Once bitten

By Bob Grant Once bitten An SEM of the tick Ixodes scapularis, carrier of Lyme disease. © David Scharf / Science Faction / Corbis The fever kicked in during the long plane journey home to Philadelphia from Africa. An intense heat washed over my body, my head throbbed, my neck muscles ached, and I tried desperately to stretch the flimsy airline blanket over my chill-wracked arms and legs. All because of a South African tick—o

Bob Grant
Bob Grant

Bob Grant is Editor in Chief of The Scientist, where he started in 2007 as a Staff Writer.

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May 1, 2010

Once bitten

An SEM of the tick Ixodes scapularis, carrier of Lyme disease.
© David Scharf / Science Faction / Corbis

The fever kicked in during the long plane journey home to Philadelphia from Africa. An intense heat washed over my body, my head throbbed, my neck muscles ached, and I tried desperately to stretch the flimsy airline blanket over my chill-wracked arms and legs. All because of a South African tick—one of an ilk that has been gifting an increasing number of inadvertent souvenirs to visitors to sub-Saharan Africa over the past couple of decades.

I hadn’t thought much of the tiny tick I pulled from my ankle and flicked into the bush more than a week earlier. My wife and I had started our South African vacation with a couple nights of camping in the majestic and remote Drakensburg Mountains on the border of Lesotho. Ticks, I...

I’m not alone. Though it’s difficult to quantify, more visitors to sub-Saharan Africa have been returning home to Europe or America reporting symptoms of South African tick bite fever. “It’s a very common bug in a very common tick that very commonly bites human beings,” says Didier Raoult, infectious disease specialist at France’s Marseille School of Medicine and the world’s leading expert on R. africae.

The eschar, or lesion, that arose on my ankle, where the African tick bit me.

In the grand scheme of things, though, I should consider myself lucky. Genus Rickettsia contains some bacteria species that wreak far greater physiological havoc than the R. africae, instances of which appear to be on the rise.

Jennifer McQuiston, a veterinary epidemiologist who studies Rickettsial diseases at the US Centers for Disease Control and Prevention, says that reports of Rocky Mountain Spotted fever (RMSF), which can be deadly in some cases, have increased threefold in the United States over the past decade. McQuiston studied an “explosive outbreak” of the disease in Eastern Arizona that started in 2002 (NEJM, 335:587–94, 2005). She notes the infection rate in Arizona is about 50 times that seen nationally, and that since 2002, more than 80 cases of RMSF have cropped up in the state, where the disease was virtually unheard of prior to the 21st century. “It’s a hotspot area.”

Philippe Parola, tropical medicine director of the World Health Organization’s Collaborative Centre for Rickettsioses and other Arthropod Borne Bacterial Diseases in Marseille, and his collaborators have found that between 1996 and 2008, more than 230 feverish international travelers sought treatment at a network of infectious disease clinics around the world and were found to be infected with R. africae or similar bacterial species. Of these ill travelers, more than 80 percent picked up their tick-borne fever in sub-Saharan Africa. In fact, R. africae and its bacterial kin, classified as the spotted fever group Rickettsioses, are second only to malaria as the most commonly diagnosed illness in travelers returning home from sub-Saharan Africa.

In the last decade, Parola explains, diagnostic tools have made detecting and identifying African tick bite fever and other Rickettsioses much more reliable and facile. Now, physicians can identify the presence of R. africae in a patient’s bloodstream by directly detecting the bacterium’s DNA in the skin lesion associated with the tick bite. “We have specific tools that allow for more specific disease diagnoses.”

As my wife and I happily traversed Africa’s southernmost horn, R. africae set about incubating in my body and increasing its numbers, preparing to mount a full frontal assault on my unsuspecting vascular tissues. The teeming bacterial masses eventually made their way into the endothelial cells lining blood vessels throughout my body. Like other spotted fever group Rickettsioses, R. africae ’s modus operandi is to invade endothelial cells in the vascular system, eventually reproducing there until they reach a critical mass that ruptures those cells. By the time we made it back to Philadelphia, my fever was in full swing, vascular tissue in my lymph nodes and brain ravaged by R. africae ’s nefarious activities.

Though I felt like a man on the brink of insanity, McQuiston confirms that I was pretty lucky to get African tick bite fever and not one of its more virulent cousins. “[African tick bite fever is] one of the more fortunate Rickettsial illnesses to get.”

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