Over the past decade or so, tens of thousands of the great apes have died of Ebola in central Africa, along with similar numbers of chimpanzees. That the disease was responsible was established in a paper published in December in Science. Now a report in the American Naturalist explains just why Ebola is spreading among the animals so furiously--and shows how it could be stopped, according to lead author Peter Walsh of the Max Planck Institute for Evolutionary Biology in Leipzig, Germany. The epidemiological tactics used to treat outbreaks of human scourges like E. coli hold the answer.ニシローランドゴリラはいずれエボラによって絶滅するかもしれない。まさに、エボラの感染拡大という"自然の成り行き"による種の絶滅を目撃する日も遠くないかもしれない。
Ebola is transmitted by contact with body fluids, and it's rapidly fatal. When people get it, they become so sick so fast--their organs literally liquefy--that others try to stay away from them. What's more, the mere fact of their quick immobility means they can't carry the virus very far. Ebola usually burns through an isolated village or community and then has nowhere else to go.
エボラは体液の接触によって感染し、急速に死に至らしめる。人間が感染すると、急激に病気になり、肉体は文字通り融解する。なので、他の人々は感染者に近づく時間がない。さらに、急速に死に至るために、ウィルスを遠くまで運べない。エボラは孤立した集落やコミュニティを破滅させて、そこからどこへも行けずに終わる。
"People always assumed it was the same for gorillas," says Walsh. This belief made particular sense since gorillas live in relatively compact packs that don't interact much with other packs. Ebola, however, is oddly aggressive in great apes, ignoring pack boundaries and advancing across great-ape habitats at a rate of about 29 miles a year. Heading into the field to study the outbreaks, as well as animal behavior that could be contributing to them, Walsh and his team soon cracked the mystery
「人々は、ゴリラも人間と同じだと考える」とWalshは言う。ゴリラは比較的小さな集団で生活し、集団の間で相互作用はないので、そう考えることに意味が出てくる。しかし、奇妙なことにエボラはゴリラでも集団の境界を越えて、年間29マイルの速さで、感染を広めている。アウトブレークおよび動物の行動のフィールド研究が、この謎の解明に役立つかもしれない。Walshの研究チームはすぐに、この謎を解明した。
.... Western gorillas, by contrast, live mostly on fruit, a scarcer resource that draws different groups of gorillas and chimpanzees to the same trees at different times of day. "They defecate and urinate in and around the trees," says Walsh, leaving infected body fluids to sicken the next group. Gorillas also examine the bodies of dead apes they come upon, perhaps because they're smart enough to want to know if whatever claimed that life is a threat to them. This provides another means of direct transmission.
ニシローランドゴリラは大半は果物で生きており、果樹が乏しいために、複数のゴリラの集団やチンパンジーの集団が、同じ果樹を違う時間帯に利用している。「彼らは、果樹のまわりで、うんこやおしっこをする。残された液体によって、次にやってきた集団への感染が広まる。」とWalshは言う。ゴリラは知能が高く、死因を知ろうとして、類人猿の死体を調べようとする。これが直接的な感染経路になる。
[Why Ebola is Killing Gorillas (2007/04/26) on TimeCNN]
絶滅を防ぐ方法として、Walshは感染地域に隣接する領域に棲息するゴリラの集団への予防接種の有効性を指摘している：
Instead, epidemiologists can use selective-vaccination techniques, which work with human communities when universal vaccination isn't practical. Just inoculate a few gorilla groups along the infection chain, and when the virus reaches them, it is stopped cold.
"We're not talking about massive vaccination anymore," says Walsh. "We're talking about getting a vaccine into key gorilla populations." And the cost? Perhaps as little as $2 million--chump change, Walsh calls it, to save our closest evolutionary kin from extinction.
