Proteinases released during in vitro maintenance of third (L3) and fourth larval stage (L4) and adult Teladorsagia circumcincta (formerly Ostertagia circumcincta), an ovine abomasal nematode parasite, were characterized on the basis of pH optima, molecular size and specific proteinase inhibitor sensitivity. Enzyme activity was maximal at alkaline pH and stage-specific release was demonstrated. Proteinases released by the adult parasite degraded a variety of protein substrates including plasminogen, albumin and haemoglobin, in a pH-dependent manner. At alkaline pH fibrinogen degradation was restricted to the α and β peptide chains although the γ peptide chain was also degraded at acidic pH. Inhibitor sensitivity studies indicated that degradation was predominantly due to metalloproteinases although aspartyl proteinase activity was indicated at acidic pH.

In an immunocytochemical study, using an antiserum and a monoclonal antibody specific for the amino acid, γ-aminobutyric acid (GABA), GABA-like immunoreactivity (GLIR) has been demonstrated for the first time in parasitic flatworms. In Moniezia expansa (Cestoda), GLIR was seen in nerve nets which were closely associated with the body wall musculature and in the longitudinal nerve cords. In the liver fluke Fasciola hepatica (Trematoda), the GLIR occurred in the longitudinal nerve cords and lateral nerves in the posterior half of the worm. GLIR was also detected in subtegumental fibres in F. hepatica. The presence of GABA was verified, using high-pressure liquid chromatography coupled with fluorescence detection. The concentration of GABA (mean ± S.D.) in M. expansa anterior region was 124·8 ± 15·3 picomole/mg wet weight, while in F. hepatica it was 16·8 ± 4·9 picomole/mg. Since several insecticides and anti-nematodal drugs are thought to interfere with GABA-receptors, the findings indicate that GABAergic neurotransmission may be a potential target for chemotherapy in flatworms too.

The nervous systems of helminths are predominantly peptidergic in nature, although it is likely that the full range of regulatory peptides used by these organisms has yet to be elucidated. Attempts to identify novel helminth neuropeptides are being made using immunocytochemistry with antisera raised against peptides isolated originally from insects. One of these antisera was raised against allatostatin III, a peptide isolated originally from the cockroach, Diploptera punctata, and a member of a family of related peptides found in insects. Allatostatin immunoreactivity was found throughout the nervous systems of Mesocestoides corti tetrathyridia, and adult Moniezia expansa, Diclidophora merlangi, Fasciola hepatica, Schistosoma mansoni, Ascaris suum and Panagrellus redivivus. Immunostaining was observed in the nerve cords and anterior ganglia of all the helminths. It was also apparent in the subtegumental nerves and around the reproductive apparatus of the flatworms, in neurones in the pharynx of D. merlangi, F. hepatica, A. suum and P. redivivus, and in fibres innervating the anterior sense organs in the nematodes. Immunostaining in all species was both reproducible and specific in that it could be abolished by pre-absorption of the antiserum with allatostatins I–IV. These results suggest that molecules related to the D. punctata allatostatins are important components in the nervous systems of a number of helminth parasites, and a free-living nematode. Their distribution within the nervous system suggests they function as neurotransmitters/neuromodulators with roles in locomotion, feeding, reproduction and sensory perception.

Parasite modification of host behaviour influences a number of critical responses, but little is known about the effects on host spatial abilities. This study examined the effects of infection with the intestinal trichostrongylid nematode, Heligmosomoides polygyrus, on spatial water maze learning by male laboratory mice, Mus musculus. In this task individual mice had to learn the spatial location of a submerged hidden platform using extramaze visual cues. Determinations of spatial performance were made on day 19 post-infection with mice that had been administered either 50 or 200 infective larvae of H. polygyrus. The infected mice displayed over 1 day of testing (6 blocks of 4 trials) significantly poorer acquisition and retention of the water maze task than either sham-infected or control mice, with mice that had received 200 infective larvae displaying significantly poorer spatial performance than individuals receiving 50 larvae. The decrease in spatial learning occurred in the absence of either any symptoms of illness and malaise, or any evident motor, visual and motivational impairments. It is suggested that in this single host system the parasitic infection-induced decrease in spatial learning arises as a side-effect of the host's immunological and neuromodulatory responses and represents a fitness cost of response to infection.

We report experimental data comparing the effects of Mesostigmatid mites and Ischnoceran lice on the reproductive performance of a single group of captive rock doves (Columba livia). Several components of host reproductive success were compared for the two groups, including number of eggs laid, hatching success, nestling growth rates, fledging success, post-fledging body mass and survival. Adult body mass and survival were also compared. There was a dramatic difference in the effects of the mites and lice. The former drove host reproductive success to zero, mainly by agitating adults and causing them to incubate eggs less faithfully. Nestling growth rates and post-fledging survival were also significantly reduced by mites. Lice showed no effect on reproductive success whatsoever, even though the feather damage they cause is known to have energetic consequences (Booth, Clayton & Block, 1993). Neither parasite had a significant effect on adult birds. Although Ischnocera are found on most species of birds, our results for lice constitute the first experimental test of the impact of Ischnocera on avian reproductive success (preliminary report by Clayton & Tompkins, 1994). We discuss reasons for the different effects of mites and lice, including the relationship of horizontal (mites) and vertical (lice) transmission to the evolution of virulence.

The objectives of this study were (1) to determine the impact of severe zinc deficiency on the establishment, growth, survival and reproduction of Heligmosomoides polygyrus in the laboratory mouse, during both primary and challenge infection protocols, and (2) to determine whether the observed effects resulted from zinc deficiency per se, or from the accompanying energy restriction. Three diet groups were used: zinc-sufficient (Zn+: 60 mg zinc/kg diet), zinc-deficient (Zn·75 mg zinc/kg diet) and energy restricted (ER: 60 mg zinc/kg diet pair fed to Zn− mice). Neither Zn− nor ER influenced the establishment of the parasite during a primary infection. However, both significantly influenced the early development of the parasite. The proportion of adult worms recovered 9 days post-infection (p.i.) was highest in Zn− mice, intermediate in ER mice and lowest in +Zn+ mice. Worms were also distributed more distally in the intestine of the Zn− mice and worm survival was highest in Zn− mice, intermediate in ER mice and lowest in Zn+ mice at both 4 and 5 weeks p.i. Although the length of female worms was reduced in Zn− mice, neither per capita fecundity nor egg viability was affected by zinc deficiency. Energy restriction, on the other hand, significantly reduced worm fecundity at 5 weeks post-primary infection, but had no effect on egg viability. Zinc concentration of adult H. polygyrus was similar among dietary groups. The effects of zinc deficiency and energy restriction were also investigated 4 and 5 weeks after a challenge infection. Whereas strong host resistance was evident in Zn+ and ER mice, based on comparison of worm numbers between challenged mice and primary infection controls, no evidence of resistance was detected in Zn− mice. As in the primary infection, female worms were shorter in Zn− mice than in ER and Zn+ mice, and energy restriction but not zinc deficiency significantly affected per capita fecundity. However, in contrast to the primary infection, ER mice had elevated rather than reduced fecundity. This study demonstrates a complex interaction between H. polygyrus and zinc and energy restriction, and highlights the importance of controlling for reduced food intake in nutrition–infection studies.

The relationship between varying intensities of Trichuris trichiura infection and iron status was examined in Jamaican schoolchildren, aged 7 to 11 years. A total of 409 children was identified with T. trichiura (epg > 1200). A control group comprised 207 uninfected children who were matched by school and class to every pair of infected subjects. Blood samples were obtained from 421 children: 264 infected and 157 controls. Compared to the rest of the children, those with heavy infections (epg > 10 000) had significantly lower (P < 0·05) Hb (11·5 ± 1·3 vs. 12·1 ± 1·1 g/dl), MCV (78·6 ± 6·3 vs. 81·2 ± 5·5 fl), MCH (26·2 ± 2·9 vs. 27·5 ± 2·5 pg) and MCHC (33·2 ± 1·5 vs. 33·9 ± 1·4 g/dl). Similarly, the prevalence of anaemia (Hb < 11·0 g/dl) amongst heavily infected children (33%) was significantly higher (P < 0·05) than the rest of the sample (11%). These differences remained significant after controlling for confounding variables including socio-economic status, age, gender, area of residence and the presence of Ascaris infections. Differences in red cell count, ferritin, and free erythrocyte protoporphyrin were not statistically significant and showed no association with the infectious load. These results suggest that in the Jamaican children studied, iron deficiency anaemia is associated with Trichuris infections over 10 000 epg, but not with less intense infections.

The timing of the energetic consequences of a developing, single-dose infection of Trichostrongylus tenuis larvae was investigated in captive red grouse Lagopus lagopus scoticus. At 12 days post-infection (p.i.), infected birds had a resting metabolic rate 16% greater than controls and thenceforth lost weight at a faster rate than controls. At 16 days p.i. infected birds consumed 38% less energy and excreted 33% less energy than controls. The estimated total daily energy expenditure and energy expended on activity for infected birds at 16 days p.i. were 36% and 83% lower, respectively, than for controls. Infected birds lost condition from 16 days p.i. onwards. The period of energy imbalance at 12–16 days p.i. coincided with development of late 4th-stage larvae into adult worms and the onset of patency. After this, the effects on energy balance diminished. Synchronous development of previously arrested T. tenuis larvae in wild birds in spring probably has similar effects to those reported here and places grouse under conditions of energy imbalance. The observed effects on energy balance provide a possible mechanism by which the parasite can reduce fecundity and survival of infected grouse.

The epidemiology of Strongyloides stercoralis was studied in families of clinical (reference) cases and their neighbours at endemic foci in Jamaica. Thirteen foci were studied based on the place of residence of a reference case. For each household of a reference case, the 4 most proximal neighbourhood households (spatial controls) were included in the study. Out of 312 persons contacted 244 were followed up using questionnaires, stool examination and serology. Prevalence of infection based on stool examination was 3·5% and on ELISA 24·2%. Prevalence increased with age but was not related to gender. Reference cases were significantly older than the general study population. The prevalence of infection based on both serology and stool examination was significantly higher in reference than in neighbouring households (the reference cases, themselves, were not included in the analysis). Furthermore, prevalence of infection was highest among persons who shared a bedroom with a reference case and decreased significantly with increasing spatial separation. This is indicative of close contact transmission which has not been previously shown for a geohelminth, but which is common among microparasites.

The importance of host cues to three species of steinernematid nematodes (Rhabdita: Steinernematidae) with different foraging strategies was compared. We presented host materials to nematodes in series to test responses to combinations of host cues. If a fixed hierarchy of cues is followed during foraging, parasites should respond most strongly to cues offered in natural order. Steinernema carpocapsae, an ambush forager, aggregated at the source of volatile host cues only after attachment to host cuticle. They also parasitized hosts more efficiently after contact with cuticle. Steinernema glaseri, a cruise forager, was unaffected by exposure to combinations of host cues. Steinernema feltiae, a nematode with characteristics of both ambushing and cruising, was affected by cue hierarchies when either contact or volatile cues were presented first. Host-associated materials encountered out of the context may not qualify as host cues for the ambush forager, S. carpocapsae. Perhaps the order in which cues are encountered is more predictable for ambushers than for cruisers. Therefore an ambusher's response to host materials has a more fixed contextual framework.

There is a general lack of basic information concerning one class of glycoconjugate, the glycolipids, from parasitic nematodes. As the prototype, the neutral glycolipid fraction derived from adult males of Ascaris suum was investigated as to its chromatographic, differential chemical staining, antigenic and chemical properties. The thin-layer chromato-graphy-resolved neutral fraction glycolipids could be classified into components of fast and slow migrating band groups. Immunoreactivity was restricted to the latter as detected by IgG and IgM anti-neutral fraction glycolipid antibody levels in serial infection sera of mice. Similarities of chromatography, antigenicity and serological cross-reactivity have been extended to the neutral glycolipid fractions of other parasitic nematodes: Litomosoides carinii and Nippostrongylus brasiliensis. Chemical, differential chemical staining and enzymatic analyses identified the Ascaris suum antigenic, slow migrating band group of components as amphoteric glycosphingolipids, and not the originally hypothesized glyco-glycerolipids or glycosylphosphatidylinositols, that contained typical neutral monosaccharide constituents and a zwitter-ionic phosphodiester linkage, most probably phosphocholine. Glycosphingolipid-immunoreactivity is eliminated on cleavage of the zwitterionic phosphodiester linkage by hydrofluoric acid treatment.

The 4 species of ruminants (dromedary, zebu cattle, sheep and goat) in arid areas of Mauritania harboured Haemonchus spp. as the most frequent internal parasite. This was a rare situation where the 3 putative species, H. longistipes (dromedary), H. placet (zebu cattle) and H. contortus (sheep and goat) occurred sympatrically. The study was undertaken on hosts slaughtered at the Nouakchott abattoir, on the basis of monthly collection of worms. The environment was very unfavourable to H. placei and unfavourable to H. contortus, as intensity of infection remained low throughout the year, whereas infection in the dromedary was 10 to 20-fold higher. The survival strategies during the long, dry season were different: the surviving stages were either 4th-stage larvae in digesta (dromedaries), 4th-stage larvae either in digesta or mucosae (cattle), or 4th-stage larvae in mucosae and few adults (sheep and goats). The prolificacy of female worms, indicative of the potential to contaminate pastures, was similar for all Haemonchus spp. in the rainy season. H. longistipes behave differently during the pre-rainy season as no increase of prolificacy could be demonstrated as observed in the other species. Traits of vulvar morphology are considered as markers of ecological adaptation and were studied. The knobbed and smooth female morphs (in equal proportions) were the most frequent in H. longistipes, the knobbed morph out-numbered the other morphs in H. placei, and all 3 morphs were present in sheep and goats with the linguiform form being predominant. Genetic characterization of the 3 species was performed by means of Random Amplified Polymorphic DNA (RAPD). Three groups were obtained from analysis of these data: 1 group with individuals of H. contortus, 1 group with individuals of H. placei, and 1 group with individuals of H. longistipes. This indicated that, although the 3 species were valid, H. contortus and H. placei were more similar. Intraspecific variability was 2-fold higher in H. contortus than in the 2 other species. The ecological, morphological and genetical studies showed that H. longistipes, H. placei and H. contortus could be arranged in increasing order of variability.

This paper describes a study of 194 children (aged 9–13) from a mountain village in Ecuador who were infected with one or more species of intestinal helminth or protozoan parasite. In addition to parasite load, the assessment consisted of a battery of psychological and neuropsychological tests, an EEG examination, measures of iodine level, presence of goitre and level of nutrition. We found that, in general, parasite infection, as measured at the baseline level, was not associated with cognitive impairment. The intensity of infection with A. lumbricoides, however, was correlated with the level of verbal ability and with inhibition-control aspects of cognitive behaviour. Multivariate analysis with level of nutrition, EEG status and parasite burden showed a consistent main effect of the degree of nutrition on neuropsychological performance, particularly the language, problem solving and inhibition-control dimensions.

Cases of human Ascaris infection occur sporadically in areas such as N. America and Western Europe, where this parasite is thought to be non-endemic. Clinical case histories suggest that many of these cases may be cross-infections from pigs. I describe patterns of variation in the ribosomal DNA of Ascaris from 9 such cases. For comparative purposes, I also describe patterns of variation in parasites obtained from pigs and humans from worldwide locations. A Hae III restriction site distinguishes two classes of rDNA repeats; repeats bearing this restriction site were found in > 96% of parasites from pig populations worldwide and in all 9 worms from humans in N. America. In contrast, repeats bearing this restriction site were detected in < 2% of parasites from humans in endemic areas. The molecular data clearly incriminate pigs as the source of infection in the N. American cases. I discuss evolutionary and public health implications of incomplete host fidelity in Ascaris.

AF2 is an endogenous RFamide-like peptide from the parasitic nematode Ascaris suum. The potent stimulatory effects of this peptide on the somatic musculature of Ascaris strongly suggest that it may have an important role in the motornervous system. Here we have investigated the possibility that AF2 may elicit a stimulatory action on Ascaris muscle by potentiating the actions of the excitatory cholinergic motornervous system either pre-synaptically, post-synaptically or both. In in vitro pharmacological experiments AF2 produced a dose-dependent increase in the frequency and amplitude of spontaneous contractions of Ascaris muscle strip which lasted for more than 1 h after a 3 min application of AF2 (10 nM–10µM; N = 7). In addition, AF2 (100 nM) potentiated the contraction elicited by ACh by 43 ± 9% (P < 0·01; N = 8). In electro-physiological recordings from muscle cells, AF2 (10–100 nM; N = 10) potentiated the amplitude of EJPs (excitatory junction potentials). For 100 nM AF2, the potentiation of the EJP was 218 ± 48% (N = 7; P < 0·01). This effect reversed after a wash of 10 min. AF2 did not potentiate the depolarization of the muscle cell elicited by bath applied ACh. These latter two observations are consistent with a presynaptic action of AF2. AF2 (10–100 nM) generated spontaneous muscle cell action potentials in previously quiescent cells. This effect took more than 1 h to wash out. These observations are discussed in terms of the paralysis of Ascaris that is elicited by AF2.

Comparison of the proteins in salivary glands, saliva and haemolymph of Rhipicephalus appendiculatus female ticks during feeding

Parasitology (1994), 109, 517–523

Fig. 2. Delete 24 kDa marker between 36 kDa and 29 kDa markers.

Fig. 6. Replace 24 to 17·6 kDa with 34, 33·5, 32·5, 31·5, 30, 29 kDa.

Fig. 7. Replace 33·2 kDa with 33·5 kDa.

Excretion of host immunoglobulin in tick saliva and detection of IgG-binding proteins in tick haemolymph and salivary glands

Parasitology (1994), 109, 525–530

Fig. 4. Replace 19·2 kDa with 14·2 kDa.

Patterns of genetic subdivision in parasite populations can provide important insights into transmission processes and complement information obtained using traditional epidemiological techniques. We describe mitochondrial sequence variation in 265 Ascaris collected from 62 individual hosts (humans and pigs) from 35 households in 3 Guatemalan locations. Restriction mapping of individual worms revealed 42 distinct mitochondrial genotypes. We ask whether the mitochondrial genotypes found in worms from individual hosts, from families of hosts and from villages represent random samples from the total Ascaris population. Patterns of genetic subdivision were quantified using F-statistics, while deviations from the null hypothesis of randomness were evaluated by a simple resampling procedure. The analysis revealed significant deviations from panmixia. Parasite populations were strongly structured at the level of the individual host in both humans and pigs: parasites bearing the same mitochondrial genotype were found more frequently than would be expected by chance within hosts. Significant heterogeneity was also observed among populations from different villages, but not from different families within a village. The clustering of related parasites within hosts suggests a similar clustering of related infective stages in the environment and may explain why sex ratios in Ascaris are female-biased. We discuss aspects of Ascaris biology which may lead to the observed patterns.

NADPH diaphorase has recently been discovered to be responsible for neuronal nitric oxide (NO) synthase activity in mammals. It thus serves as a histochemical marker for the localization of NO synthase in the nervous system. The histochemical technique was used to map out potential NO-producing neurones in the nervous system of the parasitic nematode, Ascaris suum. Positive staining for NADPH diaphorase was present in various parts of the central nervous system, in particular within selective cell bodies and fibres in the ventral ganglion, the retrovesicular ganglion, ventral and dorsal cords and sublateral lines. Intense staining was also present in the motorneurone commissures, indicating a potential role for NO as a neurotransmitter at the neuromuscular junction. NADPH disphorase-positive neurones were not confined to the central nervous system. Selective staining was also present in the enteric nervous system, in particular the pharynx and in the peripheral nervous system innervating the sensory organs.

In this paper the dynamics and control of nematode parasites of farmed ruminants are discussed via a qualitative analysis of a differential equation model. To achieve this a quantity, ‘the basic reproduction quotient’ (Q0), whose definition coincides with previous definitions of R0 for macroparasites, but extends to models with periodic time-varying transition rates between parasite stages or management interventions, is introduced. This quantity has the usual threshold property: if Q0 is less than one the parasite population cannot maintain itself in the host population, and in the long term becomes extinct; but if Q0 is greater than one the parasite can invade the host population. An alternative quantity, R(E), that is often easier to calculate is also introduced, and shown to have the same threshold property. The use of these two quantities in analysing models for the dynamics of nematodes in complex situations is then demonstrated, with reference to the dynamics of mixed parasite species in one host; the effects of breeding host animals for resistance to parasitism; and the development of parasite strains that are resistant to chemotherapy. Five examples are discussed using parameters for the dynamics of nematode infections in sheep, and some statements on control policies are derived.

Trypanosoma (Nannomonas) godfreyi sp. nov. from tsetse flies in The Gambia: biological and biochemical characterization

Parasitology109, 497–511

p. 499, para. 2, 104/ml to replace 104/μl

p. 501, para. 1, chromsomes to replace chromosome

p. 501, para. 2, 1/148 to replace 1/48

p. 504, para. 3, BAN 9 or KEN 7 to replace BAN 9 & KEN 7