Monday, 2 April 2012

The Emergence of Visceral Leishmaniasis in the US



During her March 27 lecture, Dr. Christine Petersen, DVM PhD, Assistant Professor at Iowa State University, offered a One Health perspective of visceral leishmaniasis in the US. As both a DVM and immunologist, Dr. Petersen has been involved in many aspects of One Health, including medical, veterinary, and public health.  Her research, focusing on the prevalence and prevention of zoonotic diseases, has led her to study visceral leishmaniasis in the American Foxhound population.
Dr. Christine Petersen, DVM PhD explains her research on visceral leishmaniasis and why the disease should have a One Health focus in the US.
Dr. Petersen began with a background on the disease, including theories on how it came to the US and why it remains problematic for both dogs and humans. Visceral leishmaniasis, a zoonotic, vector borne disease, exists as a spectrum of clinical disease, from cutaneous sores to disseminated disease with organ involvement. Positive serology does not guarantee clinical disease, however. Induction of visceral leishmaniasis seems to be a classic interplay of genetic background and environmental factors, as malnutrition, drug use, HIV, and childhood are all associated with disease presentation.

The disease is present in 89 countries, and it exists in “New World” and “Old World” forms. Dr. Petersen explained that the version found in the US appears to have come from colonialists, because it is the type species from Europe, not from South America as one would expect given the land connection. The first outbreak in a Foxhound kennel was reported in 1999, and currently 23 US states have seropositive Foxhounds. As sand flies are the vector in many countries globally, four species of sand flies in the US are potential vectors. However, this vector source does not appear to be the main cause of transmission to humans or animals. There have been very few reports of transmission to other animal species or humans despite contact with seropositive Foxhounds. The containment of the disease within Foxhounds and a few other foreign-borne dog breeds suggests that vertical transmission is the primary form of the disease’s transmission in the US.

Dr. Petersen proposed many thought-provoking One Health questions related to disease control and accountability in the US. She stated that good treatments do not exist for humans or canines, and so we must search for methods of controlling transmission. Although sand fly vector control efforts have been implemented in other countries, the US needs to consider how to address the vertical transmission in Foxhounds. She explained that Brazil has begun a depopulation campaign for seropositive canines. However, this effort has not reduced leishmaniasis cases in humans or animals, and it has taken an emotional toll on Brazilians who have lost beloved pets.  She noted that researchers are looking at the human-dog interactions in Brazil to better understand exposure and possible means of containing the disease.

The questions proposed by the audience at the end of Dr. Petersen’s lecture brought forth several other One Health issues. An interesting point was made regarding current military veterans’ relationship to the leishmaniasis issue. Dr. Petersen stated that 4,000 soldiers have come back from Iraq and Afghanistan with leishmaniasis, and many have brought home service dogs and adopted dogs that may also be seropositive. While efforts are being made to address the disease in soldiers, no such effort has been made to monitor dogs coming into the US. Dr. Petersen explained that until we have a “CDC” for animals in US, no one is willing to pay for the testing of animals before they enter the country. In the end, she emphasized the serious need for a One Health approach to this problem, because currently the disease will have to pervade canine populations and begin to affect human health before governmental organizations such as the CDC will intervene.

Interestingly, environmental health arose at the end of the discussion when someone inquired about the effects of climate change on disease prevalence. Dr. Petersen agreed that climate change, particularly global warming, does seem to be influencing the disease, as cases are emerging farther north around the globe. This point brought the discussion in full circle, serving as a perfect demonstration of the inter-relatedness of human health, animal health, and environmental health.

Post authored by Rachel Little, MPH candidate at UNC School of Public Health (Health Care & Prevention Program) & UNC medical student

Up Next (3 April):
                     One Health Core Competencies - Building Capacity for Response to Emerging Pandemic Threats
Felicia Nutter, DVM, PhD, DACZM, Research Assistant Professor at Tufts University Cummings SVM, USAID Grantee, RESPOND Project Senior Technical Officer
                       
The USAID PREDICT Project: Building a global early warning system for
emerging zoonoses
Chris Whittier, DVM, PhD, Associate Veterinarian at Smithsonian