Insight on whether bird flu can cross species boundaries and infect equines. Peter Green MRCVS looks at the evidence.

Equine influenza and human flu evolved from bird flu in the distant past and remain quite similar.

Scientists in Kentucky wondered whether they could artificially infect horses with bird flu in the way that people can be infected.

They investigated this in 2 ways. First, they cultured cells from the tracheas of horses that had been put down for reasons other than respiratory disease. When the cultures were well established, they infected them with 18 different strains of bird flu virus to see if the viruses multiplied in the cells.

About half the viruses did indeed multiply, showing they had successfully infected the horses’ trachea cells.

The scientists then took the 3 avian virus strains that had been most virulent in the lab and gave them to unvaccinated young ponies by means of aerosol inhalation to see if the ponies would become infected. None became infected or developed flu.

This shows that although isolated cultures of horse cells became infected with bird flu, the same cells in the living horse were able to resist infection. Bird flu does not seem able to infect horses, but who knows what might happen in the future as the viruses evolve?

It is also a good example of why laboratory cultures and tests are not always an accurate guide to what happens in the real world in living animals.