Risks of Rocky Mountain Spotted Fever Examined

A binational team of investigators at the University of California, Davis, has conducted the first comprehensive study to examine the risk factors for Rocky Mountain spotted fever in Mexicali, Mexico. They found that citywide, just 1 in 1000 ticks was infected with the disease, but in certain neighborhoods, about 1 in 10 ticks was infected.

In the study, published in the American Journal of Tropical Medicine and Hygiene, investigators examined dogs and ticks and surveyed households in about 200 neighborhoods, half of which had diagnosed human cases of the disease. About half of the 284 dogs examined were infected with ticks; some dogs had thousands each.

The survey of households found that although 80% of residents had heard of Rocky Mountain spotted fever, less than half used pesticides to prevent the presence of ticks.

Patients with Rocky Mountain spotted fever typically develop symptoms 1 to 2 weeks after being bitten by an infected tick. As the bacteria infect blood vessel linings, blood begins to pool under the skin, resulting in a rash that looks like red splotches or spots. It can be deadly if not treated with antibiotics.

Investigators noted that a Rocky Mountain spotted fever epidemic on the scale of that in Mexicali is less likely in the United States. However, as temperatures warm because of climate change, concerns exist that a particular human-feeding brown down tick strain will continue to move north, resulting in more cases in humans north of the Mexican border. Pharmacists can counsel patients about the rising risk of Rocky Mountain spotted fever and prevention methods, including preventing tick bites.

Reference

Foley J, Tinoco-Gracia L, Rodriguez-Lomeli M, et al. Unbiased Assessment of Abundance of Rhipicephalus sanguineus sensu lato Ticks, Canine Exposure to Spotted Fever Group Rickettsia, and Risk Factors in Mexicali, México. Ameri J Trop Med Hygiene. 2019;101(1): 22-32.