voa常速英語:New Vaccine Research Aimed at Cattle Killer
New research is underway to develop an advanced vaccine against East Coast fever – a parasitic disease that killed more than one-million cattle in Africa last year. Researchers say the project also could lead to better treatments for malaria and cancer in humans.
International Livestock Research Institute says East Coast fever was found in 11 African countries in 2013. It caused $300-million in losses.
A woman from the cattle herding Mundari tribe walks early morning in a settlement near Terekeka, Central Equatoria state, south Sudan, January 19, 2011.The Nairobi-based institute warns the disease is spreading rapidly and poses a threat to 28-million cattle.
Vish Nene says the disease is caused by a parasite that’s transmitted by a tick bite.
“East Coast fever is described as a cancer-like disease of cattle. And the reason for that is there is a huge expansion of infected white blood cells that occurs post-infection. And these infected white blood cells behave like cancer cells. So they proliferate in an uncontrolled fashion. They spread throughout the body of an infected animal. Eventually, you can get depression of immune responses.”
Nene, who heads the institute’s Vaccine Biosciences Program, said East Coast fever can eventually cause pulmonary edema -- a potentially fatal build-up of fluid in the lungs.
“The disease is very acute. It’ll kill an animal within three to four weeks of infection. All the signs and symptoms, et cetera – because of that scientists describe this as a lymphoproliferative disease. And that’s the link with human cancers,” he said.
A lymphoproliferative disease is one in which white blood cells are produced in excessive amounts. Also, the fact it’s caused by a parasite makes East Coast fever similar to malaria.
Despite the risk it poses to millions of cattle, the disease has not received as much attention as might be expected.
“It’s a huge problem,” he said, “Part of the reason for perhaps not having a wider awareness of this disease is that it occurs only in sub-Saharan Africa. And so it hasn’t really reached the dimensions of where it’s got the attention of other people.”
There is a treatment and a current vaccine available. Both are very expensive for African farmers – eight to 12 dollars a dose. The drug must be used very early in the disease and may leave cattle weaker and less productive.
The current vaccine has been available for many years. It’s made in part by grinding up ticks infected with the parasites.
Nene said, “It was made based on the observation that if an animal recovered from an infection it was solidly immune to reinfection. So scientists started to work on that observation and what they started to do was to deliberately infect an animal and then treat it so that it recovered. That is the basis of what is called the infection and treatment method of immunization. And that is what the live vaccine is. That’s the current vaccine that’s being used.”
Some cattle spontaneously recover from East Coast fever, while others respond to treatment. The reason, he said, appears to be the same – killer T-cells produced by the immune system.
“These killer T-cells can identify the infected white blood cells and they kill those cells. And that is what gives rise to immunity.”
The International Livestock Research Institute has received an $11 million grant from the Bill & Melinda Gates Foundation to develop an advanced vaccine for the disease. Nene said that researchers hope to accomplish two things.
“In addition to the killer T-cells that I mentioned, we also know that antibodies play a role in immunity. So we have two prongs that we are trying to address. One is: can we raise a potent antibody response that protects the animal? And can we raise a potent killer T-cell response that also protects the animals? Either one alone may work -- either one alone and then both combined to see if that’s more efficacious,” he said.
If successful, Nene said, the vaccine would be cheaper, safer and much more available. And, unlike the current vaccine, would not have to be stored in extreme cold, namely liquid nitrogen.
Nene added that developing the new vaccine will take time – possibly 10 to 15 years barring any research breakthroughs. Researchers are expected to share their findings with those trying to develop a malaria vaccine and vice-versa.
Besides East Coast fever, the institute is helping to develop vaccines for African swine fever, goat plague, contagious bovine lung plague and Rift valley fever.
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