Posted by: Green Knight | June 29, 2012

The Good, the Bad, and the Bacterial

I was reading the other day about new ideas for ways to reduce the spread of Dengue fever, aka “bone-breaking fever,” which infects 20 times as many people as the flu these days. It’s mostly a tropical disease spread by mosquitoes,  like malaria or West Nile virus, but it’s spreading to subtropical latitudes. For a little background on insect control, consider the following. In the late ’50s, there was a program that lasted into the ’80s to “eradicate” the screwfly, or the screwworm (the larva). Those nasty boogers lay eggs in wounds on animals, and the maggots eat the host; a cow or a horse or a dog can die in a week. It’s really bad stuff.

The solution was to zap or irradiate screwfly pupae with a bit of gamma radiation in the lab, then collect the hatched males, who were now sterile courtesy of the γ rays, and release them into the wild. They’d still mate with females, but couldn’t pass on any viable genetic material. Makes me think back to the ’70s…”hey, baby, I had a vasectomy, and I don’t have herpes…YET.” At any rate, it worked. Screwflies were eradicated in the US, and also, over the years, in Old Mexico through Centroamerica down to Panama. Vigilance is required to keep them from getting back in, though. Family dogs that go on vacation with their humanoids to the tropics, racehorses that go to compete down south, etc., have brought them back a few times. This is why we need our biological border patrol and why we need to fund them well.

What they’re trying to do with the mosquitoes (skeeters, or “mozzies” if you’re from Down Under) is interesting. One approach is to genetically engineer the males to be basically infertile; it’s too complicated for my typin’ fingers to detail right now. We’ve been doing genetic engineering for thousands of years, which is why we have poodles and Chihuahuas and not just wolves, and why Zea mays, aka maize or corn, exists as an edible grain (just beware of pellagra if that’s about all you eat, though, and get some niacin (B3) in your diet…that disease will make your hide all scaly and stuff, like an H.P. Lovecraft creature). Genetic engineering just happens faster in the lab than in the field, is all. The idea is to tinker with the genes to make the males nonreproductive, but some folks fear that genetic transference could occur. Well, sure, happens all the time in Nature too, not nearly as much with multicellular life forms, though.

The other approach, which I like, is a more “biological-control” type method. It involves using a bacterium, Wolbachia pipientis, which naturally infects insects, other arthropods, and nematodes already. It’s a very complicated situation, though. Wolbachia has an aggressive parasitic relationship with some species, a sort of neutral one with others, and is a necessary symbiont with still more critters. In mosquitoes, those bacteria somehow block the transmittal of Dengue, which is a virus. Virus particles are way, way tinier than bacteria. So the idea is to boost the already-existing infection rate in skeeters to cut down on ones that can transmit Dengue, and malaria, nice add-on, by selective breeding and releasing. Wohlbachia does all sorts of weird stuff to the sexuality of insects; I suggest reading the Wikipedia article for more info that will freak you out. We just are learning to deal with the LGBT thing as socially evolved humanoids; in the insect world, or the amphibian one for that matter, we’d run out of capital letters.

But above, I mentioned that the bacterium is also a symbiote with certain critters. Nematode filarial worms are the main animals of concern here. They will eat the roots of your rose bushes (hint: plant marigolds between your roses; the rotenone released by the roots will kill the ‘todes.), Some of them cause river blindness  (onchocerciasis) and elephantiasis in humans, and exacerbate heartworm problems in our doggie friends. One reason you must NOT try to treat your dog for heartworms on your own is that killing the worms is not enough. When they die, even the ones that do so naturally in an infected animal, they release all those Wolbachia bacteria, which causes serious irritation and inflammation due to an immune system over-response, and finishes the job that the nematodes began. It will kill your best friend. Please, please, pleez, folks, get yer dogs tested first and then put them on Heartgard, all year. It’s just a chewy treat once a month. Our best friends deserve it. My long-lost dogs Jake and Carnahan will thank you from beyond, where they’re waiting for me patiently, tails wagging.

Wolbachia is also even and ever weirder because it, in some cases, makes the mozzies and other insects more resistant to insecticides, and makes fruit flies and mites more resistant to RNA-virus infections. Plus, while it blocks mosquitoes from transferring Dengue (a virus) and malaria (a protozoan, orders of magnitude larger) to mammalian (and perhaps reptilian? must research this further) hosts, it also harbors the WO virus, which appears to be a symbiont of its own, and perhaps necessary to the bacterium’s survival. It’s an interesting test-subject for scientists because it does the lateral-transfer DNA thing with other bacteria more readily than any other so far studied, and thus may be the fastest-known evolutionary speciator out there. Why are the nastiest bugs the most interesting? Well, why are we still fascinated by Jack the Ripper?

[for my pals who like science fiction-type reading material, I highly recommend “The Screwfly Solution,” a 1977 short story by Raccoona Sheldon. It’s relevant to this discussion, and is a great read all by itself. A bit disturbing, though.]

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