The recent outbreak of H7N9 avian influenza in China marks the first time that this subtype has crossed the species barrier to infect humans. After some genetic detective work, Chinese scientists came to the worrying conclusion that the outbreak strain is actually a mishmash of genes from four different bird influenza viruses: one from ducks, another from migratory birds, and two from chickens.
Birds provide ideal conditions for gene exchange among influenza strains – many bird species are naturally infected with a diversity of influenza viruses, but show only mild disease symptoms, or none at all. Scientists interested in understanding how birds and the virus coexist now have a valuable resource: the genome of the duck.
New tool in battle against influenza
An international team of scientists has just sequenced the duck genome, one of the most important reservoir species for influenza. The research, published in Nature Genetics and led by Professor Ning Li of the China Agricultural University in Beijing, also identified genes that are likely to play key roles in duck immunity against avian influenza.
Before they make us sick, many emerging and existing pathogens go through complex transmission cycles involving animal or insect species. Zoonoses, or diseases that cross species barriers into humans – avian influenza, SARS, and Nipah virus, for instance – will continue to pose health threats as we encroach onto animal habitats, farm huge numbers of livestock, and consume exotic meats (or, in the case of toxoplasmosis, snuggle with our pet cats). While the development of vaccines and drugs for use in humans obviously remains essential, research that focuses on non-human links in the chain of transmission also has potential to make a huge impact on human health.
“Studying host-pathogen interactions in ducks potentially might be used to design new anti-influenza drugs, especially anti-avian influenza drugs, develop modified birds that are genetically resistant to avian influenza infection, and suppress transmission of avian influenza,” said Prof. Li in an interview with Asian Scientist Magazine. “Such applications of host-pathogen interactions in ducks will improve our ability to cope with the possible pandemic threat of influenza virus in animals and humans.”
With the duck genome in hand, Prof. Li and his colleagues were able to determine which genes are activated in response to infection with avian influenza. Some of these are members of gene families that have expanded in ducks compared to chickens, turkeys, and zebra finches, suggesting that they may play unique roles in the duck’s defense mechanisms against the virus. The researchers are planning more studies to unravel the mechanisms by which these genes, as well as other candidates, protect the duck against influenza.
The study of insect vectors of disease is another example of research aimed at targeting non-human links in transmission chains. The dengue mosquito, for example, is notoriously difficult to eliminate by conventional methods such as insecticide spraying, and an effective vaccine or drug against dengue virus for use in humans has yet to be developed. The sequencing of the mosquito genome, however, was a huge boon to researchers studying how the mosquito immune system defends against dengue virus.
Such studies have already led to field trials of novel biological control strategies targeting the vector – the release of mosquitoes carrying bacteria that render the insects refractory to dengue infection, for example. Similar methods are being applied to mosquito species that transmit malaria, a disease which takes an enormous toll on global health.
The case for studying the obscure
While it is easy to make a case for studying ducks and mosquitoes, many pathogens infect us by way of species that are relatively obscure. Research on these seemingly less medically or economically important organisms is often viewed as a waste of taxpayer dollars. On an American talk show earlier this year, Stephen Moore, a prominent economist and editor at the Wall Street Journal, ridiculed publicly-funded research on snail mating habits.
Yet, this research was funded with good reason: snail-borne diseases affect an estimated 300 million people around the world today, mostly in disadvantaged communities in Asia and Africa. The parasites that cause schistosomiasis, for example, develop in freshwater snails into forms that are infectious to humans, before being released into river water.
And what about animals that do not harbor disease? Beyond agricultural or economic priorities (such as breeding meatier farm animals) studying animals and their genomes can also help us understand human disease and potentially develop treatments.
Take dogs, for instance: recent research suggests that the genomes of dogs and humans have evolved in parallel over millennia of intimate association, such that we have come to share common genetic mechanisms for many diseases: several types of cancer, obsessive-compulsive disorder, and epilepsy, to name a few. In fact, more than 360 human diseases with a genetic basis have also been described in dogs, often with very similar clinical manifestations and drug responses.
The line between human and veterinary medicine is beginning to blur; studies of canine disease have already led scientists to new insights into human biology. For example, the identification of a genetic mutation associated with narcolepsy in Doberman Pinschers has shed light on sleep regulation in humans, while the discovery of a novel disease mechanism underlying epilepsy in dachshunds may explain related disease in humans. So the next time your dog attempts to usurp some sofa space, move over; after all, you and he already share so much more than that.
Of course, the sequencing and analysis of an organism’s genome is neither a trivial nor a cheap undertaking, and scientists should be required to make an excellent case for the use of public funds to do so – sequencing an entire zoo of animals is probably not the answer to the world’s problems. But sometimes the most elegant solutions may be hidden inside the strangest creatures; excuse me while I turn my attention to the latest scientific Jungle Book story: how does the naked mole rat not get cancer?