Essentially a sylvan disease in the past, restricted to rural areas, visceral leishmaniasis followed twentieth century migrations to the outskirts of cities. In Brazil, 1,998 cases out of the 3,303 reported cases in 2008 were found in the North and Northeast regions. The disease is transmitted by the female Lutzomyia longipalpis mosquito, an insect that is only three millimeters long, popularly referred to as a sandfly. The disease can affect dogs, foxes and even skunks, the main hosts of the disease-causing parasite, the Leishmania chagasi protozoa. A recombinant vaccine for canine visceral leishmaniasis, called Leish-Tec, the result of a partnership between the Federal University of Minas Gerais/UFMG) and the Hertape Calier Saúde Animal company, also from Minas Gerais, was 90% efficient in tests conducted in a region where the human and canine forms of the disease are endemic and where dogs of different breeds are subject to the insect’s bites. “If the number of infected dogs is reduced, the number of human cases will also drop in the long term”, says parasitologist Célia Gontijo, from Fundação Oswaldo Cruz/Fiocruz in Belo Horizonte. The vaccine is one of the various fronts that are fighting the transmission of visceral leishmaniasis, a disease that, if untreated, can lead to death in 90% of all cases, after harming such organs as the liver, the spleen and the bone marrow.
The recombinant vaccine is based on the insertion of genetic information of a protein found in the Leishmania chagasi protozoa. The protein is injected into bacteria that are later replicated. The bacteria act as a biofactory that produces the antigen for the vaccine. Launched commercially in October 2008, the vaccine is still undergoing clinical trial at the company. Once this phase is concluded, it will be ready for accreditation by the Ministry of Health. In the new study, called the phase 3 clinical trial, which started in early 2008, tests are being conducted on 1,150 dogs in a region where human and canine visceral leishmaniasis is endemic. “We are working in a city that has full control of the epidemiology of the disease and where the dogs are monitored,” explains Christiane de Freitas Abrantes, the Biotechnology manager at Hertape Calier, a company that makes veterinary products. “In this study, we are working with two groups of animals: one of them vaccinated and the other not.” To produce an unbiased analysis, the researchers chose the double-blind methodology. In other words, none of the owners of the dogs in the study know which dogs were vaccinated and which were not. So far, the company has invested approximately R$ 25 million in the development of Leish-Tec.
“The only two visceral leishmaniasis vaccines available in the world were developed in Brazil,” says professor Ana Paula Fernandes, from the UFMG School of Pharmacy, who took part in the development of Leish-Tec in partnership with professor Ricardo Tostes Gazzinelli, from the UFMG Biological Sciences Institute. Professor Gazzinelli is also the coordinator of the INCTV, the National Institute of Vaccine Science and Technology. The vaccine was designed to induce a cellular response from the organism, as the Leishmania is an intra-cellular parasite. “The genetically modified organism expresses the necessary antigen to stimulate the immune system to fight the infection caused by leishmaniasis,” says Ana Paula. The first step to achieve the recombinant vaccine was to identify the protozoa’s main genes in the activation of the immune system, in order to develop a protective response. The chosen gene encodes a protein that researchers call the A2. “The A2 protein induces the specific response for T lymphocytes, responsible for cell immunity,” she explains.
Following tests performed on experimental mice models, the UFMG transferred the technology to Hertape Calier in 2003. “After the partnership was established, the necessary additional trials were performed so that the vaccine could be marketed,” says Ana Paula. Phase 2 of the trials, which involved vaccinating dogs, began in 2004. The trial was performed on a limited number of dogs submitted to artificial infection by the parasite under controlled conditions. “We took three years to complete this phase and the results were very promising,” she reports. Based on these results, the related sales license was granted by the Ministry of Agriculture, Livestock Farming and Food Supply. A new normative rule, enacted jointly by the latter and by the Ministry of Health, demanded additional tests. “The leishmaniasis vaccine is the only one that must undergo phase 3 clinical trials, because this disease affects humans and is a serious zoonosis,” says Christiane.
Although it is still too early to state that the number of leishmaniasis cases has diminished among people because of the vaccination of dogs, a study conducted by the group headed by professor Clarisa Palatnik de Sousa, of the Microbiology Institute of the Federal University of Rio de Janeiro/UFRJ, points to favorable results in this respect. Clarisa coordinated the research that resulted in the development of the first canine visceral leishmaniasis vaccine, based on the antigens of the parasite and launched in 2004. This vaccine – the brand name of which is Leishmune – was launched by Fort Dodge, a multinational company in the field of animal health products, with a plant in the city of Campinas, State of São Paulo. A study coordinated by the researcher and published in the journal Vaccine last June states that the number of human and canine visceral leishmaniasis cases has dropped, after vaccination was conducted from 2004 to 2006 in two endemic regions in Brazil.
In Araçatuba, São Paulo State, the number of canine leishmaniasis cases dropped by 25% and of human leishmaniasis by 61%, the study reports. In the city of Belo Horizonte, the growth curve of the incidence of the disease in dogs and humans remained stable after the vaccination of the dogs. Célia Gontijo, from Fiocruz in Minas Gerais, warns that it is necessary to develop a diagnostic method that can be used on a broad scale to differentiate the positive results of the vaccine. This is needed because the tests currently applied as detection control can indicate that the vaccinated animal has leishmaniasis when in fact it has other diseases that are not transmissible to humans. Ana Paula, from UFMG, says that as Leish-Tec is comprised of a recombinant antigen, it produces very few antibodies, which are different from the ones used in routine serum detection tests.
PALATNIK de Sousa, C.B. et al. Decrease of the incidence of human and canine visceral leishmaniasis after dog vaccination with Leishmune in Brazilian endemic áreas. Vaccine. v. 27, p. 3.505-12. 2 jun. 2009.
FERNANDES. A. P. et al. Protective immunity against challenge with Leishmania chagasi in beagle dogs vaccinated with recombinant A2 protein. Vaccine. v. 26, p. 5.888-95. 29 out. 2008.