It is remarkable what word associations may trip in your brain.

Someone was talking about head lice in children the other day and I found myself mulling over my encounters with the louse, an ectoparsite (“ecto” pertaining to bugs found crawling around on the outside of the body, as opposed to those living in your intestine, lungs, blood or brains, which would be “endo”parasites and even scarier). Infestations with lice are called “pediculosis.”

I have had the possibly unique experience, compared to the average person, of contracting a brief case of horse lice and another of ostrich lice. In my line of work I have also been called upon to identify and treat lice on chickens, pigeons and guinea pigs. Probably the lice on the ostrich and that of the other birds was the same stuff – namely, avian lice, but I’ve never researched it at any length to determine if they might have been different between KINDS of birds. My sole concern was how to get rid of the pests. My methods have been successful for my patients.

The big message I wish to convey is that all lice are “species-specific.” What this means is that a bird louse can only live and multiply on other birds-of-a-feather. An equine louse can only thrive on horses or other equus species. Sure, they may jump onto another creature, an example being the veterinary student trimming the horse’s hooves with her head buried in its flank – but apart from running around for a few riotous minutes, once scraped off, they are of no further concern to a different species. Period. Bird lice can’t live on people, horse lice can’t live on people. Bird lice can’t live on horses. I know, I’ve tested this theory! I was not a willing participant, but I will bear witness that indeed, the louse of one kind of animal cannot live on another species. Species-specific! Promise! Big sigh of relief.

Many years ago I encountered the only case of lice I have ever seen in a cat. Her owner dropped her cat off in the morning on her way to work, stating that the cat had “bugs” and for heaven’s sake fix it because the cat slept with her.

Lice can often be seen with the naked eye and I quickly found a few on this black cat. Ensnared on some scotch tape, I examined the sample under the microscope. This was more than 25 years ago. There was no Internet to speak of, no cell phones, no Google or other search engines.

What I had was good old text books, several devoted strictly to the parasites of animals. And what showed up on the microscope didn’t look like any lice I recognized. Odd. Searching my books, I came across a photo demonstrating the finer points of the human head louse. I called Public Health. I called the owner, hesitating to discuss my findings. How to delicately convey that her cat was fine.

She was horrified. Turned out she taught first graders and there was a notice circulating that a head lice problem had cropped up in class. She realized that she had contracted it from her student and brought head lice home. I gave the cat a medicated bath, which cured the cat. And although this was one louse I avoided, it made my head itch every time I thought about it!