Wednesday, March 5, 2014

Parasites in Paradise: Origins and Action

By Brian Folt

    About a month ago I was hiking through La Selva, traipsing through a gallery forest alongside a large creek, having a thoroughly pleasant morning. I was searching the flooplain for Rubber Trees, a large canopy species occurring in alluvial riparian areas which deposits a thick layer of leaf litter around the buttresses. Green Macaws squawked loudly overhead, feasting on seeds in the Almond Trees, and I took a moment to photograph a Central American Anteater that I found cruising around the understory. A really tranquilo morning in the field.

    At some point I turned a corner and was startled to see a large Black River Turtle (Rhinoclemmy funerea), calmly staring at me while basking on a sunny log in the creek. We made eye contact momentarily, briefly, for an instant, before two things happened simultaneously: the turtle ducked off the log into the water, and I dove in after it. 

    The turtle, visible through the relatively clear waters, paddled away from me furiously. However, I was equipped with a few summers of childhood swim lessons, and my doggy-style stroke proved too mighty for the turtle. I pinned it to the creek bottom, and then I hoisted it out of the water. Soaked from head to toe, I pulled us from the creek, and took a moment to admire the animal. He was a handsome male, as identified by the concave plastron (bottom shell segment) and the large, thick tail that marks that sex. I thought about what I knew of the animal’s natural history: the species is largely herbivorous, spending time foraging along the water’s edge and in adjacent floodplains for plant matter. But not much else is known about the species ecology, because it has rarely been studied (there is only a single published paper on the species). 

    I then figured ‘There’s no time like the present’, so I pulled some gear from my pack and set about working up the turtle. I took a few measurements (carapace length, mass, tail length, etc.), marked the shell with a unique code for future re-identification, and recorded the capture location. I then patted him on the back and fondly returned him to the creek. 

    Over the course of the next two hours, my search for Rubber Trees evolved into a search for turtles, and I proceeded to nab four more Rhinoclemmys that day. I worked methodically down the creek, capturing any more turtles I observed. As before, each animal was marked with a unique combination of notches in the marginal scutes. Each notch corresponds to a number value, and the notch values add up to an identifying number that is unique to each individual. Using this method, individuals can then be identified during future captures. (Shout out to Turtle Guru Jim Godwin for showing me the ropes about turtle mark-recapture methods in 2012).

    After searching a 600 meter stretch of the creek, I eventually called it quits and headed back to the station, covered in more mud than when I entered the field that morning, but also equipped with more knowledge of Black River Turtles. I have since returned to the creek during the odd free hour over the last few weeks, continuing the impromptu project to study the turtles. I’ve now marked 42 individuals in the study area, and I’m beginning to get a good understanding of the species’ population structure here at La Selva. 

    During recent searches I’ve recaptured over 40 percent of the individuals that I marked during previous sampling efforts, which is exciting because these data allow me to estimate the species’ population density in the study area. This turtle has been historically collected by Amerind communities in lowland Caribbean Costa Rica for food and religious ceremonies, and the species likely continues to face negative pressure from humans. However, since La Selva is a largely protected from negative human influence (e.g., turtle consumption for food), the data collected here are important because this population may serve as reference ecological conditions in the absence of negative anthropogenic effects. 

    But maybe while I was out catching turtles I got a little more than I bargained for, because now my skin is playing host to a party of parasitic worms

     The particular worms I contracted are known as cutaneous larval migrans, a common name for nematodes of the hook worm family (Ancylostomatidae). The larvae occur in soils and sandy substrates and opportunistically parasitize vertebrate animals such as dogs, cats, pigs, etc., which are the natural definitive host. The worms then occupy the lungs and intestines and reproduce by passing eggs outside the host through the animal’s feces. However, humans are an incidental host: young parasites will opportunistically try to infect humans, but are unable to pass through all the way through the skin into the body. Instead, these worms become trapped in the dermal layer and ‘wander’ around, causing intense and unpleasant itchy lesions as they go. Unless treated, larval migrans can occur in humans for weeks before dying. 

    I’m not sure how I picked up the worms. Maybe I contracted them up while running around the creeks here in chase of River Turtles. Or it’s possible that they found me during my primary line of work, which involves substantial time digging around the leaf litter in the forest, often on my hands and knees. 

    Fortunately I got my brothers on the horn and they gave me fairly detailed directions on medication approaches: I needed to 1) visit the pharmacy to buy some anti-helminthic drugs (Thiabendazole, Albendazole, or Mebendazole), 2) take 400 mg each day on a full stomach for five days, and 3) probably not dive chest deep into muck after turtles. A quick visit to Wikipedia confirmed the first two bits of their advice (...or did they read the Wiki first?), so I saddled up and headed to visit the farmacia in town. 2500 colones later (<$6 US dollars), I had a remedy in hand, and I began my war against worms. I took the pills on a full stomach regularly, and the itchiness subsided quickly (including chigger and mosquito bites, nice secondary perk). A few days after finishing the Albendazole, most of the worm lesions cleared up nicely. I was fairly pleased/relieved to be returning to a state of quasi-cleanliness in the absence of parasites (!!!). Little did I know my new experiences with tropical maladies had not come to an end. 

Ever had parasitic worms? If so, which one, and where did you get it? Share your story in the comments below.

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