Ecology of Biomphalaria (Gastropoda: Planorbidae) in Lake Albert, Western Uganda: snail distributions, infection with schistosomes and temporal associations with environmental dynamics

In Lake Albert, an ecological study was conducted, between June 2000 and May 2003, which assessed snail population dynamics, parasite infection patterns and interplay of environmental factors upon Biomphalaria. Monthly sampling surveys were conducted at 29 sites monitoring populations of Biomphalaria stanleyi and Biomphalaria sudanica. Altogether, a total of 21,715 B. stanleyi and 8452 B. sudanica were collected during the period. Both species could be found infected with Schistosoma mansoni although infection prevalence was significantly higher (p < 0.01**) in B. stanleyi (4.4%) than in B. sudanica (3.5%). Each species occupied slightly different aquatic niches with B. stanleyi preferring deeper water habitats whilst B. sudanica was found along the shoreline in shallower water. B. stanleyi was more widely distributed among the sampling locations (19 sites) than B. sudanica (10 sites). Of the four villages included in the study area, snails from sites near Piida and Bugoigo villages had the highest schistosome infection rates, presumably attributable to the closer proximity of people with intestinal schistosomiasis. After inspection of cross-correlation plots which identified most suitable time lags, snail density dynamics could be associated with seasonal variations inclusive of: air temperature, rainfall, lake level, water temperature, water conductivity and water pH. These temporal observations better reveal the relationship between snail populations and environmental factors, providing important information concerning the relative roles of B. stanleyi and B. sudanica in transmission of S. mansoni and development of integrated strategies for disease control around Lake Albert.     

The distribution of <Emphasis Type="Italic">Biomphalaria</Emphasis> (Gastropoda: Planorbidae) in Lake Victoria with ecological and spatial predictions using Bayesian modelling

Intestinal schistosomiasis is a global disease of enormous public health importance. Assessing the local risk of transmission of the parasite causing the disease requires an appraisal of the distribution of its intermediate snail hosts, Biomphalaria spp.. In East Africa, the Lake Victorian Basin is a major freshwater ecosystem and highly endemic for intestinal schistosomiasis, although detailed distribution data for Biomphalaria have not been collected. We used on-the-ground malacological surveys and conjoint measurement of environmental determinants to develop models for analysis of variables associated with distribution and predictive snail mapping into data-deficient areas. Four expeditions were undertaken to collect snails along the Lake Victoria shoreline, visiting 223 sites overall. Environmental measurements were recorded at the time of inspection and water samples taken for quantification of anion and cation concentrations. The spatial distributions of Biomphalaria choanomphala and Biomphalaria sudanica were modelled in two Bayesian multivariate models: one non-spatial and one spatial with random effects. The results showed that chloride, nitrate, sulphate and the number of sympatric snail species were significant predictors of B. choanomphala whereas habitat, water depth, pH and sulphate were significant predictors for B. sudanica. The range of spatial autocorrelation was large (572.9 km for B. choanomphala and 175.3 km for B. sudanica). Interpolating snail abundance data by kriging revealed two ‘hot-spots’ of high abundance of Biomphalaria. These areas should be targeted in future expeditions to ground-truth the model’s predictions. Our study is the first to use Bayesian methods for determination of biomedically important snail distributions and sets crucial limnological baseline data for assessment of future changes in snail biodiversity in the Lake Victoria Basin.     

Implication of Papio anubis in the transmission of intestinal schistosomiasis in three new foci in Kime area, Ethiopia

Epidemiological studies were conducted in the Lake Langano area in the Rift Valley of Ethiopia to determine the occurrence of schistosomiasis and assess factors involved in its transmission. Microscopic examination of faecal specimens from free ranging Papio anubis (anubis baboon) troops from Bishan Gari and Burka Dita forest reserves revealed Schistosoma mansoni eggs with a prevalence of 12.1% (11/91) and 26.2%(34/130), respectively. The eggs were viable as confirmed by miracidial hatching and infectivity tests. Out of the total 12 communities (three schools, five villages and one herdsmen community) surveyed for schistosomiasis around Lake Langano, individuals excreting S. mansoni eggs were found in nine communities with prevalence of infection ranging from 1.4 to 43%. The intensity of infection ranged from 24 EPG (eggs per gram of faeces) to 243 EPG. Excretion of viable eggs by the baboons indicate that they play a role in maintenance of S. mansoni infection in the locality. The detection of S. mansoni eggs in young children, collection of cercarial-infected Biomphalaria pfeifferi in water bodies, and establishment of S. mansoni infection in lab-bred mice have confirmed establishment of transmission foci in Kime area, south-east of Lake Langano. However, the lake itself does not seem to support transmission of schistosomiasis since no snails were found along the shore of the Lake. Further investigations are indicated to fully elucidate the role baboons play in the epidemiology of schistosomiasis in the Rift Valley of Ethiopia. The risk of introduction of water-based development projects in these new endemic foci in relation to S. mansoni infection in the baboons is discussed.     

Transforming growth factor-β and Th17 responses in resistance to primary murine schistosomiasis mansoni

Discovery of the T-helper (Th) 17 cell lineage and functions in immune responses of mouse and man prompted us to investigate the role of transforming growth factor-beta (TGF-β) and interleukin (IL)-17 in innate resistance to murine schistosomiasis mansoni. Schistosoma mansoni-infected BALB/c and C57BL/6 mice were administered with recombinant TGF-β or mouse monoclonal antibody to TGF-β to evaluate the impact of this cytokine on host immune responses against lung-stage schistosomula, and subsequent effects on adult worm parameters. Developing schistosomula elicited increase in peripheral blood mononuclear cells (PBMC) mRNA expression and/or plasma levels of IL-4, IL-17, and interferon-gamma (IFN-γ), cytokines known to antagonize each other, resulting in impaired Th1/Th2, and Th17 immune responses and parasite evasion. Mice treated with TGF-β showed elevated PBMC mRNA expression of IL-6, IL-17, TGF-β, and TNF-α mRNA and increased IL-23 and IL-17 or TGF-β plasma levels, associated with significantly (P < 0.02–<0.0001) lower S. mansoni adult worm burden compared to controls in both mouse strains, thus suggesting that TGF-β led to heightened Th17 responses that mediated resistance to the infection. Mice treated with antibody to TGF-β showed increase in PBMC mRNA expression and plasma levels of IL-4, IL-12p70, and IFN-γ, and significantly (P < 0.02 and <0.0001) reduced worm burden and liver worm egg counts than untreated mice, indicating that Th1/Th2 immune responses were potentiated, resulting in significant innate resistance to schistosomiasis. The implications of these observations for schistosome immune evasion and vaccination were discussed.     

Basophil depletion downregulates Schistosoma mansoni egg-induced granuloma formation

Granuloma formation around parasite eggs during schistosomal infection is considered to be controlled by Th2 cytokines. However, it is still controversial which cell populations are responsible for the host Th2 cytokine-dependent granuloma formation. Basophils have recently attracted attention because of their ability to produce large amounts of IL-4. Therefore, we investigated whether basophils play an essential role in the induction of granuloma formation induced by Schistosoma mansoni eggs. Together with our previous observation that basophil numbers increased markedly in the spleen at 7 weeks postinfection, immunohistochemical staining using anti-mMCP8 monoclonal antibody (mAb) showed basophil infiltration in the granulomatous lesions formed around parasite eggs. To examine the roles of basophils more directly, we treated mice with anti-CD200R3 mAb to deplete basophils. Depletion of basophils resulted in a reduction of basophil number with concomitant downregulation of egg granuloma formation at 7 weeks postinfection. Moreover, we observed a significant reduction in the size of egg granulomas formed in basophil-depleted mice in the pulmonary granuloma model. Taken together, these findings indicated that basophils are essential for S. mansoni egg-induced granuloma formation, and this may serve as a novel therapeutic target in ameliorating the pathology of schistosomiasis.     

Biomphalaria alexandrina in Egypt: Past, present and future

The African species of Biomphalaria appeared as a result of the relatively recent west-to-east trans-Atlantic dispersal of the Biomphalaria glabrata-like taxon. In Egypt, Biomphalaria alexandrina is the intermediate host for Schistosoma mansoni. Biomphalaria alexandrina originated in the area between Alexandria and Rosetta and has historically been confined to the Nile Delta. Schistosoma mansoni reached Egypt via infected slaves and baboons from the Land of Punt through migrations that occurred as early as the Vth Dynasty. The suggestion of the presence of Schistosoma mansoni infection in Lower Egypt during Pharaonic times is discussed despite the fact that that there is no evidence of such infection in Egyptian mummies. It is only recently that Biomphalaria alexandrina colonized the Egyptian Nile from the Delta to Lake Nasser. This change was likely due to the construction of huge water projects, the development of new water resources essential for land reclamation projects and the movement of refugees from the Suez Canal zone to the Delta and vice versa. The situation with respect to Biomphalaria in Egypt has become complicated in recent years by the detection of Biomphalaria glabrata and a hybrid between both species; however, follow-up studies have demonstrated the disappearance of such species within Egypt. The National Schistosoma Control Program has made great strides with respect to the eradication of schistosoma; however, there has unfortunately been a reemergence of Schistosoma mansoni resistant to praziquantel. There are numerous factors that may influence the prevalence of snails in Egypt, including the construction of water projects, the increase in reclaimed areas, global climate change and pollution. Thus, continued field studies in addition to the cooperation of several scientists are needed to obtain an accurate representation of the status of this species. In addition, the determination of the genome sequence for Biomphalaria alexandrina and the use of modern technology will allow for the study of the host–parasite relationship at a molecular level.     

Density-dependent effects of snail grazing on the growth of a submerged macrophyte,Vallisneria spiralis

In order to better understand the role of herbivorous snails in freshwater ecosystems, we conducted experiments investigating food preference of the snail Radix swinhoei on leaves of the submerged plant Vallisneria spiralis with and without periphyton coverage. The effects of snail grazing on the growth of V. spiralis were assessed in a no-snail control and at three snail densities (80, 160, 240 individuals m^?2). Results showed that the snails chose preferentially leaves covered by periphyton. Grazing activity at low snail density (80 individuals m^?2) was found to stimulate V. spiralis growth, but at higher snail density (240 individuals m^?2), plant growth was apparently suppressed. An increase observed in nutrient concentrations in water column with increasing snail density may be attributed to nutrient release by snails. This study suggests that the nature of the relationship between herbivorous snails and macrophytes in freshwater ecosystems depends on the abundance of the snails. At low snail density, the relationship may be a mutualistic one, but at high density snail herbivory may impact negatively on macrophyte biomass in lakes.     

Efficiency of ginger (Zingbar officinale) against Schistosoma mansoni infection during host–parasite association

The possible protective effect of ethanolic extract of ginger against infection with Schistosome mansonii was evaluated in mice. The extract was given daily for 45 days beginning at either 2nd day or 45 days post infection. Oral supplementation of ginger extract to infected animals was effective in reducing worm burden and the egg load in the liver and intestine which coincided with the reduction in granuloma diameters. Ginger extract had also the effect to offset liver fibrosis in response to S. mansoni infection indicated by reduced liver hydroxyproline level and serum alpha–fetoprotein (AFP). The extract reduces some inflammatory mediators that play a crucial role in schistosomal liver fibrosis and its complications. These include liver xanthine oxidase (XO); nitric oxide (NO); tumour necrosis factor–alpha (TNF-α); immunoglobins E, G, and M (Ig-E, Ig-G and Ig-M, respectively), and interleukin 4, 10 and 12 (IL-4, IL-10 and IL-12, respectively). Administration of ginger extract ameliorated the infection-induced alterations in serum gamma-glutamyl transferase (GGT), alanine amintransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP). It was concluded that oral administration of ginger extract to S. mansoni infected mice could minimize the deleterious effects of this parasite on the vital functions of infected animals.     

The ecology of Biomphalaria sudanica in Lake Ziway, Ethiopia

A longitudinal study was made over a period of 24 months from January 2001 to December 2002 in Lake Ziway, Ethiopia, to elucidate factors influencing changes in the population density of Biomphalaria sudanica and to identify seasons of peak transmission of Schistosoma mansoni. Between January 2001 and December 2002, bimonthly visits were made to the lake to collect data on snail population density and schistosome infection in snails, vegetation and lake water level. Water samples were collected during the dry and rainy seasons and chemical analyses were made for major cations, anions, electrical conductivity, total hardness and pH using standard methods for the examination of water and wastewater. The seasonal fluctuation in the population density of B. sudanica was found to be highly associated with rainfall, water level of the lake and vegetation availability and abundance. Water chemical analysis showed that major cations and anions were all within the range reported for other African freshwaters. Both malacological and meteorological data show that snail population density in Lake Ziway peaks at the end of the long rainy season (June–August), coinciding with a seasonal transmission peak of schistosomiasis.     

Seeding experiments demonstrate poor performance of the hatching test for detecting small numbers of Schistosoma mansoni eggs in feces

Parasitological methods for the evaluation of schistosomiasis tend to be limited when parasitic burdens are low, which is a major characteristic of low intensity transmission areas. While the hatching test (HT) method has been considered to be “very sensitive”, reports of its capacity to detect low numbers of eggs remain scarce in the published literature. Our main hypothesis is that HT has limitations and cannot be recommended for diagnosing light infections or as a control of cure. Hence, this study aims to describe the performance of HT in detail, with respect to seeding experiments for egg numbers in the range of 4 to 24 eggs per gram (epg) of feces. Different numbers of eggs of Schistosoma mansoni were seeded in normal human feces. The first set of experiments evaluated the amount of feces (higher than 0.5 g prevented hatching), the proximity of the light source (50 cm was preferred), and the observation time required for the detection of miracidia (more than 3 h did not add to sensitivity). HT was subsequently performed with 12, 10, 8, 6, 4, and 2 eggs in 0.5 g of feces. The final set of experiments was performed to analyze the initial filtration step, in which surgical gauze versus a 500 μm nylon mesh was compared and demonstrated losses of eggs that occurred with washing and gauze (better with nylon) sieving steps. The proposed method was found to produce 100% positivity for up to 12 epg, with a sharp decrease to 33% for 8 epg and less. In conclusion, HT is not recommended for diagnosing intestinal schistosomiasis in populations with light infections, considering the complexity of the procedure and its lack of effectiveness with fecal amounts higher than 0.5 g even at optimized conditions.     

Opportunity or catastrophe? effect of sea salt on host-parasite survival and reproduction

Seawater intrusion associated with decreasing groundwater levels and rising seawater levels may affect freshwater species and their parasites. While brackish water certainly impacts freshwater systems globally, its impact on disease transmission is largely unknown. This study examined the effect of artificial seawater on host-parasite interactions using a freshwater snail host, Biomphalaria alexandrina, and the human trematode parasite Schistosoma mansoni. To evaluate the impact of increasing salinity on disease transmission four variables were analyzed: snail survival, snail reproduction, infection prevalence, and the survival of the parasite infective stage (cercariae). We found a decrease in snail survival, snail egg mass production, and snail infection prevalence as salinity increases. However, cercarial survival peaked at an intermediate salinity value. Our results suggest that seawater intrusion into freshwaters has the potential to decrease schistosome transmission to humans.     

Biological control of invasive apple snails by two species of carp: Effects on non-target species matter

Molluscivorous fish, especially carp, have been adopted as bio-control agents of the invasive apple snail Pomacea canaliculata, but previous studies have focused on their effectiveness, with little attention paid to their undesirable effects on non-target plants and animals. We conducted an 8-week mesocosm study to compare the effectiveness of two indigenous fish, common carp (Cyprinus carpio) and black carp (Mylopharyngodon piceus), in removing P. canaliculata, and their potential side effects on macrophytes and non-target mollusks in a freshwater wetland. Three species of macrophytes and a community of mollusks in the wetland sediment were enclosed in 1 × 1 × 1 m enclosures either with apple snails (AS), with apple snails and common carp (AS + CC), with apple snails and black carp (AS + BC), or without apple snails and fish. Both species of carp were effective predators of P. canaliculata, removing most of the individuals in the enclosures except a few that were too big to fit into their mouth. By reducing apple snail population, black carp reduced grazing of apple snail on macrophytes. In contrast, although common carp controlled apple snail population, it did not reduce overall loss in plant biomass as the fish might also fed on macrophytes. Both species of carp preyed on non-target mollusks. Application of bio-control agents in invasive species management needs to consider their effects on both the pest and non-target plants and animals. Adoption of common and/or black carp to control apple snail populations thus depends on the weight given to their effectiveness and subtle different effects on non-target organisms by wetland management authority.     

Field studies on the bionomics of the free-living stages of St. Lucian Schistosoma mansoni.

Densities of Schistosoma mansoni miracidia and cercariae in natural habitats in three St. Lucian valleys were monitored over a 3-year period by exposure of sentinel snails, Biomphalaria glabrata, and a cercariometric technique, supplemented by sampling of field snails. Separate measures for control of S. mansoni transmission were under evaluation in two of the valleys. Sentinel snails became infected sporadically and their infection rates per valley ranged from 0·12% to 4·99%. S. mansoni miracidial inoculation rates ranged from 1 to over 4 per infected sentinel snail. Combined rainfall of more than 3 in on the day before any day of sentinel snail exposure interfered with miracidium-snail interaction. Densities of S. mansoni cercariae ranged from 0·05 to 21 per litre of water sampled. The number of cercariae detected in a habitat by cercariometry was directly proportional to the number of infected field snails. Sentinel snail infection rates exhibited a downward and an upward trend, respectively, in the controlled and uncontrolled areas, although the changes were not significant statistically.     

Infectivity of Cryptosporidium andersoni Kawatabi type relative to the small number of oocysts in immunodeficient and immunocompetent neonatal and adult mice

Cryptosporidium andersoni is a protozoan parasite found in many countries that invades the stomachs of primarily adult cattle. Unlike the isolates of C. andersoni in cattle from other countries, C. andersoni isolates from Japanese cattle can infect mice and were identified as a novel type and later defined as C. andersoni Kawatabi type. The biological characteristics of C. andersoni Kawatabi type have not yet been well documented. In the present study, we assess the infectivity of this type isolate in mice with different immune competence status and age. We found that inoculation of more than 1 × 10⁴ oocysts is needed to establish infection in mature mice irrespective of immune status. All of the infected immunocompetent mice recovered after a patent period of approximately 20 days. In immunodeficient mice, the pre-patent period was prolonged compared with that of 1 × 10⁶ oocysts, but the pattern and the maximum shedding measured by the number of oocysts per day were almost identical. In neonatal immunocompetent and immunodeficient mice, inoculation with 1 × 10⁴ to 10⁵ oocysts was also needed to establish infection. Our results indicate that there is a threshold of oocysts needed to establish patent infection in the acidic conditions of the stomach.     

Biomphalaria species in Alexandria water channels

Of the several species of Biomphalaria snails worldwide that serve as the intermediate host for Schistosoma mansoni, Biomphalaria alexandrina is a species that is indigenous to Egypt. Recently, there has been much debate concerning the presence of Biomphalaria glabrata and the hybrid of the species with Biomphalaria alexandrina. Due to this debate, the absence of a clear explanation for the presence of B. glabrata in Egyptian water channels and the probability that they may be reintroduced, we conducted this field study to identify Biomphalaria species present in Alexandria water channels. Laboratory-adapted susceptible snails to Schistosoma mansoni of the following species were used as a reference; Biomphalaria alexandrina, Biomphalaria glabrata and their hybrid. These snails were used to perpetuate the Schistosoma life cycle at the Theodor Bilharz Research Institute (TBRI), Cairo, Egypt. Morphological and molecular studies were conducted on these reference snails as well as on the first generation of Biomphalaria snails from two areas in the Alexandria governorate. The morphological study included both external shell morphology and internal anatomy of the renal ridge. The molecular study used a species-specific PCR technique.The results demonstrated that there was an absence of Biomphalaria glabrata and the hybrid from Alexandria water channels. Moreover, the susceptibility patterns of these reference snails were studied by measuring the different parasitological parameters. It was found that Biomphalaria glabrata and the hybrid were significantly more susceptible than Biomphalaria alexandrina to the Egyptian strain of Schistosoma mansoni. The results demonstrated that if Biomphalaria glabrata was reintroduced and adapted to the local environment in Egypt, it would have important epidemiologic impacts that would have a serious effect on the health of Egyptian people.     

Snail findings from an experimental mollusciciding programme to control Schistosoma mansoni transmission on St. Lucia

An experimental molluscicide programme to minimize Schistosoma mansoni transmission has been in operation in a valley on the West Indian island of St. Lucia since September, 1970. Areas infested with the snail Biomphalaria glabrata received an initial intensive treatment. A fortnightly surveillance-treatment programme, with focal mollusciciding of any living snail colonies detected, was then developed. Snails were eliminated from some static habitats but the majority required repeated focal treatments to keep their snail colonies small and localized with low infection rates. No stream colonies were detected in the 1972 and 1973 dry seasons, although such colonies became established in other valleys. The belief that eliminating the stream colonies should have reduced S. mansoni transmission is supported by the apparent absence of cercariae in certain streams and by preliminary medical findings. A detailed cost analysis is included. Based on this experimental programme, a cheaper programme is outlined which should be suitable for use by public health authorities.     

Intermediate host specificity in Schistosoma mansoni

Miracidia of Schistosoma mansoni penetrate into many kinds of snails, but development of normal sporocysts takes place only in certain species of Biomphalaria. Different populations of this snail vary greatly in laboratory infection rates with S. mansoni originating from diverse geographic localities. Cross-exposure experiments show that compatibility factors exist in both snails and parasites. Susceptibility of stocks of Biomphalaria to particular strains of S. mansoni is genetically determined and may be modified by selection in the laboratory. In a compatible snail, the sporocyst develops without host tissue reaction; in incompatible snails the early larvae are rapidly surrounded by amebocytes and fibroblasts, and destroyed. This reaction resembles the generalized host cellular response elicited by any foreign body. An individual snail exposed to many miracidia may have both developing and encapsulated sporocysts side by side within its tissues. The weight of current evidence suggests that elicitation or absence of this cellular response resides in the recognition or nonrecognition of the sporocyst as a foreign body. The sporocyst tegument surface, which forms within a few hours after miracidial penetration, may have a molecular conformation identical with that of the snail, or may be able to bind specific host molecules, so that detection and subsequent encapsulation by host cells are averted. Presuming genetic determination of the sporocyst surface structure and of the host cell detection capability, differing infection rates would result from the particular frequencies of relevant genes in the populations concerned.     

Testosterone,gonadotropins and androgen receptor during spermatogenesis of Biomphalaria alexandrina snails (Pulmonata: Basommatophora)

Endocrine regulation of reproductive processes of the snail Biomphalaria alexandrina is poorly recognized. Thus, the aims of the study were: (1) to acquire histological images of the ovotestis; (2) to determine the hemolymph concentrations of testosterone (T) and gonadotropic hormones (luteinizing hormone: LH and follicle stimulating hormone: FSH), (3) to demonstrate androgen receptor (AR) immunolocalization in the ovotestis, and (4) to show LH and FSH protein expression in cerebral ganglia of small (diameter shell: 4–6 mm), medium (7–11 mm) and large (12–16 mm) B. alexandrina snails. These three groups represented different reproductive stages of the snail. The AR immunoexpression was found in the periphery and inside the acini of small (immature) snails as well as in spermatocytes, spermatids, Sertoli cells, the interstitial cells and the acinus lining epithelium of medium (mature) snails. Low AR immunoexpression was demonstrated in the interstitial cells of large (aged) snails. The neurons at the periphery of the cerebral ganglia and connective sheath of the ganglia showed a positive FSH and LH immunostaining. T concentration in the hemolymph was higher in medium snails than in small and large snails. In contrast, LH concentration was higher in medium snails than in small and large snails. These data suggests that gonadotropins and T play a role in the gonadal development in B. alexandrina.     

Molecular detection of Coccidioides spp. from environmental samples in Baja California: linking Valley Fever to soil and climate conditions

Coccidioidomycosis is an important human fungal infection of American deserts and nearby semi-arid regions with highly endemic areas distributed along the United States-Mexico border. Despite the increasing incidence in the last 20 yr, reports of positive isolations of the causal agent, Coccidioides spp. from environmental samples have been scarce. To resolve this paradox, it is extremely important to first identify the fundamental ecological niche of this fungus. Soil samples (n = 90) including those from heteromyids’ active burrows, latrines and other mammals’ dens were collected using an oriented sampling method from areas of Baja California, Mexico previously predicted as putative endemic “hotspots”. The total genomic DNA obtained from the collected samples was subjected to a nested PCR followed by a diagnostic PCR designed to amplify the internal transcribed spacer (ITS) 2 region of Coccidioides spp. From the 42 amplicons obtained and sequenced (37 from Valle de las Palmas (VDP) and five from San Jose de la Zorra (SJZ)), 32 were confirmed to belong to Coccidioides spp. No Coccidioides spp. were found in soils collected in Ensenada.VDP and SJZ have different soil characteristics but share a Mediterranean climate having less than 250 mm of precipitation per year, as well as a dry period of at least 6 months. The development of Coccidioides spp. is probably related to the structure of the microbial population adapted to these conditions in the semi-arid-mediterranean ecotone.     

Impaired protection against Trichinella spiralis in mice with high levels of IgE

Helminth infection induces production of a large amount of immunoglobulin E (IgE) to nonhelminth antigens. Although such “irrelevant” IgE is a major proportion of total IgE in the host, its biological significance remains unclear. Therefore, I examined protective activity against Trichinella spiralis in mice with high levels of IgE by repeated injections of anti-dansyl IgE monoclonal antibody or Nippostrongylus brasiliensis infection. Injected anti-dansyl IgE occupied IgE receptors on mast cells in naive mice. Protective activity against T. spiralis, determined with number of muscle larvae 5 weeks after infection, was impaired in mice treated with anti-dansyl IgE. The impaired protection was found in mice treated with anti-dansy IgE 7 and 14 days after infection, but not 21 and 28 days after infection, indicating that IgE-dependent protection operates at an early stage after infection. In the next experiments, mice were infected with N. brasiliensis 4 weeks before T. spiralis infection to obtain high levels of IgE. The protective activity against T. spiralis was decreased by N. brasiliensis infection. On the other hand, protection against T. spiralis was comparable in IgE-deficient SJA/9 mice and in anti-IgE-treated BALB/c mice with or without N. brasiliensis infection, suggesting that impairment of protection is dependent on IgE. These results indicate that the high levels of irrelevant IgE are beneficial for helminths and, alternatively, that anti-helminth IgE antibodies are protective for hosts. In addition, the impaired protection was found in IgE high-responder mice but not in low-responder mice, suggesting that protection against T. spiralis is controlled by IgE responsiveness in the host.