Visceral leishmaniasis, which is the most severe form of that group of diseases, affects 500 000 people in the world each year. It is caused by a protozoan, Leishmania infantum, transmitted by sand fly bites.
There is no vaccine for this disease, which can rapidly lead to death if no treatment is given. In the most heavily affected areas, the dog population is hit heavily by infection. It acts as parasite reservoir for humans. Development of a vaccine for dogs could help brake transmission of the disease to humans, by reducing this reservoir. Such prevention treatment has just been tested successfully on dogs by an IRD team in Montpellier, in conjunction with the Rocher veterinary clinic (La Garde, Var) and the biopharmaceutical company Bio Véto Test (La Seyne-Sur-Mer, Var). The first results showed total lasting protection of these animals against the disease, could open the way towards the development of a human vaccine.
Visceral leishmaniasis, which is the most severe form of the leishmaniases, hits an annual total of 500 000 people, mostly in the developing countries. It is caused by the parasite Leishmania infantum. A flagellate protozoan, it uses as vector an insect resembling a midge, the sand fly, colonizing the intestine and then the salivary glands. The female insect feeds on mammals' blood. It can thus pass the parasite on to humans by a single bite. Once in the blood stream, L. infantum passes into particular cells of the immune system, the macrophages. These eventually burst, releasing the parasites which move on to penetrate other cells. The infected subject suffers bouts of fever, anaemia, enlarged spleen and liver, and weight loss. In the absence of treatment, these clinical signs usually announce a fatal outcome.
The sand fly sucks blood from mammals other than humans. This is how, right around the Mediterranean rim, 5 million dogs, a proportion of from 1 to 42 % depending on the area, are affected by visceral leishmaniasis. These animals are thus a reservoir for these parasites, which continuously feed the mammal-sand fly-human cycle. In this context, development of a canine vaccine would help reduce the portion of the animal population infected. The risks of transmission of the disease to humans would in this way be indirectly reduced.
Up to now, several dog vaccines, mostly developed from whole dried parasites, have proved not to be really effective. A team from the IRD Montpellier research centre, working with the Rocher veterinary clinic (La Garde, Var, France) and the biopharmaceutical firm Bio Véto Test (La Seyne-Sur-Mer, Var), have recently produced and tested a new type of treatment, composed solely of antigen proteins excreted by the parasite (1). The first trials indicate that this would completely and lastingly protect dogs against the disease.