Oracle
Well-known member
Re: Bird Flu Virus Crosses Species Barrier to Kill Dogs, Study Says
In horses, two major sub-types of influenza A virus are known to circulate. The first (H7N7) was isolated in Czechoslovakia in 1956, the second (H3N8) in Miami in 1963. The H7N7 sub-type is believed to be extinct or present only at very low levels.
The H3N8 sub-type is almost certainly a mutation of a bird flu virus, and changes in the virus have seen the development of two lineages - American and European. The H3N8 sub-type was behind a severe 1989 outbreak in China, which affected 80% of horses exposed to it and killed 20%. It went on to cause outbreaks in Trinidad (1979), Argentina (1985), South Africa (1986), and Jamaica (1989). H3N8 was behind the recent Australian outbreak.
The ability of the influenza virus to occasionally cross the species barrier raises an obvious question: If equine influenza has managed to mutate to infect dogs, could people also catch flu from their horses?
Dalva Mancini and a team of researchers in Brazil have looked for evidence pointing to the transmission of influenza between horses and people. Their work revealed high levels of antibodies in horses to two human influenza A strains - H1N1 and H3N2. The researchers had taken fluids and mouth and nasal swabs from 46 horses at studs and racing stables in Sao Paulo and Rio de Janeiro, in Brazil.
About 78% of the horses carried antibodies to two strains of equine flu. Remarkably, they tested positive in even higher numbers to human influenza A virus - 80.43% for H1N1 and 93.47% for H3N2. Similar numbers had antibodies to type B influenza.
The results meant that the immune systems of the horses recognised and generated antibodies against the human flu viruses, but did not become sick. "A high incidence of human influenza virus infection was observed among the horses evaluated," the researchers said. "These results demonstrated that horses are reservoirs of the circulating influenza viruses of both the equine-specific and the non-specific strains."
"These interspecies transmissions reinforce the potential mechanisms for introduction of genes of the avian influenza viruses in reservoirs that can reach man. "The response to the type B strain in the horse sera is particularly noteworthy, since this strain is considered to be restricted to humans," they said in their findings. The researchers continued: "It may be concluded ... the high incidence of influenza viruses among animals and humans surely represents a problem to both public health and animal protection all over the world.
"The occurrence of interspecies transmission is of concern since this allows the maintenance of the influenza virus in different reservoirs."
The evidence, they said, led to the conclusion that interspecies transmission probably occurs between humans and horses.
G.A. Landolt, in a presentation to the American Association of Equine Practitioners in 2006, reviewed the transmission of influenza A viruses between species and its implications for horses. He described equine flu as a disease that generated serious health and economic problems, adding that vaccination was the cornerstone of influenza prevention. Vaccine failure, he said, could primarily be blamed on the sustained genetic evolution of the virus, called antigenic drift, as well as the occasional introduction of gene segments or entire viruses from other species, called antigenic shift. These factors, he said, accounted for the diversity of influenza viruses.
"Although the barrier to transmission of avian viruses to horses is relatively strong, it is anything but complete," he said.
A severe epidemic in horses in northeast China in 1989, he said, served as an example of such spread. Genetic evidence pointed to this virus having spread directly to horses from the bird reservoir. He says evidence shows that influenza viruses of different genotypes and subtypes can occasionally transmit between two species of mammals, pointing to a 2004 outbreak in Floria among 22 race greyhounds which showed the strain had evolved from equine influenza virus. It spread to six states. Further research has since shown this virus had been circulating in several states as early as 1999.
"The transmission of influenza from horses to dogs is especially interesting in light of the fact that dogs were not commonly regarded as hosts for influenza A viruses. "The viral and host factors that determine the species range of influenza viruses and the mechanisms by which host barriers are overcome are not completely understood. Regardless of the mechanisms involved, the equine-lineage H3N8 viruses have since become established in the dog population in the United States," he said.
Although horse strains have shown relatively little genetic diversion, the new canine variety has shown high rates of evolution.
"Although it is unclear if the canine H3N8 viruses are still capable of infecting horses, they potentially represent a serious emerging disease threat to the American horse population. "Although horses have often been regarded as isolated hosts for influenza, events of recent years clearly indicate that the species barrier for viruses jumping either to or from horses is not absolute. "The realisation of this fact has importance for control, because commercially available vaccines may not provide protection against infection with viruses stemming from other species."
(this is why I posted the equid influenza article earlier that suggests a direct correlation between vaccine evasion and recent phylogenic divergence)
Source: Influenza in horses and humans: the perils of viral marketing
April 1, 2008
http://www.horsetalk.co.nz/health/equineflu-143.shtml
In horses, two major sub-types of influenza A virus are known to circulate. The first (H7N7) was isolated in Czechoslovakia in 1956, the second (H3N8) in Miami in 1963. The H7N7 sub-type is believed to be extinct or present only at very low levels.
The H3N8 sub-type is almost certainly a mutation of a bird flu virus, and changes in the virus have seen the development of two lineages - American and European. The H3N8 sub-type was behind a severe 1989 outbreak in China, which affected 80% of horses exposed to it and killed 20%. It went on to cause outbreaks in Trinidad (1979), Argentina (1985), South Africa (1986), and Jamaica (1989). H3N8 was behind the recent Australian outbreak.
The ability of the influenza virus to occasionally cross the species barrier raises an obvious question: If equine influenza has managed to mutate to infect dogs, could people also catch flu from their horses?
Dalva Mancini and a team of researchers in Brazil have looked for evidence pointing to the transmission of influenza between horses and people. Their work revealed high levels of antibodies in horses to two human influenza A strains - H1N1 and H3N2. The researchers had taken fluids and mouth and nasal swabs from 46 horses at studs and racing stables in Sao Paulo and Rio de Janeiro, in Brazil.
About 78% of the horses carried antibodies to two strains of equine flu. Remarkably, they tested positive in even higher numbers to human influenza A virus - 80.43% for H1N1 and 93.47% for H3N2. Similar numbers had antibodies to type B influenza.
The results meant that the immune systems of the horses recognised and generated antibodies against the human flu viruses, but did not become sick. "A high incidence of human influenza virus infection was observed among the horses evaluated," the researchers said. "These results demonstrated that horses are reservoirs of the circulating influenza viruses of both the equine-specific and the non-specific strains."
"These interspecies transmissions reinforce the potential mechanisms for introduction of genes of the avian influenza viruses in reservoirs that can reach man. "The response to the type B strain in the horse sera is particularly noteworthy, since this strain is considered to be restricted to humans," they said in their findings. The researchers continued: "It may be concluded ... the high incidence of influenza viruses among animals and humans surely represents a problem to both public health and animal protection all over the world.
"The occurrence of interspecies transmission is of concern since this allows the maintenance of the influenza virus in different reservoirs."
The evidence, they said, led to the conclusion that interspecies transmission probably occurs between humans and horses.
G.A. Landolt, in a presentation to the American Association of Equine Practitioners in 2006, reviewed the transmission of influenza A viruses between species and its implications for horses. He described equine flu as a disease that generated serious health and economic problems, adding that vaccination was the cornerstone of influenza prevention. Vaccine failure, he said, could primarily be blamed on the sustained genetic evolution of the virus, called antigenic drift, as well as the occasional introduction of gene segments or entire viruses from other species, called antigenic shift. These factors, he said, accounted for the diversity of influenza viruses.
"Although the barrier to transmission of avian viruses to horses is relatively strong, it is anything but complete," he said.
A severe epidemic in horses in northeast China in 1989, he said, served as an example of such spread. Genetic evidence pointed to this virus having spread directly to horses from the bird reservoir. He says evidence shows that influenza viruses of different genotypes and subtypes can occasionally transmit between two species of mammals, pointing to a 2004 outbreak in Floria among 22 race greyhounds which showed the strain had evolved from equine influenza virus. It spread to six states. Further research has since shown this virus had been circulating in several states as early as 1999.
"The transmission of influenza from horses to dogs is especially interesting in light of the fact that dogs were not commonly regarded as hosts for influenza A viruses. "The viral and host factors that determine the species range of influenza viruses and the mechanisms by which host barriers are overcome are not completely understood. Regardless of the mechanisms involved, the equine-lineage H3N8 viruses have since become established in the dog population in the United States," he said.
Although horse strains have shown relatively little genetic diversion, the new canine variety has shown high rates of evolution.
"Although it is unclear if the canine H3N8 viruses are still capable of infecting horses, they potentially represent a serious emerging disease threat to the American horse population. "Although horses have often been regarded as isolated hosts for influenza, events of recent years clearly indicate that the species barrier for viruses jumping either to or from horses is not absolute. "The realisation of this fact has importance for control, because commercially available vaccines may not provide protection against infection with viruses stemming from other species."
(this is why I posted the equid influenza article earlier that suggests a direct correlation between vaccine evasion and recent phylogenic divergence)
Source: Influenza in horses and humans: the perils of viral marketing
April 1, 2008
http://www.horsetalk.co.nz/health/equineflu-143.shtml