks.

• Be aware that ticks in the area may carry the disease. Seek information on whether any outbreaks have been reported.
• Take particular care in the season of risk (April to October).
• Wear appropriate clothing to reduce the likelihood of any attachment to the skin. This would include long-sleeved shirts and trousers. Socks should be pulled up over the bottoms of the trousers. Consider impregnating your “hiking clothes” with permethrin. Understand how this should be best applied to the clothing and how many washes before retreatment should be done.
• Wear light coloured clothing. Ticks are easily seen and might refrain from attachment.
• Use known effective repellents on the skin.  These include DEET or Picaridin containing products.
• Avoid known tick habitats such as bushy areas with high grass in the high-risk season.
• Stay as much as you can to paths and avoid encountering low bushes.
• Perform tick checks after finishing outside activities and remove any ticks as soon as possible.  Check arm pits and groin areas closely. Other areas include the belly button, behind the ears and knees. Clean any affected area with antiseptic. It is suggested that it takes more than 24 to 36 hours for a tick to transmit the disease once attached.
• Use the proper technique to remove any tick.  Use tweezers as close to the skin as possible and avoid squeezing the body of the tick. Gloves are recommended to avoid any fluid exposure. 
• Shower in hot water and check for any ticks.
• Inspect your underclothes closely and wash your hiking clothes with hot water as soon as possible. Putting them in a dryer adds extra protection. It is always advisable to travel with extra hiking gear if washing and drying isn’t always available.

The organism was named after the American pathologist, Howard Ricketts. He described the disease in the early 1900’s. Ricketts died in 1910 while studying another rickettsial disease. He had isolated the organism he believed responsible for a major outbreak of typhus in Mexico. Unfortunately, it was responsible for his death.