Predicting the next zoonotic pandemic
news reports that the chances are high the world’s next pandemic will be
a disease originating in animals, like 60% of current documented human
infectious diseases. Even after hundreds of thousands
of human deaths from zoonoses (diseases
transmitted from animals to humans),
experts say there is still limited information
about how zoonoses are spread or just how
to predict the next outbreak.
“There is no question of whether we will
have another zoonotic pandemic,” wrote
Stephen Morse, a public health professor at
Columbia University in New York, in a
November 2012 series on zoonoses
the UK medical journal, The Lancet. “The
question is merely when, and where, the
next pandemic will emerge.”
Despite virus hunters’ (Virus hunter
Nathan Wolfe presents a TED talk –
http://tinyurl.com/3waucwm) best efforts, no zoonotic pandemic has, thus far, been
predicted before it infected humans.
“The continuing effect of the HIV/AIDS
pandemic is a reminder of the risk of zoonotic pathogens spreading from their
natural reservoirs to man,” wrote William
Karesh from New York’s EcoHealth
Alliance in the Lancet series. The NGO,
formerly known as Wildlife Trust, works to
prevent the outbreak of emerging diseases
by preserving biodiversity.
An estimated 1.8 million people die
annually from AIDS, caused by HIV, which
originated in primates.
“What is far less broadly appreciated is
that none of the approaches commonly
used to search for potential new human
pathogens… probably would have identified
simian immunodeficiency virus (SIV)
as a potential risk to man,” said Karesh.
The US Agency for International Development launched its Emerging
Pandemic Threats Programme in late
2009 to build an early warning system to
detect and reduce the impacts of zoonotic
But there are thousands of species of birds
and animals that each host different
diseases; where do you concentrate efforts?
A virologist may focus on diseases easily
spread from animal relatives, like chimpanzees,
while a social scientist points out
how rare contact is between humans and
chimpanzees and focuses, instead, on
poultry, with which people live and work in
close quarters worldwide.
Between 2003 and 5 November 2012,
608 laboratory-confirmed human cases of
infections from H5N1 bird flu were
reported to the World Health Organization
from 15 countries, of which 359 died.
Disease hunters are homing in on
emerging disease “hotspots”, mammalrich
areas with high, changing population
densities. A group of experts led by
Columbia University’s Morse are creating
a disease map, in which Rwanda and
Burundi are bright red, as is the
Indonesian island of Java, one of the
world’s most densely populated islands,
and Egypt’s Nile Delta. Other potential
sites for future outbreaks include north
India and Bangladesh, northern and
western China, and – to a lesser extent –
more densely populated parts of western
Europe and along the west African coast.
“Urbanization has boosted zoonoses’
outbreak risks as people get closer to
animals,” Sarah Schlesinger, a scientist
from New York’s Rockefeller University,
told IRIN on the sidelines of a recent HIV
Cities are growing, with roads and industries
penetrating previously uninhabited wildlife habitats; some 3.3 billion people
live in urban areas (cities and their
outskirts), according to the UN. By 2030,
the world’s urban population is expected to
exceed five billion, with 80% located in the
developed world. In places where animal
“hosts” to disease start to disappear (as their
habitats shrink), pathogens are finding a
new home in human hosts.
Some 800 million people worldwide are
engaged in urban agriculture, according to
the World Bank, which identifies periurban
livestock as a fast-growing sector that
produces 34% of the world’s meat and
nearly 70% of its eggs.
The Nairobi-headquartered International
Livestock Research Institute (ILRI) has
pointed out how urban livestock and agriculture
can breed disease in some of the
world’s most crowded places. In a recent
survey in Dagoretti, one of eight districts of
Kenya’s capital, Nairobi, the institute found
up to 11% of households were affected by
cryptosporidiosis, a diarrhoeal disease caused
by a pathogen found in cattle, raw milk, soil,
vegetables and contaminated water.
Changing harvests may be another
contributor to the spread of zoonoses. In
the southwestern USA where El Niño
(rising sea surface temperatures across the
central and eastern Pacific Ocean)
dumped more rain, vegetation growth
increased, which then attracted more rats.
Hantavirus is not fatal in rats, which carry
the disease, but is in humans who became
infected through the rats.
The interplay of biology, ecology and
sociology make forecasting the next
pandemic difficult, say experts in the
Lancet series who call for boosting cooperation
between experts (See:
HIV/AIDS: Breaking science “silos” to
find a vaccine –
http://tinyurl.com/c8kqpgz) to meet the
“huge, and rising” threat of zoonoses.
of upload: 22nd Jan 2013