There is a need for sensitive and specific rapid diagnostic tests (RDT) for canine visceral leishmaniasis. The aims of this study were to evaluate the diagnostic performance of immunochromatographic dipstick RDTs using rK39 antigen for canine visceral leishmaniasis by (i) investigating the sensitivity of RDTs to detect infection, disease and infectiousness in a longitudinal cohort study of natural infection in Brazil, and (ii) using meta-analysis to estimate the sensitivity and specificity of RDTs from published studies.
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The host-specific relationship between fig trees (Ficus) and their pollinator wasps (Agaonidae) is a classic case of obligate mutualism. Pollinators reproduce within highly specialised inflorescences (figs) of fig trees that depend on the pollinator offspring for the dispersal of their pollen. About half of all fig trees are functionally dioecious, with separate male and female plants responsible for separate sexual functions. Pollen and the fig wasps that disperse it are produced within male figs, whereas female figs produce only seeds. Figs vary greatly in size between different species, with female flower numbers varying from tens to many thousands. Within species, the number of female flowers present in each fig is potentially a major determinant of the numbers of pollinator offspring and seeds produced. We recorded variation in female flower numbers within male and female figs of the dioecious Ficus montana growing under controlled conditions, and assessed the sources and consequences of inflorescence size variation for the reproductive success of the plants and their pollinator (Kradibia tentacularis). Female flower numbers varied greatly within and between plants, as did the reproductive success of the plants, and their pollinators. The numbers of pollinator offspring in male figs and seeds in female figs were positively correlated with female flower numbers, but the numbers of male flowers and a parasitoid of the pollinator were not. The significant variation in flower number among figs produced by different individuals growing under uniform conditions indicates that there is a genetic influence on inflorescence size and that this character may be subject to selection.© 2013 Springer-Verlag Wien.
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Females of the pollinator fig wasp Elisabethiella baijnathi Wiebes carry mites (Tarsonemella sp. nr. africanus) and nematodes (Parasitodiplogaster sp.) between figs of Ficus burtt-davyi in Grahamstown, South Africa. The mites are phoretic on the outside of the wasps and phytophagous, feeding on galled flowers. The nematodes are transported inside the wasps and eventually eat them. Both mites and nematodes were present throughout the year. The prevalence (fig occupancy rates) of mites and nematodes in different crops ranged between zero and 100 %. Crop size did not influence the prevalence of either mites or nematodes. Contrasting dispersion patterns and relationships with fig wasp foundress numbers indicate that the mites, but not the nematodes, disperse between figs after being carried there by the pollinators, and they may also utilize non-pollinating fig wasps as vectors.
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Objective To evaluate the environmental and ecological factors associated with Leishmania transmission and vector abundance in Chaparral, Tolima-Colombia. Methods First, we compared the ecological characteristics, abundance of phlebotomies and potential reservoir hosts in the peridomestic environment (100m radius) of randomly selected houses, between two townships with high and low cutaneous leishmaniasis incidence. Second, we examined peridomestic correlates of phlebotomine abundance in all 43 houses in the higher risk township. Results The high transmission township had higher coverage of forest (23%vs. 8.4%) and shade coffee (30.7%vs. 11%), and less coffee monoculture (16.8%vs. 26.2%) and pasture (6.3%vs. 12.3%), compared to the low transmission township. Lutzomyia were more abundant in the high transmission township 2.5 vs. 0.2/trap/night. Lutzomyia longiflocosa was the most common species in both townships: 1021/1450 (70%) and 39/80 (49%). Numbers of potential wild mammal reservoirs were small, although four species were found to be infected with Leishmania (Viannia) spp. In the high transmission township, the overall peridomiciliary capture rate of L. longiflocosa was 1.5/trap/night, and the abundance was higher in houses located nearer to forest (ρ=-0.30, P=0.05). Conclusion The findings are consistent with a domestic transmission cycle with the phlebotomies dependent on dense vegetation near the house. © 2012 Blackwell Publishing Ltd.
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Background. Pentavalent antimony is the agent recommended for treatment of cutaneous leishmaniasis ( CL). Its use is problematic, because it is expensive and because of the potential for drug-associated adverse effects during a lengthy and painful treatment course.Methods. We tested the efficacy of thermotherapy for the treatment of CL due to Leishmania tropica in a randomized, controlled trial in Kabul, Afghanistan. We enrolled 401 patients with a single CL lesion and administered thermotherapy using radio-frequency waves (1 treatment of>= 1 consecutive application at 50 degrees C for 30 s) or sodium stibogluconate (SSG), administered either intralesionally (a total of 5 injections of 2-5 mL every 5-7 days, depending on lesion size) or intramuscularly (20 mg/kg daily for 21 days).Results. Cure, defined as complete reepithelialization at 100 days after treatment initiation, was observed in 75 (69.4%) of 108 patients who received thermotherapy, 70 (75.3%) of 93 patients who received intralesional SSG, and 26 (44.8%) of 58 patients who received intramuscular SSG. The OR for cure with thermotherapy was 2.80 (95% confidence interval [CI], 1.45-5.41), compared with intramuscular SSG treatment (P = .002). No statistically Pp. 002 significant difference was observed in the odds of cure in comparison of intralesional SSG and thermotherapy treatments. The OR for cure with intralesional SSG treatment was 3.75 ( 95% CI, 1.86-7.54), compared with intramuscular SSG treatment (P<.001). The time to cure was significantly shorter in the thermotherapy group P<.001 ( median, 53 days) than in the intralesional SSG or intramuscularly SSG group (median, 75 days and>100 days, respectively;). P = .003Conclusions. Thermotherapy is an effective, comparatively well-tolerated, and rapid treatment for CL, and it should be considered as an alternative to antimony treatment.
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Cytokine and proliferative responses to Necator americanus infection were measured in a treatment-reinfection study of infected subjects from an area of Papua New Guinea where N. americanus is highly endemic. Before treatment, most subjects produced detectable interleukin (IL)-4 (97%), IL-5 (86%), and interferon (IFN)-gamma (64%) in response to adult N. americanus antigen. Pretreatment IFN-gamma responses were negatively associated with hookworm burden, decreasing by 18 pg/mL for each increase of 1000 eggs/gram (epg) (n=75; P<.01). Mean IFN-ã responses increased significantly after anthelmintic treatment, from 166 to 322 pg/mL (n=42; P<.01 ). The intensity of reinfection was significantly negatively correlated with pretreatment IL-5 responses, decreasing by 551 epg for each 100 pg/mL increase in production of IL-5 (n=51; P<.01). These data indicate that there is a mixed cytokine response in necatoriasis, with worm burden-associated suppression of IFN-g responses to adult N. americanus antigen. Resistance to reinfection is associated with the parasite-specific IL-5 response.
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Helminth parasites are well known to induce an immune response in their hosts characterised by elevated IgE, peripheral blood or local tissue eosinophilia, and in some cases, intestinal mastocytosis. This immunological response has a strong T-helper 2 (Th2) cytokine bias and is reminiscent of the immunological constellation found in allergic diseases. However, the molecular forces driving the Th2 response to helminth parasites are still not understood. By using the human hookworm parasite Necator americanus as an example, the authors of the current article propose that in the course of its life cycle, this parasite becomes innately allergenic through the secretion of a molecular array designed to promote tissue migration and homing, feeding and survival against immunological attack. This complex array comprises proteases, lectins and other classes of molecules. Subsequent immunological and physiological events seemingly protect the host from both the allergic sequelae of exposure to environmental allergens and, moreover, from the parasite itself.
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Advances in hookworm immunoepidemiology are reviewed. Recent studies demonstrate a mixed Th1/Th2 response in human hookworm infection, with immunosuppression of specific and nonspecific IFN-gamma responses. There is increasing evidence for protective immunity in human hookworm infection, including anti-larval IL-5- and IgE-dependent mechanisms, and for immunological interactions between hookworm infection and other diseases.
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Zoonotic visceral leishmaniasis (VL) is a disease of dogs, humans and other animals caused by the intracellular macrophage parasite Leishmania infantum. We examined the relationship between DLA class II alleles ( DRB1, DQA1, DQB1) and the course of infection in a cohort of Brazilian mongrel dogs exposed to natural L. infantum infection. DLA alleles were typed by sequence-based typing. DLA-DRB1 genotype was significantly associated with levels of anti- Leishmania IgG and parasite status assessed by PCR. Dogs with DLA-DRB1*01502 had higher levels of specific IgG and an increased risk of being parasite positive compared with dogs without this allele, controlling for other alleles and significant variables. No significant associations were seen for DLA-DQA1 or DLA-DQB1 alleles. These results suggest that the DLA-DRB1 locus plays a role in determining susceptibility to canine VL. As the domestic dog is the main reservoir for human infection, the identification of genetic factors influencing canine resistance or susceptibility to VL may provide insights into the immunology and potential control through vaccination of VL.
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Malignant hyperthermia (MH) and central core disease (CCD) are autosomal dominant disorders of skeletal muscle. Susceptibility to MH is only apparent after exposure to volatile anesthetics and/or depolarizing muscle relaxants. CCD patients present with diffuse muscular weakness but are also at risk of MH. Mutations in RYR1 (19q13.1), encoding a skeletal muscle calcium release channel (ryanodine receptor), account for the majority of MH and CCD cases. Fifteen RYR1 N-terminal mutations are considered causative of MH susceptibility, five of which are also associated with CCD. In the first extensive UK population survey, eight of 15 mutations were detected in 85 out of 297 (29%) unrelated MH susceptible cases, with G2434R detected in 53 cases (18%). Mutation type was shown to affect significantly MH phenotypes (in vitro contracture test (IVCT) response to caffeine, halothane, and ryanodine). RYR1 mutations associated with both CCD and MH (R163C, R2163H, R2435H) had more severe caffeine and halothane response phenotypes than those associated with MH alone. Mutations near the amino terminal (R163C, G341R) had a relatively greater effect on responses to caffeine than halothane, with a significantly increased caffeine:halothane tension ratio compared to G2434R of the central domain. All phenotypes were more severe in males than females, and were also affected by muscle specimen size and viability. Discordance between RYR1 genotype and IVCT phenotype was observed in seven families (nine individuals), with five false-positives and four false-negatives. This represents the most extensive study of MH patient clinical and genetic data to date and demonstrates that RYR1 mutations involved in CCD are those associated with one end of the spectrum of MH IVCT phenotypes.
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Evaluating the risk of disease spill-over from domestic dogs to wildlife depends on knowledge of inter-specific contact rates and/or exposure to aetiological agents in dog environments. Here, contact rates of crab-eating foxes (Cerdocyon thous) with sympatric domestic dog populations were measured over 25 months in Amazon Brazil. Foxes and dogs were serologically and clinically monitored for exposure to canine parvovirus (CPV-2) and canine distemper virus (CDV), pathogens known to have caused wildlife population declines elsewhere. Twenty-two of 24 (92%) tagged foxes visited one or more houses in a median 2 (range 1-3) villages per night where dog densities ranged from 7.2 to 15.4 per km(2) (mean 9.5 per km(2)). Foxes spent an average 6.4% (0-40.3%) of their 10 h nocturnal activity period in villages, the equivalent of 38 m (range 0-242) per night. The rate of potential exposure to disease agents was thus high, though varied by 3 orders of magnitude for individual foxes. Overall, 46% of the fox population was responsible for 80% of all contacts. None of the 37 monitored foxes however showed serological or clinical evidence of infection with CPV-2 or CDV. Seroprevalences for CPV-2 and CDV antibodies in the local domestic dog population were 13% (3/23) and 9% (2/23), respectively. and 89% of 97 monitored pups born during the study presented clinical signs consistent with active CPV-2 infection (haemorrhagic diarrhoea, vomiting, rapid morbidity and emaciation). Although there was no evidence for infection with either virus in foxes, the high level of contact of foxes with peridomestic habitats suggests that the probability of potential spill-over infections from dogs to foxes is high. (C) 2001 Elsevier Science B.V. All rights reserved.
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Calreticulin was recently identified as a hookworm (Necator americanus) allergen, implying secretion, and contact with cells of the immune system, or significant worm attrition in the tissues of the host. As human calreticulin has been shown to bind to and neutralize the haemolytic activity of the complement component C1q, and to be putatively involved in integrin-mediated intracellular signalling events in platelets, it was of interest to determine whether a calreticulin from a successful nematode parasite of humans, with known immune modulatory and antihaemostatic properties, exhibited a capacity to interfere with complement activation and to interact with integrin domains associated with cell signalling in platelets and other leucocytes. We can now report that recombinant calreticulin failed to demonstrate significant calcium binding capacity, which is a hallmark of calreticulins in general and may indicate inappropriate folding following expression in a prokaryote. Nevertheless, recombinant calreticulin retained sufficient molecular architecture to bind to, and inhibit the haemolytic capacity of, human C1q. Furthermore, recombinant calreticulin reacted in surface plasmon resonance analysis (SPR) with peptides corresponding to cytoplasmic signalling domains of the integrins alphaIIb and alpha5, in a calcium independent manner. SPR was also used to ratify the specificity of a polyclonal antibody to hookworm calreticulin, which was then used to assess the stage specificity of expression of the native molecule (in comparison with reverse transcriptase-polymerase chain reaction), to indicate its apparent secretion, and to purify native calreticulin from worm extracts by affinity chromatography. This development will allow the functional tests described above to be repeated for native calreticulin, to ascertain its role inthe host-parasite relationship.
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The sensitivity and specificity of PCR, serology (ELISA) and lymphoproliferative response to Leishmania antigen for the detection of Leishmania infantum infection were evaluated in a cohort of 126 dogs exposed to natural infection in Brazil. For PCR, Leishmania DNA from bone-marrow was amplified with both minicircle and ribosomal primers. The infection status and time of infection of each dog were estimated from longitudinal data. The sensitivity of PCR in parasite-positive samples was 98%. However, the overall sensitivity of PCR in post-infection samples, from dogs with confirmed infection, was only 68%. The sensitivity of PCR varied during the course of infection, being highest (78-88%) 0-135 days post-infection and declining to around 50% after 300 days. The sensitivity of PCR also varied between dogs, and was highest in sick dogs. The sensitivity of serology was similar in parasite-positive (84%), PCR-positive (86%) and post-infection (88%) samples. The sensitivity of serology varied during the course of infection, being lowest at the time of infection and high (93-100%) thereafter. Problems in determining the specificity of serology are discussed. The sensitivity and specificity of cellular responsiveness were low. These data suggest that PCR is most useful in detecting active or symptomatic infection, and that serology can be a more sensitive technique for the detection of all infected dogs.
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To elucidate the local tissue cytokine response of dogs infected with Leishmania chagasi, cytokine mRNA levels were measured in bone marrow aspirates from 27 naturally infected dogs from Brazil and were compared with those from 5 uninfected control animals. Interferon-gamma mRNA accumulation was enhanced in infected dogs and was positively correlated with humoral (IgG1) but not with lymphoproliferative responses to Leishmania antigen in infected dogs. Increased accumulation of mRNA for interleukin (IL)-4, IL-10, and IL-18 was not observed in infected dogs, and mRNA for these cytokines did not correlate with antibody or proliferative responses. However, infected dogs with detectable IL-4 mRNA had significantly more severe symptoms. IL-13 mRNA was not detectable in either control or infected dogs. These data suggest that clinical symptoms are not due to a deficiency in interferon-gamma production. However, in contrast to its role in human visceral leishmaniasis, IL-10 may not play a key immunosuppressive role in dogs.
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Most theoretical models of age-related mate choice predict that females should prefer older males because they have proven survival ability An alternative view is that older males represent inferior mates because of negative genetic correlations between early and late fitness components, or because older males have traded off longevity against other fitness components, have accumulated deleterious germ-line mutations, or are less well adapted to current conditions than more recently born individuals. While numerous studies have reported female choice for older males, few have explicitly examined the fitness consequences of such a preference. We present evidence from a lekking sandfly Lutzomyia longipalpis, showing that choosy females discriminate against older males and gain a fitness benefit from their choice. When permitted free choice from an aggregation consisting of males aged zero to two days (young), four to six days (middle-aged) and eight to ten days (old), females preferentially mated with middle-aged males, but all measures of female reproductive success were independent of male age. In contrast, when a second set of females was randomly assigned single virgin males of known age, the eggs of those paired to old mates exhibited lower hatching success than the eggs of females mated to young or middle-aged males. These results suggest that females avoid mating with older males because they represent poorer quality mates. Age-related differences in male quality may have a genetic basis, but could equally well arise through a phenotypic decline in sperm quality or sperm transfer ability with male age. The lack of evidence of female discrimination against older males from other studies may be because these did not explore the reproductive success of the full age range of males.
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In this paper we describe the relationship between antibodies to Necator americanus stage-specific antigens and parasite burden in an endemically-infected population in Papua New Guinea. Using an age-structured analysis, we show that the correlation coefficient between levels of IgG against adult worm excretory-secretory (ES) antigen and parasite burden declined significantly with host age from positive in younger hosts to significantly negative in older hosts. A trend towards similar patterns was present for anti-larval IgG both pretreatment and after reinfection, and for anti-ES IgM and anti-ES IgE pretreatment. These patterns are consistent with a role for these isotypes in a protective immune response, although parasite-induced immunosuppression may provide an alternate explanation. This is another demonstration of possibly protective responses to N. americanus infection.
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Abundance of the sandfly Lutzomyia longipalpis, the vector of Leishmania chagasi, was surveyed using CDC light-suction traps in fifteen villages and 180 homesteads on Marajó island, Pará State, Brazil. Flies were most abundant in cultivated areas, secondary growth and open woodland, away from savanna grassland and forest. Within homesteads, the abundance of flies in animal sheds was weakly associated with the number of hosts kept therein, and inversely related to the number elsewhere, both human and animal. Houses harboured more flies if dogs were present and if the house had: a roof of thatch rather than of tiles or tin; a thatched roof which had not been treated with insecticide; relatively more holes in walls and roof. The sex ratio of flies was more male-biased at higher densities. We weigh the importance of these variables as risk factors for Le. chagasi infection.
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Reinfection with hookworm (Necator americanus) following chemotherapy was studied over 2 years in a rural village in Madang Province, Papua New Guinea. The prevalence of hookworm infection had returned to pre-treatment levels after 2 years, and the geometric mean hookworm burden had returned to 58% of the pre-treatment value. The rate of acquisition of adult worms was independent of host age, and was estimated as a geometric mean of 2.9-3.3 worms/host/year (arithmetic mean 7.9-8.9 worms/host/year). There was significant predisposition to hookworm infection; the strength of this predisposition did not vary significantly between age or sex classes.
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Experiments were undertaken to determine the relative attractiveness of humans, dogs and chickens to Lutzomyia longipalpis, the principal vector of Leishmania chagasi causing American visceral leishmaniasis. Field experiments in two villages on Marajó Island, Pará State, Brazil, showed that one boy attracted significantly more flies than one dog or chicken, and slightly fewer flies than a group of six chickens. Experiments with laboratory-bred female flies showed that a significantly greater number of flies engorged on a single human than oneither a single dog or chicken, and man-biting catches demonstrated the willingness of flies to bite in the field. It appears that Lu.longipalpis has catholic feeding habits, the attractiveness of different hosts being largely a function of their relative sizes. These results are discussed with reference to the epidemiology of visceral leishmaniasis in Brazil.
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The infectivity of wild and laboratory strains of Heligmosomoides polygyrus (Nematospiroides dubius) in laboratory mice and in three species of wild British rodent was compared. Wild strains, of the subspecies H. p. polygyrus, were isolated from wild caught Apodemus sylvaticus. Only very low-level infections of the wild strains became established in laboratory mice. Similar worm burdens of the laboratory strain became established in laboratory mice and A. sylvaticus, although infections in A. sylvaticus were more short lived. Cortisone treatment of hosts increased the establishment and survival of the heterologous worm strain to that of the homologous strain. In contrast, neither strain of parasite established in Clethrionomys glareolus or Microtus agrestis, and cortisone treatment of C. glareolus did not increase establishment. Infection of laboratory mice with the wild-strain parasite induced significant immunity to a challenge infection with the laboratory strain.
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One quarter of the world's human population suffers infection with helminth parasites. The population dynamics of the ten or so species, which cause disease of clinical significance have been well characterized by epidemiological field survey. The parasites are in general highly aggregated between hosts, and their populations seem to be temporally stable and to recover rapidly from perturbation, including interventions designed to alleviate disease. This paper reviews current understanding of the population regulation of helminth species of medical significance. Both empirical (field and laboratory) and theoretical results are included, and we attempt to interpret the findings in the broader context of the population ecology of free-living species. We begin by considering the evidence for regulation from field data concerning the temporal stability of helminth populations within communities and from the results of perturbation experiments. The detection of regulatory processes is then discussed (with regard to statistical and logistical considerations), and the evidence from both the field and laboratory studies reviewed. Deterministic models are described to investigate the possible consequences of regulation imposed at different points in the parasite life-cycle. The causes and consequences of parasite aggregation are considered, and a stochastic model used to investigate the impact of different combination of regulatory processes and heterogeneity generating mechanisms.
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Baseline data from an immuno-epidemiological study of hookworm infection in a rural village in Madang Province, Papua New Guinea are reported. Necator americanus was found to be the commonest helminth infection, with a prevalence of near 100% and intensity of 40 worms per host in adults. Enterobius vermicularis, Ascaris lumbricoides and Trichuris trichiura were also present, at prevalences of 53, 10 and 3% respectively; Ancylostoma duodenale was absent. The frequency distribution of N. americanus was highly over-dispersed, and was well described by a negative binomial distribution with aggregation parameter, k, of 0.370. Intensity of infection was significantly related to host age, but did not differ between the sexes. Haemoglobin levels and haematocrit values were indicative of anaemia in the community, but were unrelated to hookworm infection. Levels of antibodies (IgG, IgA and IgM combined) against adult Necator cuticular collagen and excretory-secretory (ES) products were determined. Serum concentrations of the two types of antibody were significantly correlated with each other. Significant positive correlations were found between anti-ES antibody levels and hookworm egg production, and between anti-collagen antibody levels and host age. It is suggested that the level of anti-collagen antibodies may reflect cumulative exposure to infection, whereas levels of anti-ES antibodies may be more dependent on current worm burden. No evidence was found to suggest that either antibody response is important in regulating parasite population growth. Similarly, the presence of a positive correlation between eosinophil concentration and infection intensity in adults indicates that eosinophilia reflects, rather than determines, the host's worm burden.
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Discusses possible ways in which acquired immunity may influence the population dynamics of macroparasite infections, and evaluates experimental evidence in laboratory and agricultural animals, discussing possible consequences of immunity for human helminth infections and their control. The role of immunity in protozoan epidemiology is discussedbriefly, together with the consequences of acquired immunity for mixed-species parasitic infections. -from Authors
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Five, 20, and 80 cysticercoid infections of Hymenolepis diminuta were established in 1-, 2- and 5-month-old male Wistar rats. Worm numbers, dry weights and egg outputs were determined on day 28 post infection. Worm recovery was found to be independent of cysticercoid dose in 1-month-old rats, but density-dependent in older rats. Density dependence affected both worm dry weight and egg production in all 3 age classes of host studied. However, at the highest dose both dry weight and egg production were significantly decreased in 2- and 5-month-old rats compared with 1-month-old rats. The results cannot be explained solely in terms of competition for a resource, and suggest that immunological mechanisms may have an important role in the "crowding effect".
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