Comparative morphology of Ancylostoma tubaeforme (Zeder, 1800) and Ancylostoma caninum (Ercolani, 1859).

As a result of studies of Ancylostoma from European, African, and Australian dogs and cats, it was found that dogs harbored A. caninum and cats A. tubaeforme. A detailed study of these hookworms from dogs and cats in the United States confirmed the observations made by other investigators that A. caninum is not the common species in cats. A. tubaeforme differs from A. caninum in the following features: smaller size, larger ventral and esophageal teeth, shorter esophagus, thicker cuticle, smaller bursa, different arrangement of lateral bursal rays, smaller costa dorsalis, longer spicules, and shorter, narrower female tail. The two species apparently have world-wide distribution and A. caninum is seldom or never found as a natural infection of cats or A. tubaeforme as a natural infection of dogs. In 1800 Zeder (Biocca, 1954) described hookworms he found in a cat in 1783, giving them the name Strongylus tubaeformis. Then in 1859 Ercolani (Biocca, 1954) published a description of the dog hookworm, naming it Sclerostoma caninum. Later S. caninum was transferred to the genus Ancylostoma, but S. tubaeformis apparently was overlooked by most investigators. For nearly 100 years the common hookworm of both dogs and cats was referred to as Ancylostoma caninum. A number of investigators (Scott, 1928, 1929; McCoy, 1931; Foster and Cort, 1932; and others) found that it was difficult to infect dogs with larvae from cats and cats with larvae from dogs. However, the differences were believed to be physiological rather than morphological, and the two were considered different strains of the same species. In 1954 Biocca published the results of his detailed study of Ancylostoma from dogs and cats in Italy. He found that there were two species rather than two strains of one species. In his paper he gave the original descriptions of both Zeder and Ercolani, a redescription of A. tubaeforme, and the major morphological differences between the two species. Bohm (1955) in Austria, Rohde (1959) in Germany, and Fitzsimmons (1961a, b), who studied hookworms from both African (Nyasaland) and Australian dogs and cats, agreed with the findings of Biocca. In the United States the writer has noticed in chemotherapeutic trials of several active compounds that the activity is not always the Received for publication 4 June 1962. same against Ancylostoma from dogs and those from cats. After consulting the papers by Biocca and Rohde, a detailed examination was made of hookworms obtained from dogs and cats in this country. As the morphological differences agree with those found by other investigators in Europe, Africa, and Australia, it is evident that we are dealing with two differ nt species, each of which appears to have a world-wide distribution. The major differences are described and illustrated below. MATERIALS AND METHODS Ancylostoma were obtained from 12 dogs and 9 cats used in chemotherapeutic trials in this laboratory. Numerous measurements were made from relaxed worms obtained either as a result of treatment or at autopsy. Numbers of worms were fixed; the anterior and posterior ends cut off; the middle sections discarded; and the ends dehydrated, cleared, and mounted for detailed study. The best of the numerous mounted ends were photographed to illustrate the major differences between the two species. Ancylostoma from a number of other dogs and cats were examined to determine whether natural infections of A. caninum occurred in cats or A. tubaeforme in dogs. DIFFERENTIATION OF THE TWO SPECIES (All measurements in millimeters, unless otherwise stated) Sizes of worms: Measurements of lengths and widths of 20 mature males and 20 mature females of each species gave the following ranges and averages: A. tubaeforme: males, 9.5 to 11.0 by 0.30 to 0.35 (avg. 10.3 by 0.32); females, 12.0 to 15.0 by 0.38 to 0.43 (avg. 13.2 by 0.41); A. caninum: males, 11.0 to 13.0 by