Pathogenicity of hookworms. The significance of population regression for the pathogenicity of hookworms.

A method is described to estimate the reduction of the hookworm population in the host during the infection period (population regression). A formula is proposed to estimate the average worm population during the infection period, on the assumption that a decreasing hookworm population causes a decrease in daily blood loss. Daily blood loss per worm was calculated for Ancylostoma caninum: 43 microliters; for A. ceylanicum: 14 microliters for A. braziliense: 5 microliters. Accordingly hookworms cause blood loss one half to two thirds smaller than formerly assumed.

[Roundworm infection (Toxocara and Toxascaris) in dogs in the Netherlands (author's transl)]. / Spoelworminfecties bij Nederlandse honden.

The incidence of roundworm infections was determined by examination of the faeces in a total number of 544 adult dogs in the Netherlands during the period from 1972 to 1977. The incidence of roundworm infections varied from 13 to 34 per cent (average 22.9 per cent) during this period, from 2 to 31 per cent (average 14.5 per cent) for Toxocara canis infections, from 8 to 15 per cent (average 11.2 per cent) for Toxascaris leonina infections and from 0 to 11 per cent (average 2.8 per cent) for combined T. canis and T. leonina infections.

[Epidemiological aspects of Uncinaria stenocephala infections in the Netherlands (author's transl)]. / Enige epidemiologische aspecten van Uncinaria stenocephala infecties in Nederland.

A series of experimental infections in a total number of twenty-two dogs showed that transmission of the parasite Uncinaria stenocephala from one dog to another is readily achieved by oral route. Cutaneous infection was only successful when large doses were used. From the topographical distribution of some intestinal U. stenocephala worm populations in dogs it was concluded that the hookworm population is concentrated in the proximal part of the ileum. The expulsion of worms observed may be evidence of the size or persistence of the worm population. The prepatent period was found to be (at least) thirteen days, both in dogs and in foxes. Daily worm-egg counts showed a fluctuating rhythm, particularly during the first 2-3 weeks of the patent period. Relatively high peaks were also recorded in some cases. The maximum number of worms eggs was estimated at well over 5,000 eggs per female U. stenocephala worm (in dogs). U. stenocephala eggs and larvae are capable of surviving at low temperatures. U. stenocephala infection was found to be present in twenty-five (86 per cent) out of twenty-nine foxes obtained and examined in 1975, the worm load varying from one to 176 hookworms and averaging thirty worms per fox. From the preliminary results of a number of experimental transmissions it was concluded that foxes and dogs harbour adapted strains of U. stenocephala, which prevents cross infections between these reservoirs from occurring to more than a limited extent.

Changes in hookworm distribution in Surinam.

During the months May-July, 1974, a follow-up investigation was carried out on hookworm infections in dogs and cats in order to study changes in the hookworm distribution in Surinam since 1967. Fifty-two cats and 152 dogs were examined for the presence of helminths in the oesophagus, small intestine, coecum and heart. In total 15,942 helminths were isolated; most of these (14,006) were hookworms belonging to the species Ancylostoma caninum, A. tubaeforme, A. ceylanicum and A. braziliense. The average size of the hookworn load in dogs and cats appeared to have decreased since 1967, especially as regards A. ceylanicum. The distribution area of A. braziliense had extended largely by 1974 to the east and south in Surinam. In west Surinam A. braziliense infection was not found, just as in 1967.. The remaining parasites were Dipylidium caninum, Toxocara sp., Dirofilaria immitis, Spirocerca sanguinolenta, Spirometra mansonoides, Taenia taeniaeformis and Trichurisvulpis.

Intestinal helminths in dogs and cats on the Antillian Islands Aruba, Curaçao and Bonaire.

An investigation into the prevalence, identity and size of population of intestinal helminths in dogs and cats was carried out in the Dutch Antillian Islands, Curaçao, Bonaire and Aruba during April and May 1974. Ninety-one dogs and 83 cats were examined. In all, 4,824 helminths were isolated and identified. The following species were isolated from dogs: Dipylidium caninum (most frequent), Ancylostoma caninum (frequent in Curaçao), Toxocara, Taenia hydatigena and Ancylostoma braziliense. Species isolated from cats: Dipylidium caninum (most frequent) Ancylostoma tubaeforme (frequent in Curaçao), Oncicola canis, Taenia taeniaformis, Spirometra (mansonoides), Platynosomum (fastosum), Toxocara, Trichuris and Thelazia. The man-infecting hookworm species Ancylostoma ceylanicum was not found at all and A. braziliense was only found in dogs in Aruba in light infections. Remarkable differences in the prevalence of parasitic infections were demonstrated between Curaçao and the two other islands Aruba and Bonaire, especially regarding the frequency and worm burden of the hookworms. It was suspected that this was due to the recent increase in the number of dogs in Curaçao.

The topographic distribution of Necator americanus and Ancylostoma duodenale in the human intestine.

During an investigation in Dar es Salaam, Tanzania, 28 human intestinal tracts were systematically inspected on the presence of hookworms. In total, 643 hookworms (508 Necator americanus and 135 Ancylostoma duodenale) were isolated from 19 intestinal tracts. The localization of these hookworms was determined. N. americanus worms were concentrated in the duodenum and jejunum, whereas A. duodenale worms rather prefer the jejunum and proximal ileum. Some preference of hookworms for the antimesenteric site of the intestinal wall was found. The relative distance between adjoining worms in the observed hookworm populations was 3.8 cm on the average for Necator and 5.5 cm for Ancylostoma. The distribution of the sexes in the worm-population revealed no monosexual or bisexual prevalence of the hookworms.