Could self-vaccinating cattle cut disease?
[KUALA LUMPUR] Scientists are testing a vaccine that spreads by itself as a solution to a highly infectious buffalo and cattle disease that costs millions of dollars a year.
But experts have raised questions about the safety of using such an approach.
Haemorrhagic septicaemia is hard to vaccinate against where livestock roam freely, because animals are difficult to capture and restrain long enough for an injection.
Now Malaysian scientists have developed a live vaccine — a disabled form of the bacterium, that triggers an immune response without causing the disease. Researchers spray the vaccine up an animal's nose and they breathe it out where it remains airborne and is inhaled by animals within two metres of them.
Haemorrhagic septicaemia is one of the most important bacterial diseases in buffalo and cattle in many African, Asian and Middle Eastern countries, causing losses of millions of dollars a year.
Outbreaks can occur several times a year and most infected animals do not survive — many drop dead within hours.
Mohd Zamri Saad, head of a team studying the disease at Putra University, Malaysia, told SciDev.Net that researchers are half way through a two-year field trial of the vaccine, and early results suggest they are reaching the 75-80 per cent vaccination rate needed to prevent outbreaks from spreading.
The field trials are being conducted in Kota Belud, Sabah, on nearly 100 animals belonging to a few farmers.
After vaccinating 30 per cent of a herd, self-vaccination does the rest leading, overall, to 80 per cent immunity. The animals remain immune for up to four months while the vaccine itself survives for just a fortnight in the wild.
Jan Naessens, senior scientist and immunologist at the International Livestock Research Institute in Nairobi, Kenya, welcomed the invention but warned that, because the vaccine is alive, it could alter itself so it can cause the disease again.
He said that there are some bacteria that cause severe infection in cattle only when there are other viruses or bacterium around (co-infection) that creates an optimum condition for them to multiply uncontrollably.
And Naessens cautioned that the vaccine's capacity to transmit so easily could cause problems. "Regulation of such a vaccine would need a lot of additional data on potential environmental hazards before it could be released," he said.
But Zamri said that the research team had to obtain approval from the university's ethics committee, which follows international safety standard. Other precautionary measures are taken, including preventing intermingling with animals that are not taking part in the trial, and the monitoring of all disease outbreaks in the area.
He said that co-infection "seldom occurs with this disease" and is "not an important concern at this stage", but added that if studies into co-infection were a requirement for commercialisation of the vaccine they would certainly conduct them.