Canine Leishmaniasis Control in the Context of One Health

Dogs are the main reservoir of Leishmania infantum and in some countries have been regularly culled as part of government policy to control visceral leishmaniasis. At the 13th Symposium of the Companion Vector-Borne Diseases World Forum in Windsor, UK, March 19–22, 2018, we consolidated a consensus statement regarding the usefulness of dog culling as a means of controlling visceral leishmaniasis. The statement highlighted the futility of culling infected dogs, whether healthy or sick, as a measure to control the domestic reservoir of L. infantum and reduce the risk for visceral leishmaniasis.

The Companion Vector-Borne Diseases (CVBD) World Forum is a group of scientists working on canine and feline vectorborne diseases (6). This group contributes to an ongoing discussion and update on vectorborne diseases from around the world and their effects on dogs, cats, and humans. Because the topic of canine leishmaniasis is of global importance and thus frequently discussed, a consensus was reached that we should be more proactive in our position toward controlling this disease. At the 13th Symposium of the CVBD World Forum, held in Windsor, UK, during March 19-22, 2018, we discussed the control of canine leishmaniasis caused by L. infantum in the context of One Health and consolidated a consensus statement about the usefulness of dog culling as a means of controlling VL. This statement targets areas where VL caused by L. infantum is endemic and dog culling has been a common practice. We present this consensus statement and highlight the futility of culling infected dogs, whether clinically healthy or sick, as a measure to control the domestic reservoir of L. infantum and reduce the risk for VL in humans.

Scientific Reasons Why Dog Culling Is Unacceptable
In areas of Asia (e.g., China) where government regimes have promoted massive culling of all dogs (regardless of seropositive status), in association with widespread use of DDT for vector control (7), the disease incidence declined for many years. However, whether this was an effect of dog elimination, vector control, or both is difficult to say (5,7). In fact, during the past 20 years, a mass of scientific evidence has accumulated from around the world and under different ecologic scenarios that demonstrates the failure of dog culling as a control strategy, particularly in Brazil (5,7). A dog culling strategy is not supportable for several reasons.
First, no reliable body of scientific evidence supports the effectiveness of dog culling as a means of reducing the incidence of VL (8,9). Second, alternative reservoir hosts may play a role in maintaining the life cycle of L. infantum (3,4) and must be taken into consideration when an integrated control strategy is formulated. Third, culled dogs are rapidly replaced with young dogs that are often more susceptible to primary infection (10). Fourth, serologic diagnostic tools often used for screening dogs as part of a culling program have limitations in terms of sensitivity and specificity (e.g., cross-reactivity where other Leishmania spp. or trypanosomatids occur) (11,12). Fifth, dog culling is not a cost-effective, valid alternative from a socioeconomic perspective (e.g., effect of dog removal on their owners and drugs for euthanasia) to government institutions (7), particularly in developing countries, that promises a long-term solution to the problem. Finally, effective control of L. infantum transmission requires integrated approaches focusing not only on the dog as an indirect source, but also the parasite and, importantly, the sand fly vector (13). Thus, the use of dog culling as a strategy to reduce the incidence of VL in humans cannot be justified and should no longer be used.

Our Consensus Advice and Practical Recommendations
All veterinarians take an oath, an example of which is: "I solemnly swear to use my scientific knowledge and skills for the benefit of society through the protection of animal health and welfare, the prevention and relief of animal suffering, the conservation of animal resources, the promotion of public health, and the advancement of medical knowledge" (https://www.avma.org/KB/Policies/Pages/ veterinarians-oath.aspx). For the control of VL by L. infantum, scientific data clearly align closely with the sentiments expressed by all veterinarians in adhering to their oath, certain in the knowledge that preventive methods should be used, rather than the practice of dog culling, which we believe to be unethical and unjustifiable from a scientific viewpoint.
Using the basis of a One Health approach toward the prevention of zoonotic Leishmania infection in animals and humans, the members of the CVBD World Forum advocate the following recommendations concerning L. infantum infection in companion animals: The members of the CVBD World Forum recommend the following measures to reduce the risk for L. infantum infection in dogs and in humans: 1. Promote phlebotomine sand fly bite prevention to reduce the risk for L. infantum infection in noninfected dogs and its spread from already infected dogs. 2. Improve the general health and nutritional status of dogs. 3. Implement latest concepts regarding the clinical management of canine leishmaniasis, including approaches to diagnosis and treatment. 4. Improve environmental and housing conditions to enhance phlebotomine sand fly control and reduce the exposure of humans to the vectors.