Colombian Jungle Cows to Syrian Social Media: Researching Leishmaniasis
Dusk has fallen in the jungle outside of Tumaco, Colombia. A team of researchers has traveled via jeeps and canoes to the western side of the country, leaving behind the glimmering lights of the Cali metropolitan area. They load the supplies for their remote three-day expedition and placate perhaps the most important item of their trek, a cow borrowed from a nearby village.
D. Scott Smith, his newly-minted public health degree hanging at home in Colorado, is a part of this multinational research team composed of guides, veterinarians, parasitologists, and doctors. He has never been to Colombia, but his Fulbright scholarship for neglected tropical diseases has brought him to the front lines of public health. The team needs to capture sand flies, a blood-feeding insect that survives in both jungle and urban habitats. Unfortunately several sand fly species, found in over 90 countries worldwide, have a preference for human blood in addition to other mammals.[1,2] While sand flies live in the United States, other countries like Colombia have more sand flies with a species of protozoan parasite living within them called Leishmania.
These Leishmania parasites are what cause the leishmaniasis disease; they take advantage of the sand fly’s ability to bite and enter the bloodstream of mammals. Smith and his colleagues are hiking through the jungle to find sand flies and determine if the insects have the Leishmania parasites inside them. The team winds their way through thick vegetation. They lead the cow through a tangled sea of green barely illuminated by headlamp light. It may not seem like the smartest decision at first, but the animal is one of the team’s most vital tools.
They arrive at a research site nestled between the trees with just enough of an opening to set down the equipment. Smith helps to unpack the supplies; the researchers lay a plastic tarp in the center of the clearing and place crisp white boxes on top. It’s a stark contrast against the jungle’s earthy tones.
As for the cow, the team ties its halter to a tree on the side. A white sheet is suspended between the researchers and the animal to create a division. They point flashlights towards the white cloth wall and wait. The cow wasn’t just brought here to chew its cud; it is actually bait for the sand flies.
In order to attract hungry female sand flies that can transmit leishmaniasis, you need mammals. This particular night there were two kinds—bovine and human. Unlike other types of traps, animal-baited traps allow researchers to obtain live insects which are easiest to analyze for Leishmania. Depending on whether the sand flies try to take a blood meal from the cow or the team makes quite the difference for data analysis; researchers learn which types of sand flies prefer humans versus those that prefer other mammals.
If the sand flies head for the cow, attracted by its warmth and smell, they will unwittingly run into the white sheet in front of the researchers. If the sand flies land on the researchers, they will hopefully be snatched up before they get a chance to bite. The goal is to identify the insects and promptly add them to the white collection boxes on the tarp.
Several team members are armed with rubber tubing affixed to tapered glass at one end. These “aspirators” function like a sand fly vacuum. When insects land on the sheet or clothing, a team members sucks on tubing to pull the insect into the glass end – don’t worry, the filter inside will prevent them from inhaling the sand fly – and blows the sand fly out into the collection container. Smith and the research team members stay up all night vigilantly catching the sand flies. They are easy to capture despite their small size. The team will stop collecting once the sun rises and the nocturnal sand flies rest from their night of feeding.
Back at a biomedical research center (CIDEIM) in Cali, the scientists determine what species of parasite the sand flies from that area have. The Leishmania species is critical to knowing what type of leishmaniasis they will cause in humans. The most common form of the disease is cutaneous leishmaniasis, CL. While this form isn’t inherently life-threatening, the spot where the sand fly injects the protozoan parasites into human skin causes a welt that usually grows into a volcano-like ulcer. The sores usually heal slowly (months to years) on their own without medication, but they can leave disfiguring scars that can affect mental health.[1–3]
The parasite species also helps to determine what type of treatment (if any) will be administered. Some species might trigger more severe – and potentially deadly – forms of the disease. However, the medications to kill Leishmania making a home in human immune system cells are often toxic and/or expensive. Adding to the problem, some Leishmania are also becoming resistant to the medications we use.[1,2]
D. Scott Smith’s trips into the Colombian jungle took place in 1987, but leishmaniasis is still a concern worldwide. Smith’s interest in parasitology has continued. He is now a professor at Stanford University and Chief of Infectious Diseases & Geographic Medicine at Kaiser Permanente in Redwood City, CA. When Dr. Smith isn’t teaching or seeing patients, he also volunteers with the MENTOR Initiative. One of this organization’s projects is to reduce cutaneous leishmaniasis in Syria.
Since the start of the violent conflict in 2011, CL cases in Syria has increased dramatically. While cutaneous leishmaniasis used to be well managed, Syria is now one of the countries most affected by the disease.[2,6] Sand flies can breed easier in the absence of coordinated interventions like insecticide spraying and garbage removal. Some cities, such as Aleppo, have been divided in two by armed groups, making it more difficult to control sand flies and distribute leishmaniasis medicine.
Amidst the strife of war, scientists and organizations are trying to combat this neglected tropical disease. For instance, it can be hard to determine the prevalence of CL in a region due to the conflict, so one researcher analyzed YouTube and Facebook videos made by doctors in different communities to learn more about the disease in their area. One town reported that they only had enough medication to treat two of more than 600 CL patients.
The World Health Organization and the MENTOR Initiative have also tried to help hard-to-reach areas in Syria combat leishmaniasis by distributing long-lasting insecticide treated nets. Sand flies are one-third the size of mosquitoes (or even smaller), so standard mosquito netting isn’t effective unless it is treated with insecticide. MENTOR is also advocating for more community studies to track leishmaniasis outbreaks. In areas where the organization works in Syria, cutaneous leishmaniasis affects nearly every family.
Keep in mind that across the world 350 million people are at risk of leishmaniasis. As a neglected tropical disease, leishmaniasis affects some of the poorest regions, but public health interventions are possible.[1–3] Another hope that researchers, including Dr. Smith, have is that progress is being made on a human vaccine for leishmaniasis. It will take innovative scientists from many fields to collaborate on disease elimination. Dr. Smith and fellow “leishmaniacs” conducting research on the ground are just one part of the global effort to reduce leishmaniasis.
- Dickson D. Despommier, Daniel O. Griffin, Robert W. Gwadz, Peter J. Hotez, C. A. K. (2017). Parasitic Diseases (6th ed.). New York: Parasites Without Borders.
- Hayani, K., Dandashli, A., & Weisshaar, E. (2015). Cutaneous Leishmaniasis in Syria: Clinical Features, Current Status and the Effects of War. Acta Dermato-Venereologica, 95, 62–66. https://doi.org/10.2340/00015555-1988
- Centers for Disease Control and Prevention. (2013). Leishmaniasis FAQs. Retrieved October 20, 2017, from https://www.cdc.gov/parasites/leishmaniasis/gen_info/faqs.html
- Alten, B., Ozbel, Y., Ergunay, K., Kasap, O. E., Cull, B., Antoniou, M., … Medlock, J. M. (2015). Sampling strategies for phlebotomine sand flies (Diptera: Psychodidae) in Europe. Bulletin of Entomological Research, 105(6), 664–678. https://doi.org/10.1017/S0007485315000127
- Burki, T. (2017). Leishmaniasis unleashed in Syria. The Lancet Infectious Diseases, 17(2), 144–145. https://doi.org/10.1016/S1473-3099(17)30016-6
- Alasaad, S. (2013). War diseases revealed by the social media: massive leishmaniasis outbreak in the Syrian Spring. Parasites & Vectors, 6(94). https://doi.org/doi:10.1186/1756-3305-6-94
- Onuekwe, C. E. (2014). WHO partners with MENTOR Initiative to control leishmaniasis in Aleppo and Deir ez-Zor. Retrieved from http://www.emro.who.int/syr/syria-news/who-partners-with-mentor-initiative-to-control-leishmaniasis-in-aleppo-and-deir-ez-zor.html
Smith, Darvin Scott. (2017, October 24). Leishmaniasis research [Personal interview].
Cover image courtesy of Jeramiah Winston.
Fig. 1: “10276” by James Gathany is courtesy of the Public Health Image Library.
Fig. 2: Courtesy of D. Scott Smith.
Fig. 3: “15069” is courtesy of the Public Health Image Library.