A review of parasitic fauna of Egyptian amphibia

To identify demographic, behavioural and environmental determinants of intestinal parasitic infection, evaluate the impact of a variety of dry sanitation systems on intestinal parasitic infection, and evaluate the safety of using stored biosolids in agriculture in order to guide future sanitation interventions in rural areas of El Salvador. Interviews were conducted with 109 households in eight communities where double-vaulted and solar urine-diverting desiccating latrines, pit latrines or no latrines were used. Faecal samples from 499 individuals were tested for enteric helminths and protozoa. Users of solar desiccating latrines had the lowest prevalence of enteric parasite infection. Double-vault, urine-diverting desiccating latrines effectively reduced the transmission of some pathogens, but may not achieve the conditions sufficient for the complete destruction of the more environmentally persistent pathogens, Ascaris lumbricoides and Trichuris trichiura. Contact with inadequately treated latrine biosolids was associated with an increased risk of Ascaris infection. Solar latrines were associated with the overall lowest prevalence of enteric parasitic infections. Members of households where latrine biosolids were used in agriculture had a higher prevalence of infection than those where biosolids were buried. We therefore recommend the promotion of solar latrines in rural areas of El Salvador over other dry sanitation systems, and recommend that stored biosolids not be used in agriculture.

The majority of the recent reductions in the Earth’s biodiversity can be attributed to direct human impacts on the environment. An increasing number of studies over the last decade have reported declines in amphibian populations in areas of pristine habitat. Such reports suggest the role of indirect factors and a global effect of human activities on natural systems. Declines in amphibian populations bear significant implications for the functioning of many terrestrial ecosystems, and may signify important implications for human welfare. A wide range of candidates have been proposed to explain amphibian population declines. However, it seems likely that the relevance of each factor is dependent upon the habitat type and species in question, and that complex synergistic effects between a number of environmental factors is of critical importance. Monitoring of amphibian populations to assess the extent and cause of declines is confounded by a number of ecological and methodological limitations.

In 1989, it dawned on participants at the First World Congress of Herpetology that observed declines in amphibian populations might actually be global in scope and unprecedented in severity. Three decades of research since then has produced an enormous increase in our knowledge of amphibian ecology and appreciation of the complexity of possible causes for amphibian population declines. In September 2019, 30 yr after the First World Congress ended, a day-long, international symposium on amphibian population declines was held at the Redpath Museum of McGill University in Montreal, Canada. Symposium participants drew upon the knowledge gained over three decades of study to look ahead with fresh ideas to address this vital aspect of the global decline of biodiversity. Despite tremendous progress over the past three decades there is still much about amphibian ecology, population biology, and pathology that remains unknown. Amphibian declines have turned out to be more complex than originally expected and the result of multiple possible causes acting across landscapes, among taxa, or between populations in ways that are not at all uniform. The papers in this special issue of Herpetologica, which stem from the symposium, explore much of our current understanding of amphibian declines and their causes.

BackgroundThe decline in amphibian populations across the world is frequently linked to the infection of the chytrid fungus Batrachochytrium dendrobatidis (Bd). This is particularly perplexing because Bd was only recently discovered in 1999 and no chytrid fungus had previously been identified as a vertebrate pathogen.ResultsIn this study, we show that two large families of known virulence effector genes, crinkler (CRN) proteins and serine peptidases, were acquired by Bd from oomycete pathogens and bacteria, respectively. These two families have been duplicated after their acquisition by Bd. Additional selection analyses indicate that both families evolved under strong positive selection, suggesting that they are involved in the adaptation of Bd to its hosts.ConclusionsWe propose that the acquisition of virulence effectors, in combination with habitat disruption and climate change, may have driven the Bd epidemics and the decline in amphibian populations. This finding provides a starting point for biochemical investigations of chytridiomycosis.

The present study was conducted to detect and identify blood parasites infecting toads Amietophrynus (Bufo) regulariss and find out the association between the infection of the parasites and host factors sex, length, body weight, and age. One hundred and twenty Amietophyrnus (Bufo) regularis (99 males and 21 females) were collected from May to August 2016 in two localities in Khartoum State (Al-Sorojia and Jebel Aulia). They were examined for blood parasites using blood films stained in Giemsa’s. A total of 77 (64.16%) of specimens were infected by 880 parasitic protozoa made-up of 879 (99.89%). Apicomplexa composed of Haemogregina spp. (89.66%), Hepatozoon spp. (10.22%), and 1 (0.11%) Kinteoplastides composed of Trypanosoma spp., while 43 (35.83%) were uninfected. No nematodes were recovered. The infection rate based on sex shows that females significantly (χ2 =12.520, p≤0.05) have a higher rate of infection than males. For the toad maturity, there was a significant difference in the infection rate between the mature group and the immature (χ2 =19.471, p=0.003). The infection rate increases with decreasing of weight and length with a negative correlation (rs = –0.022, p = 0.814 and rs = –0.004, p = 0.966, respectively). This study showed a high level of parasitic infection in African common toads in Khartoum State which contributed to the decline in amphibian populations. Further research on amphibian parasitism and its threats to human health is warranted.

Soil, water, and amphibian tissues collected between 1995 and 1999 from 15 study sites in Bermuda were analysed for pesticides and heavy metals. The most abundant pesticide residue in soil was p,p′-dichlorodiphenyldichloroethylene (DDE) which was found at all sites in concentrations ranging from 0.003 to 4.023 p.p.m. No pesticide residues were found in water. DDE was also recovered from the livers and fat bodies of marine toads (Bufo marinus) and whistling frogs (Eleutherodactylus johnstonei). Analyses of food sources consumed by these anuran species revealed residue levels of p, p′-DDE ranging from 0.05 to 0.217 p.p.m. Other soil residues included dichlorodiphenyltrichloroethane (DDT) at eight study sites, Dicofol(kelthane) at eight sites, dieldrin at five sites, and polychlorinated biphenyls (PCBs) as Arochlor 1254 and Arochlor 1260 at seven sites. Analyses of toad livers revealed significant concentrations of cadmium, chromium, copper and zinc. Livers of Bermuda toads exhibited altered hepatocytic morphology and an increased number of melanomacrophages and possible granulomas, while spleens showed a marked decrease in white pulp. Spleen cells from Bufo marinus collected at one site having high levels of cadmium exhibited a decreased B cell response to lipopolysaccharide. The incidence of trematode infection in Bufo marinus increased from 53.8% in 1995 to 90% in 1999. Deformity rates in the limbs of subadult and adult toads ranged between 15 and 25%. Examination of 1,995 newly-metamorphosed toads revealed deformity rates as high as 47%. The current comprehensive study suggests that environmental pollutants may account for immunosuppression, increased susceptibility to infections, limb malformations and possible decline in amphibian populations from Bermuda.

The decline of amphibian populations worldwide is a recognized phenomenon. A variety of important causes have been linked to the declines but perhaps the most renowned cause, in terms of popular press exposure, funding dispersal and papers published, is disease. In particular, chytridiomycosis, a disease caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), is a lethal emerging infectious disease that has had profound effects in some amphibian species, but occurs without catastrophic effects in others (Fisher, Garner & Walker, 2009b). Bd affects species differentially. In many cases it is the major threat to animals already stressed by other critical challenges, such as habitat destruction, pollution, invasive species and climate change. In addition to its impact on amphibian populations, the spread and presence of Bd is likely to impact human activities via effects on the pet, bait and food trade (Schloegel et al., 2009, 2010).

As part of an overall “biodiversity crisis” many amphibian populations are in decline throughout the world. Numerous causes have been invoked to explain these declines. These include habitat destruction, climate change, increasing levels of ultraviolet radiation, environmental contamination, disease, and the introduction of non‐native species. In this paper, we argue that amphibian population declines are caused by different abiotic and biotic factors acting together in a context‐dependent fashion. Moreover, different species and different populations of the same species may react in different ways to the same environmental insult. Thus, the causes of amphibian population declines will vary spatially and temporally. Although some generalizations (e.g. those concerning environmental stress and disease outbreaks) can be made about amphibian population declines, we suggest that these generalizations take into account the context‐dependent dynamics of ecological systems.

Abstract.Over the last two decades, numerous studies have shown that alien predators contributed to amphibian population declines. Both experimental studies and correlative field surveys implicated alien species of fish, bullfrogs and crayfish as major contributors to amphibian population decline, and in some instances local extinction. Additional studies have demonstrated that alien predators also caused long‐term changes in aquatic communities. Recent studies have examined the feasibility of removing alien predators, and provide some evidence that amphibian populations can recover. Applying information gained from past studies to the recovery of amphibian populations will be the challenge of future studies. International, national and local policies that regulate alien predators should be based largely on the body of scientific evidence already in the literature. Scientists need to be more involved with policy‐makers to most effectively change laws that regulate alien predators.

The virulence of a pathogen can vary strongly through time. While cyclical variation in virulence is regularly observed, directional shifts in virulence are less commonly observed and are typically associated with decreasing virulence of biological control agents through coevolution. It is increasingly appreciated, however, that spatial effects can lead to evolutionary trajectories that differ from standard expectations. One such possibility is that, as a pathogen spreads through a naive host population, its virulence increases on the invasion front. In Central America, there is compelling evidence for the recent spread of pathogenic Batrachochytrium dendrobatidis (Bd) and for its strong impact on amphibian populations. Here, we re-examine data on Bd prevalence and amphibian population decline across 13 sites from southern Mexico through Central America, and show that, in the initial phases of the Bd invasion, amphibian population decline lagged approximately 9 years behind the arrival of the pathogen, but that this lag diminished markedly over time. In total, our analysis suggests an increase in Bd virulence as it spread southwards, a pattern consistent with rapid evolution of increased virulence on Bd's invading front. The impact of Bd on amphibians might therefore be driven by rapid evolution in addition to more proximate environmental drivers.

Silent Springs: Why Are All the Frogs “Croaking”?

BackgroundPrevious epidemiological studies have examined the prevalence and risk factors for a variety of parasitic illnesses, including protozoan and soil-transmitted helminth (STH, e.g., hookworms and roundworms) infections. Despite advancements in machine learning for data analysis, the majority of these studies use traditional logistic regression to identify significant risk factors.MethodsIn this study, we used data from a survey of 54 risk factors for intestinal parasitosis in 954 Ethiopian school children. We investigated whether machine learning approaches can supplement traditional logistic regression in identifying intestinal parasite infection risk factors. We used feature selection methods such as InfoGain (IG), ReliefF (ReF), Joint Mutual Information (JMI), and Minimum Redundancy Maximum Relevance (MRMR). Additionally, we predicted children’s parasitic infection status using classifiers such as Logistic Regression (LR), Support Vector Machines (SVM), Random Forests (RF) and XGBoost (XGB), and compared their accuracy and area under the receiver operating characteristic curve (AUROC) scores. For optimal model training, we performed tenfold cross-validation and tuned the classifier hyperparameters. We balanced our dataset using the Synthetic Minority Oversampling (SMOTE) method. Additionally, we used association rule learning to establish a link between risk factors and parasitic infections.Key findingsOur study demonstrated that machine learning could be used in conjunction with logistic regression. Using machine learning, we developed models that accurately predicted four parasitic infections: any parasitic infection at 79.9% accuracy, helminth infection at 84.9%, any STH infection at 95.9%, and protozoan infection at 94.2%. The Random Forests (RF) and Support Vector Machines (SVM) classifiers achieved the highest accuracy when top 20 risk factors were considered using Joint Mutual Information (JMI) or all features were used. The best predictors of infection were socioeconomic, demographic, and hematological characteristics.ConclusionsWe demonstrated that feature selection and association rule learning are useful strategies for detecting risk factors for parasite infection. Additionally, we showed that advanced classifiers might be utilized to predict children’s parasitic infection status. When combined with standard logistic regression models, machine learning techniques can identify novel risk factors and predict infection risk.

The massive reductions in amphibian populations taking place across the globe are unprecedented in modern times. Within the Neotropics, the enigmatic decline of amphibians has been considered predominantly a montane phenomenon; however, recent evidence suggests amphibian and reptile populations in lowland forests in Central America are waning as well. Unfortunately, very little baseline data are available for conducting large scale time series studies in order to further investigate and confirm declines in the lowland forests of tropical America. Here we compare leaf litter herpetofauna abundance at sites in the Central Amazon, sampled first in 1984–1985 and again in 2007. We find no evidence for a decline in abundance or biomass of amphibians over a period of 22 years at this site. This conclusion differs markedly from the decline of 75% in amphibian populations over 35 years at a lowland site in Costa Rica. To explore potential declines in lowland Neotropical amphibian populations in detail, we suggest that existing baseline data be comprehensively compiled and analyzed for previously sampled sites and that these sites be re-sampled using comparable methodologies.

Effects of parasitic infections on clinical outcomes, self-rated quality of life and physical fitness in Côte d'Ivoire

Xenobiotics are regularly being released into the environment due to increasing human exploitative activities. Individual actions and/or complex interactions among these xenobiotics, e.g., radiation, chemical contaminants, parasites/pathogens, toxic metals, climate change, among others, adversely affect amphibian populations. These xenobiotics are stressors that either kill or induce sub-lethal effects on amphibians. In this chapter, the use of adult African toads as bioindicators of xenobiotic-induced geno- and systemic toxicity is considered. Some xenobiotics also generate reactive oxygen species that elicit systemic toxicity and genotoxicity. Also, xenobiotics can directly induce sub-lethal toxicity in the organ systems. Alterations in body biochemistry, haematological indices, body morphology, and histopathology were common findings in systemic toxicity-affected African toads. Micronucleus and abnormal nuclear malformations were the common biomarkers of this anomaly. Damage induced by xenobiotics may also lead to pathophysiological, inflammatory, and genotoxic disorders, while reproductive abnormalities and morphological deformities are present as well. These alterations may incapacitate the toad and eventually lead to its death. These factors constitute a threat to amphibian health and are the hallmarks of population decline. However, there is a need for a better understanding of the causal relationship between environmental toxicant impacts and the decline in amphibian populations.