Chapter XI: Parasites

Like all other animals, snakes are infested with a multitude of vegetable and animal parasites, both external and internal. About 300 species of Ophidian parasites have been recorded; yet our knowledge of them is very imperfect. Although some 2,000 species of snakes are known, parasites have not been recorded for more than 168 species, and in the great majority of these (102) only a single parasite: a tick, a hæmogregarine, or some intestinal worm. Owing to the more frequent opportunity of dissecting them, the common menagerie snakes have yielded better records, notwithstanding the fact that they usually lose most of their parasites through constant handling, prolonged fasting, and artificial surroundings. Thus, we have a list of thirteen species for the Indian _Python molurus_, and one of twenty-two species for the _Boa constrictor_. But no systematic search appears to have been attempted, save, perhaps, in the case of a few European species.

It is interesting to notice that it was the finding of an Ophidian parasite which prompted Francesco Redi to write his famous "Observations on the Living Animals which are found within Living Animals." This work, a veritable treatise of comparative parasitology, published in 1684, caused the great naturalist, physician, and poet to be regarded as the father of that science. He tells us that in dissecting a curious dicephalous _Vipera aspis_, caught at Pisa, he found within the intestines a number of roundworms (_Ascaris cephaloptera_), and on the surface of one of the two lobes of the liver five cysts enclosing a small worm, which he rightly ascribed to the same species.

The parasites of snakes are here enumerated by Dr. L. W. Sambon, in systematic order.

ARTHROPODA.--Two families of the class Arachnida, the Ixodidæ and the Linguatulidæ, furnish numerous species parasitic on snakes.

Of the Ticks (Ixodidæ) we find, as a rule, species of the genera _Amblyomma_ and _Aponomma_, the latter genus being almost entirely confined to Reptiles. A single species of the genus _Hæmaphysalis_ (_H. punctata_, Can. and Franz, 1877) has been reported once from _Vipera aspis_. A few larval forms found on various snakes have been reported under the generic name _Ixodes_, but they probably belong either to _Amblyomma_ or _Aponomma_.

The Ophidian Tick-parasites, like those of mammals, birds, lizards, and tortoises, appear to be in many cases the means of transmission of protozoal infections from snake to snake.

The Tongue-worms (Linguatulidæ) are, without doubt, of the greatest possible interest. Their systematic position has ever been a puzzle to zoologists, and even now is a matter of controversy. They have been looked upon as Hirudinea by Winsberg (1765), Cestoda by Chabert (1787), Acanthocephala by Humboldt (1808), Trematoda by Rudolphi (1809), and Nematoda by Nordmann (1832). It was Van Beneden (1848) who first recognized their Arthropod nature, but he placed them amongst the Crustacea. Schubärt (1853) suggested that their proper position is amongst the Mites (Acarina), and Leuckart (1860) adduced important anatomical and embryological evidence in support of this view, which was confirmed by Railliet in 1883 and by Sambon in 1910.

No less than three out of the four genera of Linguatulids so far established are represented by species parasitic on snakes. They are the genera _Porocephalus_, _Reighardia_, and _Raillietiella_.

The genus _Porocephalus_ is of special interest, because some of its species, such as _Porocephalus armillatus_, a parasite of African Pythons (_Python regius_, _P. sebæ_) and Puff-adders (_Bitis arietans_, _B. nasicornis_, _B. gabonica_), and _Porocephalus moniliformis_, a parasite of Oriental Pythons (_Python molurus_, _P. reticulatus_), are, in their nymphal stage, deadly parasites of mammals, including man.

The genus _Reighardia_ was established by Professor H. B. Ward, in 1899, for a Linguatulid of gulls and terns, first described, in 1861, by De Filippi. In 1910 Sambon included in this genus other similarly structured Linguatulids from crocodiles, monitors, and snakes.

The genus _Raillietiella_ was established by Sambon in 1910 for a Linguatulid (_Raillietiella boulengeri_) of the African Puff-adders (_Bitis arietans_, _B. gabonica_). Amongst the characters of this genus is one of great structural and phylogenetic importance--viz., the position of the female sexual orifice at the anterior end of the abdomen, whilst in the other known genera it is at the posterior extremity.

According to Prowazek, Sambon, and Laveran, the Ophidian Linguatulids, which live as blood-suckers in the air-passages of their hosts, are able to foster and transmit the hæmogregarines of these hosts.

ACANTHOCEPHALA.--The early encysted stages of several species of Thorn-headed worms (_Acanthocephala_), belonging to the family _Echinorhynchidæ_, have been reported from snakes belonging to very different genera, such as _Boa_, _Tropidonotus_, _Zamenis_, _Drymobius_, _Xenodon_, _Dipsadomorphus_, _Oxyrhopus_, _Erythrolamprus_, _Diemenia_, _Naja_, _Elaps_, _Vipera_, _Lachesis_. Their further development probably occurs in ophiophagous birds. Thus, _Echinorhynchus oligacanthoides_, Rud., the immature stages of which occur encapsuled within the body cavity of _Lachesis lanceolatus_ and other neotropical snakes, when adult is found attached to the intestinal mucosa of _Milvus bidentatus_.

NEMATODA.--The roundworms (_Nematoda_) so far described from snakes belong to the families Ascaridæ, Strongylidæ, Trichotrachelidæ, and Filariidæ. Some of the genera belonging to these families, such as _Cucullanus_, _Nematoxys_, _Oxysoma,_ are as yet represented by a single species in a single host; others, such as _Ascaris_, _Polydelphis_, _Heterakis_, _Strongylus_, _Diaphanocephalus_, _Physaloptera_, _Trichosoma_, number already several species more or less widely distributed.

Eelworm infection (ascariasis) is very common in snakes, and not infrequently the infection is a heavy one; Sambon twice found over fifty specimens of _Polydelphis_ in Puff-adders (_Bitis arietans_). This investigator has shown that the snake eelworms undergo an encysted stage of development within the body cavity of their hosts before migrating into the intestinal lumen for the purpose of fertilization and oviposition. Thus, Redi was quite right in considering the immature, encysted forms found in one of the livers of his double-headed Asp as belonging to the same species of eelworm (_Ascaris cephaloptera_) as that which the snake harboured in its intestine.

Professor A. Railliet, whilst examining specimens of _Polydelphis_ which had been preserved for nearly two months in a 3 per cent. solution of formalin, found that the ova within their uterine tubes had undergone development, and still contained living embryos; indeed, some of these hatched under the microscope, and moved very actively in the preserving fluid. This is in no way surprising, because even after several years of preservation in formalin solution the embryos of other species of eelworms (_Ascaris equorum_, _A. marginata_) have been found in a living condition.

TREMATODA.--The Flukes (_Trematoda_) of snakes, so far described, belong to the following genera: _Agamodistomum_, _Astiotrema_, _Brachylaimus_, _Cotylotretus_, _Dicrocoelium_, _Diplodiscus_, _Distoma_, _Halipegus_, _Lecithodendrium_, _Metorchis_, _Opisthogonimus_, _Opisthorchis_, _Plagiorchis_, _Saphedera_, _Telorchis_, _Tetracotyle_, _Zeugorchis_.

CESTODA.--Save a few larval forms (_Cysticercoides_, _Piestocystis_, _Sparganum_), the known tapeworms (_Cestoda_) of the Ophidia belong to the genera _Bothridium_ and _Proteocephalus_.

PROTOZOA.--Numerous species of Hæmogregarines have been described from snakes. As a rule the forms seen in the peripheral blood are sporonts, the schizogonic cycle occurring in the lungs. The sporonts do not greatly alter their host cells; they are invariably doubled up within a more or less thick capsule. Some species show a marked sexual differentiation, others not. _Trypanosomes_, _Spiroechaudinniæ_, and _Plasmodidæ_ have also been described from the blood of various snakes.

Within the alimentary tube have been found species of _Trichomonas_ and _Caryospora_.

BACTERIA.--Acid-fast bacilli have been described in tubercular lesions found in snakes by Sibley, Gibbs and Shurley, Shattock, Hausemann, and Sambon.

The so-called "canker," which so frequently develops in the oral cavity of captive snakes, is also a bacterial disease, due to a specific bacterium of thick, rod-shaped form.

LIST OF PARASITES HITHERTO
RECORDED FROM EUROPEAN SNAKES

TROPIDONOTUS NATRIX, L.

ACANTHOCEPHALA.

_Echinorhynchus inæqualis_, Rudolphi.
_Echinorhynchus polyacanthus_, Creplin.

NEMATODA.

_Strongylus auricularis_, Zeder.
_Strongylus catanensis_, Rizzo.
_Trichosoma mingazzini_, Rizzo.
_Oxysoma brevicaudatum_, Zeder.
_Nematoxys commutatus_, Rudolphi.
_Ascaris cephaloptera_, Rudolphi.

TREMATODA.

_Opisthorchis caudatum_, Polonio.
_Dicrocoelium assula_, Dujardin.
_Diplodiscus conicum_, Polonio.
_Tetracotyle colubri_, v. Linstow.
_Distoma acervocalciferum_, Gastaldi.
_Distoma allostomum_, Diesing.
_Distoma nematoides_, Mühling.
_Saphedera naja_, Rudolphi.
_Brachylaimus signatum_, Dujardin.
_Telorchis ercolanii_, Monticelli.
_Lecithodendrium nigrovenosum_, Bellingham.
_Plagiorchis mentulatus_, Rudolphi.

CESTODA.

_Ligula panceri_, Polonio.

TROPIDONOTUS TESSELLATUS, LAUR.

NEMATODA.

_Strongylus denudatus_, Rudolphi.
_Physaloptera abbreviata_, Rudolphi.
_Physaloptera striata_, v. Linstow.

TREMATODA.

_Plagiorchis mentulatus_, Rudolphi.

TROPIDONOTUS VIPERINUS, LATR.

ACANTHOCEPHALA.

_Echinorhynchus lobianchii_, Monticelli.

TREMATODA.

_Distoma allostomum_, Diesing.
_Opisthorchis caudatum_, Polonio.
_Telorchis ercolanii_, Monticelli.
_Astiotrema monticellii_, Stossich.

CESTODA.

_Ligula pancerii_, Polonio.

PROTOZOA.

_Hæmogregarina viperina_, Billet.

ZAMENIS GEMONENSIS, LAUR.

ACANTHOCEPHALA.

_Echinorhynchus cinctus_, Rudolphi.
_Echinorhynchus polyacanthus_, Creplin.
_Echinorhynchus heterorhynchus_, Parona.

NEMATODA.

_Strongylus catanensis_, Rizzo.
_Filaria parvomucronata_, Rizzo.
_Trichosoma sonsinoi_, Parona.

TREMATODA.

_Distoma subflavum_, Sonsino.
_Brachylaimus baraldii_, Sonsino.
_Saphedera naja_, Rudolphi.

CESTODA.

_Cysticercus acanthotetra_, Parona.
_Cysticercoides rostratus_, Mingazzini.

COLUBER QUATUORLINEATUS, LACEP.

ACANTHOCEPHALA.

_Echinorhynchus oligacanthus_, Rudolphi.

NEMATODA.

_Ascaris cephaloptera_, Rudolphi.

TREMATODA.

_Plagiorchis sauromates_, Poirier.

PROTOZOA.

_Hæmogregarina_, sp.

COLUBER LONGISSIMUS, LAUR.

PROTOZOA.

_Hæmogregarina colubri_, Börner.

CORONELLA AUSTRIACA, LAUR.

NEMATODA.

_Tricheilonema megalochilum_, Diesing.
_Physaloptera colubri_, Rudolphi.

CESTODA.

_Piestocystis dithyridium_, Diesing.

PROTOZOA.

_Monocercomonas colubrorum_, Hammersch.

CORONELLA GIRONDICA, DAUD.

PROTOZOA.

_Hæmogregarina coronellæ_, França.

VIPERA BERUS, L.

NEMATODA.

_Physaloptera dentata_, v. Linstow.

TREMATODA.

_Agamodistomum viperæ_, v. Linstow.
_Tetracotyle colubri_, v. Linstow.

VIPERA ASPIS, L.

ARTHROPODA.

_Hæmaphysalis punctata_, Can. & Franz.

ACANTHOCEPHALA.

_Echinorhynchus cinctus_, Rudolphi.

NEMATODA.

_Ascaris cephaloptera_, Rudolphi.
_Diaphanocephalus viperæ_, Rudolphi.

PROTOZOA.

_Caryospora simplex_, Léger.
_Hæmogregarina samboni_, Giordano.

VIPERA AMMODYTES, L.

NEMATODA.

_Ascaris ammodytis_, Rudolphi.
_Ascaris cephaloptera_, Rudolphi.

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