Local surfers and fishermen say they cannot remember any shark attacks off the palm-fringed beaches of Recife before 1992. Then suddenly they started. In 1994 alone, there were 11 attacks along a 10-kilometre stretch of coast. The sharks go mainly for surfers, though three swimmers have also been attacked, all of them outside the coral reef which shelters most of the beaches.

Researchers believe that surfers are more susceptible to shark attacks because of the movements they make on the surface of the water while waiting for waves, and because they spend more time in deep water.

The first response of the local government was to put up signs in Portuguese and English which said: “Surfers, be cool! Respect natural boundaries. Do not go beyond the reef.” But the signs neglected to mention sharks. Local oceanographer Fabio Hazin accused the government of “hiding its head in the sand”. Locals began spray-painting sharks onto the signs, and surfers held a protest on the beach, complete with a bloody, mauled mannequin.

When the new state government came into power in January, it promptly banned surfing, and bolstered Hazin’s shark research efforts at the Federal Rural University of Pernambuco. Since the crisis began, Hazin’s team has caught more than 200 sharks in order to study their behaviour and life cycle. The shark meat is donated to feed hungry local children. Meanwhile, police have begun patrolling the beaches, confiscating boards from surfers who defy the ban.

“What is happening in many areas of the world is that aquatic recreation is beginning to take off, and so shark attacks are more frequent,” says George Burgess, director of the International Shark Attack File at the University of Florida in Gainesville. The recent spate of shark attacks off popular beaches in Hong Kong supports this view. However, Brazilian surfers have been holding championships off the beaches near Recife since the 1970s, so the increase in surfing cannot entirely explain the sudden surge in shark attacks.

In a preliminary unpublished report, Hazin and his colleagues point an accusing finger at the Port of Suape, built in 1989 just south of the three beaches where most of the attacks have occurred. The port may be bringing people and sharks into closer contact, they say. The researchers found a correlation between months when there are more passing ships, and months when there are shark attacks. Sharks are known to follow big ships, especially if sailors are dumping rubbish overboard. Hazin’s team has found an onion, a pineapple and a can of beer in the stomachs of local sharks.

From the imprint in a bite-shaped piece of styrofoam bodyboard, the biologists have identified one of the culprits as a bull shark, although there is also evidence that tiger sharks are responsible for some attacks.

The Brazilians are now seeking advice on whether to install safety nets around the beaches of Recife. Gill nets, which kill sharks but also kill dolphins and turtles, seem to have kept attacks to a minimum in Australia and off South African beaches near Durban. Hard plastic exclusion nets, which enclose a beach and keep the sharks out without killing them, only work in calmer waters, according to Geoffrey Cliff of the Natal Sharks Board.

Educating local surfers to avoid going out at dawn and dusk when the sharks are most active, to avoid water where there are birds diving and fish jumping, and to avoid channels where sharks tend to congregate, may help.

This type of advice, however, may simply be water off a surfer’s back. “Those surfers who get bitten by sharks here wear their scars as a badge of honour,” says Burgess. “The more dangerous they think it is, the more attractive surfing is for some people,” says Hazin. “I try to emphasise that they’re not only risking their lives, they’re damaging the state economy.”

��è����Ƶs had long wondered at what point in sperm formation the male
sex cells become capable of fertilising an egg. ‘We wanted to know how
far back we could go,’ says Ryuzo Yanagimachi, a reproductive biologist
at the University of Hawaii School of Medicine in Honolulu. In the testes,
spermato-cytes – the earliest sperm cells – divide by meiosis to halve their
complement of chromosomes. So when the mature sperm fuses with an egg, carrying
a second half-set of chromosomes, the fertilised egg will have a complete
set. The round spermatids are the first stage after meiotic division.

Last year, Yanagimachi and his colleagues, Atsuo Ogura and Junichiro
Matsuda of Japan’s National Institute of Health, reported that they had
been able to fertilise mouse and hamster eggs with these round spermatids
by fusing them using an electrical pulse, or by injecting the spermatid
into the egg with a micropipette. In the current issue of the Proceedings
of the National Academy of Sciences, they report that four of these fertilised
eggs developed into apparently normal offspring. Since they submitted their
paper for publication, they have produced at least 15 more offspring.

The fact that eggs fertilised by this technique produce offspring that
appear normal is significant because researchers were not sure at what stage
in sperm formation the chromosomes in the nucleus became imprinted, a chemical
transformation that marks the chromosomes as coming from the male, and is
necessary for the development of the placenta among other things. ‘By using
round spermatids you’re snatching up something halfway through a process,’
says J. Michael Bedford, an expert in male reproduction at Cornell University
Medical College. Bedford says the new experiments have a ‘nice absolute
elegance to them. The results imply strongly that everything that happens
to that cell once meiosis is completed has to do solely with the mechanics
of getting the male sperm into the egg.’

The field of male fertility is gathering momentum. Some men are infertile
because they have too few sperm, their sperm swim too slowly, or cannot
penetrate the egg. In the past two years, fertility specialists have begun
to offer treatment in which a single sperm is injected into an egg, which
is then returned to the womb. Last year, researchers reported that this
technique, called intracytoplasmic sperm injection, or ICSI, had been used
successfully in cases where the man had no sperm in his ejaculate, but researchers
were able to take sperm directly out of the testes. This procedure, called
testicular sperm extraction, or TESE, was developed by Sherman Silber, director
of the infertility clinic at St Luke’s Hospital in St Louis, Missouri, and
researchers at the Free University of Brussels.

Silber says that the birth of Yanagimachi’s mice is ‘just fantastically
important’ to experts in male fertility. With ICSI and TESE, says Silber,
‘we have solved the infertility problem for 98 per cent of men. But for
the other 2 per cent, it’s incurable.’ In these 2 per cent, which represents
about 8000 men in the US, there are no mature sperm, even in the testes.
Silber hopes these men could be helped by Yanagimachi’s research. Although
most of these men do not even produce spermatids, Silber and Yanagimachi
believe that eventually they will be able to find a way to induce meiosis
in spermatocytes in culture, and then use the resulting spermatids to fertilise
an egg.

Last week, the US National Academy of Sciences advised that if the exiled
people of Rongelap choose to go home, they will have to make changes to
their traditional way of life. Instead of living off the land, they should
eat at least some imported food, and use special fertiliser to reduce the
amount of radioactivity that accumulates in locally grown food.

‘The people of Rongelap have obviously been traumatised by their involuntary
involvement in nuclear testing,’ says the academy’s report. In 1957, after
being treated for radiation sickness and subjected to extensive testing,
the people of Rongelap were taken back to their atoll with an assurance
from the US government that the radioactivity had declined to safe levels.
But, as the years passed, they grew increasingly alarmed about the high
rates of cancer and other health problems in the islands.

In 1985, with the US government still telling them it was safe to stay,
the people of Rongelap went into exile for a second time. Greenpeace evacuated
them on its ship Rainbow Warrior to a more crowded and urban life on Kwajalein,
another atoll 300 kilometres away. The evacuees have remained there for
the past nine years. ‘The older generation, in particular, still wants to
go back,’ says Banny de Brum, charge d’affaires at the Marshall Islands
embassy in Washington DC. ‘They were close to their land. And they have
limited resources living where they are now.’ There are now about 1000
descendants of the people who were living on Rongelap at the time of the
nuclear tests, and Marshallese officials say that about 400 would like to
go home.

The academy’s report was commissioned in an attempt to reassure the
people of Rongelap that the Department of Energy (DOE) is using good science
in preparing for the return of exiled people to the atoll. The Republic
of the Marshall Islands has also commissioned its own scientific review,
which should be completed in the next few months. ‘They trusted the US
in the past,’ says Holly Barker of the Marshall Islands embassy in Washington.
‘People have been told over and over again that it’s okay to live on these
islands. I’m not sure whether a scientific study done by a group of people
in the US will be that reassuring at this point.’

The US would like the people of Rongelap to go home, and they want to
return. But they will only go if the US can assure them that no one will
receive more than 100 millirems (1 millisievert) above the dose received
from background radiation. James Neel, a human geneticist from the University
of Michigan in Ann Arbor and chairman of the committee that wrote the academy’s
report, describes this standard as ‘rather stringent’. The committee said
that unless remedial action was taken, people returning to the island now
could receive doses above this level.

More than 90 per cent of the radiation dose that people on Rongelap
are likely to receive will come from caesium-137 in the soil and plants.
But the panel advises against stripping the topsoil from the island, ‘owing
to the fragile ecology’. Instead, it recommends removing a layer of soil
around the central village and each house and putting down a layer of crushed
coral.

The committee also says that if people are to live safely on Rongelap,
they will have to make adjustments to their traditional way of life. It
recommends a diet in which about half the calories come from imported foods,
and warns against too much coconut. Coconut meat and milk play a large role
in the traditional Marshallese diet, but caesium collects in coconuts. To
try to reduce the amount of radioactive caesium in coconuts and other wild
fruits, the committee recommends applying potassium chloride fertiliser
on the island. Coconut palms and other plants take up potassium in preference
to caesium.

The committee also suggests that people should be forbidden to gather
food in the northern islands of Rongelap and the neighbouring Rongerik atoll,
which are most heavily contaminated. Traditionally, people visited these
northern islands to collect the coconut crab, a land crab which accumulates
high concentrations of caesium. Even with these precautions, the report
recommends that anyone who returns to Rongelap should have a yearly whole-body
radiation count and provide a urine sample to assess their exposure to plutonium.

The report acknowledges that there is a ‘degree of distrust of information
received from DOE’ among the people of Rongelap. The Marshallese have maintained
for decades that they were deliberately exposed to fallout, and returned
to a contaminated island too soon. They believe that they now have proof
– contained in 28 boxes of documents turned over to them by Hazel O’Leary,
Secretary of Energy, under her department’s ‘openness initiative’.

With the information that has come to light in the past few months,
the Republic of the Marshall Islands is making a bid to have its case considered
by President Clinton’s Advisory Committee on Human Radiation Experiments.
The committee was formed to decide how victims of radiation experiments
should be compensated. However, it has said that it will not take up the
cases of people accidentally exposed during nuclear testing. So the Marshallese
must convince the committee that their exposure was premeditated, and that
it therefore constituted a medical experiment.

Marshallese Senator Tony de Brum told the committee earlier this month
that the documents declassified by the energy department prove that the
US government has repeatedly lied to the Marshallese, and withheld crucial
information during the negotiations which ended the US trusteeship of the
Marshall Islands in 1983.

One key to their case lies in documents discussing Project 4.1, described
as a study of the response of human beings to radioactive fallout. According
to de Brum, the documents make it clear that the project was planned the
year before the Bikini blast that contaminated Rongelap. Marshallese from
Rongelap and two other atolls evacuated after the detonation were described
as ‘subjects’ in the study. When a preliminary report on Project 4.1 was
issued, it referred instead to human beings ‘accidentally exposed’ to fallout.

The Pasteur Institute in Paris has been arguing for a larger share of
the royalties since 1991, when Gallo acknowledged that the strain of HIV
used in developing the diagnostic test probably came from the French laboratory.

Under an agreement made in 1987, France and the US were entitled to
take 20 per cent of the royalties from sales of the kits in their own countries.
The remainder of the royalties have been pooled, with 25 per cent going
to the World AIDS Foundation, which funds AIDS research in the developing
world, and the rest split equally between the US and France. Under the new
agreement, France will receive 50 per cent of the pooled royalties and the
US 25 per cent; the World AIDS Foundation will continue to receive 25 per
cent.

According to Harold Varmus, the director of the NIH, the new formula
is intended simply to ‘remedy an imbalance’. So far, the US has earned about
$20 million in royalties and the Pasteur Institute $14 million. Varmus claims
that the intention had always been to share the royalties equally, but that
the difference in the number of kits that would be sold in each country
was not taken into account when the 1987 agreement was drawn up. Under the
new agreement, the US and France should have earned about the same amount
in royalties by the time the patents expire in 2002.

The head of the Pasteur Institute, Maxime Schwartz, is more circumspect.
He says that while he is satisfied with the agreement, ‘it would not be
illogical for Pasteur to get more or even all’ of the pooled royalties from
sales of the test kit. However, the agreement was probably the best the
institute would get without going to court, he says. ‘The process would
have been very long and costly and relations with the NIH have been poisoned
enough,’ he says.

For Schwartz, the most important aspect of the agreement is official
recognition from the US that the strain of virus used to develop the test
kit came from the Pasteur Institute. Failure to acknowledge the Pasteur
Institute’s role would have been a serious obstacle to the future exchange
of information and samples between scientists. ‘The conflict has made people
more careful.

In an attempt to prevent the decline of these species, Russell Greenberg
of the Smithsonian Institution’s Migratory Bird Center in Washington DC,
is trying to convince coffee companies to market a ‘bird-friendly’ brand
of coffee, grown only on shaded plantations.

Four years ago, Greenberg and several colleagues calculated that populations
of North American birds that winter in the Caribbean and Latin America
were declining by 1 per cent a year – mainly because their habitat was
disappearing. Greenberg’s research team set out to determine which types
of agricultural land would serve as habitats for birds.

They found that coffee and cocoa plantations, along with other cultivated
wooded areas such as acacia plantations, are the only habitats left for
many birds in some areas of Central America, the Caribbean and Colombia.
Almost half the permanent cropland in these countries consists of coffee
plantations.

Over the past two years, Greenberg and his colleagues have counted more
than 180 species of bird on traditional ‘shade’ coffee plantations in the
Ocosingo area of the state of Chiapas, Mexico. Many coffee growers there
are indigenous Maya Indians who have small ‘rustic’ plantations, shaded
by the only remaining pockets of original forest in the area. Other growers
provide shade by planting new trees.

Both new and old forest on coffee plantations provide refuges for migratory
birds and local birds. Among the migratory birds the team spotted were American
redstarts, black-throated green warblers, solitary vireos and Baltimore
orioles. Year-round residents include parrots and toucans.

However, an increasing number of coffee growers in many countries, including
Costa Rica and Colombia, have cut down the trees to grow ‘sun’ coffee. Coffee
grown in full sun produces higher yields, at least initially. But it also
requires more weeding, and more chemical fertilisers and pesticides. In
contrast, shade trees help to fix nitrogen in the soil, prevent erosion,
contribute natural mulch, and provide habitat for forest animals.

The bird study was ‘rudely interrupted’ in January during the uprising
in Chiapas, says Greenberg. One of his colleagues was mistaken for a rebel
leader by the Mexican secret police, who confiscated the computer discs
from the bird project. ‘The police thought they were the war plans,’ says
Greenberg. Luckily, the researcher had buried a copy of the data.

Greenberg believes that ‘there is a growing constituency of people,
mostly bird-watchers, who want to do something for migratory birds but they
don’t know what to do’. Many have called the Migratory Bird Center to ask
where they can buy bird-friendly coffee. The answer is nowhere – yet. But
the most fashionable purveyor of upmarket, speciality coffees in the US,
Starbucks of Seattle, has given Greenberg’s proposal a ‘polite’ reception.

Although it is not labelled bird-friendly, much of the coffee consumed
in the US is still grown on shaded coffee plantations. Greenberg’s first
goal is simply to identify ‘shade’ coffee as such so that consumers can
choose bird-friendly brands. This should give coffee importers an incentive
to buy from growers on traditional plantations. ‘We should be paying people
more to grow coffee in an ecologically correct way,’ says Greenberg.

El Nino has been implicated in weather changes around the world. But
the team led by Mark Cane at the Lamont-Doherty Geological Observatory
in New York was ‘astonished’ at how strong the effect seems to be, so far
away in southern Africa.

In this week’s Nature, Cane and his colleagues report that they can
predict more than 60 per cent of the variation in the yield of maize in
Zimbabwe from measurements of the sea surface temperatures in the eastern
equatorial Pacific. By teaming up with Roger Buckland, a food security expert
with the Southern African Development Community in Zimbabwe, the scientists
found that the model they have for predicting the changes in ocean temperature
could forecast the Zimbabwe maize crop with ‘significant skill’, in time
to warn the farmers before the planting season.

No one understands precisely how El Nino influences the weather in
Africa. Nor do the researchers know why the correlation between temperature
change and crop yield is stronger than that between temperature change and
rainfall. They suggest that because farmers grow just a few hybrid varieties
of maize, there is a tendency for the entire crop to either succeed or fail
and that this amplifies the effect of good or poor rains. Changes in air
temperature, or in the timing of the rainfall, might also influence the
crop. Another theory is that the population of fieldmice that feed on maize
might be affected by the weather.

‘The beauty of this study is that in spite of the fact that we have
a relatively poor understanding of the mechanism, we can nevertheless predict
the maize yield with pretty astonishing skill,’ says Cane’s colleague, Gidon
Eshel.

The researchers have enough confidence in their model to urge that predictions
based on El Nino be passed on to African farmers. Their goal is to end costly
and frantic relief efforts, such as were needed in 1991 and 1992 when southern
Africa suffered its worst drought this century. ‘We’re not trying to blame
anybody. But we are saying that given the forecasting scheme we have now
we could have predicted that drought,’ says Eshel. Forewarned, farmers
can help to avert famine by switching to drought-resistant crops.

According to Cynthia Rosenzwieg, an agronomist with Columbia University
and NASA, it is time to put the findings to practical use in forecasting.
However, she urges caution, especially in view of the modellers’ failure
to predict the unusual length of the current El Nino, now in its third year.
‘Care has to be taken as we move into the real world,’ says Rosenzwieg.
‘We’re talking about people’s livelihoods here.

Djerrasi’s proposal was inspired by a chance meeting with Stanley Leibo,
a cryobiologist at Ontario Veterinary College in Guelph. ‘At least 50 million
head of cattle a year are inseminated with frozen bull sperm,’ says Leibo.
He and his colleagues recently thawed out the 37-year-old semen from a bull
and found the sperm still swimming vigorously.

Djerassi and Leibo acknowledge that men would have to be convinced that
long-term storage of human sperm is reliable. So they propose that the military
should begin a massive sperm banking programme – without the vasectomies
at first – in order to test the idea of freezing and storing semen on a
grand scale. Djerassi says the banked sperm would also serve as ‘genetic
insurance’ for soldiers whose fertility might be impaired by chemical weapons.

Leibo and Djerassi, who air their ideas in this week’s issue of Nature,
say bar-code labels and techniques such as the polymerase chain reaction,
which allows scientists to identify specific fragments of DNA from tiny
samples, would ensure that sperm deposits do not get mixed up. Leibo says
the success in keeping track of semen samples from livestock should give
men confidence. ‘From an emotional and philosophical viewpoint, the effects
of a mix-up might not be the same in bulls as in humans,’ says Leibo. ‘But
I assure you that a breeder of prize cattle would be just as upset if the
cows were inseminated with the wrong semen.’

Arthur Caplan, a bioethicist at the University of Pennsylvania, is very
sceptical. ‘The chance of this being a popular approach to birth control
is zero,’ he says. Men would not trust the government with their sperm,
nor would they trust private enterprise, says Caplan. ‘What if you don’t
pay your frozen sperm storage premium one year?’ he asks. ‘ What if United
Sperm Technologies goes out of business? Let’s just say I don’t think it’s
a fertile idea.’

Djerassi, who is based at Stanford University, has been advocating more
research into male contraceptives for decades. ‘The burden of contraception
has fallen on women,’ he says. Yet his proposal would put women through
the unpleasant procedure of artificial insemination. There is also the question
of a possible association between vasectomies and prostate cancer, which
has still not been ruled out.

Djerassi says his method is not for everyone. He admits that such a
high-tech method of contraception will be of no use in developing countries.
And in promiscuous young men, substituting vasectomies for condoms would
increase the risks of spreading sexually transmitted diseases.

In the end, the idea may be doomed simply because young men resist the
idea of vasectomies. Leibo acknowledges that many men believe that a vasectomy
‘will somehow or other interfere with their, quote, manhood’.

In infected humans, adult schistosomes produce a thousand eggs a day,
which clog up the bladder, liver and intestines. The disease kills 750 000
people a year. Some eggs are passed in the urine and faeces, and if they
find their way into freshwater, they hatch into larvae which take up residence
in freshwater snails. The larvae pass through several stages in the snail,
eventually leaving to find a new human host. In the water, they need only
come into contact with human skin, when they burrow through into the bloodstream.

Biologists Armand Kuris of the University of California at Santa Barbara,
Sam Loker and Bruce Hofkin of the University of New Mexico, and parasitologist
Gerald Mkoji of the Kenyan Medical Research Institute in Nairobi, plan to
introduce the crayfish (Procambarus clarki) into ponds, canals and cattle
tanks in three villages where the disease is endemic.

They plan to test the effectiveness of the scheme by deworming 100 children
in each of six villages: the three with the crayfish and three controls.
The drug praziquantel is effective against schistosomiasis but is too expensive
for most Africans.

The crayfish’s predilection for the snails was discovered by chance.
Louisiana crayfish were introduced into Kenya some 25 years ago to start
what is now a thriving export industry. But at some point, the penned crayfish
escaped. In the late 1980s, Loker and Hofkin noticed that snails which carry
schistosome larvae had gone from waterways inhabited by the crayfish. Kuris
says the crayfish eat the snails ‘like popcorn’.

The researchers now want to stock isolated water sources where most
infections are transmitted. The animals will come from local crayfish farms.

Aklilu Lemma, a visiting professor at the department of immunology and
infectious diseases at Johns Hopkins University in Baltimore, remains sceptical
about using predators to control schistosomiasis. He says the snails are
so small that they can hide in the mud. ‘It’s enough to have a few infected
snails left to transmit the disease,’ he says. Lemma has discovered that
a chemical in the soapberry plant (Phytolacca dodecandra), which is native
to Ethiopia, can kill molluscs. He intends to test the chemical next summer.

Donald Heyneman, a parasitologist at the University of California at
San Francisco, calls the crayfish plan ‘a worthy effort’, but worries about
the risks of introducing the crayfish to areas beyond Kenya where they could
prey on fish and amphibians.

The crayfish trial, which is being funded by the US Agency for International
Development, has been approved by the Kenyan government. Kuris is well aware
of the risks of releasing a new predator into the environment, but in this
case the risk is diminished because crayfish are already on the loose.

The panel’s recommendation, made last week, marks a watershed in the
short but chequered history of AIDS vaccines. Many had feared that the National
Institutes of Health would rush headlong into spending tens of millions
of dollars on the trial, under pressure to ‘do something’ in the face of
the epidemic, and bowing to the power of the pharmaceuticals industry. But
at the end of a day of anguished debate, the vote against the trial was
unanimous, scientists associated with drugs companies having been asked
to abstain.

The decision by the AIDS Research Advisory Panel reflects the growing
doubt among scientists and activists about the usefulness of the first generation
of AIDS vaccines developed over the past five years. Until now, these vaccines
have been tested only to ensure that they are safe and that they produce
an immune response. The next step is to see whether they can protect against
infection. But researchers have few grounds for believing that they can
do so.

The panel is also worried by scientists’ lack of understanding of how
to measure immunity to HIV, and by the expense of any trial big enough to
detect an effect of the vaccine. It also fears that volunteers might be
slow to come forward, and believes that the public could be confused or
angered by trials of a vaccine that might give incomplete protection.

Despite these doubts, only two months ago a smaller advisory group had
recommended expanding vaccine trials, but on a small scale. So the outcome
of last week’s meeting was uncertain until the end. Anthony Fauci, director
of the National Institute of Allergy and Infectious Diseases (NIAID) in
Bethesda, Maryland, immediately accepted the panel’s recommendation.

While at least 30 different experimental AIDS vaccines are being tested
in laboratories around the world, the committee voted on only two, both
made from the gp120 segment of HIV’s protein envelope. These two have been
tested for safety in some 300 people in the US by the National Institutes
of Health. One is made by Genentech of San Francisco and the other by Biocine
of Emeryville, also in California. At last week’s meeting, the two companies
urged the panel to recommend large-scale trials.

But most AIDS researchers believe these vaccines can provide only partial
immunity, at best. Last year, scientists showed that the first-generation
vaccines were unable to block the infection of cells in the laboratory by
strains of HIV taken directly from people, rather than strains grown in
culture. And scientists believe that most of these vaccines cannot produce
sufficiently long lasting and high levels of antibodies or T cells to offer
full protection.

Fauci maintains that the decision by the committee should not be seen
as a setback in the quest for an AIDS vaccine. And he stressed, as did the
committee, that the decision should not necessarily discourage other countries
that might want to test the vaccines. He argued that in countries where
HIV is a major threat to public health, even a partially protective vaccine
might be valuable. ‘Ethical principles certainly do not change among different
countries,’ he said, ‘but risk-benefit ratios and the dynamics of the epidemic
do.’ The US Army and Thai researchers are testing one of the first-generation
vaccines in Thailand.

Before voting, the committee considered the latest data on the vaccines.
At least 11 people in early trials of first-generation vaccines have become
infected with HIV despite having received one or more doses. Researchers
stress that these so-called ‘breakthrough’ infections were not caused by
the vaccine itself, which does not contain the viral genetic material needed
to infect someone. Rather, they simply indicate that the vaccines are failing
to protect people fully when they have taken risks. There is also concern
over one participant in a trial who rapidly developed AIDS after becoming
infected. Researchers are now intensively studying these breakthrough cases,
says Patricia Fast of NIAID.

AIDS activists at the meeting warned that launching a trial of a vaccine
that offered only partial protection could deepen the mistrust of science
in the communities most affected by AIDS. The activists also sought to reassure
researchers that they would rather wait for a promising vaccine than see
a premature trial go ahead just for the sake of doing something. Martin
Delaney of Project Inform, a group based in California, said people with
HIV had become frustrated with mediocre AIDS drugs, and warned against repeating
the same mistake with vaccines.

Fauci and others estimated that it would only be one to four years
before a vaccine using a different and perhaps more promising strategy,
such as incorporating parts of HIV into vaccinia or canarypox viruses,
would be ready for large trials.

Jeffrey Sacks of the US Centers for Disease Control and Prevention in
Atlanta and his colleagues analysed data on 178 dog bites reported to authorities
in Denver, Colorado, in 1991. Each of the dogs had bitten someone outside
the family for the first time. For statistical analysis, the researchers
matched the dogs with others that had never bitten anyone. German shepherds,
chow-chows, male dogs, unneutered dogs, dogs less than five years old, and
dogs weighing more than 20 kilograms were significantly more likely to be
found in the biting group. Dogs that were chained in yards also appeared
more often in the biting group. Golden retrievers and standard poodles were
the least likely to bite.

‘This is not to say that every German shepherd is bad,’ says Sacks,
a medical epidemiologist who was once bitten by a dog in a former job as
a postman. ‘We recognise that whether or not a dog bites also involves owner
management and victim behaviour.’

Officials at the Humane Society of the United States, which monitors
dog bites nationwide, say that the breeds that bite most often change from
year to year and from place to place, making it difficult to single out
particular breeds to blame. Rachel Lamb of the Humane Society is concerned
that the new study ‘will give people a false sense of security if their
dog is not on the list’. While acknowledging that dogs have different temperaments,
created by years of breeding for different purposes, she says: ‘You can
take a German shepherd and train it to be an incredible family dog. Or you
can take a golden retriever and make it into a killer. Our priority is decreasing
the number of dog bites, and we have found that focusing on breeds is not
going to work.’ What works, she says, is ‘educating the dog owners to neuter
their dogs, not to chain them, and not to train them to attack’.

But Sacks points out that while chow-chows have not been singled out
as biters before, German shepherds have been implicated in at least five
earlier studies. He acknowledges that because smaller dogs may not bite
as hard, victims may be less likely to report these bites to the authorities,
skewing the data on which breeds bite. ‘If a Chihuahua bites you, you may
be less likely to end up at the doctor’s,’ says Sacks. ‘So the deck may
be stacked against larger dogs.