Analysis of samples taken from Australian bats during the mid-1990s has reinforced the view that urine may play a major part in transmitting the deadly Hendra virus to horses.
Hendra virus was first identified in Australia in 1994. Pteropid bats, commonly known as flying-foxes, are the natural reservoir.
The virus has spilled over to horses on 51 known occasions, and from infected horses to humans on seven occasions, four of which proved fatal.
Australian researchers tested archived tissue samples from 310 bats collected in Queensland in 1996 and 1997.
The research team undertook genetic screening of the samples for evidence of the virus, using a polymerase chain reaction (PCR) test.
Evidence of the virus was detected in 20 individual flying-foxes, representing 6.4 percent of the 310 bats, from various tissues including spleen, kidney, liver, lung, placenta and blood samples.
Detection was significantly higher in Pteropus Alecto and P. conspicillatus, identifying these species as a risk factor for infection.
Lauren Goldspink, from the Queensland Centre for Emerging Infectious Diseases, and her colleagues found that the virus had a predilection for the spleen, suggesting this organ played an important role in Hendra infection, perhaps in either the maintenance of infection or the immunological processing of the virus. It could be an active site of viral replication, they said.
The lack of detections in the foetal tissues of the four pregnant females in the sample that were positive for the virus suggested that vertical transmission – directly from the mother to an embryo, fetus, or offspring during pregnancy or childbirth – was not a regular mode of transmission in naturally infected flying-foxes.
The findings supported the view that placental and foetal tissues were not a major source of infection for horses, they said, and reinforced the view that flying-fox urine was a key transmission pathway.
From the 20 Hendra-positive flying-foxes, a total of 30 tissues tested positive, predominantly spleen samples (94.7 percent) and kidney samples (31.3 percent). Liver, lung, red blood cells, serum and placenta also yielded some positive results.
The researchers, reporting their findings in the open-access peer-reviewed journal, PLOS ONE, said they recorded the first detection of Hendra virus in the tissues of P. conspicillatus, providing evidence of systemic infection in this species.
They said their findings indicated that the bat species P. alecto and P. conspicillatus were likely the primary reservoir host of the virus, and played a major role in the cross-species transmission to horses.
The research team said their analysis identified certain species as a significant risk factor for Hendra infection, but not reproductive status, season, latitude and year.
Additional research into routes of excretion in naturally infected flying-foxes, and thus the modes of transmission to horses, would complement their findings and enable better targeted risk management advice to the horse industry, they said.
Goldspink was joined in the research by Daniel Edson, Miranda Vidgen, Hume Field, and Craig Smith, who are also from the Queensland Centre for Emerging Infectious Diseases; and John Bingham, from the Australian Animal Health Laboratory, which is part of the Commonwealth Scientific and Industrial Research Organisation (CSIRO).
Goldspink LK, Edson DW, Vidgen ME, Bingham J, Field HE, Smith CS (2015) Natural Hendra Virus Infection in Flying-Foxes – Tissue Tropism and Risk Factors. PLoS ONE 10(6): e0128835. doi:10.1371/journal.pone.0128835
The full study can be read here.