Lassa fever: Coming to an airport near you

Out of all the scary diseases, none seem to make people horripillate quite as much as the viral hemorrhagic fevers: Ebola, Lassa, Marburg and the rest. That might be due to their still-murky origins, crossing over from the edges of the world of animals into the infringing habitats of men. It might be their uncomfortable classification in biosafety level 4, reserved for life-threatening infections that spread by fine exhaled aerosols and for which there is no vaccine and no treatment. (Four is the highest level. There is no 5.) Probably it is due in part to the enduring impact of the 15-year-old book The Hot Zone by Richard Preston, which in its early pages conducts a master class in describing truly revolting symptoms:

He is holding an airsickness bag over his mouth. He coughs a deep cough and regurgitates something into the bag. The bag swells up. Perhaps he glances around, and then you see that his lips are smeared with something slippery and red, mixed with black specks, as if he has been chewing coffee grounds. His eyes are the color of rubies, and his face is an expressionless mass of bruises. The red spots, which a few days before had started out as starlike speckles, have expanded and merged into huge, spontaneous purple shadows: his whole head is turning black-and-blue.

The cultural response to the viral hemorrhagic fevers has always struck me as interesting. They’re terrifying, and yet we love to hear about them, in a Scary Stories to Tell in the Dark kind of way. When I’ve asked people why the fascination (because I, myself, am much more frightened of parasites, thanks to Carl Zimmer. And brain amoebas), they usually say back to me that it feels like a don’t-leave-the-campfire fright, a safe fright — because, you know, Ebola is over there somewhere. It’s not like it’s coming here.

The problem with that is that VHFs do come here. Actively infectious VHF has been diagnosed in the United States at least six times — most recently in January, in Philadelphia.

The latest issue of Emerging Infectious Diseases describes the case: a 47-year-old man from Liberia who has been living in the US but went home for a week for a visit. He started in the capital, Monrovia, and then spent five days in his home village on the rural northern border, sleeping in a hut. There were rats running through the hut, and a few dead rats on the floor. On the day he left, he started to have fever and chills, and his joints hurt. He made the natural assumption that he was having a bout of malaria, and started taking chloroquine and  amoxicillin. He flew back to the US, continued to feel sick, and on the fifth day of his symptoms went to a hospital in Philadelphia with a 103 degree fever, a mildly elevated pulse, and swollen lymph nodes in his neck.

Just as in Africa, the initial assumption was that the man had malaria, until a blood test turned up negative and a diagnostic blood smear showed no sign of parasites. By the third day, between his travel history and his symptoms, the hospital staff started to suspect a VHF. By the fifth day, thanks to a PCR result, they had proof of their suspicions: The traveler had Lassa hemorrhagic fever.

If you had to catch a VHF, Lassa might be your preference: It kills only about 2 of every 100 people who contract it, compared to 50 or more of those who contract Ebola. But it spreads person to person, and it has spread in hospitals, where its case-fatality rate can be closer to 20 percent.

There was no spread in the Philadelphia hospital. In fact, when disease detectives traced the man’s 140 contacts — the health care workers who took care of him, the travelers who sat next to him, his family in the US, his wife at home in Africa, whom he had sex with during his visit — no one developed the telltale symptoms. All of them remained well. The man himself recovered, and was discharged from the hospital 21 days after first falling ill.

There was also no confirmed spread in 1989, when an American citizen who was born in Nigeria went home for his mother’s funeral — she too had been thought to have malaria — contracted Lassa, returned to suburban Chicago, and died. Including his wife and six children, who did receive drugs prophylactically, 102 people were thought to have been exposed. Equally, there was no spread in 2004, when a man of Liberian origin who went home frequently to manage some agricultural properties came back to New Jersey with a high fever, chills, diarrhea and back pain, so sick that he was hospitalized hours after his arrival. He died very quickly and Lassa was identified by post-mortem. When his route was retraced — he had changed planes in London — 188 people were identified as possible contacts. None of them fell ill.

Because I’m curious about how people react to the idea of contagion as well as to actual diseases, I find it interesting to tease out the lessons in these stories, especially the most recent one. There’s the permeability of national borders to pathogens: We are, truly, only a plane ride away from anything. There’s the necessity of training doctors to recognize tropical diseases; in the Philadelphia case, Lassa was on the differential diagnosis, the list of possible causes, by about hospital day 3.

More than anything, though, I wonder about what we allow, and even invite, to frighten us. Lassa, true, is not Ebola — and the Ebola outbreaks in Africa (Gulu in 2000, Kikwit in 1995) were horrific. But they were also contained. We spend a lot of energy, collectively, confronting the disease equivalent of monsters under the bed. Maybe it’s time to realize how often they are only shadows, and to turn our attention to the real killers instead.

Cite: Amorosa et al., Emerging Infectious Diseases, 2010. DOI: 10.3201/eid1610.100774

Image courtesy Flickr user daliborlev under CC


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