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Plague as a weapon

April 10, 2007
Courtesy The Lancet
and World Science staff

Sci­en­tists are wor­ried that a dis­ease as­so­ci­at­ed with dev­as­tat­ing me­di­e­val epi­demics may make a come­back as a weap­on.

An ar­ti­cle in this week’s is­sue of the med­i­cal jour­nal The Lan­cet dis­cusses the pos­si­bil­i­ty that the bac­te­ri­um re­spon­si­ble for plague—known in the Mid­dle Ages as the Black Death—could serve as a bioter­ror­ism agent. 

Shoot­ing dead­ly ar­rows, a shad­owy fig­ure of death seals the fates of plague vic­tims in this anon­y­mous 15th-century paint­ing, Al­le­go­ry of the Plague.

Infections from the mi­crobe, Yer­si­nia pes­tis, take sev­er­al forms.

In the ar­ti­cle, Mike Pren­tice of Uni­ver­si­ty Col­lege in Cork, Ire­land and Li­la Ra­hal­i­son of the Pas­teur In­sti­tute in An­ta­na­na­ri, Mad­a­gas­car, re­viewed the bac­te­ri­um’s ge­net­ic make­up, his­to­ry and modes of trans­mis­sion.

The mi­crobe mul­ti­plies in fleas that have fed on in­fected an­i­mals’ blood. This causes a block­age in the flea’s feed­ing sys­tem that makes the flea con­tin­u­al­ly re­gur­gi­tate and feed again, de­liv­er­ing the germ in­to the blood of what­ev­er it is bit­ing—of­ten a ro­dent or a hu­man.

Bu­bon­ic plague, the most com­mon form, has a sud­den on­set and causes diz­zi­ness, high fe­ver, pain­ful swellings and hemmhor­ages. These some­times turn black, ac­count­ing for the name Black Death. The most wide­spread ep­i­dem­ic is es­ti­mat­ed to have killed three quar­ters of the pop­u­la­tion of Eu­rope and Asia af­ter start­ing in Con­stan­ti­no­ple in 1334.

An­oth­er form of in­fec­tion, pneu­mon­ic plague, is quick­ly fa­tal and is the on­ly type di­rect­ly trans­mis­si­ble from per­son to per­son, by air droplets re­leased dur­ing cough­ing or sneez­ing.

Plague’s abil­i­ty to spread via droplets makes pos­si­ble aerosol-based weap­ons ca­pa­ble of caus­ing wide­spread pneu­mon­ic plague out­break, ac­cord­ing to Pren­tice and Ra­hal­i­son. Ex­ac­er­abat­ing the dan­ger, they added, is the bac­te­ri­um’s wide dis­tri­bu­tion, ease of cul­tur­ing, and availa­bil­i­ty of ex­pert ad­vice from form­er weap­ons sci­en­tists.

The dis­ease still pre­vails in parts of Asia and spo­rad­i­cal­ly oc­curs else­where; an es­ti­mat­ed 2,500 cases are re­ported an­nu­al­ly.

Un­treat­ed bu­bon­ic plague kills 50 to 90 per­cent of vic­tims, the re­search­ers said, though time­ly di­ag­no­sis and ther­a­py cut those per­centages to be­tween five and 15. An­tibi­otics are ef­fec­tive, but a Y. pestis strain in Mad­a­gas­car shows dis­turb­ing signs of hav­ing evolved re­sist­ance to some of these, they added. Some vac­cines are in de­vel­op­ment, one of which has reached phase II tri­als, the mid­dle stage in the clin­i­cal tri­als pro­cess.

Plague con­trol efforts in­volve mon­i­tor­ing and re­duc­ing ro­dent pop­u­la­tions where plague per­sists, the re­search­ers wrote. But “re­moval of the fleas’ nor­mal food sup­ply by poi­son­ing their usu­al hosts can in­crease hu­man con­tact with starv­ing fleas,” they added. Thus, “flea con­trol by ap­pli­ca­tion of in­sec­ti­cides in plague out­break ar­eas is al­so im­por­tan­t.”

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Scientists are worried that a disease associated with devastating medieval epidemics may make a comeback as a weapon. An article in this week’s issue of the medical journal The Lancet discusses the possibility that the bacterium responsible for plague, known in the Middle Ages as the Black Death, could serve as a bioterrorism agent. The microbe, Yersinia pestis, causes several types of infections. In the article, Mike Prentice of University College in Cork, Ireland and Lila Rahalison of the Pasteur Institute in Antananarivo, Madagascar, reviewed the bacterium’s genetic makeup, history and modes of transmission. The microbe multiplies in fleas that have fed on infected aminals’ blood. This causes a blockage in the flea’s feeding system that makes the flea continually regurgitate and feed again, delivering the germ into the blood of whatever it is biting – often rodent or human. Bubonic plague, the most common form, has a sudden onset and causes dizziness, high fever, painful swellings and hemmhorages. These sometimes turn black, accounting for the name Black Death. The most widespread epidemic is estimated to have killed three quarters of the population of Europe and Asia after breaking out in Constantinople in 1334. Another form of infection, pneumonic plague, is quickly fatal and is the only type directly transmissible from person to person, by air droplets released during coughing or sneezing. Plague’s ability to spread via droplets makes possible aerosol-based weapons capable of causing widespread pneumonic plague outbreak, according to Prentice and Rahalison. Exacerabating the danger, they added, is the bacterium’s wide distribution, ease of culturing, and availability of expert advice from former weapons scientists. The disease still prevails in parts of Asia and sporadically occurs elsewhere; an estimated 2,500 cases are reported annually. Untreated bubonic plague kills 50 to 90 percent of victims, the researchers said, though timely diagnosis and therapy cut those percentages to between five and 15. Antibiotics are effective, but a Y. pestis strain in Madagascar shows disturbing signs of having evolved resistance to some of these, they added. Some vaccines are in development, one of which has reached phase II trials, the second of three stages in the clinical trials process. Plague control strategies involve monitoring and controlling rodent populations where plague persists, the researchers wrote. But “removal of the fleas’ normal food supply by poisoning their usual hosts can increase human contact with starving fleas,” they added. Thus, “flea control by application of insecticides in plague outbreak areas is also important.”