About Sloth Parasites
A parasite is an organism that lives in or on a host and benefits by deriving nutrients at said host’s expense. A parasite differs from a symbiote in that a symbiote offers some benefit to the host in exchange.
There is very little research on parasitic infections in sloths. The majority of research that has been conducted has taken place on captive sloth populations, which live a very different lifestyle than wild sloths, with very different diets, vulnerabilities, and exposure.
Are sloths full of parasites?
Sloths have green, algae-colored fur that hosts a vast number of invertebrates, and one may think that so much flora and fauna would signify a relationship balanced heavily in favor of parasites.
However, these organisms are not parasites, and they do not cause any negative effects or ill health in the sloths. Most of the organisms that call a sloth home have a mutualistic symbiotic relationship, where both the sloths and their passengers benefit.
Coccidia parasites are commonly found in domestic and captive wild animals, including sloths. Coccidia includes a wide variety of parasites that produce varying degrees of disease severity, from mild diarrhea and appetite suppression to dehydration.
Captive sloths have frequently been found to be infected with Eucestoda, commonly known as tapeworm. All types of tapeworms parasitize vertebrates and colonize their digestive tracts, living anywhere from a few days to multiple decades. This type of infection is characterized by diarrhea and weight loss over time.
Thanks to their low body temperature, sloths are not as prone to tick infestations as most mammals. However, sometimes when sloths spend extended periods on the ground (such as when they are moving between deforested areas), they may pick up ticks during tick season.
Amblyomma varium is known by parasitologists as the giant sloth tick, as it is host-specific to Bradypus and Choloepus sloths. It is one of the largest tick species in the world.
Captive sloths have sometimes been diagnosed with scabies, which is caused by the mite parasite Sarcoptes scabiei. This zoonotic skin affliction is characterized by itching and a bumpy rash which can be easily treated with topical anti-parasite medication. Special care must be taken when dealing with scabies, which is easily transmitted via contact with an infected person, or even fabric items an infected person has been in contact with.
Secondary skin infections due to itching are common, and animals afflicted with this parasite will often lose drastic amounts of weight. Scabies in animals is often referred to as sarcoptic mange.
Leishmaniasis is a zoonotic (meaning “carried by animals”) disease caused by the Leishmania parasite.
Colloquially known as “papalomoyo” in Costa Rica, Leishmaniasis is a common affliction amongst coastal Caribbean populations. Cutaneous (meaning “of or on the skin”) leishmaniasis is the most common—and luckily the most treatable—variation of the disease. However, Leishmaniasis is not isolated to the tropics; it is found on almost every continent, most commonly infecting humans and dogs, and sometimes cats and horses.
The disease is usually transmitted through the bite of female sandflies, who inject the immature form of the parasite (promastigote), which then matures inside the host (you, me, our pets), produces more promastigotes (baby Leishmanias), which are then transmitted back to sandflies via another bite, and the cycle begins again.
It is possible for Leishmaniasis to transmit by other routes, such as from a mother to an unborn child, or through the reuse of unsterilized needles, but the most common transmission mode is through sandflies. The presence of this disease in Europe is mainly due to the translocation of pets around the world.
So what does this have to do with sloths?
A commonly believed myth associates sloths with leishmaniasis, although this myth varies in its specifics. Some say a victim can acquire the disease by being bitten by a sloth, others claim that sandflies live in sloth fur. While sloths do have a whole ecosystem living within their fur, sandflies do not and cannot live on a sloth. Sloth bites in humans are infrequent and could not transmit Leishmaniasis.
As with most myths, there is a grain of truth at the heart of this one: sloths are reservoir hosts of the Leishmania parasite. This means that the parasite can live in them without causing disease in the sloths. In fact, studies have suggested that sloths are one of the largest Leishmaniasis reservoirs in Central and South America. Reservoir hosts, such as sloths, dogs, and cats, cannot pass the disease onto humans.
Several different forms of Leishmaniasis exist. They vary in severity depending on if you have contracted cutaneous (of or on the skin), mucosal (of or on mucus membranes, such as inside the mouth or in the nose), or visceral (of or inside vital organs) leishmaniasis.
Cutaneous Leishmaniasis is the least severe version, causing skin lesions and swollen lymph glands, and visceral Leishmaniasis is fatal if left untreated, causing fever, anemia, and hepatosplenomegaly (enlargement of the liver and spleen).
A personal story
SloCo’s founder, Dr. Rebecca Cliffe, once contracted cutaneous leishmaniasis, which developed into mucosal leishmaniasis. “I remember the sandfly that bit me. I was walking my new puppy on the beach at dusk and was annoyed by the itchy bump that later appeared on my arm. I forgot about it and only really noticed something unusual when the bite was still there two weeks later.”
“We watched the little hole in my arm slowly grow for 4 weeks before deciding to have it tested. Within 24 hours, the doctor had called and told me that I had tested positive for leishmaniasis and should begin treatment immediately. I didn’t know it at the time, but that was just the tip of the iceberg.”
“As it turned out, there are no nice treatment options. The Costa Rican method involves up to 60 injections of glucantime – a toxic chemical that kills the parasite but also comes with a high risk of liver and heart damage. That didn’t sound like much fun, so I decided to seek treatment in the UK since I had been due to return during August anyway. When I finally arrived at my doctor’s office and presented him with a flesh-eating parasite, he looked at me like I had two heads. I was advised to go to the emergency room at the Liverpool School of Tropical Medicine to find more specialised help.”
“Depending on the species of leishmania I was infected with, I now had two treatment choices:
1) I could be admitted to the hospital for three weeks of intravenous medication (chemotherapy), which basically involves the same toxic chemicals as the Costa Rican injections (think heart problems and liver failure). Famously, TV presenter Ben Fogle endured this treatment after contracting leishmaniasis in Peru, and he ended up bed-bound with pneumonia – no thank you!
2) OR I could trial a new oral medication from Germany called Miltefosine. This horrifically expensive drug comes with a bunch of awful side effects, including sickness so severe that many people simply can not finish the treatment. This option wasn’t guaranteed to work either and had never before been used to treat leishmaniasis from Costa Rica. Furthermore, this medication is only effective against one subspecies of the parasite – the most dangerous subspecies.”
“As it turned out, fate made the decision for me. I was diagnosed as having the dangerous subspecies (one that is prone to infecting the mouth and nose causing disfigurement) and so I was prescribed 4 weeks’ worth of Miltefosine pills.”
** You can read about Dr. Cliffe’s experience here: http://beckycliffe.com/battle-leishmaniasis-flesh-eating-parasite/ **