CHAPTER X 

 FEEDING HABITS OF NEMATODE PARASITES OF VERTEBRATES 



J. E. ACKERT and J. H. WHITLOCK, Kansas State College. Manhattan, Kansas 



'J'lit' obscured habitats of the parasitic nematodes preclude 

 ready observations upon their feeding haljits. Indications of 

 their nutritive needs have been gained from chemical analyses 

 of the worm bodies. Weinland (litOl) found that glycogen 

 made up one fourth to one-third of the dry substance of the 

 ascarid body. Flury (1912) was led to believe that ascarids 

 had essentially the same chemical constitution as other animals. 

 He found only such minor differences as a lack of uric acid, 

 creatinine and the substitution of a high molecular alcohol 

 (ascarjl alcohol) for glycerol in combination with fatty acids. 

 From these studies it seemed probable that the nutritive needs 

 of parasitic nematodes are fundamentally the same as those of 

 other animals, although Aekert (1930) has shown that there is 

 no evidence to indicate that Atirarklia galli needs Vitamin .\, 

 Vitamin B (complex), or Vitamin D. 



As most of the research on the feeding habits of nematodes 

 has been upon adult forms, they will be discussed first; then 

 tl larval forms will be compared with the adults, and the sec- 

 tion will close with a brief review of digestion in the parasitic 

 nematodes. Although there are many diverse groups of nema- 

 todes, few methods of parasitic feeding have been evolved. 

 The similarity of these feeding habits in nematode groups 

 which are widely separated morphologically would make a dis- 

 cussion of nutrition from a primarily taxonomic standpoint 

 repetitious; hence the subject will be discussed from an eco- 

 logical and physiological standpoint rather than from that of a 

 morphological classification. 



Ecologically, iiarasitie nematodes may be grouped as to 

 whether they are associated with the physiological interior or 

 exterior of the host body. The physiological exterior of the 

 body, as here considered, is marked by any epithelial mem- 

 brane lining a cavity which communicates with the exterior of 

 the host body. 



Most of the parasitic helminths are associated with the physi- 

 ological exterior of the bodj', particularly the mucosae. This 

 group will be subdivided upon the l>asis of being attached to 

 the mucosae most of the time or usually unattached. Attached 

 nematodes maj- hold their positions by the buccal capsule grasp- 

 ing the mucosa {Ancylostoma, A'ecator, Strongylus) or by pene 

 tration of the mucosa (Fhysaloptcra, Trichuris). Nematodes 

 unattached to the mucosa may be closely associated with it 

 (Haemonchus, Mctastrongylns) or not closely associated with 

 it {A.icaris, Ascaridia, Hrtcrakis, Oxyuris). Nematodes in- 

 habiting the physiological interior of their hosts are best ex 

 emplified by Dirofilaria, Spirocerca and Strongyloides. 



Nematodes in the Physiological Exterior of the Body 



NEMATODES ATTACHED TO Ml'COSA BY BUCCAL 

 CAPSULE 



The best examples of this group are the hookworms Aiii-i/hi 

 stoma and Necator which apparently remain attached to the 

 intestinal mucosa much of the time. The sucker-like oral open 

 ing and the adjacent teeth or cutting plates afford effective 

 means of attachment and bloodletting. Since the earliest 

 recorded observations, blood has been considered as a prob 

 able food of hookworms. Grassi, according to Leichtenstern 

 (1886), saw hookworms eject blood both from the mouth and 

 the anus. Leichtenstern thought, as did Grassi, that much 

 more blood is withdrawn by the parasite than is necessary for 

 its food. As the fecally deposited red cells seemed to be prac 

 tically unchanged, Leichtenstern inferred that the plasma must 

 be the main source of nourishment. In 1888 Ernst noted the 

 emission of blood from the mouth cap.sule and Whipple (1909) 

 observed the oral and anal emission of blood in both Xecator 

 and Ancylostoma. Whipple believed that there was a rapid 

 ingestion of blood by the parasite. Aekert and Payne (1923) 

 who took Necator suillus repeatedly from the intestines of 

 freshly killed swine frequently noted female specimens v\-ith 

 bodies colored red from ingested blood. On the other hand 

 some workers, notably Looss (190.5) and Ashford and Igara 

 videz (1911), maintained that blood is not the normal food of 

 hookworms. They observed worms lacking blood even when 

 they were attached to the intestine. They found tissue ele 

 ments and shreds of mucosa in both the esophagus and intestine 

 and concluded that the parasites fed primarily on the mucous 

 membranes; the blood in the tract was thought to be due to 

 accidental hemorrhage from hookworm bites. Support for the 

 view that portions of the mucosae serve as food for such worms 

 was given by Hoeppli (1930), who found that Ancylostoma 

 duodenale is more than a blood sucker. The piece of mucous 

 membrane taken in )iy the mouth capsule is rasped by the teeth. 



Blood from surface vessels pours into the buccal capsule where 

 .secretions from the esophageal glands partially digest the 

 blood and loosened portions of the mucosae. "After this di- 

 gestion has taken place, the liquefied masses are swallowed by 

 the worm." Evidence that disintegration had taken place wa.s 

 furnished by staining the tissue at the bottom of the mouth 

 capsule and in the lumen of the esophagus. 



Wells (1931) in a series of ingenious experiments was able 

 to observe living Ancylostoma canitium in the act of feeding. 

 He was able to observe the attachment of the hookworms to 

 the mucosa, study the details of the blood-sucking process, the 

 passage of the blood through the intestine of the worm, and 

 its ejection through the anal orifice. From the volumes of 

 blood withdrawn by the parasite and the rapid rate at which it 

 passed through the intestine. Wells was of the opinion that the 

 food of the hookworm consists of simple dift'usable substances 

 in the host blood. 



In studies upon the food of the dog hookworm, Ancylostoma 

 caniiiiim, Hsii (1938) made serial sections of hookworms taken 

 from living hosts and found red blood cells in all worms; ho 

 also found fragments of host tissue and white blood cells all 

 of which were in stages of disintegration. As further evidence 

 of blood as food for the hookworms, Hsii reported the find g of 

 pigment granules in the cytoplasm of the worms' intestinal 

 cells, which gave positive iron reaction. These granules, which 

 were found in large quantities throughout the whole intestine, 

 the author interpreted as owing their origin to the breaking 

 down of red blood corpuscles. Hsii did not find intestinal con 

 tents of the host, worm eggs, or bacteria in the hookworms' 

 intestines. He concluded that the food of A. caninum consisted 

 of blood and mucosa cells. 



Other nematodes that attach by means of buccal capsules in- 

 clude such forms as Strongyhis, Chabertia and Camallanus, all 

 of which are known to draw intestinal epithelium into their 

 mouths. From the disintegrated condition of the tissue so 

 drawn in, it is probable that epithelial tissue and blood form 

 a portion of their food. Whitlock (unpublished), who has 

 worked extensively with living equine strongyles, has noted in 

 the worm intestines material resembling partially digested 

 blood. Wetzel (1931b), studying Chabertia ovina (Fab.) in 

 sheep colons, found that the nematodes feeds on the propria 

 mucosae which it draws into its buccal capsule. The tissue 

 fragments which are loosened by the gnawing of the nematode 

 are partially digested, according to Wetzel, by secretions from 

 the dorsal esophageal gland. 



Support of the view that C. ovina attacks the mucous mom 

 brane is afforded by the work of Kauzal (1936) who found 

 numerous small hemorrhages on the mucous membrane of the 

 large intestine of sheep which he attributed to C. ovina. He 

 examined 250 of these specimens quantitatively for iron which 

 he assumed to be derived from haemoglobin. The presence of 

 the haemoglobin and the reddish tint of the intestinal con 

 tents of the immature C. ovina led Kauzal to infer that thi.s 

 nema ingests considerable quantities of blood. That the at 

 tachment to the intestinal mucosae by the buccal capsule is a 

 widespread feeding phenomenon among the Strongyloidea is 

 further shown by Magath (1919) for Camaltanus amcricanus in 

 the turtle intestine and by Hoeppli and Hsii (1931) t'oi- h'ul- 

 icephalus sp. in the enteric caual of snakes. 



NEMATODES ATTACHED MUCH OF THE TIM 10 I'.V 

 PENETRATION OF THE MUCOSA 



Typical examples of this group are Trichuris and Physalop- 

 tera. The food of Trichuris apparently is secured while the 

 anterior extremity is imbedded in the mucous membrane of 

 the large intestine. Christofferson (1914) who reviewed the 

 literature on Trichuris (Trichoccphalns) up to 1914, observed 

 a peculiar cell transformation about the imbedded anterior por 

 tion of these nematodes. Hoeppli (1927) found such changes 

 in human and baboon intestines in which the Trichuris made 

 tunnels in the mucosa parallel with the surface of the intestinal 

 lining. Surrounding the anterior ends of the trichurids in 

 these tunnels, the epithelial cells, according to Hoeppli, were 

 transformed into syncytial-like structures with eosinophilic 

 homogeneous protoplasm and pycnotie nuclei as a result of the 

 action of a liquifying secretion from the worm. Hoeppli 's 

 studies (1927, 1933) led him to believe that the liquified syn- 

 cytial material was taken by the trichurids as food. 



That Tricliuris may take blood was indicated by the studies 

 of Guiart (1908) who found blood-engorged trichurids. Garin, 

 cited by Otto (1935), likewise found Trichuris filled with blood 

 and reported that blood was found in the stools of 50 out of 



3.50 



