“One health means the recognition that human beings are not alone; we are part of the whole. We have left behind our old, anthropocentric view that human health is not linked to animal and environmental health.”
Dr. Filipe Dantas-Torres, Laboratory of Immunoparasitology, Department of Immunology, Aggeu Magalhães Institute (Fiocruz), Brazil
It was in 2001 when I saw the first case of canine visceral leishmaniasis. I was a veterinary student at that time. We visited a remote rural area in Northeastern Brazil and found this dog showing clinical signs suggestive of visceral leishmaniasis. The dog was unable to stand alone. The other clinical signs were really bad: severe weight loss, apathy, enlarged lymph nodes and nails, and skin lesions. The dog’s diagnosis was ultimately confirmed by a cytological examination of stained bone marrow smears. Indeed, in remote rural areas, dogs can be severely affected by visceral leishmaniasis. The reason for this is that many dog owners there have limited or no access to information and veterinary services.
|As with many animal diseases, veterinarians are the experts to advice pet owners how best to protect their dogs from leishmaniasis. Scientifically-tested repellents reduce sandfly bites and, therefore, the risk of pathogen transmission.|
Visceral Leishmaniasis: A Public Health Threat
Leishmaniasis does not just affect animals – it is also a human disease. In fact, it is one of 17 WHO listed neglected tropical diseases caused by Leishmania parasites, which are transmitted by blood-feeding phlebotomine sandflies. According to global estimates, approximately 0.9 to 1.6 million cases of leishmaniasis – in all clinical forms – and 20,000-40,000 human deaths occur each year. Visceral leishmaniasis (VL) is the most severe form of the disease, being potentially fatal if untreated. And nearly 95 percent of the visceral leishmaniasis cases reported in the Americas occur in Brazil. About 4,200 to 6,300 cases in humans are estimated to occur in this country each year.
Social Impact of the Disease: Children Hide Their Faces
Visceral leishmaniasis, and also cutaneous leishmaniasis, have a huge impact on the lives of people living in endemic foci in Brazil. This is particularly true for people living in poor, rural settings with limited access to information and basic healthcare services. For instance, our research group recently conducted a study on cutaneous leishmaniasis in indigenous villages located in a remote rural area in Northeastern Brazil. During one of our visits, I met many children that have suffered from cutaneous leishmaniasis. They were all very ashamed because of the scars – especially the kids with scars on their faces.
During a recent study on the prevention of canine visceral leishmaniasis in Northeastern Brazil, I also met Carlos Augusto, the owner of Panqueco, a mongrel dog. Carlos was very afraid of his dog being positive with leishmaniasis because he himself had visceral leishmaniasis, the most debilitating disease he has ever had, he said. Some people living in areas where fatal cases are being reported may avoid dogs altogether. This is especially true for those people who are not aware of prevention strategies or who cannot afford them.
Past Strategies for Fighting the Disease
Dogs are the main reservoirs of Leishmania infantum, the causative agent of zoonotic visceral leishmaniasis. In addition to being numerous and often in close proximity to humans, infected dogs represent a source of Leishmania infantum to sandflies. While many infected dogs will remain asymptomatic, some of them will develop overt disease and present high parasitic loads. Dogs with high parasite numbers in skin are usually highly infectious to sandflies. Even dogs without any clinical signs may contribute to the disease transmission cycle, as they are capable of infecting sandflies during their blood meal.
|Under the microscope: Even dogs free of any clinical signs could be carrying visceral leishmaniosis, a zoonotic disease, which can also infect humans.|
Back in the 1960s, there was limited knowledge about visceral leishmaniasis control. Some countries, such as China, were using three basic strategies: vector control, human treatment and euthanasia of Leishmania-positive dogs. Brazil decided to adopt the same strategies but without any reliable scientific information to support it. So at that time, Brazil’s Ministry of Health recommended this three-part approach: early treatment of human cases, vector control and even the practice of euthanasia.
The Ministry of Health believed that euthanasia of seropositive dogs could considerably reduce the availability of parasites to the vectors, and this could significantly reduce the number of human cases. However, this assumption was speculative, not scientifically grounded. Nowadays, a few factors are acknowledged: Other animals may serve as a source of infection to sandfly vectors; serological tests will not pick up all infected dogs but only estimate exposure levels; euthanized dogs are rapidly replaced by susceptible ones; and some dog owners will not give up their dogs. Moreover, the limited availability of human and financial resources, coupled with the infrastructure constraints of public health laboratories, make the rapid, systematic elimination of dogs unrealistic in most parts of Brazil.
In fact, none of these strategies were enough to contain the disease, which continues to spread in Brazil. Still, it is important to emphasize that many of the prevention strategies currently available – including repellents, vaccines and immunomodulators – were unknown or unavailable during the 1950s and 1960s.
Prevention is Key – Perspectives in Science
“Prevention is better than cure” is a common saying. Today, we know that in the case of a life-threatening disease like visceral leishmaniasis, prevention is the only way to go – for personal protection and for animal health. Insecticides with residual action can be used for the control of adult sandflies. This chemical control aims to avoid or reduce contact between the transmitting insect and the human population.
Further strategies to protect dogs from the risk of infection also are available now and, in particular, the use of insecticide-impregnated collars has been recommended by Brazil’s Ministry of Health.According to available scientific information, the best-practice recommendation for prevention of canine visceral leishmaniasis is the use of topical repellents. Scientifically-tested repellents reduce sandfly bites and, therefore, pathogen transmission.
A mature female sandfly is usually no bigger than 3 mm
– about the size of a pencil tip.
It is hairy, with a v-shaped wing, and its name comes from its color, not habitat.
However, visceral leishmaniasis still represents a public health threat in Brazil, and protecting dogs is important for protecting people. Expert groups such as LeishVet, Brasileish and TroCCAP play a key role in elaborating guidelines for the prevention of visceral leishmaniasis in dogs. An integrated, ‘One Health’ approach is needed to control visceral leishmaniasis in Brazil. Better quality of life and access to primary healthcare is also fundamental to reduce the burden of the disease among the poorest of the poor.
During the past three decades enormous progress was achieved in leishmaniasis research. We are now beginning to understand the intimate relationship between Leishmania parasites, vectors and hosts. I feel that we should put in practice the scientific information gained in the past decades and improve the management of the disease in Brazil and other endemic countries. Of course, sandfly vectors will never be eliminated from this planet, and there will always be people living in high-risk areas. Still, our priority should be to reduce the level of exposure through better housing conditions. We also need to reduce the number of clinical cases and deaths through better nutrition and increased access to healthcare services. Improved quality of life and a reduction in socio-economic disparities in the tropics could reduce leishmaniasis and many other neglected tropical diseases.
|Unable to stand on its own: This dog was the first real case of visceral leishmaniasis that Filipe Dantas-Torres saw during his studies – on a trip to a remote area in Northeastern Brazil.|
Of course, I endorse the one health initiative because humans, animals and the environment are part of the whole. We need to encourage physicians and veterinarians to exercise a holistic view during their clinical practice. As researchers, we also need to look at the whole – the children who hide their faces in shame, the sicky and the healthy dogs and the people afraid of both of them – if we are to understand the parts. Just like a puzzle.
 PLOS, 2012