An ongoing outbreak of Rocky Mountain spotted fever (RMSF) in Mexico has some experts worried that ticks carrying this disease may be moving into the United States, according to a study published earlier this month.
RMSF is spread by ticks carrying the bacteria Rickettsia rickettsii. It’s characterized by fever, headache, rash, and other symptoms.
When not treated early with the right antibiotic, it can lead to severe complications, including death.
In Mexico and the southwestern United States, the main carrier of the bacteria is the brown dog tick. In the eastern United States, the bacteria is mainly carried by the American dog tick. In the Rocky Mountains area, it’s carried by the Rocky Mountain wood tick.
The brown dog tick is unusual in that it can live entirely indoors, allowing it to quickly infest a house or kennel. This ability can increase the spread of the disease.
While the tick prefers to feed on dogs, it will also feed on people and other mammals if it has the chance.
Brown dog tick outbreak in Mexico
RMSF is responsible for killing more people in North America than any other tick-borne illness.
In the latest study, researchers from the Universidad Autónoma de Baja California and University of California, Davis reported that the brown dog tick was linked to about 80 deaths from RMSF in the Mexican state of Sonora between 1997 and 2007, as well as recent outbreaks in Arizona.
The outbreak in the city of Mexicali began in 2008. At least 13 people died in one impoverished neighborhood between 2008 and 2009. Over 80 percent of local dogs tested positive for R. rickettsii.
And now, experts think the current outbreak in Mexico may be on the move.
“The RMSF epidemic in Mexicali hasn’t been contained and may be spreading to other parts of Baja California and into the United States,” the researchers wrote.
Dr. Steven Meshnick, a professor in the departments of epidemiology and microbiology and immunology at UNC Gillings School of Global Public Health emphasized that tick migration isn’t driven by the movement of people.
“None of the tick-borne diseases are spread person-to-person,” said Meshnick. “All of these diseases — which are endemic in the United States — are primarily diseases of feral mice and deer. And they’re spread by a variety of ticks.”
Researchers from the new study wrote that previous outbreaks in Arizona and Sonora were contained with “aggressive” intervention.
This included dog spay and neuter programs to control the dog populations, treating houses for ticks, and using long-acting tick collars on dogs.
Protect yourself from tick-borne diseases
In 2016, over 4,000 people had spotted fever rickettsiosis, according to the Centers for Disease Control and Prevention (CDC).
These diseases are found throughout the contiguous United States, but over 60 percent of cases occur in Arkansas, Missouri, North Carolina, Oklahoma, and Tennessee.
RMSF and similar tick-borne diseases are now tracked together in this category, because common tests using antibodies in the blood can’t differentiate between these infections.
Meshnick said one of contributions of the new study is that “they were able to do PCR and show that this infection was, indeed, Rickettsia rickettsii.”
The PCR (polymerase chain reaction) test is able to identify very small amounts of DNA in a sample.
Protecting yourself from RMSF is the same as for other tick-borne diseases — prevent tick bites and get early treatment if you’re bitten and develop symptoms.
The first step is to steer clear of tick habitats — usually grassy or wooded areas — whenever possible. This may just mean walking in the middle of hiking trails to avoid picking up a tick hitchhiker.
If you do venture out, use Environmental Protection Agency-registered insect repellents like DEET and picaridin or permethrin-treated clothing. These can deter ticks from latching onto you or your clothing.
Also use a tick collar to keep your dog from bringing ticks into your house.
After spending time in tick country, check yourself, clothing, gear and pets.
“Ticks usually wander around for minutes or hours before they actually find a spot on your body that they like and start taking their blood meal,” said Meshnick. “So inspection really works.”
Adult ticks are easier to find, but in their larval or nymph stages, ticks are about the size of a poppy or sesame seed. The CDC has pictures of different ticks, but you don’t need to be a tick expert to get help.
As with Lyme disease, early treatment for RMSF is essential, because that reduces the risk for later complications or death.
If you become sick after being bitten by a tick or after spending time in an area where ticks live, see your doctor.
Doctors can treat based on symptoms, even without an offending tick in hand, especially in tick-heavy parts of the country.
“If someone comes into the clinic in the summer with a fever and maybe a rash or some memory of a tick bite, most primary care doctors in North Carolina will just put them on doxycycline, which is pretty nontoxic and 100 percent curative,” said Meshnick.