Agricultural editor PHILIPPA STEVENSON answers key questions about an epidemic that shows no signs of waning.
Predictions from Britain that the foot-and-mouth outbreak could hit 1100 UK farms, last for many months, and mean the slaughter of two million animals comes as no surprise to Massey University epidemiologist Roger Morris.
Professor Morris,
who heads Massey's Epicentre, developers of the internationally acclaimed epidemic tracking software EpiMAN, calculates the epidemic will peak at between 500 and a thousand farms.
France, too, had major concerns because the disease was confirmed in one site west of Paris and suspected in another some distance away east of the capital, he said.
"It's clear that a whole new wave of transmissions have occurred despite the movement standstill, and that it's gone to a number of new areas.
"It has been seeded around the country [UK] more extensively than was first apparent due to [stock] movements and there is now local and probably windborne spread going on."
Professor Morris said it would be months after the outbreak peaked before authorities could be confident the virus had been eradicated.
It already had a vastly greater geographic spread than Britain's worst epidemic in 1967-68 when just over 2364 farms were hit, but in a relatively small area of Wales.
Once an epidemic "got up a head of steam" there was no way to quickly stop it.
"People have to come to terms with the fact that there is going to be continuing spread for a period of time and that we can slow it ... but by the time you find some infections there will be new ones," said Professor Morris, whose Epicentre staff members have set up EpiMAN in the UK to assist the eradication attempt.
Since the outbreak in France, Swiss authorities had also made a request for the software, he said.
Britain's chief veterinary surgeon, Jim Scudamore, said last week the current outbreak was already far worse than the 1967-68 epidemic.
"Once we reach a peak we can begin to estimate how long it will take to go down, how long the tail will be. It could be a very long tail," he told the Guardian newspaper.
Agricultural internet site editor, Jim Muirhead, of ThePigSite.com, said the 1967 outbreak lasted just over seven months. The severity of this year's made it "reasonable to assume the outbreak will not be formally eradicated much before Christmas."
However, should pigs be infected "control really would be lost and those consequences are unthinkable," he said. Pigs spread the virus readily through the large amount of air they expel.
Comparisons of the UK outbreaks showed that by the time the epidemic was over in 1968 the number of animals slaughtered topped 442,000, averaging 187 animals killed per farm.
Because of today's greater scale of farming, by day 23 of the current epidemic the number of animals either killed or destined to be slaughtered had topped 205,000, averaging 880 animals per farm, or nearly five times the 1967-68 average.
"If this outbreak follows a similar trajectory to that in 1967 we could expect half the number of cases and five times the devastation, or in numbers, over 1100 outbreaks and two million animals slaughtered," Mr Muirhead said.
Why the slaughter?
There is no cure for foot-and-mouth, a highly infectious disease caused by a very tiny virus. There are seven main types of the disease and a number of subtypes. There is no cross-immunity between the main types.
It is very easily spread between animals, by contaminated vehicles, clothing or footwear and on the wind, travelling up to 60km over land and nearly 300km over water.
Although the disease is rarely fatal, except in very young animals, all affected animals (cattle, sheep, pigs, goats, buffalo, hedgehogs, deer, camels and elephants) lose condition and secondary bacterial infections may prolong convalescence. Some get deformed hooves, making it difficult and painful to walk.
Cows have a significant drop in milk yield, which never fully recovers, and growth rates slow. The drop in economic performance puts affected farmers at a disadvantage, and possibly out of business.
Why not vaccinate?
Vaccines are available but to be effective the specific strain of the virus has to be identified and a vaccine produced to match it. This vaccine will not provide immunity against a different type or sub-type.
The immunity an animal gains is not long lasting, and they would need to be vaccinated twice a year at significant economic cost. Pigs do not respond well to vaccination, leaving some exposed to the disease.
Vaccination creates foot-and-mouth antibodies in the animal, making it impossible to identify if the animal has had the disease.
If a country uses vaccinations it is immediately classified as an "infected area" and is unable to market animals to many parts of the world, including the US, Canada and Asia. Britain, for instance, has a valuable trade in animal genetics. This, and other areas of farming industry would disappear overnight.
Once a vaccination programme is started, the disease becomes "endemic" and the virus would become permanently present in the population.
As a consequence it could then infect all cloven-hoofed animals in the country and while vaccinated animals might be protected, wildlife would not.
How is the virus destroyed?
Foot-and-mouth tends to be a winter disease because it is less virulent in warm conditions.
The virus is easily killed by sunlight and heat, low humidity, or certain disinfectants but it may remain active for a varying time in a suitable medium such as the frozen or chilled carcass of an infected animal and on contaminated objects.
What is the risk of introduction to NZ?
Professor Morris, a member of the United Nations expert group that monitors trans-national disease spread, said that foot-and-mouth had shown a remarkable resurgence worldwide in the last five years.
Three years ago, the group believed the disease was waning but then outbreaks occurred in Taiwan, Korea, Japan and South Africa because of food smuggling.
The Ministry of Agriculture and Forestry said one estimate made of the likelihood of introduction into New Zealand is once every 53 years.
A separate analysis of risks posed by imports by arriving travellers or mail is that it might be imported two or three times a century.
How would it affect New Zealand?
Agriculture Minister Jim Sutton said if the disease got to New Zealand, the standard of living could drop by 25 per cent.
MAF said it was estimated in 1991 that a "modest outbreak" affecting 25 farms would cost $8 million to control and cause a loss of $1168 million to the national income, or about 37 per cent of export revenue.
Can people contract foot-and-mouth?
There has been only one recorded case of foot-and-mouth in a human, in Britain in 1966. It was similar to influenza with some blisters. It is a mild shortlived, self-limiting disease.
Links:
www.maf.govt.nz
www.thepigsite.com
Herald Online feature: Foot-and-mouth disaster
UK outbreak map
World organisation for animal health
UK Ministry of Agriculture, Fisheries and Food
The European Commission for the Control of Foot-and-Mouth Disease
Pig Health/Foot and Mouth feature
Virus databases online
Foot-and-mouth tipped to last through to Christmas
Agricultural editor PHILIPPA STEVENSON answers key questions about an epidemic that shows no signs of waning.
Predictions from Britain that the foot-and-mouth outbreak could hit 1100 UK farms, last for many months, and mean the slaughter of two million animals comes as no surprise to Massey University epidemiologist Roger Morris.
Professor Morris,
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