Studied by Rembert Dodoens in 1581
I stumbled across the works of this 16th century Flemish physician, because he shares his first name with that of my first son’s and because I myself looked at “vermis in vesica” (worms in bladders). However, there were three big differences between Dr Dodoens (who published his observations in Latin under the name Rembertus Dodonaeus) and myself: I publish in English and not in Latin and my observations on worms dealt mostly with the urinary bladders of frogs and were carried out with the aid of a microscope, while Dr Dodaens had worked on human corpses and had no microscope for his studies (the microscope was invented years later by Antoni Van Leeuwenhoek in 1674).
I concentrated on frog urinary bladders and frog intestine, because these tissues are ideal structures for the students of the parasitology course I had to teach at Waikato University. Very frequently one can locate some flatworms, known as Digenea trematodes or flukes, in the urinary bladder. Some of these worms are so closely linked to their frog host species that the name Batrachotrematidae of the worm’s family already indicates the close relationship between host and parasite. Other types of flatworms, also present and visible without the help of a microscope because of their large size, are so-called polystomatid Monogenea. Adult tapeworms never reside in the bladder, but their larvae known as plerocercoids can occur in some muscle tissue outside the bladder. Specimens of the ubiquitous nematodes, simply called roundworms, are almost always noticeable in the gut but not the bladder. Because of their whitish coloration and small size it is best to use a microscope to identify them.
When it comes to a microscopic examination of the liquid bladder content the students are usually in for a surprise. If they happen to have a nice frog specimen, then its bladder could be like an “aquarium” for protozoans like flagellates with their undulating membrane or whip-like flagella. Ciliates and amoeba are larger, but the former are fast and the latter are slow. The urinary habitat is not an easy one to survive in. Nitrogenous wastes like urea have to be tolerated and frequent emptying represents a danger of being flushed out. Residing in blood or lymph vessels avoids that, but of course it poses other problems.
Rejection and attacks of the pathogen by antibodies is one problem, the flow of the blood is another, but it is also a boon for the parasite as it supplies nutrients and facilitates transport. The blood flukes Schistosoma mansoni, S. japonicum and 4 others reside in veins and produce eggs that pass out with the faeces, hatch into larvae that mature in a freshwater snail from which the infectious stage is released into the water to find a human host’s skin. Once in the human host, the larvae enter the blood system, mature in the liver and as adults lodge themselves in the blood vessels of the intestines. If that is not worse enough, another parasite, the nematode Wucheria bankcrofti seeks out lymph vessels to live in and then blocks the lymphatic system, causing ‘elephantiasis’. This can lead to grotesque deformations of limbs and other body parts. Varicose veins, so common in the legs of elderly people, however, have nothing to do with parasites in the blood or lymphatic system (although Dr Dodoens had different ideas), but are thought to be the result of a life on two legs. Incidentally, mammals using all four legs to support their bodies throughout their lives fail to develop varicose veins (not even the legs of an elephant have them).
However, animals do suffer from blood parasites (and in the case of seal pups there can even be larval Uncinaria lucasi hookworms in the seal mother’s milk), which takes us back to Dr Rembert Dodoens “Vermis in Vesica”: worms in humans, yes; but worms in human breast milk, no!
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2020.
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