Science Made Cool

Friday Parasites

There's an interesting post about 16th-century Japanese depictions of disease-causing organisms over at the Pink Tentacle Web log. They're basically hypothetical parasites responsible for various forms of ill health. The illustrations have an appealing Dr. Seuss quality, and one almost wonders if they're the result of some early-adopter Japanese physician getting his hands on a Dutch-made microscope and trying to fit what he saw into the traditional paradigm of Chinese medical theory. Several look like plausible parasites or microorganisms. 

(Slow posting week, in part because of a real-life viral parasite working its way through Science Made Cool's crack team of coughers, snifflers, and 12-hour sleepers.)

Friday Parasite: Hidden Until Huge

This is Rafflesia arnoldii, a plant that produces the largest single flower in the world. But the flower is all you'll ever see of this particular plant -- the rest of it lives as a parasite inside the vine the flower sits on.

 

Friday Parasite: Parasites for Kids

Kids love to gross each other out, so What’s Eating You? by Nicola Davies, a book about parasites aimed at the elementary school set, should give them plenty of ammunition for disgusting lunchroom conversations. The book is nicely done – it translates many of the same complicated parasite-host relationships I’ve discussed in these posts (plus plenty of others I haven’t gotten to yet) into kid-friendly prose, and uses lots of specific examples to drive home the idea that every organism, including you, is a pretty enticing environment to a lot of parasites. Many examples are of parasites that affect humans, but Davies doesn’t completely neglect the rest of the animal kingdom – devoting a couple of pages to a discussion of everybody's favorite -- the mind-controlling parasites like Sacculina and hairworms. Another chunk of the book is also devoted to ways that hosts fight back, with their immune systems and good grooming. Kids that are still too young to tackle Parasite Rex will enjoy this one.

What’s Eating You? (Parasites – The Inside Story)
by Nicola Davies; illustrations by Neal Layton
Candlewick Press, 2007

Friday Parasite: Even Parasites Have Parasites

Today's parasite is Pochonia chlamydosporia, a fungus that exploits nematode worms that are themselves — wait for it — parasites. The root knot nematodes parasitize plants; a worm will burrow into a plant's roots and feed on its cells, forming galls and damaging the plant until it can no longer absorb water or nutrients effectively. Unfortunately for us, they think a lot of our food plants are tasty. But the fungus may help us control the worms.

Pochonia chlamydosporia can live in the soil on its own without any ill effects. But when root gall nematodes are about, the fungus turns mean. When nematode eggs appear on the surface of a plant's roots, the fungus moves in. Literally. Its threadlike hyphae grow into the worm eggs, digesting protein and fats along the way. Possible biocontrol agent? Time will tell.

Friday Parasite: Brain Lesions

A cyst from a mouse brain, formed by Toxoplasma gondii.

               

(And yes, it's really Saturday -- technical difficulties kept me from posting this yesterday.)

Photo by S.J. Upton, Kansas State University

Friday Parasite: Sleep Tight

                                       

This little guy is Cimex lectularius, the common bed bug. They’re small, bloodsucking insects that hide in tiny crevices in homes by day, and come out at night to prey on sleeping humans. Any one bed bug doesn’t eat very much —only one meal a week, on average. But they breed like crazy: mature females can lay five new eggs each day over their four-month lifetime, so before you even know they’re there, a couple of bugs can turn into a large infestation. 


Photo from Environmental Health and Safety, Harvard University.

Friday Parasite: Compulsory Mimicry

Parasites really can be insidious. A parasitic nematode called Myrmeconema neotropicum infects ants, making their bodies swell up to resemble ripe berries -- just the kind of berries birds like to eat. The ants get snapped up, and the nematodes find a new home in the bird's gut.

Mimicry is pretty common in the natural world. We're all familiar with creatures like stick insects, which resemble other things in order to avoid getting eaten. But the Myrmeconema nematode turns that on its head -- it makes its host more likely to be eaten.

So if you find yourself looking like a large berry, see if you have nematodes.

Friday Parasite #52: Hooking Up

This is the human hookworm Ancylostoma duodenale,   an intestinal parasite that takes a long and roundabout journey to its final home. Most intestinal parasites get in through the front door, so to speak -- entering their hosts through contaminated food or water. Hookworms are different. They get in through your feet.

Hookworm larvae are found in soil that has been in contact with contaminated fecal matter. When the larvae find the warm bare skin of a new host, they burrow in and wend their way through its body. But they still don't head for the intestines -- they use the circulatory system as a highway to the host's lungs.
to the lungs. Once they're inside the lungs, they crawl up the trachea toward the mouth, where they can get swallowed and finally reach their warm, dark, intestinal home.

Friday Parasite #51: Trypanosomes

                           

Trypanosoma brucei (in blue) cavorting among the red blood cells they infect. This particular trypanosome causes sleeping sickness in humans, and is carried from person to person by tsetse flies.

Photo by Jürgen Berger and Dr. Peter Overath, Max Planck Institute for Developmental Biology.

Friday Parasite #50: Big Ticks

At least, the biggest tick species in the United States. Say hello to Amblyomma tuberculatum. It's generally found on its primary host, the gopher tortoise. Sometimes on rather odd spots.

                  

   Source: Keirans, J. E. and L. A. Durden 1998. Illustrated Key to Nymphs of the Tick Genus Amblyomma (Acari: Ixodidae) Found in the United States. J. Med. Entomol. 35: 489-495.