Infectious disease expert warns of spread of Rocky Mountain spotted fever

08/05/05

Hopkins scientist believes that physician awareness is needed to combat emerging infectious diseases

An infectious disease expert at Johns Hopkins who has spent nearly three decades studying the life-threatening, tick-borne infection known as Rocky Mountain spotted fever warns that the first widespread outbreak of the bacterial disease in Arizona is a growing and dangerous sign of how humans can inadvertently help spread infectious organisms beyond traditional state boundaries.

In an article to be published in The New England Journal of Medicine, the Hopkins pathologist and microbiologist J. Stephen Dumler, M.D., a professor at The Johns Hopkins University School of Medicine, highlights the importance of the recent outbreak in Arizona as the first confirmed cases that could be traced back to ticks carried into to the state on feral dogs, an animal group whose population has markedly increased. And, as the number of dogs has increased, so have the number of ticks. A detailed study of this latest outbreak by the United States Centers for Disease Control and Prevention (CDC) is featured in the same edition of the NEJM online Aug. 11.

According to Dumler, the disease, most often marked by a telltale spotty rash that appears five to 10 days after the first signs of infection, has been largely confined to the South Central and Southeastern United States, although sporadic cases have been reported in all 48 continental states, mostly North Carolina. (Hopkins' home state of Maryland is among the top 10 states for the disease, with at least 79 cases reported in 2004, up from 19 in 2000.)

The scientist also reports that the number of people infected with Rocky Mountain spotted fever, which is fatal in up to 10 percent of those who contract it, has peaked for the third known time this century, with more than 1,800 cases reported nationally in 2003 and 2004. However, scientists believe the number of unreported cases is much greater.

Dumler's opinion is that growing awareness among physicians about the disease's early signs and symptoms may be the best means of curbing the potentially deadly impact of the disease, which can be effectively treated with specific antibiotics if caught early.

"Rocky Mountain spotted fever is a dangerous and potentially fatal disease, unlike its more widespread cousin, Lyme disease, which is almost never fatal," he says. In the latest study, researchers at the U.S. Centers for Disease Control report on 16 cases in which two children contracted the fever and died. "Because its first symptoms are very hard to distinguish from many other illnesses, it is often hard to diagnose unless you are looking out for it," he adds.

The first signs of Rocky Mountain spotted fever, the scientist says, are body-wide aches and pains accompanied by headache and a sudden high fever, sometimes as high as 105 degrees Fahrenheit (or 40.5 degrees Celsius). Symptoms may also include sore throat and nausea. The spotty rash, which occurs in at least 85 percent of patients, does not appear until later in the infection and resembles a pinpoint pattern of pink-to-red spots over the entire body, or parts thereof. The rash is also noticeable on the soles of the feet and palms of the hands, where rashes do not usually appear. At this later stage of infection, antibiotic therapy becomes somewhat less effective.

In the CDC-led study, government researchers took blood and skin tissue samples from 16 patients across Southeastern Arizona suspected of having the infection. Laboratory tests, including immunohistochemical staining, confirmed that 11 had the disease, while the remaining five were still probable cases.

When the researchers examined the patients' home environments for possible clues to the source of infection, they found fever-infected ticks in all patients' yards. Ticks were found in the cracks of stucco walls on patients' homes, in crawl spaces under these homes and on furniture placed outside for children and pets. All patients owned and had come in contact with dogs with the infected ticks. Four of the patients had a recent history of tick bite.

Tests of the dogs' blood confirmed their infection with the spotted fever bacterium. Feral dogs and brown dog ticks are not a species found naturally in the Arizona region, but were introduced to the state as domesticated dogs that moved with their owners into the area.

"This study shows that Rocky Mountain spotted fever can show up in unexpected places, and the study should put physicians on alert for the earliest signs and symptoms of the disease," says Dumler. "Our next step is to develop faster and more reliable tests to detect the disease so that physicians can more readily make a diagnosis and begin treatment as early as possible."

Initial treatment for adults, he says, involves immediate, twice daily 100-milligram doses of the oral antibiotic doxycycline (a version of the common tetracycline) until the patient's fever subsides. Patients continue to take the medication for an additional five days to prevent the disease from rebounding. Infected children would receive the same drug, but at a lower dose.

Rocky Mountain spotted fever is a bacterial disease caused by Rickettsia rickettsii, which can be spread by ticks that carry the bacteria and then bite humans, leaving behind the tick's bacteria-filled saliva. Once inside the body, the infection spreads rapidly, causing inflammation of the blood vessels, shock and the build-up of fluid inside the lungs and brain. The precise origins of Rocky Mountain spotted fever are not known, but the disease is only known to occur in North and South America.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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