An epidemiological survey was conducted during a 4-month period of intense malaria transmission in Dielmo, a holoendemic Senegalese village. Two thick blood smears per inhabitant were collected weekly. The sex ratio of Plasmodium falciparum gametocytes (gamete precursors) was studied in 50 gametocyte carriers. All age classes were represented (mean 19·7 years; range: 2 months–75 years); 42 (84%) of them did not receive antimalarial treatment. Overall 668 thick smears were examined until 100 gametocytes had been counted or for 40 min. A total of 11 204 gametocytes were observed with a mean sex ratio of 0·346 (95% CI 0·317–0·374), i.e. 2·89 females per 1 male. Among the 284 thick smears in which at least 10 gametocytes were observed, the mean percentage of male gametocytes was 27·8%, with a range of 0–82%. Great variability was observed between gametocyte carriers and also between thick smears from the same gametocyte carrier. A multivariate analysis was performed which highlighted the fact that only 2 variables had a significant effect on the sex ratio. Anaemia was associated with an increased percentage of males (Prevalence Rate Ratio [PPR] of male gametocytes was multiplied by 1·65 if haematocrit rate <32%) and a wave of gametocytes was associated with an increased percentage of female gametocytes (PRR was multiplied by 0·48 during the peak of gametocytaemia and for the 2 weeks following this peak). The variables without significant effect on sex ratio were: age, sex, clinical status and sickle cell trait status of the gametocyte carrier, density of asexual parasites, quinine treatment, and gametocyte density (when taking account of its waves). These results are discussed in regard of possible differential production, mortality or sequestration of one gametocyte sex and selective advantages for the transmission of parasites.

Studies of invertebrate–parasite interactions frequently report that infection reduces host fecundity. The extent of the reduction is likely to be determined by a wide range of host and parasite factors. We conducted a laboratory experiment to evaluate the role of parasite genetics and infection genetic diversity on the fecundity of mosquitoes carrying malaria parasites. The malaria vector Anopheles stephensi was infected with either of 2 different genotypes of the rodent malaria parasite Plasmodium chabaudi, or by a mixture of both. Mixed genotype infections reduced mosquito fecundity by 20%, significantly more than either of the 2 single genotype infections. Mixed genotype infections were associated with high gametocyte densities and anaemia in mice, both of which were correlated with reduced bloodmeal size in mosquitoes. Bloodmeal size was the most important predictor of mosquito fecundity; the presence and number of parasites had no direct effect. Parasite density influenced the propensity of mosquitoes to feed on infected mice, with a higher percentage of mosquitoes taking a meal as asexual parasite and gametocyte density increased. Thus mosquitoes may preferentially feed on hosts who will most impair their fecundity.

There is no published account which allows the morphological discrimination of microfilariae of Onchocerca volvulus and M. ozzardi from each other. However, they occur together in parts of Brazil and Venezuela, and presumably there is always the possibility that migration could establish new sympatric populations in the future. The objective of this study was to evaluate simple morphological characters that might be used for species-diagnosis of microfilariae. The conclusions were that the location of microfilariae in the blood or skin, the body size and the nucleation of the nerve ring are expected to be useful first indications of species identity, but cannot be used for confident diagnosis. The structure of the cephalic armature (stained with alcian blue) seems to be species specific, but is of limited application because it is often difficult to see. However, the pattern of nucleation of the tail (as expressed by the ratio of the length of the terminal nucleus compared with the length of the tail space) is distinctive and is expected to be diagnostic.

The age dependency of the mortality, spontaneous de-tailing and infectivity of cercariae of Schistosoma mansoni has been determined at 25 °C. Infectivity was assessed with respect to stratum corneum-like differentiated human keratinocyte cultures (validated by comparison with fresh human skin samples) and displayed a complex age-dependent pattern. From 1 to 9 h post-emergence cercariae showed a plateau of maximal infectivity (around 90% attachment). Thereafter, infectivity declined. Immediately after release, infectivity at around 60% was significantly lower than the plateau values and this could be an adaptation for spatial dispersal of cercariae. Age-dependent patterns of cercarial mortality and spontaneous de-tailing closely mirrored the infectivity pattern except in relation to the low initial infectivity value. These findings suggest that, at a population level, the age-dependent decline in cercarial infectivity towards human skin is essentially driven by cercarial mortality. The recently described phenomenon of delayed tail loss (DTL) in S. mansoni cercariae infecting human skin is confirmed in the present study. For cercariae aged up to 13·5 h post-emergence, 90% or more of invading cercariae took their tails with them into the keratinocyte culture. The infection dynamics described in this study suggest that diurnally shed S. mansoni cercariae, with peak emergence around mid-day, will have near maximal infectivity towards humans in contact with water through all remaining daylight hours in the tropics.

This study determined the complete mitochondrial (mt) genome sequence of the canine heartworm, Dirofilaria immitisThe complete nucleotide sequence for the mitochondrial genome of Dirofilaria immitis is available from the EMBL database under the Accession Number AJ537512., and compared its structure, organization and other characteristics with Onchocerca volvulus and other secernentean nematodes. The D. immitis mt genome is 13814 bp in size and contains 36 of the 37 genes typical of metazoan organisms, and lacks the ATP synthetase subunit 8 gene. All of the genes are transcribed in the same direction. For the entire genome, the nucleotide contents are ∼55% (T), ∼19% (each for A and G) and ∼7% (C), which is very similar to those of the protein-coding genes. In the latter genes, most (∼69%) third codon positions have a T, but rarely (∼1–9%) have an A or a C. The C content (8–12%) is higher at the first and second codon positions compared with the third position (∼1%). These nucleotide biases have a significant effect on the codon usage patterns and, thus, on the amino acid composition of the proteins. The mt genome organization of D. immitis is essentially the same as that of O. volvulus, but is distinctly different from other secernentean nematodes sequenced thus far. Irrespective of transpositions of transfer RNA (trn) genes and the non-coding, AT-rich region, there are 4 gene- or gene block-translocations between the mt genome of D. immitis and those of Caenorhabditis elegans, Ascaris suum and the 2 human hookworms, Ancylostoma duodenale and Necator americanus. For D. immitis, the 22 trn genes have secondary structures typical of other secernentean nematodes, and possess a TV-replacement loop instead of a TΨC arm and loop. Like O. volvulus, the mt trnK and trnP of D. immitis use the anticodons CUU and AGG, whereas in other nematodes, UUU and UGG are employed, respectively. Also, the secondary structures of the 2 ribosomal RNA (rrn) genes are similar to the models for other nematodes. Overall, the availability of the complete D. immitis mt genome sequence provides a resource for future studies of the comparative mt genomics and of the population genetics and/or phylogeny of parasitic nematodes.

To study the prevalence of the polymorphism in position 200 of the beta-tubulin gene in the mechanism of benzimidazole (BZ) resistance in cyathostomes of horses, an allele-specific PCR was used to detect the genotype of individuals of BZ-susceptible and BZ-resistant populations. The molecular analysis of 100 adults recovered from an anthelmintic-naïve horse revealed 80% homozygous TTC/TTC individuals, 17% heterozygous TTC/TAC and 3% homozygous TAC/TAC. A naturally infected horse was treated with increasing fenbendazole (FBZ) dosages to select a BZ-resistant population of cyathostomes. The PCR based analysis of 3rd-stage larvae (L3) during the experiment revealed a decrease of the homozygous TTC/TTC genotype and an increase in heterozygous TTC/TAC and homozygous TAC/TAC individuals. After treatment 42·3% of the adults (n=104) were homozygous TTC/TTC, 55·8% were heterozygous TTC/TAC and only 1·9% showed the homozygous genotype TAC/TAC. The results of the molecular analysis lead to the proposal that polymorphism within codon 200 is not the only reason for the development of BZ resistance in small strongyles.

The present study was designed to assess the role of inulin and sugar beet fibres (SBF) on adult O. dentatum in growing pigs. Four experimental diets were formulated based on barley flour with added insoluble fibre from oat husk (Diet 1), a pure carbohydrate source inulin (Diet 2), soluble fibre from sugar beet fibre (SBF) with a high proportion of soluble fibre components (Diet 3) or inulin plus SBF (Diet 4). Thirty-two 10-week-old pigs were divided randomly into 4 groups each of 8 pigs. After 3 weeks adaptation on Diet 1 all pigs were infected with a single dose of 6000 L3O. dentatum. At week 7 p.i. one group was switched to Diet 2, another group to Diet 3 and another group to Diet 4. The remaining 8 pigs continued on Diet 1 until the end of the experiment and served as controls. At week 13, all pigs were necropsied and their worm burdens determined. The worm recoveries from the pigs on the inulin supplemented diet (Diet 2) were reduced by 97% compared to the controls (Diet 1). Further, the inulin-fed pigs exhibited markedly reduced faecal egg counts. The pigs on inulin plus SBF diet (Diet 4) and on SBF diet (Diet 3) had 86% and 70% adult worm reductions compared with the controls, respectively. The results from this study indicate that highly degradable and rapidly fermentable carbohydrates such as dietary inulin have a profound deworming effect on O. dentatum infection.

A β-1,3-glucan-binding lectin from the penetration glands of Diplostomum pseudospathaceum cercariae was isolated by affinity chromatography using yeast glucan and curdlan as affinity matrices. Further purification to homogeneity was performed by cation-exchange chromatography. The protein migrated as a double band around 24 kDa in gels after SDS–PAGE. The protein is of strongly basic nature – its pI shown by native IEF was around 10. The mass of the protein determined by MALDI-TOF mass spectrometry was 23·9 kDa. N-terminal sequence as well as some internal sequences showed significant alignments with several cysteine protease sequences found in databases. The protein bound a biotinylated synthetic analogue of the irreversible inhibitor of cysteine proteases, E-64 and, moreover, its proteolytic activity was demonstrated in substrate gels. The enzymatic activity could be inhibited by the cysteine protease inhibitor E-64; therefore, the investigated protein was considered to be a bifunctional molecule possessing both lectin and enzyme activities. Glycanohydrolytic activity was not proved. The detected characters of this molecule lead to a hypothesis on its role in penetration of Diplostomum cercariae into fish hosts – that of binding to the carbohydrates of fish mucus and concurrent cleaving of protein components of the mucus and skin.

The population structure and recruitment of Argulus coregoni was monitored at a Finnish fish farm during the open water periods of 1999 and 2001 by weekly sampling of attached argulids. In 2001 the numbers of rainbow trout examined increased in the autumn when the A. coregoni population was declining. When the water temperature exceeded 10 °C, at the end of May, A. coregoni egg hatching commenced. A mean number of 98 (S.D.±5·4) juvenile A. coregoni was recorded on each fish, before the start of female egg laying in July 1999. The abundance of lice was lower in 2001. The main recruitment of A. coregoni juveniles occurred in early summer, but the hatching of eggs continued until September. However, no pulses of hatching were recorded later in the summer and the numbers of lice on fish substantially decreased after mid-July in both years. On average, only 0·6 (S.D.±0·72) parasites/fish were found between August and late October 2001 and none in November. We suggest that there is 1 main A. coregoni generation annually in Central Finland. Environmental conditions, especially temperature, affects the population cycle of A. coregoni: we found a more synchronous and intense population cycle during the summer 1999, when the early summer was warmer than in 2001. The overall sex ratio (female[ratio ]male) of A. coregoni was nearly 1[ratio ]1 in June 1999, but was male biased (1[ratio ]1·4) in June 2001. It was also shown that from July onwards, many females detached from the fish host in order to lay their eggs on the bottom of the pond. Large males were often bigger than the largest females between mid-July and early September 2001, when as many as 3·7 (S.D.±1·48) times more males than females were present in the lice samples.

The saliva of haematophagous insects has a series of pharmacological activities which may favour blood feeding. In the present study, an inhibitory effect on the complement system was observed in salivary extracts obtained from the phlebotomine sand flies Lutzomyia longipalpis and Lu. migonei. Saliva from Lu. longipalpis was capable of inhibiting both the classical and alternative pathways, while that from Lu. migonei acted only on the former. Other haematophagous insect species were screened for inhibition of the classical pathway. The triatomine bugs Panstrongylus megistus, Triatoma brasiliensis and Rhodnius prolixus were also able to inhibit the classical pathway whereas the mosquito Aedes aegyti and flea Ctenocephalides felis were not. The activity of Lu. longipalpis saliva on the classical pathway was partially characterized. The inhibitor is a protein of Mr 10000–30000 Da, which is very resistant to denaturation by heat. The inhibition of the complement system by phlebotomine sand flies may have a role in the transmission of Leishmania to the vertebrate hosts. The inhibitor molecule is thus a promising component of a vaccine to target salivary immunomodulators.