So, my daughters used to have a pair of pet rats, that we were given as adults. They were very good pets, gentle with the girls and interesting for them to play with. The thing is, though, their coats were always kind of rough and had a bit of what we thought was dandruff. As they got older[1], their hair seemed to get thinner, and in the fall of 2011 they started getting rather itchy. And then on December 3, 2011, we looked at one of them particularly closely because he had developed some sores on his shoulder. At this point, Sandy noticed that one of the pieces of “dandruff” was moving. And then another. And then another. And then we got out the microscope, and found that what he had, was these:

Well, that was a pretty state of things. He had lice! Quickly checking the other rat, he obviously turned out to have lice, too.

These lice were pretty tiny, about a millimeter long or less. They were also laying white eggs on the rats’ hairs, which it turned out was one of the things that made their hair feel rough. We think that they probably had the lice at a low level all along, and had been keeping them under control by grooming themselves and each other. But as they got older and less energetic, they were grooming less thoroughly and the louse population had exploded.

On the bright side, lice tend to be pretty host-specific[2]. These were specifically rat lice, probably Polyplax spinulosa, which only parasitize rats and occasionally other rodents. Not dogs or people. Whew!

So. Problem identified, but now what? One always hears horror stories about how hard lice are to get rid of, involving baths with insecticidal shampoos, repeated at intervals to get rid of the new ones as they hatch from the eggs, and combing with nit combs to get the eggs off of the hairs, and completely changing all bedding, and on, and on, and on. . . and even then, sometimes they persist. Help?

But, modern veterinary technology comes to the rescue! It seems that a number of drugs have been developed for this very problem! The one we were able to buy locally is marketed under the trade name “Frontline”. It contains Fipronil, and is applied topically as a liquid to a point right between an animal’s shoulder blades (where they can’t reach to lick it off – it is much more toxic if ingested all at once than if it slowly soaks through the skin). The Fipronil solution then gradually soaks through their skin into the bloodstream. Fipronil is dramatically more toxic to insects than to mammals, and so levels that are still low enough to be safe for the rats are close to 100% lethal for any insect that drinks their blood, which includes lice. The only thing was that when you buy an applicator of Frontline, it is sized for more common household pets, like cats. Rats are a lot smaller, so they can’t take the whole dose. So what we ended up doing, is we got one applicator sized for a cat, and I borrowed a micropipettor from the lab so that we could accurately dose the rats with a portion of it. It turns out that the appropriate dose for a rat is 80 microliters (which would be a bit less than 2 drops from an eyedropper).

So, we gave them the treatment, and cleaned out their cage to get rid of any lice that might have been crawling in the bedding. Within less than a week, we could no longer find living lice on them, although they still had the eggs. So a month later, we gave them a second treatment, and then completely emptied out and scrubbed their cage. By this time, the nits on their hairs had mostly disappeared, their coats were growing back more thickly, and most importantly, they had stopped scratching themselves. This took care of the problem, and there were no more lice for the rest of their lives.

And in the future, any time that we get a new pet, you can bet we are going to check them over for lice first thing.

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[1] The normal lifespan of a rat is on the order of 3-5 years. Ours were already at least pushing 3 years old when they were given to us (and might have been even older than 3), and we’d had them for nearly another year before the louse problem surfaced. So they were getting pretty elderly by that time. They both died of old age a few months after the delousing, but at least they got to spend the end of their lives not being itchy.

[2] It isn’t just rats that have specific louse species associated with them. Most mammals and birds seem to have their own special species of lice. Humans, for example, have three louse species. Which reminds me of this little aside about lice from the novel “Earth Abides” (a very depressing story about the earth after a virulent airborne disease wipes out practically the entire human race):

Of half a million species of insects only a few dozen were appreciably affected by the demise of man, and the only ones actually threatened with extinction were the three species of the human louse. [. . . ] throughout hundreds of millennia, the lice had adjusted their life nicely to their world, which was the body of man. They existed as three tribes, taking as their domains, respectively, the head, the clothing, and the private parts. Thus, in spite of racial differences, they amicably maintained a tripartite balance of power, setting for their host an example which he might well have followed. At the same time, becoming so exactly adapted to man, they lost the capacity of existing upon any other host.

The overthrow of man was therefore their overthrow. Feeling their world growing cold, they crawled off in search of some new warm world to inhabit, found none, and died. Billions perished most miserably.

At the funeral of Homo sapiens there will be few mourners. Canis familiaris as an individual will perhaps send up a few howls, but as a species, remembering all the kicks and curses, he will soon be comforted and run off to join his wild fellows. Homo sapiens, however, may take comfort from the thought that at his funeral there will be three wholly sincere mourners.