Nairobi; Kenya: The Kenya Agricultural Research Institute (Kari) has developed a vaccine against a contagious lung infection in livestock, known as bovine pleuropneumonia (CBPP) or lung plague.
Kari researchers say the new vaccine is effective and affordable. Initial trials indicate a second vaccination (a booster) raises protection levels of between 80 per cent and 90 per cent.
The current vaccines give low protection rates of only between 30 and 60 per cent, making it difficult to contain the disease.
“The strength of vaccines in the market has often been reduced through attenuation– growing several times in new conditions until it loses its strength,” said Hezron Wesonga, the Kari Principal Researcher.
“This has been done 44 times, hence the name T1 44. T1 stands for Tanzania 1, an organism originally isolated from Tanzania. Being a live vaccine, it requires cold storage from production until it is administered. This makes it demanding on the need for cold storage and at the same time, some experts claim it can cause disease under some conditions,” Wesonga added.
The vaccine was realised after testing a large number of potential formulations for their ability to protect cattle against experimental infection.
“We then identified one that appears to provide significant protection against the devastating lung damage caused by the bacteria,” said Andrew Potter, the Director of Vaccine and Infectious Disease Organisation (VIDO), who also took part in the research.
“We are refining the vaccine to include other components which might enhance protection. While the results look promising, there is still much work before this vaccine can be used by farmers,’’ he added.
The current ones also require refrigeration storage facilities, making them hard to be used in poor countries. “The type of vaccine we are developing is a so-called subunit vaccine which is much more stable than current vaccines at high temperatures. As such, we expect that there will not be as strict a requirement for refrigeration or freezing of the product during transportation and use, although this is something that we will need to examine in both the laboratory as well as in the field,’’ said Potter. “Ultimately, this should make the vaccine compatible with administration in a variety of settings, including areas where the ability to maintain a strict cold chain is problematic,’’ he added.
The causative agent of CBPP is temperature sensitive and may die out before administration at the time point of vaccination in the field.
To preserves the organism at high temperatures as well as solve cool storage challenge, a trial was designed to use media in vaccine preparation. The study involved 90 cattle purchased from Kakamega, a region historically known to be free from CBPP.
About 1.3 million people in Kenya, the Government says are at risk of livestock losses caused by CBPP.
The disease becomes more complex to contain in the past two decades, greater attention have been shifted to vaccine development.
Contagious disease
Lung plague is a highly contagious pneumonia accompanied by pleurisy – inflammation of the pleurae, which impairs their lubricating function and causes pain when breathing. Vulnerable cattle become infected by inhaling droplets disseminated by coughing in affected cattle. In countries where cattle movement can readily be restricted, the disease can speedily be contained by slaughter.
Tracing the source of infected cattle detected at abattoirs, blood testing, and imposition of strict rules for cattle movement they say can also aid in control of the disease.
Susceptible herds may show up to 70 per cent morbidity, but much lower infection rates of about 10 per cent associated with clinical signs are more common.
For a vaccine to be effective, experts suggest the need for high herd coverage within a country. Interventions used to control the disease involve wide-scale quarantine (culling) and administering antibiotics. But what makes the new CBPP superior?
“The difference from what is being developed is that the new one is a sub-unit vaccine and does not require the stringent conditions for storage and can therefore be made available in hot conditions without fear of vaccine failure, especially in regions where infrastructure is a challenge,’’ said Wesonga.
The vaccine will have a significant benefit compared to conventional CBPP vaccines in terms of safety and cost.
“It will be relatively easy to differentiate vaccinated from infected animals, something that is not possible with the live vaccines currently in use. We also expect it will have an impact on the usage of antibiotics used to control the disease,” he said.
To scale up the vaccine use, more however, needs to be done. “We have been working at a laboratory-scale which is sufficient for small scale vaccine testing, but we will need to move the manufacturing of the vaccine into a larger scale system,’’ said Potter. “In addition, we will need to work out the details on how the vaccine works in the field rather than an experimental setting,’’ he added.
