Two new disease threats have been identified by veterinary scientists. One could devastate the Irish farm industry and the other could devastate the global population, it was claimed yesterday.
Blue tongue is the most feared sheep disease in the world after foot-and-mouth, according to Dr Philip Mellor of the UK's Institute of Animal Health. Until 1998 it had been found only on the southern edge of Europe, but now it is moving north and Britain and Ireland are at risk, he said.
A different virus, bird flu, could trigger a global pandemic of virulent human influenza, warned Dr Dennis Alexander of the UK's Veterinary Laboratory Agency. Both were speaking at the British Association's Festival of Science in Salford, greater Manchester, yesterday.
Birds have their own flu virus and they are a major source of viruses that could trigger human pandemics, said Dr Alexander. Birds get two types of flu: one is a mild respiratory infection but the other is lethal.
Normally, people cannot catch or transmit avian flu, said Dr Alexander. But in a recent outbreak in the poultry industry in the Netherlands, a few people became infected.
The worry is that if one person got both the human flu and the bird flu at the same time, the viruses would recombine, with the virulent bird flu genes getting into viruses that are highly infectious to humans, said Dr Alexander.
The pathogenic forms of bird flu are rare, but there have been 20 outbreaks in birds since 1959, and the frequency is increasing, said Dr Alexander. In a recent outbreak on chicken farms in north-east Italy, 14 million birds were killed in order to eradicate the disease, and the outbreak cost €500 million.
No one working with sick birds during the Italian outbreak contracted avian flu, but since the Dutch experience contingency plans are being developed, said Dr Alexander.
Dutch workers were given masks and antiviral drugs in case they had human flu.
It used to be thought that human and bird flu viruses might mix in pigs, and that this accounted for flu outbreaks in China, where pigs, ducks and humans frequently live in close proximity. The Dutch experience suggests that the next pandemic need not involve pigs.
"Infections in birds is being taken much more seriously," said Dr Alexander.
Blue tongue disease is a viral disease of sheep that is also carried by goats and cattle, said Dr Mellor. It is transmitted by some species of biting midges from the genus Culicoides. The northward movement of the disease is because midge species are moving north "almost certainly due to global climate change", Dr Mellor said. "It has been estimated that every one degree rise in average temperature is a 90km increase in latitude."
The northward movement of the disease has meant it is now being transmitted by other Culicoides species that live in cooler climes. These new vector species include the commonest biting midges in these islands, the ones that bite us in our gardens, he said. Just how long the disease takes to get here depends on prevailing winds and the presence of susceptible animals. "Flocks in the UK are totally susceptible," he said.
The disease is more pathogenic to sheep than foot-and-mouth, with up to 70 per cent of infected animals dying. It is characterised by bleeding around the mouth, eyes and hooves, and infected animals have trouble eating, seeing and walking. Unlike foot-and-mouth, it is not directly transmitted between sheep, except in semen. It requires the midge vector.
This means it can be controlled with insecticides, although Dr Mellor is hopeful that if a single strain arrived here, it would be possible to control it with vaccines. The current outbreak in southern Europe involves five strains, he said.
Vaccination is controversial because the vaccines are live virus strains which are capable of some transmission themselves. Many people worry that they can revert to high virulence if they recombine with natural strains, he said.