Rat Lice

2012 June 13

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.

[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.

10 Responses
  1. sandy permalink
    June 13, 2012

    Two things I’d like to add. One is that a treatment similar to Frontline, Revolution, is actually safer for small animals. And how do I know this? When we got new pets, Guinea Pigs, I checked them right away for lice and sure enough, they had them. I’m guessing Tim has that cued up for later.

  2. June 13, 2012

    Personally, we’ve always treated our pets with Washington Week in Review.

  3. June 15, 2012

    I didn’t know Frontline (and Advantage, presumably) was absorbed into the bloodstream.

    Also, I love those stories where Man needs to learn cooperation and compassion from the animals by observing one behavior of one set of animals, a behavior very carefully chosen and one not involving, say, cannibalism.

  4. June 19, 2012

    Hm, actually, I don’t know if Frontline (or any of the various other topical pest-killing treatments) are absorbed into the blood or not. Browsing around for information, there seem to be two camps: one group of people insists that it only spreads mechanically over the animal’s skin along with the natural skin oils, and the other group is equally insistent that it gradually diffuses into the blood at a low level. I’m not seeing any actual technical papers describing any actual formal tests of absorption, so I’m not entirely sure that anybody actually knows for sure whether it is absorbed in the blood at a high enough level to kill parasites or not.

  5. Kevin permalink
    May 3, 2014

    How do you keep other rats from grooming the insecticide off the application area on their pals and overdosing?

  6. May 4, 2014

    Kevin: I’d wondered about that, too. I really have no idea how much of a problem this might be. How thoroughly do rats groom each other?

  7. Kevin permalink
    May 4, 2014

    They groom each other, often specifically on their backs and necks, constantly. Especially the males as it is a dominance thing to pin another rat and force grooming, or flipping him over and…forcing grooming. I saw one of my boys literally grab another by the back of the neck and in a swinging motion flipped him up in the air and onto his back. Females do this too, but it is a bit more friendly and more mutual.

    Just lost our Sneezy night before last. The lice he had, which the vet misdiagnosed as other rats bullying ’cause of the hair loss, were producing some kind of brown crud that clogged up his head, basically. Seconds after his passing they all started to jump ship, and that is when I discovered the misdiagnosis and knew it was lice. Yes, no humans were bitten although he would hang out on the bed sometimes. None of his friends have them visible, and we separated him after the vets diagnosis to protect him, so hopefully we won’t have to treat as that worries me.

  8. Sergio permalink
    May 29, 2018

    My friend have lice looks exactly like the one on picture how can we get rid of them we try everything has getting worst

  9. Sergio permalink
    May 29, 2018

    Need help asap

  10. Kevin permalink
    May 29, 2018

    Sergio, the solutions above (frontline, etc…) work well according to the users. I used a topical spray on my rats and their cage and bedding which just seemed a bit safer to me. It was a standard anti-parasitic (fleas, lice) formulated for Rabbits.

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