Leishmaniasis: The Disease and Scientific Developments

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Leishmaniasis: The Disease and Scientific Developments | W. Jean Dodds, DVM

 

Leishmaniasis is of significant disease concern, especially in warmer tropical climates, and it is spreading because of global warming. With only a few incidents reported in North America, the majority of our readers do not currently have to worry about leishmaniasis based on their geographical location. Due to travel and climate change, however, we all should be aware of its existence and the serious adverse effects on human and companion dog health.

  • More than 20 Leishmania spp. are known. Mutations of the parasite do occur.  
  • 30 different sand fly species carry the disease. Other sand fly species may be able to mutate and become vectors of leishmaniasis.
  • Extremely climate-sensitive.
  • Endemic in many parts of South America, Asia, East Africa, Southern United States, Central America and Southern Europe.
  • Neglected Tropical Disease (NTD) – The World Health Organization states that leishmaniasis is one of seventeen NTD’s. These diseases affect mainly the poorest populations (over 1 billion people) worldwide who rely on farming or very low-income jobs for survival. The Centers for Disease Control puts it simply, “NTD’s trap the poor in a cycle of poverty and disease,” by impairing cognitive or physical abilities that contribute to a decrease or arrest in productivity.  
  • Treatment options differ based on species of Leishmania and the geographical location.

How does leishmaniasis affect dogs? For years, we have known that dogs can be reservoirs for leishmaniasis. Unfortunately, mitigation of disease spread efforts relied on culling or euthanizing dogs. It is indeed a sad practice, but we should remember that many impoverished countries cannot provide basic sanitation or healthcare to their citizens let alone diagnose and treat dogs. However, over the past 30 years, diagnostic tools have rapidly advanced, new perspectives have focused on dogs, and the few outbreaks in the United States amongst canine populations have prompted more research.

What is leishmaniasis?

Leishmania spp. protozoan parasites are the cause of leishmaniasis. Depending on the species of Leishmania, humans and dogs can develop either the visceral or cutaneous (integumentary) form. For instance, Leishmania mexicana is endemic in Texas and Oklahoma and causes cutaneous leishmaniasis; the clinical symptoms are skin sores, skin ulcers, papules, etc. Visceral is the most serious form of the disease and is typically caused by Leishmania infantum.

Variable Clinical Signs of Canine Visceral Leishmaniasis Disease in Dogs:  

  • Overgrowth or quite brittle nails
  • Weight loss/poor condition
  • Lack of energy
  • Decreased appetite
  • Anemia
  • Crusty areas on skin
  • Bloody nose
  • Bloody stool
  • Watery or goopy eyes
  • Big lymph nodes/swollen glands
  • “Pot-bellied” appearance
  • Renal failure

Treatment options for dogs in the United States are minimal but can be effective if initiated before renal insufficiency sets in. The biggest concern is possible transmission to humans, so pet caregivers need to be quite meticulous in caring for a dog with leishmaniasis, and provide a high-quality protein diet. Vaccines against canine leishmaniasis are not entirely effective and in any event, are not licensed in the United States.

New Knowledge about Leishmaniasis Transmission

Around the year 2000, kenneled Foxhounds in New York State started to show symptoms of Canine Visceral Leishmaniasis and some passed away.

How did it arrive in the New York area? The MON-1 genotype was isolated in these Foxhounds, which is most frequently found in dogs from the Mediterranean Basin. So, it is surmised that a few infected Foxhounds were transported to the United States from Europe.

As transmission of leishmaniasis is known to occur after infected via sandfly bites, how did the disease keep spreading, when no sandflies were identified in the area and the dogs at area shelters had also tested negative for canine leishmaniasis? The evidence strongly points to vertical (transplacental) and horizontal (venereal, blood transfusions, wounds) transmissions between dogs. While this conclusion seems obvious, we need to remember that in endemic areas the sand fly is a known vector, but other possible routes of transmission can be occurring in non-endemic areas.

The nature of Foxhound clubs is to breed and trial dogs and travel for events around North America. Researchers embarked on an ambitious study of these clubs and tested over 12,000 Foxhounds. 18 states and provinces have confirmed Foxhound cases of canine visceral leishmaniasis. This raises the immediate concern that some sandfly species. Particularly those in the Southeast are somehow primed to mutate and possibly become vectors of the disease, thus increasing the chances of human infection. By the way, the study also sampled humans who had close contact with the Foxhounds; they were found not to be infected.    

Further, we must always keep in mind that infection does not mean clinical disease has developed or even will develop, although the infection can still spread to others. Regarding leishmaniasis, studies have shown that the presence of infection in dogs, like an asymptomatic carrier state, is much higher than those dogs that develop symptomatic disease.  Investigators have also identified several factors influencing susceptibility to leishmaniasis disease: secondary immunosuppression or immune changes such as in pregnancy or tick-borne disease; concomitant infections; poor or imbalanced nutrition; parasite virulence; and, genetic predisposition. In fact, several studies have isolated the gene(s) that may contribute to susceptibility.

Advancements in Diagnostics  

A variety of blood tests detect leishmaniasis as an infection, disease or both based on the immune response to exposure or parasite load. Of course, we aim to detect leishmaniasis at the earliest infectious stage.  

  • Indirect Immunofluorescent assay (IFA) – Outdated technology that measures immune reactivity against the whole parasite; really only detects leishmaniasis disease, and can cross-react with antibodies to the kinetoplastid Trypanosoma cruzi (Chagas Disease). Therefore, more testing would need to be done to find out which disease it is involved.
  • kELISA – Measures a specific Leishmania antigen and can detect infection at an earlier stage than IFA.
  • Quantitative Polymerase Chain Reaction (qPCR) – Measures actual parasites in the blood stream by detecting parasite DNA. This highly-sensitive test is heavily relied on these days to detect infection. It must be noted that a minimum number could be a false positive, so a reputable laboratory must be used. [Hemopet sends bloodwork of our Greyhound blood donors to a laboratory in San Diego for qPCR testing.]
  • T-Cell Proliferation (TCP) – Most effective to detect leishmaniasis infection at the earliest stage because it literally measures the T-cell proliferation against parasite antigens. Unfortunately, this assay is performed on an experimental basis due to the time and materials required for successful analysis of this cellular response.

W. Jean Dodds, DVM
Hemopet / NutriScan
11561 Salinaz Avenue
Garden Grove, CA 92843

References

Duprey, Zandra H. et al. “Canine Visceral Leishmaniasis, United States and Canada, 2000–2003.” Emerging Infectious Diseases 12.3 (2006): 440–446. PMC. Web. 12 Feb. 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3291440/.

“Leishmaniasis.” World Health Organization, n.d. Web. 12 Feb. 2017. http://www.who.int/leishmaniasis/en/.

Petersen, Christine A. “Leishmaniasis, An Emerging Disease Found in Companion Animals in the United States.” Topics in companion animal medicine 24.4 (2009): 182–188. PMC. Web. 12 Feb. 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2805016/.

Petersen, Christine A., and Stephen C. Barr. “Canine Leishmaniasis in North America: Emerging or Newly Recognized?” The Veterinary clinics of North America. Small animal practice 39.6 (2009): 1065–vi. PMC. Web. 12 Feb. 2017. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2824922/.

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