Response of preadult Necator americanus to some known anthelmintics in hamsters

An immunological and biochemical comparison of hookworm species

The successful development of diagnostic tests capable of distinguishing human hookworm species will ultimately depend on an increase in our knowledge of their comparative biochemistry. Here, David Pritchard, Paul McKean and Gerry Schad describe some aspects of the comparative biochemistry of Necator americanus and Ancylostoma duodenale, and emphasize differences between the species that could form the basis of discriminatory diagnostic tests.

Distinction of human hookworm larvae based on lectin-binding characteristics

A comparative study of lectin binding to ensheathed (EnL3) and exsheathed (ExL3) L3 larvae of Necator americanus, Ancylostoma duodenale and Ancylostoma ceylanicum revealed a number of differences between these hookworm species. These differences could provide a novel approach to distinguish infective L3 larvae in field conditions. For example, binding of Ulex europaeus agglutinin (UEA) and Ricinus communis agglutinin (RCA120) to N. americanus EnL3 distinguished them from those of A. duodenale and A. ceylanicum. Furthermore, UEA and RCA120 negative EnL3 could be separated into the two Ancylostoma sps. tested, as Dolichos biflorus agglutinin and Soybean agglutinin bound to EnL3 of A. ceylanicum but not to those of A. duodenale.

Response of adult Necator americanus to some known anthelminthics in hamsters

Adult Necator americanus infection in laboratory hamsters (the hamster-hookworm model) was examined as an anthelminthic screening system. Three reference anthelminthics--pyrantel (PYTL), mebendazole (MBZ) and ivermectin (IVRN)--were used to assess the sensitivity of adult N. americanus and also to investigate the value of the hamster-hookworm model for predicting clinical results. Serial drug dosages were used, and the ED50 was determined from the resulting cure rates. In addition, percentage worm reductions were calculated by reference to the worm burdens in control groups. The results showed that the hamster-hookworm model was able to differentiate anthelminthics on their efficacy. Absolute activity (100% worm reduction) followed treatment with 8 mg kg-1 MBZ, 38-40 mg kg-1 PYTL and 18 mg kg-1 IVRN. Based on ED50 data of PYTL and MBZ, adult N. americanus appeared to be two to five times more sensitive than pre-adult stages. However, with IVRN the reverse appeared true. MBZ appeared to be most active and PYTL least active in terms of curing infected animals, but there were no obvious differences between the rates of worm reductions following single or multiple doses of anthelminthics. It is considered that the hamster-hookworm model will prove of value in identifying and characterizing possible new anthelminthics.

Response of laboratory-adapted human hookworm and other nematodes to ivermectin

The activity of ivermectin was examined in Necator americanus, a human hookworm, adapted to the laboratory hamster. A dose of 30 mg kg-1 X 1 or 10 mg kg-1 X 2 was required for complete clearance of pre-adult N. americanus; however, hamsters carrying adult N. americanus were completely cured of infection by doses of 15 mg kg-1 or 7.5 mg kg-1 X 2. The doses of ivermectin required for complete elimination of N. americanus were much higher than those reported for other intestinal nematodes. The probable reasons for these higher doses are discussed. Tests were also carried out with other rodent parasites, namely Nematospiroides dubius, Strongyloides ratti and Trichuris muris. Doses as low as 0.3 mg kg-1 X 1 completely eliminated adult N. dubius from mice, whereas++ S. ratti needed a repeated dose (0.3 mg kg-1 X 2). None of the mice was cured of T. muris infection even at doses of 10 mg kg-1 X 2, although some degree of cure was apparent at the toxic dose. It thus appears that ivermectin is in no way superior in its activity against N. americanus and T. muris than the existing anthelmintics.