The Weird World of Parasites

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Great fleas have little fleas
Upon their backs to bite ‘em,
And little fleas have lesser fleas,
And so ad infinitum

[This little verse is often attributed to Ogden Nash, but other sources say the culprit was one Augustus De Morgan (1806-1871), and the poem appears in De Morgan’s A Budget of Paradoxes.]

often get very close to their prey after a successful shot, to get a good look and to admire and feel the coat or feathers of their quarry. Many readers would have noticed parasites like ticks sticking to the bodies of antelopes, or tiny little creatures leaving the bodies of their hosts to seek a new universe. The vast majority of such parasites are harmless to humans, since most of them are host-specific and don’t feed on people – they may cause some itchiness and anxiety though!

Visitors to the African bush may fall victim to ‘Tick-bite Fever’ (TBF). This is a bacterial infection caused by Rickettsia conori or R. africae. The parasitic ticks carrying this infection come primarily from rodents or domestic dogs, but many people are bitten by infected immature ticks that wait on grass-stems for a suitable host to come past, upon which the tick grabs hold and rides along with its new mobile home. Experienced outdoor folk will take care to wear protective clothing, use an insect repellent on skin and clothing, and carefully look for ticks on their bodies after returning from the field. TBF is treatable with -biotics like doxycycline, and the earlier treatment begins the quicker the infection can be controlled. In the days before antibiotics this could be quite a serious disease, and I remember my grandfather being extremely ill with TBF before modern medicine was available.

I spent 18 years of my life working as a Medical Entomologist at the South African Institute for Medical Research in Johannesburg, South Africa and got to learn quite a lot about the weird of parasites. During the 1970s and 1980s there was a lot of interest in the so-called ‘zoonotic diseases’, that is bacterial, viral or other infections in wild animals that can be transmitted to humans, often via some kind of biting creature, be it ticks or mites (arthropods with four pairs of legs) or by insects, which have three pairs of legs. Our work at the SAIMR involved the collection of ectoparasites (that live on the surface of the body, as opposed to within the internal organs) from wild birds and mammals, to gain a better understanding of which of them might possibly be vectors of human disease.

This work involved a lot of fieldwork, during which we collected numerous specimens of birds and mammals through trapping or shooting. Every specimen we killed for this research was thoroughly searched for parasites, even to the extent of dissolving the skin and feathers to recover ticks, mites and lice for identification and classification. In the process we discovered numerous species that were new to science; these were described and named in scientific publications, by our members or collaborating specialists from around the world. We also worked in various parks where animals were being hunted for research or population management reasons.

We were allowed to examine culled elephants in the Kruger National Park for parasites, and we found specimens of the strange-looking elephant louse Haemtomyzus elephantis, which lives on the host’s skin and has an elongated proboscis to get through the tough hide to suck blood.

One of our collaborators stuck a finger in an elephant’s ear and pulled out a blob of wax which was deposited into a bottle of alcohol preservative.. When the wax was later examined under the microscope, a little mite was discovered, a previously unknown species that was named Loxoanoetus bassoni – how weird is that?

During this same operation, I noticed a metallic green fly slowly buzzing past, and I caught it easily in my hand and transferred it to a test tube. It turned out to a specimen of Platycobboldia loxodontis; the female fly lays its eggs in the elephant’s mouth, and the larvae (called ‘stomach bots’) go through all their developmental stages in the stomach. When the larvae are mature, they gather under the elephant’s tongue, from where they drop to the ground, burrow into the soil and pupate. The adult fly later emerges from the ground and finds a mate so the whole cycle can be repeated.

My particular job was to become a specialist on the parasitic insects belonging to the order Phthiraptera (pronounced “thiraptera” and derived from the Greek ‘phthir’ meaning louse and ‘aptera’ meaning wingless). The literal translation, wingless lice, is appropriate for all members of the order. While this was not exactly my idea of a glamorous career, I soon became fascinated by the sheer variety of these tiny creatures that have to spend their whole lives on living birds or mammals, and cannot survive for long once they have lost their host. The lice are divided into two main groups, those that chew the feathers or hair of their hosts, and those that suck blood.

One of the fascinating things about lice is that you can find several different species living on the same host species, where they occupy different niches or habitats on the body. Their distribution may depend on the grooming behaviour of the host – some sluggish lice live in places where the host finds it difficult to groom itself, while others are nimble and can avoid the bill of a bird grooming its feathers. We don’t know much about the different niches on the bodies of birds and mammals, and there is little opportunity these days for people to do research of this kind.

We found that the Springbok, the sports emblem of South Africa, is rather a lousy creature that is host to no less than six different species of the blood-sucking genus Linognathus. But for one of these species, we don’t know where on the they live and how they evolved into different entities over time. However, Linognathus digitalis was discovered living in the interdigital fossae on the feet of the Springbok. It is characterised by having enormous spiracles – these are the openings along the body of the insect through which it draws oxygen for its respiration. One can guess that this unusual feature is an adaptation to the sweaty, dusty environment in which this parasite goes about its life – a weird indeed!

Dr John Ledger is a past Director of the Endangered Wildlife Trust, now a consultant, writer and teacher on the environment, energy and wildlife; he is a columnist for the African Hunting Gazette. He lives in Johannesburg, South Africa. John.Ledger@wol.co.za

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