Fig. 73.—Strongylus pergracilis. a, Head and neck; b, c, d, e, tail of the male in various positions; f, tail of the female; g, section showing termination of the oviducts; h, three eggs. Highly magnified. Original.
The tapeworms of birds are undoubtedly injurious to their bearers. All the worms appear to be armed with cephalic hooks; at least, such is the case with the species described by Krabbe, who has supplied figures of the hooks drawn to a scale. Dr Krabbe’s beautiful monograph is a perfect model of its kind. In the accompanying figure the hooks have fallen (Fig. [72]). On account of the frequency of their occurrence, some persons have supposed that tapeworms are not injurious to their hosts, forgetting that it is not the mere fact of the existence of tapeworms, but their excessive numbers during particular seasons that give rise to avian epizoötics. The same rule holds good with other parasites. Of course, in fledgelings, as also obtains in yearlings amongst our domesticated animals, a very few parasites are sufficient to prove destructive to the bearer. Thus, as regards the so-called “grouse-disease,” during one season it may be due to tapeworms, during another to strongyles, during a third to excessive abundance of both these parasites. Unfortunately, other avian epizoötics, not necessarily due to parasites of any kind, may be mistaken for helminthic epizoöty. The same thing happens amongst quadrupeds. We have, for example, parasitic equine epizoötic outbreaks, and likewise non-helminthic equine epidemics (as in the case of the Egyptian horse plague of 1876). The true nature of any epizoöty can only be determined by competent investigation. That was well shown in the grouse epidemic of 1872. In that epizoöty the greater number of the birds succumbed to the injuries produced by a nematode worm (Strongylus pergracilis, Fig. 73), but, without doubt, the occasional presence of numerous tapeworms (Tænia calva) hastened the consequent fatality. The following table, giving the results of examination of twelve diseased grouse from the Earl of Cawdor’s estate, will show how inconspicuous a part tapeworms played in the epidemic of 1872. For further details I must refer to my brochure on the ‘Grouse Disease,’ and to some other memoirs quoted in the bibliography below.
| No. of specimen. | Condition of bird. | State of viscera. | Tapeworms present. | Strongyles present. |
|---|---|---|---|---|
| 11 | Good | Full | None | Abundant. |
| 12 | Emaciated | Putrid | Two | Very numerous. |
| 13 | Good | Full | None | Abundant. |
| 14 | " | " | " | " |
| 15 | " | " | One | " |
| 16 | " | Shrunken | Two | Very numerous. |
| 17 | Emaciated | Much shrunken | None | " |
| 18 | Thin | Shrunken | " | " |
| 19 | " | " | " | " |
| 10 | Emaciated | Distended | Man | " |
| 11 | Thin | Rather full | Several | Abundant. |
| 12 | " | " | None | Very numerous. |
I have said that tapeworms prove fatal to young birds, even to nestlings. A notable instance of this is recorded by Mr Eames. The parasites were examples of Tænia angulata. Apart from the epidemiological aspects of the subject, it is not uninstructive to notice the variety of helminths that infest the common fowl and game birds. Accordingly, I append a similar but more extended list than that previously given in the supplement to my introductory treatise:
| Entozoa of game birds and the common fowl. | Common fowl. | Pheasant. | Caper- caillie. | Black Grouse. | Red Grouse. | Grey Partridge. | Red Partridge. | Quail. |
|---|---|---|---|---|---|---|---|---|
| Monostoma verrucosum, Zeder | * | |||||||
| Distoma oxycephalum, Rudolphi | * | |||||||
| " ovatum, Rudolphi | * | |||||||
| " lineare, Zeder | * | |||||||
| " dilatatum, Miram | * | |||||||
| " fuscatum, Rudolphi | * | |||||||
| Filaria Mansoni, Cobbold | * | |||||||
| Ascaris vesicularis, Froelich | * | * | * | * | * | * | ||
| " gibbosa, Rudolphi | * | |||||||
| " inflexa, Rudolphi | * | * | ||||||
| " compar, Schrank | * | * | * | * | ||||
| Spiroptera hamulosa, Diesing | * | |||||||
| " helicina, Molin | * | |||||||
| Dispharagus nasutus, Dujardin | * | |||||||
| " spiralis, Molin | * | |||||||
| Strongylus pergracilis, Cobbold | * | |||||||
| Sclerostoma syngamus, Diesing | * | * | * | |||||
| Trichosoma longicolle, Rudolphi | * | * | * | * | ||||
| Tænia malleus, Goeze | * | |||||||
| " microps, Diesing | * | * | ||||||
| " exilis, Dujardin | * | |||||||
| " calva, Baird | * | |||||||
| " linea, Goeze | * | * | * | |||||
| " infundibuliformis, Goeze | * | * | ||||||
| Ligula reptans, Diesing | * |
In regard to this list I can only afford space to remark that several of the species are possibly mere varieties. Some of the worms are of great interest. It occasionally happens that Distoma ovatum is found in the albumen of the fowl’s egg, and it is even more common to obtain Ascaris inflexa from the same situation. For a recent example I am indebted to Dr Walker, of Peterborough. Spiroptera helicina resides in the feet, occasioning enlargement of the joints and consequent distress to the bearer. Probably the most important in the list is my Strongylus pergracilis. Here I may mention that on the 10th of April, 1878, I received a letter from Dr Manson, of Amoy, announcing his acquaintance with a filaria infesting the eye of the fowl. On the 9th of May I also received from Dr Manson the head of a bird showing examples of the worm. As the species is new to science I have proposed to call it Filaria Mansoni, after the discoverer. The male is 5/8″ and the female 3/4″ in length. Of the injurious nematodes, giving rise to avian epizoöty, probably one of the most destructive is Ascaris maculosa infesting pigeons. On the 9th of October, 1873, I received a letter from Dr J. Alexander Macdonald, of Woburn, Bedfordshire, stating that he had forwarded to me a pigeon which had been found dead on the previous morning. It seems that the owner of the bird had erected a large pigeon-house, and had imported a number of Antwerp smerles, these birds all continuing in a perfect state of health until about a week before the above-mentioned date, when, to use Dr Macdonald’s words “first one and then another was attacked, and so on, until four or five of the pigeons had died after a few hours’ illness.” The suddenness of these attacks not unnaturally suggested poisoning; and, accordingly, says my informant, the owner “had the curiosity to open one of the birds, when, to his astonishment, he found the intestines stuffed with worms.” Two days later I received a letter from Dr Macdonald, stating that several others of the flock had died, and it further appeared to him probable that the daily list of sick and dying would continue to increase. On the 14th of the month three more of the birds were dead. On the 4th of the following November, the same correspondent obligingly informed me that the epidemic had been “at last mastered.” It seems that altogether twelve birds had perished. On the 9th of October one of the birds was carefully examined by me, and the results were so interesting that I am constrained to give a few of the particulars originally communicated to the Zoological Society. As stated in my paper, the whole intestinal tract of the dead bird was crowded with these ascarides. The small intestine was inflamed throughout, and showed several large ulcerated patches; nevertheless, there were no traces of emaciation. From this it was evident that the parasites had grown quickly, the malady having a correspondingly rapid formation. The distribution of the parasites was curious. One specimen, two inches long, reached from the crop to the proventriculus. The cavities of this organ and of the gizzard were crammed with worms completely blocking the passage. Three of the worms had also placed themselves within the pyloric opening, their bodies partly lodging within the duodenum. The duodenum itself was crowded with worms, their numbers somewhat decreasing downwards. I removed thirty-six worms from the œsophagus, proventriculus, and stomach, besides 166 others from the intestinal canal, thus obtaining a total of no less than 202 nematodes from this small host. Considering the large size of these entozoa, the extent of infection must be pronounced remarkable. The largest females measured 21/2″ in length. One of the most interesting facts—serving to exemplify a well-known habit of lumbricoid worms generally—consisted in the circumstance that two of the parasites had succeeded in perforating the horny lining membrane of the gizzard. The injuries had been accomplished during the life of the host, for the walls of the gizzard were inflamed opposite the perforations. There was a little half digested food within the stomach, the débris of which, when placed under the microscope, showed several ova. There were no free embryos, neither had the development of the freed eggs proceeded beyond yelk-segmentation. Free eggs were also found both in the small and large intestine. The eggs measured about 1/360″ by 1/700″ in diameter. Referring to my paper for further anatomical details, I can only add that, despite these facts, the ascarides in question do not appear to be a very frequent source of epizoöty. It was remarked by Dujardin that Heister, at Rostok, and Gebauer, at Breslau, found this parasite abundant at the beginning of the eighteenth century; but, according to examinations conducted at Vienna, the worm was found in the common pigeon in only eleven instances out of 245, and thrice only in thirty-eight examples of the ring-dove; moreover, the examination of eighty-seven other pigeons and doves of different species yielded entirely negative results. The Dublin helminthologist, Bellingham, noticed the occurrence of this parasite in Ireland.
Fig. 74.—Tail of the male Ascaris vesicularis. From a ring-necked pheasant. Original.
Any attempt so much as to enumerate the species of nematoids infesting birds would carry me far beyond the aim and scope of this treatise. One of the commonest species is Ascaris (Heterakis) vesicularis. Many hundreds of forms have been described by Dujardin, Diesing, Molin, Krabbe, and other systematists, and it remains for some future laborer to condense the facts which are dispersed throughout a very wide-spread literature. As regards the particular species of nematoids that are either actually known or conjectured to be injurious to birds I can only find space to repeat some of the particulars which I have elsewhere recorded in respect of Sclerostoma syngamus. In 1799 a letter from Dr Wiesenthal, of Baltimore, U.S., was published in the ‘Medical and Physical Journal,’ containing an account of a parasite infesting the trachea of fowls and turkeys in America. The communication is dated May 21st, 1797, and is the first public record concerning the entozoon. Dr Wiesenthal says: “There is a disease prevalent among the gallinaceous poultry in this country, called the gapes, which destroys eight-tenths of our fowls in many parts, and takes place in the greatest degree among the young turkeys and chickens bred upon old-established farms. Chicks and poults, in a few days after they are hatched, are found frequently to open their mouths wide and gasp for breath, at the same time frequently sneezing and attempting to swallow. At first the affection is slight, but gradually becomes more and more oppressive, and it ultimately destroys. Very few recover; they languish, grow dispirited, droop, and die. It is generally known that these symptoms are occasioned by worms in the trachea. I have seen the whole [windpipe] completely filled with these worms, and have been astonished at the animals being capable of respiration under such circumstances.”