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DefensesDownMutation boosts West Nile risk

A genetic mutation has been identified thatincreases a person’s susceptibility to WestNile virus, a new study indi-cates. Ironically, this mutationhad previously been shown toprovide a barrier against HIV,the virus that causes AIDS.

The protein eliminated bythe mutation was previouslythought to be useless and evena liability. The new findingsuggests that it might be anessential weapon in fendingoff the mosquito-borne virus,says Philip M. Murphy, animmunologist at the NationalInstitute of Allergy and Infectious Diseasesin Bethesda, Md.

West Nile virus is most dangerous to eld-erly people and others who have compro-mised immune systems. Although 80 per-cent of infections go unnoticed, the viruscaused illness in 2,819 people in the UnitedStates in 2005, leading to encephalitis ormeningitis in 1,189 of them and killing 105,according to the Centers for Disease Con-trol and Prevention in Atlanta.

The mutation that has been implicatedin West Nile disease susceptibility shutsdown the production of a protein calledchemokine receptor-5 (CCR5). This pro-tein is the primary cell-surface receptorthat is commandeered by HIV, which usesit to enter white blood cells. The mutationthat prevents CCR5 production renders 1 percent of whites highly resistant toinfection by HIV but hasn’t been found inother races. Scientists had reasoned thatpeople were better off without CCR5.

In the new study, Murphy and his col-leagues worked with researchers in Ari-zona and Colorado to analyze blood andspinal-fluid samples from 395 people inthose states who had been infected withWest Nile virus.

The CCR5 mutation showed up in more

than 4 percent of the West Nile patients butin only 1 percent of 1,318 healthy blooddonors used as a comparison group, theresearchers report in the Jan. 17 Journal ofExperimental Medicine.

“This appears to be a reasonably carefulanalysis” of this mutation in people withand without West Nile infections, saysRichard A. Kaslow, an infectious-diseasephysician at the University of Alabama atBirmingham.

In people with the mutation, lacking theCCR5 protein may lead to “a brain infec-tion from West Nile that is not well con-trolled,” Murphy says.

In a study of mice reported in the Oct. 17,2005 Journal of Experimental Medicine,Murphy’s team found that all animalsgenetically engineered to lack CCR5 diedwhen exposed to West Nile virus. However,normal mice fended off the virus by pro-ducing extra CCR5 proteins on the surfaceof white blood cells, which were usheredinto the brain, where they protected against

the infecting virus. Several companies have

designed drugs aimed at block-ing CCR5, in an attempt to stopHIV from invading white bloodcells. The approach mimics theprotection against HIV con-ferred by the CCR5 mutation.The drugs are being tested inpeople.

The new findings suggestthat people taking the CCR5-blocking drugs to prevent orquell HIV infection may need

to take precautions to avoid West Nile dis-ease, Kaslow says. —N. SEPPA

Cosmic PushFinding pieces of a dark puzzle

Scientists call it the most elemental riddlein all of physics and astronomy: What’s tear-ing apart the universe by turning gravity’sfamiliar tug into a cosmic push?

Astronomers discovered the handiwork ofthis mysterious push, dubbed dark energy,8 years ago, when studies revealed that cos-mic expansion isn’t slowing down, as hadbeen predicted, but is speeding up (SN:5/22/04, p. 330). One of the leading theo-ries is that dark energy is distributed uni-formly in space and time—akin to the casefor what Albert Einstein called the cosmo-logical constant (SN: 12/17/05, p. 390).Understanding dark energy would unify theforce of gravity with the subatomic realm,providing deep insights into the origin andevolution of the universe, says cosmologistSean Carroll of the University of Chicago.

So, when a report last week indicatedthat dark energy behaves even morestrangely than researchers had suspected,it garnered extraordinary publicity—as wellas vehement reactions among researchers.The study, described by astronomer BradleySchaefer of Louisiana State University inBaton Rouge, indicates that dark energyvaries over time. The work suggests thatdark energy put the brakes on cosmicexpansion in the past but is now accelerat-ing it, Schaefer reported at the Januarymeeting of the American AstronomicalSociety in Washington, D.C.

SCIENCENEWSThis Week

2,819U.S. cases inwhich WestNile viruscaused illnessin 2005

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LIGHT ON DARK ENERGY NASA’s Swift Satellite records gamma-ray bursts, rendered hereby an artist, which a new study suggests provide a novel way to determine the nature of amysterious cosmic force.

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Such a universe would have some mind-bending properties, including a previouslyunsuspected force in nature generated by anunknown elementary particle. Further-more, Einstein’s well-supported theory ofgravitation would require major modifica-tions, adds Carroll.

The implications of Schaefer’s study areso provocative, says Carroll, that for now,“no one believes it.” He and others also ques-tion the data.

In fact, the most important aspect of thenew study, Schaefer and Carroll agree, is notthe result but the method used to get it. Thisis the first time that gamma-ray bursts, themost powerful explosions in the universe,have been used to analyze dark energy.

Schaefer acknowledges that his findingsaren’t as precise as those from more-estab-lished methods for studying dark energy.

Astronomers originally found evidencefor dark energy by using another, dimmertype of explosion known as a supernovatype 1a. Because gamma-ray bursts can beseen at much greater distances than super-novas can, they could, in theory, be used toprobe cosmic expansion at earlier times.Gamma-ray bursts vary in brightness muchmore widely than supernovas do, making itmore of a challenge to use them. To com-pensate, Schaefer took into account fiveproperties of 52 gamma-ray bursts to gaugetheir intrinsic brightness.

Gamma-ray bursts “hold great promise”for studying dark energy, says cosmologistDon Lamb of the University of Chicago, buthe adds that he disagrees with Schaefer’sanalysis of dark energy at large distances.Lamb’s team is doing its own study ofgamma-ray bursts and to date has found thatdark energy does indeed resemble the cos-mological constant, Lamb told Science News.

With satellites expected to find a wealthof gamma-ray bursts over the next few years,scientists will have an opportunity to deter-mine what these explosions can reveal aboutdark energy, says Schaefer. —R. COWEN

Dieting to Savea SpeciesMother parrots that eatless avoid excess of sons

Now that conservationists are countingcalories for the endangered, flightless par-rots of New Zealand, the birds are recover-

ing from a shortage of female chicks, biol-ogists report.

The world population of the kakapo(Strigops habroptilus), a hefty, nocturnal par-rot, numbers only about 86 birds, says BruceRobertson of the University of Canterbury inChristchurch, New Zealand. About 5 yearsago, conservationists realized that amongthe birds that they were tending, only 30 per-cent of the offspring were female. That’shardly the way to make a lot of new kakapos.

Using a bit of evolutionary theory calledsex allocation, researchers proposed thatfeeding the females less could shift themale-female ratio of chicks. Now, a geneticanalysis of chicks from the 2002 seasonshows that the scheme works, Robertsonand his colleagues report in an upcomingBiology Letters.

Kakapos once waddled all over New Zealand, but European settlers andtheir predatory animals found theground-dwelling, strong-scented birdseasy to catch. In the 1980s, conserva-tionists whisked the last 51 known kaka-pos to island sanctuaries.

The birds rummage along the ground forfern rhizomes and plants from which theysuck juices. Every few years, rimu trees burstout with a bumper crop of their tiny orangefruits, and the kakapos feast and lay eggs.

To boost reproduction, conservationistshad provided frequent feasts of apples andother treats. Females did plump up, andmore chicks tended to survive.

However, the improvement in femalecondition might have backfired, biologistsincluding Robertson and José Tella ofDoñana Biological Station in Seville, Spain,suggested at the beginning of the decade.A clue came from the mating system, inwhich kakapo males set up displays andfemales review them.

Kakapo males spend summer nights

meticulously clearing dirt patches wherethey then spend hours calling in females.Success in attracting a mate varies greatlyfrom one male to the next.

Sex-allocation theory predicts that insuch species, females will produce an abun-dance of sons when moms are fit and theirsons are likely to grow up capable of attract-ing mates. During hard times, puny sonsgenerally get shut out of fatherhood, so extradaughters are a better bet.

In 2001, wildlife managers put the heav-iest females on a restricted diet but contin-ued to feed the thin ones liberally. Robert-son and his colleagues now report that thediet indeed ended the excess of sons. Thefemales on short rations laid 9 male and 10female eggs, and the already lean femalesproduced 7 male eggs and 9 female ones.

“It’s a nice application of evolutionarytheory to conservation biology,” says Tim-othy Wright of New Mexico State Univer-sity in Las Cruces, who has also studied par-rot conservation. —S. MILIUS

Diabetes froma Plastic?Estrogen mimic provokesinsulin resistance

Exposure to small amounts of an ingredi-ent in polycarbonate plastic may increase aperson’s risk of diabetes, according to a newstudy in mice.

The synthetic chemical called bisphenol-A isused to make dental sealants, sturdymicrowavable plastics, linings for metal food-and-beverage containers, baby bottles, andnumerous other products. When consumed,the chemical can mimic the effects of estro-

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CREATURE OF THE NIGHT The kakapo parrot, which can weigh more than 1.5 kilograms,forages during darkness. The birds can live about 60 years.

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