Commitment to the production of female and male gametocytes was studied in the NF54 line of the human malaria parasite Plasmodium falciparum. The development of sibling parasites derived from individual schizonts was followed, and 2 antisera against the female gametocyte-specific protein Pfg377 and the male gametocyte-specific protein α-tubulin II were used to determine the sex of sibling gametocytes. The experiment showed that individual cohorts of sibling gametocytes were stained in a mutually exclusive fashion by only one or the other antiserum, indicating that individual schizonts committed to yield sexual parasite progeny produce gametocytes of the same sex. This work suggests that in P. falciparum commitment to sexual differentiation occurs prior to schizont maturation, at the same moment when the sex of the resulting gametocytes is determined.

IFNγ receptor (IFNγR) deficient mice and IL-4 deficient mice were infected with blood-stage Plasmodium chabaudi AS in order to analyse the role of Th1 (IFNγ) and Th2 (IL-4)-associated cytokines in the development of protective immunity to the parasite. A high mortality rate and failure to reduce the primary parasitaemia to subpatent levels was observed in the IFNγR deficient mice. IL-4 deficient mice controlled a primary P. chabaudi AS infection in a similar manner to control mice and no mortality was observed. IFNγR deficient mice had a reduction in parasite-specific IgG and a significantly increased level of total IgE compared to control mice. There was no reduction in the level of parasite-specific IgG in IL-4 deficient mice. Cytological analysis of the cells present in the spleen and liver during the primary parasitaemia revealed a reduction in the numbers of lymphocytes, monocytes and polymorphonuclear (PMN) cells in the liver at the peak of parasitaemia in both IFNγR deficient mice and IL-4 deficient mice compared to control mice. Adoptive transfer studies demonstrated that cells isolated from the liver at day 11 post-infection could confer some protective immunity to P. chabaudi AS infection.

Light and transmission electron microscopy revealed pericytes of brain capillaries of moles (Talpa europaea L., 1758) as parasitized intracellularly. These host cells were enlarged and of globular or ellipsoid shape, and incorporated a cell-within-cell sequence of primary, secondary and, rarely found, tertiary developmental stages of an eukaryotic organism. Other stages like spores were not discovered either in brain or in other organs. Due to the vertebrate host, and the parasitic cells showing the enveloped state this parasite can be classified as belonging to the Myxozoa rather than Paramyxea. Since spores, which would allow an exact identification of the parasite, could not be detected and mammals are very unusual hosts for Myxozoa, the parasite was designated a myxozoan-like organism.

Endosymbiotic bacteria of the genus Wolbachia infect a number of invertebrate species in which they induce various alterations in host reproduction, mainly cytoplasmic incompatibility (CI). In contrast to most other maternally transmitted parasites, manipulation of host reproduction makes the spread of Wolbachia possible even if they induce a physiological cost on their hosts. Current studies have shown that fitness consequences of Wolbachia infection could range from positive (mutualist) to negative (parasitic) but, in most cases, Wolbachia do not have strong deleterious effects on host fitness and the status of association remains unclear. Here, we show that in the Drosophila parasitoid wasp Leptopilina heterotoma, Wolbachia infection has a negative impact on several host fitness traits of both sexes. Fecundity, adult survival and locomotor performance are significantly reduced, whereas circadian rhythm, development time and offspring sex-ratio are not affected. Although the cost of bacterial infection can be overcome by effects on host reproduction i.e. cytoplasmic incompatibility, it could influence the spread of the bacterium at the early stages of the invasion process. Clearly, results underline the wide spectrum of phenotypic effects of Wolbachia infection and, to our knowledge, Wolbachia infection of L. heterotoma appears to be one of the most virulent that has ever been observed in insects.

The vectorial capacity of Biomphalaria pfeifferi from Ndiangue, Senegal, was investigated with an allopatric isolate of Schistosoma mansoni from Nkolbisson, Cameroon. The snail infection rate after exposure to a single miracidium per snail (MD1) was 56·3%, and 91·6% for snails exposed to 5 miracidia per snail (MD5). The minimum pre-patent period was 21 days. The mean total cercarial production for the MD1 group was 18511 cercariae per snail, and 9757 cercariae for the MD5 group. The maximum production of cercariae for 1 day was 4892 observed in a snail from the MD1 group at day 43 post-infection. The mean longevity of snails was higher in group MD1 (88 days p.i.) than in group MD5 (65 days p.i.). The chronobiological emergence pattern revealed a circadian rhythm with one shedding peak at mid-day. Comparisons are made with the vectorial capacity of the sympatric combination of B. pfeifferi Senegal/S. mansoni Senegal.

The World Health Organization suggested that the prevalence of Schistosoma mansoni among 7- to 14-year-olds be used to guide treatment strategies in endemic areas. This study explores how well the prevalence in that age group predicted the overall prevalence in the community in data from stool examinations (Kato–Katz method) from 180000 people in 3 municipalities in Brazil in 1984 and 1985. The median prevalence was higher in 1984, before community treatment was introduced. There was a strong relationship between the prevalence among 7- to 14-year-olds and the overall prevalence in the community. We present sensitivities and positive predictive values for the use of prevalence in the indicator group to select communities for mass treatment as recommended by WHO. For a range of assumptions sensitivity and positive predictive value were never both above 80%. We suggest that the estimates of validity presented in this paper inform future evaluations of strategies for S. mansoni control.

This paper describes, for the human onchocerciasis focus of southern Venezuela, the age profiles of Onchocerca volvulus microfilarial (mf) and nodule prevalence, mf intensity, and mf aggregation for the whole examined population (836 Yanomami people) living in 20 villages, and for these communities classified according to endemicity levels (hypoendemic: [les ] 20%; mesoendemic: 21–59%; hyperendemic: [ges ] 60% infected). Mf prevalence and intensity increased with age, particularly in the hyperendemic areas, and there were no marked differences between the sexes. The prevalence of nodules followed the same age pattern. Fifty percent mf prevalence was reached in the 15–19 year age-class when the population was taken as a whole; nearly in the 10 to 14-year-olds for the hyperendemic level, in those aged 20–29 years in mesoendemic areas, and not reached at all in hypoendemic villages. The degree of mf aggregation was measured by the k value of the negative binomial distribution and by the variance to mean ratio (VMR). The relationship between the standard deviation (S.D.) of mf counts and the mean mf density was also explored. These 3 indices (k, VMR, and S.D.) showed a tendency to increase with both mean mf load and host age. Since infection intensity and host age were themselves positively related, it was not possible to draw definite conclusions about age-specific changes of parasite aggregation. There was not a significant decrease of mf intensity after an earlier peak neither was there a shift towards younger ages of the maximum no. of mf/mg reached as the endemicity level increased. These results are discussed in relation to detection of density dependence in the human host, selection of an indicator age-group for rapid epidemiological assessment (REA) methods, and strategies of ivermectin distribution in the Amazonian focus. It is recommended that, for the Amazonian onchocerciasis focus, the indicator group for REA consists of all those aged 15 years and over.

In the previous paper it was concluded that those aged [ges ] 15 years of both sexes could comprise the indicator group for rapid epidemiological assessment (REA) of onchocerciasis in the Amazonian focus. This paper explores relationships between community microfilarial (mf) prevalence, intensity, and nodule prevalence in 20 Yanomami communities, that would allow identification of REA methods in the region. The mean nodule ratio (prevalence of nodules/prevalence of mf) was 0·54 when onchocercomata in the indicator group were considered. The Spearman correlation coefficient between mf and nodule prevalence was 0·686 (P = 0·001). Palpation of nodules had 92% specificity and 32% sensitivity when compared to skin-snipping for the diagnosis of onchocerciasis. The predictive value positive increased from 75% to 81% when the indicator group was used. A microfilarial prevalence > 75% in this group would be indicative of hyperendemic status in the village, between 30 and 75% of mesoendemicity, and < 30% of hypoendemicity. For the assessment of infection intensity, biopsies may be taken from the iliac crest for all endemicity levels. Five of the hyperendemic villages surveyed in this work had a community microfilarial load (CMFL) greater than 10 mf/skin snip; the remaining 5 had a CMFL between 5 and 9. These levels of infection merit high priority ivermectin treatment. In Latin America, communities at both moderate and severe risk are included in mass chemotherapy programmes (i.e. when mf prevalence is over 20%). Roughly, a nodule prevalence in the indicator group > 10% would suggest a community mf prevalence > 20% with a sensitivity of 85% and a specificity of 71%. A multiple linear regression model of the arc-sine transformed mf prevalence in the village (all ages) on nodule prevalence in those aged [ges ] 15 years and altitude of the village explained 72% of the variance. The model combining nodule and altitudinal information had a sensitivity of 92% and a specificity of 71% in comparison to an estimated mf prevalence of 21% or more. It is suggested that the usefulness of the REA methods proposed be assessed in other areas of the Amazonian onchocerciasis focus.

We set out to study how anti-filarial IgG4 and IgE, which have been studied extensively in adult populations, are influenced by gender and by the degree of filarial endemicity during childhood. Development of specific IgG4 and IgE was examined in 502 children aged 3 months to 12 years, who were resident in 3 villages in South-Sulawesi with microfilaria prevalences of 6, 23 and 42%. Specific IgG4 and IgE could be detected as early as 18 months after birth, in low amounts, and increased to levels comparable to those produced by adults at the age of 3 years. A higher prevalence of anti-filarial IgG4 in boys, indicating higher filarial infection compared to girls, became apparent after the age of 7. The specific IgG4 response was strongly influenced by the degree of filarial endemicity and production of this antibody was considerably delayed in the low transmission village. With respect to IgE, it was noted that specific IgE was consistently higher in boys from infancy onwards indicating a predisposition for high IgE production in males. The influence of filarial endemicity was less profound on IgE than on IgG4. In conclusion, reactivity to filarial antigens begins early in life and is differentially influenced by gender and transmission intensity.

Infective larvae of the dog roundworm Toxocara canis survive in the tissues of their hosts for extended periods in a state of developmental arrest, successfully evading immune destruction. This survival strategy is thought to be mediated by T. canis excretory/secretory (TES) products which downregulate or divert the immune response. We purified one of the major TES products, TES-70 and gained amino acid sequence from 4 tryptic peptides. These peptides were matched to a predicted protein from a cDNA that was isolated by expression screening a T. canis cDNA library with mouse anti-TES serum. The predicted protein (Tc-CTL-4) is similar to, but larger than, Tc-CTL-1, a 32-kDa C-type lectin secreted by T. canis larvae. Tc-CTL-4 has a signal peptide, 2 Cys-rich domains and a C-terminal calcium-dependent C-type lectin domain that shares sequence similarity with host immune cell receptors such as macrophage mannose receptor and CD23. The lectin domain was expressed in bacteria and antiserum to the purified recombinant protein was used to confirm that Tc-ctl-4 did encode the native TES-70 glycoprotein. TES-70 selectively bound to ligands on the surface of Madin–Darby Canine Kidney cells in vitro in a calcium-dependent manner, inhibitable by mammalian serum, indicating that a host glycan is the native ligand for this new parasite lectin.

The intergenic spacer of the ribosomal RNA gene array from the monogenean Gyrodactylus salaris was isolated using PCR amplification. PCR products were cloned and sequenced. Three different fragments of 0·63, 1·0 and 2·62 kb, were consistently obtained. These showed homology at the 5′ and 3′ termini but differed in their overall size and intervening sequence. The 5′ end showed homology to various 28S ribosomal RNA gene sequences, suggesting that this represented the 3′ terminus of the G. salaris 28S ribosomal RNA gene. A number of features common to other eukaryotic intergenic spacers were found in the longest sequence, including A + T rich sequences, palindromic sequences and tandemly repeated elements. Two regions of 23 bp sequences arranged in non-identical tandem repeats were identified. There were 9 repeats in both regions, separated by 81 bp of non-repetitive sequence. The repeat units from the two regions shared some similarity at their 3′ ends. The G. salaris intergenic spacer sequence was examined for sequence motifs involved in the transcription of the ribosomal RNA genes in other species. Several regions with homology to transcription start sites were identified.

We recently showed that, in our Trichinella spiralis rat model, first exposure, but not re-exposure to infective-stage larvae evoked heat shock responses in 4 test organs. Our work, however, failed to implicate either early complete clearance of challenge muscle larvae (ML), or rapid elimination of newborn larvae (NBL) in the phenomenon noted in reinfected rats. This study clarifies that issue using 2 established facts in T. spiralis biology and anti-T. spiralis immunology. That is, adult worms injure gut cells and immune destruction of NBL requires release of material also toxic to host cells. To approach the above problem we analysed relevant and irrelevant rat organs for increased heat shock protein (HSP) production at 1, 7, 14, 20 and 27 p.i. during first and second infections. Organs examined were intestines, mesenteric lymph nodes (MLN), heart and lungs. Using densitometric analyses of immunoblots, increased HSP expression was detected on day 7 in intestines from both primary and secondary-infected rats albeit that the change in the latter was just short of significant. Interestingly, MLN only exhibited increased HSP levels in the reinfected rat model with increased HSP levels persisting for 1 week. A lasting shock response was detected in reinfected rats; in contrast, first exposure resulted in shock responses being evident in lungs at either day 7 or day 14, only. These findings suggest that (i) in immune rats, a few challenge ML develop into adults, produce NBLwhich are trapped within MLN, and (ii) that anti-T. spiralis and/or anti-NBL immunity is associated with an, as yet, uncomprehended stress to host's heart tissues.