Johannes Streenstrup Parasites

Many of the larger helminths (e.g. Ascaris lumbricoides, Dracunculus medinensis and Taenia spp.) and ectoparasites must have been visualised in ancient times (Foster, 1965)—in fact, since Homo sapiens first became aware of his immediate environment. D. medinensis was certainly recognised on the shores of the Red Sea in the pre-Christian era. The first clear documentation of these organisms is to be found in the Papyrus Ebers (c. 1550 BC) and other ancient Egyptian writings (Nunn, 1996); these writers were also aware of Schistosoma spp., which remain to this day a major scourge of that country. Aristotle was familiar with helminths involving dogs, fish, and pigs (Cysticercus cellulosae) (Foster, 1965); the presence of this latter helminth in the tongues of pigs is alluded to in a comedy (The Knights) by Aristophanes. Galen (AD 131-199) recognised three human (macro)parasites: A. lumbricoides, Taenia spp. and Enterobius vermicularis. Aretaeus the Cappodocian (AD 81-138) was apparently familiar with human hydatidosis.

The Arabs seem to have added little (if anything) of importance to existing knowledge of human parasitoses; they, too, were familiar with D. medinensis. A twelfth century nun, Hildegardis de Pinguia, recognised the ectoparasite (a mite) causing scabies (Foster, 1965). The first fluke to be well documented was Fasciola hepatica; this was accurately described by Anthony Fitzherbert (1470-1538) in A Newe Treate or Treatyse most Profytable for All Husbandemen in 1532.

Helminths were in some cases considered to improve the health of an infected individual (Foster, 1965); the ancient Chinese, for example, believed that a man should harbour at least three worms to remain in good health, and in eighteenth century Europe many regarded the presence of 'worms' in children as being beneficial to their health. By contrast, there were reports of fanciful or imaginary worms causing all manner of disease(s); parasites were in fact implicated in the seventeenth century in the aetiology of many diseases, including syphilis and plague.

The Doctrine of 'Spontaneous Generation'

From ancient times until the mid-nineteenth century, there was a widespread belief that parasites arose by 'spontaneous generation'— either on or in the human body (Foster, 1965), that was part of a much broader hypothesis which held that all living things arose in this manner. In the seventeenth century, William Harvey (1578-1657) cast doubt on this doctrine and Jan Swammerdam (1637-1680) was firmly of the opinion that it did not occur. Antony van Leeuwenhoek (1632-1723) did not consider that weevils spontaneously generate in corn

Principles and Practice of Clinical Parasitology

Edited by Stephen Gillespie and Richard D. Pearson © 2001 John Wiley & Sons Ltd seed, and Francesco Redi (1626-1697) disproved the widely-held contemporary view that flies arise spontaneously from meat. By carrying out careful dissections of A. lumbri-coides, Edward Tyson (1650-1708) showed there were two sexes and that in fact they multiplied by sexual reproduction; like most contemporaries, however, he believed that the original parasites arose by 'spontaneous generation'. Georges Leclerc, Comte de Button (1717-1788) and Albrecht von Haller (17081777) undoubtedly believed in 'spontaneous generation' and, as late as 1839, the anatomist Allen Thompson (Foster, 1965) wrote that this form of generation was 'to be looked upon as no more than an exception to the general law of reproduction . . .'. Two distinguished parasitologists of the later eighteenth century—Marcus Bloch (1723-1799) and Johan Goze (1731-1793) (see below)—both believed that parasites were 'inborn' in their hosts. V. L. Brera (1772-1840), professor of medicine at Pavia, wrote in 1798 that he was opposed to the idea of spontaneous generation; although believing that worms develop from eggs ingested with food, he considered that this occurs only in individuals whose constitution is favourable to the worm, i.e. that a 'host-factor' has a significant role in the parasite-host equation. The 'doctrine of spontaneous generation of parasites' was not finally abandoned until late in the nineteenth century (Foster, 1965).

ORIGINS OF THE SPECIALITY—PARASITOLOGY

The Italian, Redi (see above) has perhaps the best claim to the title, 'father of parasitology': he wrote Osservazioni intorni agli animali viventi che si trovano negli animali viventi, and was especially interested in ectoparasites (Foster, 1965), particularly lice, although in his classical text he also described dog and cat tapeworms, and had in 1671 produced an illustration of Fasciola hepatica. Another early text was that due to Nicolas Andre (1658-1742), De la generation des vers dans le corps de l'homme (1699); he was the first to illustrate the scolex of a human tape worm—Taenia saginata. He also associated worms with venereal disease(s) but apparently doubted a cause-effect relationship (Foster, 1965). Andre considered that predisposing factors (to infection) were bad air and bad food (both of which contained 'seeds of worms') and overindulgence in food.

One of the most influential figures in eighteenth century parasitology was Pierre Pallas (1741-1811), whose other major interest was exploration (of the Russian Empire) (Foster, 1965); after graduation at Leyden in 1760, he wrote a thesis, De infestis viventibus intraviventia. He also wrote a zoological text, Miscellanea zoologica, in which he concentrated on bladder worms—all of which, he considered, belonged to a single species, Taenia hydatigena.

Goze (see above), an amateur naturalist, made several important contributions to hel-minthology; his monumental Versuch einer Naturgeschichte der Eingeweidewürmer tierischer Körper was published in 1787. He discovered the scolex of Echinococcus spp. in hydatid cysts. Bloch (a doctor of medicine in Berlin) (see above), whose prize-winning essay Abhandlung von der Erzeugung der Eingeweidewürmer was published in 1782, was the first to draw attention to the hooklets on the head of the tapeworm.

The Nineteenth Century

This century saw several important texts on helminthology. Brera (see above) (at Pavia, where he had access to Goze's fine collection of helminths) poured scorn on the idea that the presence of worms was either necessary for, or contributed to, health. However, like others before him, he confused the two species of human tapeworm—Taenia solium and T. saginata. Despite Brera's contributions, Carl Rudolphi (1771-1832), the foremost parasitologist of his day, contributed the most important parasitolo-gical work of the early nineteenth century. He utilised the microscope for histological studies, and his scholarly two-volume work Entozoorum sive vermium intestinalium historia naturalis (1808), together with Entozoorum synopsis cui accedunt mantissa duplex et indices locupletissima (1819), substantially increased the list of known parasites. Other important texts about this time were due to J. S. Olombel (Foster, 1965) in 1816, and Johann Bremser (1767-1827) in 1819. Another parasitologist of distinction in the early nineteenth century was Felix Dujardin (1801-1860); in 1840 he was appointed to the chair of zoology at Rennes, and was the first worker to appreciate that trematodes and ces-todes pass part of their life-cycle in an intermediate host, and that 'bladder worms' are part of the life-cycle of tapeworms; these observations were regrettably not published. He also introduced the term 'proglottis' (a segment of the tapeworm). His major parasitological text was Histoire naturelle des helminthes ou vers intestinaux (1845).

Early English Texts on Parasitology

At the outset of the nineteenth century there was virtually nothing written on this subject in English, nearly all work emanating from mainland Europe. Matthew Baillie (1761-1823) had included relevant passages in Morbid Anatomy of Some of the Most Important Parts of the Human Body (1793); he noted that tapeworm infections were uncommon in Britain (Foster, 1965). In the 1840s several continental works on helminthol-ogy were translated into English, most by George Busk FRS (1807-1886) Surgeon to The Seamen's Hospital Society (Cook, 1997a) and issued by the Ray Society; in 1857, the Sydenham Society published two volumes which contained translations of Manual of Animal and Vegetable Parasites (by Gottleib Kuchenmeister, 18211890), and Tape and Cystic Worms (by Carl von Siebold, 1804-1885). However, the Ray Society had already published On the Alternation of Generations; or, the Propagation and Development of Animals through Alternate Generations (1845) (Figure 1.1) by the Danish naturalist Johannes Steenstrup (1813-1897); in Chapter 4 of this seminal text he described cercariae (liberated by fresh-water molluscs) which remained encysted for several months and contained the parasitic fluke Distoma. Steenstrup had therefore elucidated, and published, the complete life-cycle of one species of liver fluke—thus illustrating his hypothesis of the 'alternation of generations'.

Emergence of Thomas Spencer Cobbold (1828-1886)

Until the 1860s, parasitology was virtually neglected in Britain; during his lifetime, Cobbold became the major British authority on the subject. The son of a Suffolk clergyman (Anonymous, 1886), he served an apprenticeship with a Norwich surgeon, J. G. Crosse; after a few months of postgraduate study in Paris, he returned to the anatomy department of John Goodsir at Edinburgh, where he studied comparative anatomy, and observed many animal parasites, including Fasciola gigantica in the giraffe. In 1857, he obtained the post of Lecturer in Botany at St Mary's Hospital, London and in 1861 he was appointed to a lectureship at the Middlesex Hospital; in 1864 he was elected FRS, and in 1873 he obtained the post of professor of botany and helminthology at the Royal Veterinary College, London. In 1864, he published Entozoa, an Introduction to the Study of Helminthology; this book and its successor (Figure 1.2) contained a detailed account of all the (known) parasites to affect Homo sapiens. Following publication of this text (which had many enthusiastic reviews), Cobbold set up as a physician with a specialist interest in parasitic disease. Due to his, by then, worldwide reputation, he presented, on behalf of Patrick Manson (1844-1922; Figure 1.3) the discovery of the development of 'embryo' filariae (microfilariae) in the body of the mosquito, to the Linnean Society of London on 7 March 1878. In 1879 he published Parasites: a Treatise on the Entozoa of Man and Animals including Some Account of the Ectozoa.

Other European Contributions in the Nineteenth Century

A French parasitologist (primarily a general practitioner), who is now largely forgotten, was Casimir Davaine (1812-1882); he wrote extensively on anthrax—before Robert Koch (1843-1910) and

Fig. 1.1 Title page of Steenstrup's text, published in 1845. This, for the first time, linked the adult parasite with its intermediate (cystic) form
Fig. 1.2 Title page of Cobbold's text. Published in 1869, this formed a supplement to his major text of 1864
Fig. 1.3 Patrick Manson (1844-1922), who discovered the man-mosquito component of lymphatic filariasis, and founded (with the Rt. Hon. Joseph Chamberlain) the formal discipline of tropical medicine

Louis Pasteur (1822-1895), as well as on many other aspects of science, including fungus diseases of plants, the development of the oyster, the science of teratology, the movement of leucocytes, and investigations involving: rotifers, nematodes and infusoria. His work, in fact, gives a very full account of the state of parasitology in the mid-nineteenth century. He described Pentatrichomo-nas hominis and Inermicapsifer madagascariensis, and first advocated the widespread diagnosis of intestinal helminthiases by examination of faecal samples (1857). He also demonstrated that the eggs of A. lumbricoides remain infective for long periods of time in a damp environment. However, his major contribution to parasitology was Traité des entozoaires et des maladies vermineuses de l'homme et des animaux domestiques (I860); although records of the various species are brief, this text contains excellent illustrated descriptions.

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