Archive for the ‘plague’ Category
a lousy piece
the human body louse, Pediculus h humanus, which has the smallest genome of any insect (at least as of 2010)
Lice cause typhus, sort of. And typhus was likely the cause of many a plague in antiquity.
I’m just finishing off a little book published back in 1976, The life that lives on man, which has been left unread on my shelves for years. I think I may have expected something sensationalist, or maybe I just didn’t want to know too much about the sort of stuff that makes the skin crawl – but I must’ve picked the book up from somewhere, for some reason. I often feel like some sort of ignoramus who wants to know everything and then impart it to – somebody. Maybe someone special who only exists in my mind’s eye.
Anyway, lice and typhus. Michael Andrews, author of the above-mentioned book, covers everything we generally don’t want to know about the beings that thrive on our skinscape, sometimes to our detriment. And he provides me with a lifetime of material to investigate, if only I could avoid thinking about the rest of the universe.
Ok enough. I’ve learned from Andrews’ book that lice (Phthiraptera) come in some 5000 varieties, aka species, and of course have been on us since the beginning of recorded time (not all varieties of course). They can be roughly divided into Mallophaga, which feed on feathers, hair and shedding skin, and Anoplura, which suck blood, and likely developed later:
There are two genera of lice found on man and only one species of each, although there are over 200 other species of sucking lice. Pediculus humanus and Phthirus pubis [crab louse] are closely related but are adapted to different modes of life and different areas of the human habitat.
I won’t mention ‘crabs’ again (though I copped a dose a few decades ago myself), my focus here will be on Pediculus humanus humanus (the human body louse, as opposed to Pediculus humanus capitis, the head louse) and its relation to Rickettsia, ‘bacillus-like elliptical organisms which come midway in characteristic between virus and bacterium’ (Andrews). One ‘intra-cellular’ version of these organisms, carried by the body louse, causes typhus fever in humans, and typhus fever has caused an untold number of human deaths for thousands of years. The number will never be calculated because plague was plague in them days, and descriptions of specific symptoms and aetiology were scarce and no doubt inaccurate in detail.
So my own accuracy mightn’t be reliable in the following, I’m just trying to explore the issue, and in fact my attention was caught not so much by the horror of typhus but by the mention of organisms ‘midway between virus and bacterium’, which sounded sufficiently mysterious as to be worth mentioning. The term ‘bacillus’ originally referred to the rod-like shape of such micro-organisms. As Wikipedia puts it:
Bacillus (Latin “stick”) is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum Bacillota, with 266 named species.
There are different types of typhus, and three principal ones, murine, scrub and epidemic, and I’m focussing on number three. That’s the one spread by Pediculus h humanus. It’s also called louse-borne typhus and jail fever, amongst other things. The specific ‘bacillus-like elliptical organism’ is Rickettsia prowazekii (eureka!), and Wikipedia has a headachingly fascinating intro on the germ:
Rickettsia prowazekii is a species of gram-negative, alphaproteobacteria, obligate intracellular parasitic, aerobic bacillus bacteria that is the etiologic agent of epidemic typhus, transmitted in the faeces of lice. In North America, the main reservoir for R. prowazekii is the flying squirrel. R. prowazekii is often surrounded by a protein microcapsular layer and slime layer; the natural life cycle of the bacterium generally involves a vertebrate and an invertebrate host, usually an arthropod, typically the human body louse. A form of R. prowazekii that exists in the faeces of arthropods remains stably infective for months. R. prowazekii also appears to be the closest semi-free-living relative of mitochondria, based on genome sequencing.
That last sentence is a zinger, which I must needs ignore, for now. Note that bacilli are known to be gram-positive while R prowazekii is gram-negative. The essential difference is in the thickness of the peptidoglycan-based cell wall, which is more layered in the positive types. The two types are named from the Gram stain, developed by Hans Christian Gram in the late 19th century (the positive bacteria turn purple, the negative ones turn red). There are a number of other differences between the types (see the references), including their relative resistance to antibiotics (gram-negatives are highly resistant).
It’s interesting to note that according to the MSD manual, immunisation, along with louse control, is highly effective for prevention of epidemic typhus, but vaccines are no longer available. Presumably this means that the disease isn’t common these days, in the WEIRD world, or not common enough to warrant maintaining vaccine supplies. And that there are more effective forms of treatment. Prevention being better than cure,
Lice may be eliminated by dusting infested people with malathion or lindane. Bedding and clothing should be washed at least once a week in hot water (> 54 C) and dried on high heat. Non-washable clothing and items can be dry-cleaned or sealed in a plastic bag and stored for 2 weeks. Bedding and clothing also can be treated with the insecticide permethrin.
For those infected, doxycycline, a broad spectrum antibiotic with a long half-life in the human body, is recommended.
I’m still left wondering about something we’ll never know. How many of those pandemics of the distant past, which wiped out thousands and sometimes millions, were caused by this or that vector and its parasitising bacillus? Andrews hints that maybe the plague that swept through Athens at the time of Pericles was typhoid fever. That plague contributed greatly to Athens’ eclipse, as it killed Pericles along with half the Athenian population, fatally weakening its resistance to Sparta and ending the Peloponnesian War. But who knows, we might find out some day, human ingenuity being such… And then there are the alternative histories, if only they’d known, and been able to prevent…
References
Michael Andrews, The life that lives on man, 1976