The spread of a fatal form of brain disease can be virtually eliminated by a vaccine developed by a team of scientists from University of Melbourne, led by Professor Marshall Lightowlers of the Faculty of Veterinary Science, who said that the team had been striving towards eradication of the parasite involved for almost thirty years.
In an interview Prof. Lightowlers said “A recent pilot trial undertaken in Cameroon against the parasite Taenia solium which causes 50 million tapeworm infections and 50,000 deaths from brain disease in the developing world each year, resulted in the total elimination of transmission of the diseases. Because the vaccination procedure used was relatively simple and sustainable, it has a genuine potential to form the basis for widespread control of the parasite's transmission and a reduction, or elimination, of the human brain disease known as neurocysticercosis. This disease has been identified as one that could be eradicated from the globe, so this is a very significant hurdle which means the end is well and truly in sight.”
Pigs and humans in close proximity
In countries without proper sanitation, and where pigs and humans live in close proximity, there is a constant cycle of re-infection from the parasite. An area in Cameroon was chosen as a trial location because ninety percent of its pigs are allowed to free range, and around forty percent of farmers who keep pigs do not have a proper latrine.
The researchers initially treated 240 three month old piglets with a drug to eliminate any parasites, then applied the new vaccine to half of the animals to test the level of efficacy in preventing re-infection by the parasite, and distributed the piglets in pairs of vaccinated and unvaccinated animals to pig keeping households. Testing the piglets after 12 to 14 months, live parasites were found in 20 of the control pigs and none in the vaccinated animals.
Professor Lightowlers said the next step for his team is to determine the optimum vaccine schedule for protection against the Taenia solium parasite, adding “Vaccination could ultimately be applied directly to humans, but developing it to that point would be a vastly more expensive process and one that would become irrelevant if the disease could be eradicated in pigs.”
Tapeworms can grow many metres in length and live in humans for years without seriously affecting a persons' health, although by diverting nourishment they cause loss of energy in infected persons, and thus reduced ability to perform farm work. Tapeworm eggs however, can hatch in a human's intestines and the parasite travels to the brain where it often causes the fatal condition of neurocysticercosis.
The disease results in brain and spinal column cysts, which are the most common cause of acquired epilepsy in the developing world, and the World Health Organization estimates that over half the world's people live in countries where the parasite is endemic.
Pigs contract the larval form of the parasite from ingesting human faeces, and the parasite is then transferred to persons' who eat under-cooked pig meat. More seriously, it is also transferred from human to human via exposure to tapeworm eggs in human faeces, as latrines are usually absent at this level of subsistence worldwide, and villagers squat anywhere. Health authorities consider that the vaccine could be of great value wherever the parasite and its accompanying human diseases occur, especially throughout South East and East Asia, China and Japan.
Further development of the vaccine is receiving support from the Global Alliance for Livestock Veterinary Medicines (GALVmed). Development and testing of the vaccine by the University of Melbourne has been funded by the National Health and Medical Research Council and the Wellcome Trust, whose assistance is acknowledged.