Weighing human lives against dogs'

Canine parasite rarely cured in humans stirs debate

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How much is a dog's life worth? Less than a human life, obviously, but how much less? Would you kill 1,000 dogs to save one human? A million dogs? Perhaps you're an absolutist, and you'd sacrifice every dog in the world to save one person. But what if you weren't sure how many people you'd save? How many dogs would you euthanize for a 10 percent chance of saving one human?

This sounds like chatter at an exceptionally morbid cocktail party, but it's not the slightest bit hypothetical. For the past 20 years, public health experts in parts of Asia, Africa, South America and Europe have debated the ethics and efficacy of large-scale dog culling to prevent transmission of a deadly human disease.

Leishmaniasis is a parasitic infection that can affect several parts of the human body. The most dangerous form, visceral leishmaniasis, causes swelling of the internal organs and kills 95 percent victims within two years without treatment. Treatment is somewhat expensive and complicated, as parasites in different regions respond differently to medication, and many of the medications have high toxicity. Drug resistance is also becoming a problem. Officially, the disease is responsible for 50,000 deaths annually, with South Asia, Sudan and Brazil suffering most of the burden, but that estimate is probably low. Most countries eased off leishmaniasis monitoring decades ago, when they thought the disease was under control. In many parts of the world, however, it is now resurgent.

One of the difficulties in dealing with leishmaniasis is that the protozoan parasites that cause the disease have so many places to hide. In South Asia, humans appear to be the main reservoir. The bite of the sand fly spreads leishmaniasis from person to person, the same way mosquitoes spread malaria. In other places, particularly Brazil, the sand fly spreads the disease from wild or domestic animals to people. Although there is much debate in the scientific literature on this point, many public health experts are convinced that domestic dogs are the primary contributors to the spread of the disease. In some Brazilian neighborhoods, veterinarians report that as many as 50 percent of dogs test positive for the parasite that causes visceral leishmaniasis in humans.

Brazilian veterinarians, like their colleagues in many other leishmaniasis-affected countries, are required to euthanize these animals. Treating canine leishmaniasis is notoriously difficult. Even when doctors are able to suppress the symptoms, there's no way to be sure that the parasite is gone. Leishmaniasis screening tests measure antibodies against the disease, and those antibodies remain in the dog's system long after treatment, making a cured dog indistinguishable from an infected dog. Euthanasia is, in theory, the safest option.

The program is intended to save human lives, and some could argue dog lives simply aren't worth as much.