Mystery Fever Leads to New Pathogen From Peru

SAN FRANCISCO, June 7 -- A 43-year-old woman has brought a previously unknown pathogen back from Peru.

The finding is an important reminder to physicians that not all pathogens are known, according to Jane Koehler, M.D., of the University of California at San Francisco.

Her group's genetic detective work revealed that the pathogen was not Bartonella bacilliformis, an organism endemic in the Andes and responsible for Oroya fever, but a new member of the genus that had never been seen before.

The new species -- named Bartonella rochalimae, after Brazilian investigator Henrique da Rocha-Lima -- is related to the cause of Oroya fever, but also to the microbes that cause trench fever and cat-scratch fever, Dr. Koehler and colleagues reported in the June 7 issue of the New England Journal of Medicine. Trench fever is caused by B. quintana and cat-scratch fever by B. henselae.

There are now 20 known members of the Bartonella genus, only three of which frequently cause disease in humans, they said.

The woman had spent three weeks traveling in Peru, and a few weeks after returning to the U.S. she developed fever, insomnia, myalgia, nausea, headache, and mild cough.

When she went to hospital, eight days after the fever started, she had an enlarged spleen, a fever of 37.3C (down from a peak of 38.9C) and healing insect bites on her ankles. Given her travels, doctors initially suspected Oroya fever.

In this case, the woman was treated empirically with oral levofloxacin (Levaquin) for five days and a week later had no symptoms, no fever, and her spleen was no longer palpable, the researcher reported.

Meanwhile. Dr. Koehler - working with colleagues here, at Massachusetts General Hospital in Boston, and at the CDC in Atlanta - had been studying blood specimens from the patient.

While the new bug looks identical to B. bacilliformis, the cause of Oroya fever, it is genetically quite different, they found, and is most closely related to B. clarridgeiae, which is usually found in cats.

After the microbe was identified, the woman was treated with oral clarithromycin (Biaxin) for 10 days. Follow-up blood cultures were negative for the bacteria.

"When a patient has a high and persistent fever, we need to come up with the correct diagnosis and treatment as soon as possible - particularly for those with a weakened immune system, who can die from the infection," Dr. Koehler said. "Also, different Bartonella species respond to different drugs, so it is essential to explore further and pinpoint which one is involved."

Dr. Koehler added, "As we continue to discover new pathogens and how humans get infected with them, we improve our ability to diagnose, prevent and treat our patients.".

The study is an example of "meticulous bedside-to-bench research" of the type needed to identify new pathogens, according to Gary Wormser, M.D., chief of infectious diseases at New York Medical College in Valhalla, N.Y.

Writing in an accompanying perspective article, Dr. Wormser noted that the discovery might imply that some cases of Oroya fever - transmitted by the sand-fly endemic to the region - are actually caused by the new bacteria.

Also, Dr. Koehler and colleagues said there's some evidence that the bacteria may be transmitted by some other form of insect, which could change the distribution pattern of the disease.

It's still not known whether there's an animal or insect reservoir for B. rochalimae or how humans become infected, they said.