The changing face of Hendra virus: what do we really know for certain?

There have been many discoveries reported since the first description in 1994 of a novel paramyxovirus affecting horses. The ecology of this virus in the natural reservoir host has been described, and a vaccine developed to protect horses from disease. However, there is much still to learn about Hendra virus (HeV) ecology and epidemiology. How does the virus transmit from bats to horses? Why is transmission generally sporadic in nature and what factors influence inter-species transmission? With the discovery in an equine case of a variant strains of HeV not detectable by routine diagnostic methods, much of our current knowledge of the ecology of this virus in its natural host is once again challenged.