Differential drivers of intraspecific and interspecific competition during malaria-helminth co-infection.

Various host and parasite factors interact to determine the outcome of infection. We investigated the effects of two factors on the within-host dynamics of malaria in mice: initial infectious dose and co-infection with a helminth that limits the availability of red blood cells (RBCs). Using a statistical, time-series approach to model the within-host 'epidemiology' of malaria, we found that increasing initial dose reduced the time to peak cell-to-cell parasite propagation, but also reduced its magnitude, while helminth co-infection delayed peak cell-to-cell propagation, except at the highest malaria doses. Using a mechanistic model of within-host infection dynamics, we identified dose-dependence in parameters describing host responses to malaria infection and uncovered a plausible explanation of the observed differences in single vs co-infections. Specifically, in co-infections, our model predicted a higher background death rate of RBCs. However, at the highest dose, when intraspecific competition between malaria parasites would be highest, these effects of co-infection were not observed. Such interactions between initial dose and co-infection, although difficult to predict a priori, are key to understanding variation in the severity of disease experienced by hosts and could inform studies of malaria transmission dynamics in nature, where co-infection and low doses are the norm.

Terror in the dirt: Sensory determinants of host seeking in soil-transmitted mammalian-parasitic nematodes.

Infection with gastrointestinal parasitic nematodes is a major cause of chronic morbidity and economic burden around the world, particularly in low-resource settings. Some parasitic nematode species, including the human-parasitic threadworm Strongyloides stercoralis and human-parasitic hookworms in the genera Ancylostoma and Necator, feature a soil-dwelling infective larval stage that seeks out hosts for infection using a variety of host-emitted sensory cues. Here, we review our current understanding of the behavioral responses of soil-dwelling infective larvae to host-emitted sensory cues, and the molecular and cellular mechanisms that mediate these responses. We also discuss the development of methods for transgenesis and CRISPR/Cas9-mediated targeted mutagenesis in Strongyloides stercoralis and the closely related rat parasite Strongyloides ratti. These methods have established S. stercoralis and S. ratti as genetic model systems for gastrointestinal parasitic nematodes and are enabling more detailed investigations into the neural mechanisms that underlie the sensory-driven behaviors of this medically and economically important class of parasites.

No impact of strongylid infections on the detection of Plasmodium spp. in faeces of western lowland gorillas and eastern chimpanzees.

BACKGROUND: Although a high genetic diversity of Plasmodium spp. circulating in great apes has been revealed recently due to non-invasive methods enabling detection in faecal samples, little is known about the actual mechanisms underlying the presence of Plasmodium DNA in faeces. Great apes are commonly infected by strongylid nematodes, including hookworms, which cause intestinal bleeding. The impact of strongylid infections on the detection of Plasmodium DNA in faeces was assessed in wild, western, lowland gorillas from Dzanga Sangha Protected Areas, Central African Republic and eastern chimpanzees from Kalinzu Forest Reserve, Uganda. METHODS: Fifty-one faecal samples from 22 habituated gorillas and 74 samples from 15 habituated chimpanzees were analysed using Cytochrome-b PCR assay and coprological methods. RESULTS: Overall, 26.4% of the analysed samples were positive for both Plasmodium spp. and strongylids. However, the results showed no significant impact of intensity of infections of strongylids on detection of Plasmodium DNA in gorilla and chimpanzee faeces. CONCLUSION: Bleeding caused by strongylid nematode Necator spp. cannot explain the presence of Plasmodium DNA in ape faeces.

Molecular features of hookworm larvae (Necator spp.) raised by coproculture from Ugandan chimpanzees and Gabonese gorillas and humans.

Species composition of Necator hookworms was surveyed in (i) Ugandan chimpanzees living around farms and villages at Bulindi, (ii) Gabonese gorillas under habituation in Moukalaba-Doudou National Park (MDNP), and (iii) Gabonese villagers living adjacent to MDNP. Internal transcribed spacers (ITS) of rDNA and partial cytochrome c oxidase subunit 1 (Cox1) gene of mtDNA were analyzed from larvae obtained by coproculture. Three ITS types (I, II and III) and three Cox1 haplotype groups (A, B and C) were demonstrated. ITS type I and Cox1 haplotype group A, representing Necator americanus, were demonstrated in the hookworm larvae from Gabonese gorillas and humans, but not from Ugandan chimpanzees. Type II and haplotype groups B and C, presumably representing N. gorillae, were found in larvae from Ugandan chimpanzees and Gabonese gorillas and humans. These features were overall similar with those found previously in the Central African Republic. Meanwhile, type III was proven in a larva from a Gabonese gorilla as the first demonstration from a non-human primate. Cox1 haplotypes obtained from Ugandan chimpanzees formed a subgroup within group B, presumably reflecting dispersal and diversification processes of the apes.

Dose-ranging study for trials of therapeutic infection with Necator americanus in humans.

Epidemiological studies suggest that a hookworm infection producing 50 eggs/gram of feces may protect against asthma. We conducted a dose-ranging study to identify the dose of hookworm larvae necessary to achieve 50 eggs/gram of feces for therapeutic trials of asthma. Ten healthy subjects without asthma or airway hyperresponsiveness to inhaled methacholine received 10, 25, 50, or 100 Necator americanus larvae administered double blind to an area of skin on the arm. Subjects were seen weekly for 12 weeks and were then treated with mebendazole. Skin itching at the entry site and gastrointestinal symptoms were common at higher doses. Lung function did not change. Levels of blood eosinophils and IgE increased transiently, and levels of IgG increased progressively. All doses resulted in at least 50 eggs/gram of feces in the eight subjects who completed the study. Infection with 10 N. americanus larvae is well tolerated, elicits a modest host eosinophil response, and is potentially suitable for use in preliminary clinical therapeutic trials.

Hookworm infection and disease: advances for control.

Advances in epidemiology and in control strategies of hookworm infection and associated disease were reviewed. Recent estimates indicate that hookworms infect approximately 1.3 billion people worldwide, and 96 million suffer from associated morbidity, including also insidious effects on nutritional status and on physical and intellectual development. Recent research studies on iron loss and iron-deficiency anaemia associated to hookworm infection were irondeficiency anemia associated to hookworm infection were reviewed. Recommendations for planning strategies for the control of hookworm infection were addressed and epidemiology, targets, chemotherapy, health education, sanitation, monitoring and evaluation in helminth control programmes were discussed. Special relevance was given to chemotherapy with new, single dose broad spectrum, safe anthelminthic drugs as the mainstay of control strategy to reduce intensity of infection, iron-deficiency anaemia and other morbidity indicators associated with hookworm infections. For the control of transmission of hookworm infection, periodic chemotherapy should be implemented in the context of ongoing improvement of sanitation and promotion of health education. These elements should be integrated into the prevailing system of primary health care and must be based on multisectoral collaboration to ensure sustainability of control programmes.

Enterobius, trichuris, capillaria, and hookworm including ancylostoma caninum.

Infections by the nematodes Enterobius, Trichuris, Capillaria, and hookworm are some of the most widespread gastrointestinal infections worldwide. This article is designed not only to provide an overview of the different parasites in terms of epidemiology, clinical manifestation, and disease but also to highlight particular areas of intensive research activity that are providing new insights into both the biology of the host-parasite relationship and possible new approaches to infection management for the future.

Necator americanus: temperature, pH, light, and larval development, longevity, and desiccation tolerance.

The effect of incubation temperature and pH on the hatch rate of eggs of Necator americanus, and the desiccation tolerance of the resulting infective stage-3 larvae were investigated in the laboratory under controlled conditions. Hatching did not occur below 15 C and above 35 C. A 21% hatch rate was obtained at 15 C while a 10.6% hatch rate was obtained at 35 C. The highest hatch rate (93.7%) was obtained at 30 C. The optimum pH for hatching was 6.0, but the larvae did not reach the infective stage. Incubation temperature of the eggs affected the longevity and desiccation tolerance of resultant infective larvae. Larvae hatched at 30 C and maintained at 26 C under bright fluorescent light had a 50% survival time (S50) of 4 days. In the dark or shade, the S50 for larvae raised at 30 C was 5 weeks, while that of larvae hatched at 20 C was 7 weeks. Incubation temperature also affected the desiccation tolerance of larvae. Larvae developed at 20 C were more resistant to desiccation at various relative humidity values than larvae hatched at 30 C.

Uncinariasis infantil como problema de salud pública / Infantile hookworn as a public health problem

El síntoma de la uncinariasis es la anemia ferropriva, la cual es dependiente de la intensidad, la especie de uncinaria, la capacidad del huésped para resistir la infección y de mantener una reserva adecuada de hierro. En latinoamérica tropical, el Necator americanus y con frecuencia menor Ancylostoma duodenale son muy prevalentes. La infección se confirma demostrando los huevecillos en las heces; la diferenciación de las especies requiere del examen de los gusanos adultos o del estudio microscópico de las larvas. La prevención de la contaminación fecal del suelo, el saneamiento, la educación del público incluyendo el uso de zapatos y la quimioterapia específica más la suplementación dietética del hierro y proteínas, son medidas preventivas muy efectivas

Studies on the co-occurrence of two species of human hookworm in a riverine community in Nigeria.

A total of 1,623 stool specimens from different individuals were examined to assess the infection prevalence and the pattern of occurrence of Necator americanus and Ancylostoma duodenale in a riverine community in Nigeria. 56.3% of 823 males and 52.63% of 800 females were positive for both species of hookworm, 25.1% of infected males, and 26.1% of infected females had A. duodenale while 46.7% of infected males and 51.2% of infected females had N. americanus. 28.2% of males and 22.7% of females had mixed infections of both species. The occurrence of each species was independent of the other. The distribution of infection was age-dependent, while sex had no effect on infection pattern. In A. duodenale infection, egg counts rose between 15 and 25 years of age, but declined with increasing host age. Egg counts in N. americanus infection were more stable with increasing age of the host. The probability of recovering N. americanus eggs in the faeces was higher than that of A. duodenale. In mixed infections, egg out put of N. americanus was higher than that of A. duodenale as indicated by the higher conditional probability of recovering N. americanus eggs in the presence of A. duodenale. The egg production of A. duodenale seems to be suppressed by N. americanus when both co-occur.

Necator americanus infection: a longitudinal study of an urban area in Nigeria.

A longitudinal study was carried out in Owerri, capital of Imo State, Nigeria, to assess the pattern of Necator americanus infection during a 27-month period. The mean annual prevalence fell from 59.0% in 1978, to 55.5% in 1979 and 51.1% in 1980. The egg count (apparent intensity of infection) fell in a similar pattern. Maximum and minimum conversion rates were 55.2 and 13.7%, respectively, and conversion rates fell by approximately 20% between 1979 and 1980. The highest reversion rate was 55.0% between 1979 and 1980. The population density of available third-stage larvae fluctuated seasonally and this was significant in determining the pattern of infection.