The US Centers for Disease Control and Prevention (CDC) warned of an outbreak of Rocky Mountain spotted fever (RMSF), a deadly tickborne disease, that has affected five people and killed three in the US since July. The CDC issued a health alert on Friday, urging health care providers to promptly treat suspected cases of RMSF with doxycycline, an antibiotic.

What is RMSF and how is it transmitted?

RMSF is a serious and potentially fatal disease caused by the Rickettsia rickettsii bacteria, which are transmitted by the bite of infected ticks. Many patients do not recall being bitten by a tick. The disease is endemic in northern Mexico and parts of the southwestern US, where it is carried by the brown dog tick.

What are the symptoms and complications of RMSF?

The symptoms of RMSF can be mild at first, but can quickly progress to life-threatening complications. The symptoms include:

  • Low-moderate fever
  • Headache
  • Stomach problems
  • Abdominal pain
  • Muscle pain
  • Rash
  • Swelling around the eyes and on the back of the hands

The complications of RMSF can include:

  • Changes in mental state
  • Coma
  • Brain swelling
  • Respiratory problems
  • Multiorgan damage

The mortality rate of RMSF is 5% to 10%, with about half of the deaths occurring within eight days of the onset of illness.

What is the link between the outbreak and travel to Mexico?

According to the CDC, the five cases of RMSF were linked to travel to Tecate, Baja California, in northern Mexico, within the previous two weeks. Four of the patients were children and three were US residents. All five required hospitalization and three died from the disease.

The CDC advises health care providers to start treatment with doxycycline immediately if a patient presents with symptoms of RMSF and has a history of travel to northern Mexico, rather than waiting for laboratory confirmation.

How can RMSF be prevented?

The CDC urges anyone who has traveled to northern Mexico and develops symptoms of RMSF within two weeks of their return to the US to seek medical attention as soon as possible. To prevent tick bites, the CDC recommends:

  • Treating pet dogs for ticks
  • Using insect repellent when outdoors
  • Wearing protective clothing when outdoors
  • Checking for ticks after spending time outdoors or around dogs
  • Removing any ticks promptly

What is the CDC doing to investigate and control the outbreak?

The CDC has provided more details on the outbreak of RMSF in southern California and its possible origin in Mexico. According to the CDC, the outbreak is likely caused by a new strain of R. rickettsii bacteria that has emerged in the brown dog tick population in Tecate, Baja California. The brown dog tick is usually found across the entire US, but only those in Arizona and the surrounding regions are known to carry R. rickettsii.

The CDC has also identified three genetically distinct populations of brown dog ticks, which vary in the percentage of ticks that carry the R. rickettsii bacteria. These differences are a major contributor to the variation in RMSF cases across the region. The CDC has also found high rates of RMSF infection in dogs in areas where no human cases had been reported.

The CDC is working with the Mexican government and local health authorities to investigate the outbreak and implement prevention and control measures. The CDC is also conducting a study to better understand the spread of RMSF and the factors that influence the vectoring capacity of the brown dog tick. The CDC hopes that the findings from this study will help predict and prevent future outbreaks of RMSF.

CDC Issues Health Alert for Rocky Mountain Spotted Fever Outbreak Linked to Mexico