Creature Comforts: A few of my favorite freeloaders
• Employ stealth tactics to siphon off nutrients without any notice of the host.
• Picking on unthrifty, very young, weak, or debilitated hosts is asking for trouble.
• Don’t get greedy.
• Don’t kill the host.
Heartworms, hookworms, tapeworms, coccidia, giardia, fleas, ticks, lice, scabies, ear mites — so many choices to discuss, but alas, so little space and time. Parasites come in all shapes, sizes and with variably complicated life strategies. Here are just three interesting ones:
The Eyes — Er — Eyelashes Have It
There’s a species of Demodex mite that dwells within the hair follicles and sebaceous glands of the skin. These microscopic mites are species-specific, meaning dogs, cats, and other animals each have their own type. Human Demodex mites inhabit the skin around our eyelashes. It’s estimated that anywhere from 23 – 100% of people are hosts for this parasite. You read that correctly. Most people or animals that have Demodex don’t know it.
Demodex mites typically cause no troubles to their hosts, happily doing their own thing, getting married, having families (all within about 14 days) living out their several-week-long lives, undisturbed. While this story often makes people want to scratch their own eyes out, it really shouldn’t. Dermatologists only prescribe treatments to control Demodex mites for patients with skin abnormalities consistent with Demodex overpopulation. In all cases of Demodicosis, doctors look for an underlying immune or skin issue that caused the mite population explosion. So, even though it isn’t their fault, Demodex are often eliminated from the site in an effort to treat the skin.
Round and Round
The humble roundworm is a fairly common parasite that inhabits animals’ small intestines. Roundworm infestations can be acquired in utero, while nursing, eating prey, or from direct consumption of the eggs in infected stool. Since young animals are prone to eating all sorts of weird stuff, they make excellent targets for the parasite to begin a new invasion.
Roundworms complete their entire life cycles within their host: egg to larva to egg-producing adult — a process that takes place in the GI tract and other internal tissues in a span of approximately 14-28 days (for the species Toxocara canis.) It’s a pretty efficient survival strategy, provided nothing goes wrong. Youngsters can become overburdened with multiple types of internal parasites, which necessitates treatment. Roundworms are easy to eliminate from animals with safe, effective dewormers, but if you’re squeamish, I’d advise not serving spaghetti for dinner after just administering dewormer to your new puppy or kitten.
Roundworms can end up being accidentally ingested by non-ideal hosts (like people.) This scenario’s kinda scary for both the parasites and for the accidental host: the roundworm larvae don’t know where to migrate to complete their life cycle, and end up getting confused, potentially causing serious illness (liver disease and blindness being two biggies) in the infected person. This is not ideal for either party.
It’s Not Just a Fluke …
… it’s a parasitic creative GENIUS. The parasitic flatworm Dicrocoelium dendriticus is an internal parasite of ruminants commonly called a “liver fluke” that employs the help of several different hosts throughout its life cycle. While this tactic is not unique to the flatworm (the ticks that carry Lyme Disease, for instance, utilize several different critters on their path to maturity and self preservation) this particular parasite has upped the ante.
Like most internal parasitic worms, it starts out as a microscopic egg in a pile of poo, in this case, the dung of cows or sheep. The egg is ingested by a snail, hatches into an immature worm within this intermediate host, migrates through different tissues of the snail, and is eventually expelled through the snail’s respiratory system within tiny slime balls. What eats snail slime balls? Ants. An ant that ingests the tiny, immature fluke then becomes a temporary (paratenic) host for the parasite.
This is where it gets really interesting. The fluke finds its way into the ant’s central nervous system and practices mind control! Each night, the ant will climb to the tippy-top of a blade of grass, and clamp its mandibles to the grass all night. Cleverly, the parasite allows the ant to resume its normal activities by day, but compels the ant to perform the strange behavior each night, while the grass is cool and dewy. This cycle continues until the ant is consumed by a grazing animal. Score! Once inside the digestive tract of the cow or sheep, it can reach full maturity and invade the liver and bile ducts, and will go on to reproduce, shed eggs in the animal’s stool, and begin the cycle, again.
The liver fluke is a LITERAL master mind. Want to avoid getting liver flukes? Don’t eat any ant zombies. Fair warning.
— Daverio is a veterinarian at Williamsport West Veterinary Hospital. Her column is published every other Sunday in the Lifestyle section. She can be reached at firstname.lastname@example.org.