D.L. Lee

A design equation for human intestinal nematode egg removal in waste stabilization ponds

Abstract The percentage removal ( R ) of human parasitic nematode eggs in waste stabilization ponds can be described by the empirical equation R = 100 [1 − 0.141 exp (−0.38θ)] where θ is the mean hydraulic retention time (d). The lower 95% confidence limit of this equation. R = 100 [1 − 0.41 exp (−0.49θ+0.0085θ 2 )] is recommended for the design of ponds to meet the WHO microbiological guideline of ≤ one egg per litre for restricted irrigation.

Why do some nematode parasites of the alimentary tract secrete acetylcholinesterase

Many gastrointestinal nematodes secrete large amounts of acetylcholinesterases. Antibodies are produced against these secreted acetylcholinesterases and appear to give some protection against infection with some nematodes. The theory that acetylcholinesterase secreted by gastrointestinal nematodes may act as a biochemical holdfast by reducing contractions of the alimentary system has not been substantiated; a vasoactive intestinal polypeptide-like protein is secreted by some species and may be the biochemical holdfast. Secreted acetylcholinesterases may alter host cell permeability, have an anti-coagulant role, affect glycogenesis, and/or be important in certain aspects of acetate and choline metabolism. Probably the most important role for acetylcholinesterase secreted by nematodes is immune modulation and/or reduction of inflammation in the vicinity of the nematode. The reason why some species of gastrointestinal nematodes resistant to benzimidazoles contain elevated amounts of acetylcholinesterase is unclear.

Comparison of techniques for the enumeration of human parasitic helminth eggs in treated wastewater

Abstract Four methods for the enumeration of human parasitic nematodes in treated wastewater were compared in field trials in the northeast of Brazil. Effluents from a series of waste stabilisation ponds and a physico‐chemical lime treatment plant were used. Comparisons were made on a daily and 24 hour basis. The recovery of eggs was found to be consistently higher using the method currently recommended by the World Health organisation (1) (commonly known as the Bailenger method) but only when 10 1 samples, rather than 11 samples, were processed.

Wastewater reuse in agriculture and the risk of intestinal nematode infection.

The increasing use of wastewater for crop irrigation in arid and semi-arid zones means that wastewater parasitology is becoming on important research area. The World Health Organizations (WHO) current guideline states that only treated wastewater containing no more than one human intestinal nematode egg per litre should be used for irrigation. This guideline was based on very limited epidemiological evidence. In this article Rachel Ayres, Rebecca Stott, Duncan Mara and Donald Lee describe their recent work in Yorkshire and northeast Brazil and suggest that their results may be the first evidence for relaxing the WHO guideline for restricted irrigation to no more than ten intestinal nematode eggs per litre.

The mast cell and eosinophil response of young lambs to a primary infection with Nematodirus battus.

Helminthologically naive 8-week-old lambs were administered 50,000 infective-stage larvae of the trichostrongyle nematode Nematodirus battus. Initial mean adult worm burdens were significantly reduced (P < 0.01) at day 21 post-infection (p.i.). Peripheral blood eosinophil counts showed a significant increase (P < 0.001) by day 25 p.i. when compared with uninfected control animals. Sections of small intestine taken at post-mortem from the area of adult worm establishment over the course of infection showed a significant increase in mucosal eosinophil and mast cell numbers during the period of adult worm rejection, when compared with uninfected control animals. These results show that young lambs develop significant increases in the numbers of cells associated with an inflammatory reaction in the intestine during the development of a partially protective immune response to this parasitic nematode.

Detection of benzimidazole resistance in trichostrongylid nematodes

Benzimidazole anthelmintics (Box 1) have an important role in the control of economically-important nematode parasites of sheep and other ruminants. But effective control and management strategies using such compounds require a clear appraisal of the resistance or susceptibility of the target worms. Currently available tests for benzimidozole resistance in trichostrongylid nematodes tend to be costly, time-consuming and technically-demanding - as a result, attention is now turning to biochemical assays.

A vasoactive intestinal polypeptide-like protein excreted/secreted by Nippostrongylus brasiliensis and its effect on contraction of uninfected rat intestine

The 50-30 kDa fraction isolated from the excretory/secretory products (E/S) of the nematode Nippostrongylus brasiliensis significantly decreased the amplitude of contraction of segments of uninfected rat intestine when injected into the lumen of the segments maintained in an organ bath. Dot blot analysis of the fraction suggested that it was similar in immunoreactivity to porcine vasoactive intestinal polypeptide (VIP). When antiserum to porcine VIP was mixed with N. brasiliensis E/S and the mixtures were injected into the lumen of segments of rat intestine, the inhibitory effect of the E/S on amplitude of contraction decreased. When physiological concentrations of porcine VIP (12.9 pmol/ml) were injected into the lumen of segments of uninfected rat intestine the amplitude of contraction decreased significantly. Western blot analysis of the E/S, using antiserum to porcine VIP, recognized a 30 kDa protein in the E/S and also in whole worm homogenate suggesting that synthesis of the peptide occurs inside the nematode. Peptide histidine isoleucine (PHI)-like immunoreactivity was detected in a 68 kDa fraction of the E/S and the homogenate but this fraction did not affect the amplitude of contractions of the intestine.

The accumulation, distribution and viability of human parasitic nematode eggs in the sludge of a primary facultative waste stabilization pond

Investigations into the enumeration, distribution and viability of nematode eggs in the sludge from a primary facultative waste stabilization pond showed that pond sludges are not nematologically safe for immediate land application. Up to 12% of Ascaris lumbricoides eggs were viable after the pond had been in operation for 2.5 years. Eggs were recovered from the sludge along the full length of the pond, although there were significant decreases in egg concentration and viability with increasing distance from the inlet.

Inhibition of acetylcholinesterase secretion from nippostrongylus brasiliensis by benzimidazole anthelmintics

Treatment of rats infected with Nippostrongylus brasiliensis with a single, oral therapeutic dose of the anthelmintic benzimidazole carbamates oxfendazole or mebendazole resulted, 24 hr later, in a marked reduction (60-90%) in the secretion of a low molecular weight acetylcholinesterase from the parasites when they were incubated in vitro. This effect coincided with the expulsion of parasites from the host as a result of the therapy. When parasites were incubated in vitro with 0.1 mM oxfendazole, mebendazole, flubendazole, parbendazole, cambendazole or thiabendazole a similar effect was observed; with oxfendazole and mebendazole the effect was apparent within 1 hr and lasted for at least 4 hr after removal to fresh, drug-free medium. Whether treated in the host or in vitro the reduction in secretion was balanced by an equivalent rise in acetylcholinesterase activity within the parasites. It is suggested that the inhibition of protein secretion may be a specific manifestation of a general effect of these compounds on microtubule function.

Changes in the level of acetylcholinesterase of Nematospiroides dubius and Trichostrongylus colubriformis following paralysis by levamisole in vivo

Acetylcholinesterase (acetylcholine acetylhydrolase; EC 3.1.1.7) levels of Nematospiroides dubius from laboratory mice and Trichostrongylus colubriformis from lambs have been measured. The anthelmintic levamisole (leavo isomer of 2,3,5,6-tetrahydro-6-phenylimidazo-(2,1b)-thiazole (Tetramizole)) did not affect the level of acetylcholinesterase in N. dubius in vivo but caused a reduction in the level of the enzyme in T. colubriformis following paralysis in vivo. The effect of levamisole on acetylcholinesterase in the nematodes is explained in terms of the differing roles of the enzyme in these two species.