scholarly journals Cryptic disease-induced mortality may cause host extinction in an apparently stable host–parasite system

2017 ◽  
Vol 284 (1863) ◽  
pp. 20171176 ◽  
Author(s):  
Andrés Valenzuela-Sánchez ◽  
Benedikt R. Schmidt ◽  
David E. Uribe-Rivera ◽  
Francisco Costas ◽  
Andrew A. Cunningham ◽  
...  
Keyword(s):  
Batrachochytrium Dendrobatidis ◽  
Population Decline ◽  
Parasitic Infection ◽  
Parasite Prevalence ◽  
Host Population ◽  
Population Declines ◽  
Epidemic Disease ◽  
Susceptible Host ◽  
Conservation Practice ◽  
Host Parasite

The decline of wildlife populations due to emerging infectious disease often shows a common pattern: the parasite invades a naive host population, producing epidemic disease and a population decline, sometimes with extirpation. Some susceptible host populations can survive the epidemic phase and persist with endemic parasitic infection. Understanding host–parasite dynamics leading to persistence of the system is imperative to adequately inform conservation practice. Here we combine field data, statistical and mathematical modelling to explore the dynamics of the apparently stable Rhinoderma darwinii – Batrachochytrium dendrobatidis (Bd) system. Our results indicate that Bd-induced population extirpation may occur even in the absence of epidemics and where parasite prevalence is relatively low. These empirical findings are consistent with previous theoretical predictions showing that highly pathogenic parasites are able to regulate host populations even at extremely low prevalence, highlighting that disease threats should be investigated as a cause of population declines even in the absence of an overt increase in mortality.

Host life-history variation in response to parasitism

Parasitology ◽  
1985 ◽  
Vol 90 (1) ◽  
pp. 205-216 ◽  
Author(s):  
D. J. Minchella
Keyword(s):  
Genetic Variation ◽  
Life History ◽  
Parasitic Infection ◽  
Host Susceptibility ◽  
Life History Variation ◽  
Susceptible Host ◽  
Finite Set ◽  
Host Life ◽  
Host Parasite ◽  
Parasite Populations

Over half of all living species of plants and animals are parasitic, which by definition involves intimate association with and unfavourable impact on hosts (Price, 1980). This paper will only consider parasites whose ‘unfavourable impact’ adversely affects the birth and/or mortality rates of their hosts (Anderson, 1978). Most organisms are potential hosts and must deal with the problem of parasitism. The probability of parasitic infection of a host is influenced by both environmental and genetic factors. Traditionally it was assumed that a host was either resistant or susceptible to a particular parasite and therefore the interaction between a parasite and potential host had only two possible outcomes: either the resistant host rebuffed the parasitic attack and remained uninfected or the parasite successfully invaded and significantly reduced the reproductive success of the susceptible host. This approach, however, ignored the intraspecific genetic variation present within both host and parasite populations (Wakelin, 1978). Since the outcome is determined by the interaction of a finite set of host genes and parasite genes, genetic variation in host susceptibility and parasite infectivity (Richards, 1976; Wakelin, 1978) suggests that more than two outcomes are possible. Variation in host and parasite genomes does not begin and end at the susceptibility/infectivity loci. Other genes may also influence the outcome of host–parasite interactions by altering the life-history patterns of hosts and parasites, and lead to a variety of outcomes.

scholarly journals Mass Amphibian Mortality during Overwintering Related To Fungal Pathogen But Not Larval Environment: An Explanation for Declines?

2018 ◽  
Author(s):  
Samantha L. Rumschlag ◽  
Michelle D. Boone
Keyword(s):  
Environmental Conditions ◽  
Fungal Pathogen ◽  
Batrachochytrium Dendrobatidis ◽  
Host Population ◽  
Leopard Frog ◽  
Host Quality ◽  
Population Declines ◽  
Northern Leopard Frog ◽  
Population Growth Rates ◽  
Size At Metamorphosis

AbstractDevelopment of infectious diseases within hosts may be shaped by environmental conditions that cause tradeoffs in energetic demands for immune responses against demands for host growth and survival. Environmental conditions may influence these tradeoffs by affecting size of hosts, or tradeoffs may change across seasons, thereby altering the impacts of diseases on hosts. In the present study, we exposed northern leopard frog (Lithobates pipiens) tadpoles to varying larval environments (low leaf litter, high density of conspecifics, 40 µg/L atrazine, caged fish, or control) that influenced size at metamorphosis, a measure of host quality. Subsequently, we exposed these metamorphs of to Batrachochytrium dendrobatidis (Bd), a fungal pathogen linked to worldwide host population declines, at metamorphosis and/or 12 weeks later, prior to overwintering. Bd exposure dramatically reduced survival during overwintering and the effect was strongest when frogs were exposed both at metamorphosis and before overwintering. Larval environments, which determined host size, did not influence effects of Bd. Stage-structured models built to assess the impacts of Bd exposure on host populations suggest that Bd exposure at metamorphosis or before overwintering would reduce annual population growth rates by an average of 19% and 41%, respectively. Our study indicates that northern leopard frog hosts suffered little effects of Bd exposures following metamorphosis and that lower host quality did not hamper a frog’s ability to respond to Bd. Instead, we provide evidence that Bd exposure can reduce survival and result in population size reductions via reduced recruitment from overwintering mortality, providing a plausible mechanism for enigmatic declines of amphibians in temperate regions.

scholarly journals Disease driven extinction in the wild of the Kihansi spray toad (Nectophrynoides asperginis)

2019 ◽  
Author(s):  
C. Weldon ◽  
A. Channing ◽  
G. Misinzo ◽  
A.A. Cunningham
Keyword(s):  
Captive Breeding ◽  
Batrachochytrium Dendrobatidis ◽  
Population Decline ◽  
Population Monitoring ◽  
Habitat Modification ◽  
Epidemic Disease ◽  
Amphibian Species ◽  
Extinction Event ◽  
In The Wild ◽  
Kihansi Spray Toad

AbstractThe Kihansi spray toad, Nectophrynoides asperginis, became extinct in the wild despite population monitoring and conservation management of its habitat in the Kihansi gorge, Tanzania. Anecdotal evidence has indicated human induced habitat modification, predators, pesticides and disease as possible causes of a rapid population decline and the species extirpation. Here, we systematically investigate the role of disease in the extinction event of the wild toad population. The amphibian chytrid fungus, Batrachochytrium dendrobatidis, was detected in spray toads that died during the extinction event and subsequently in other amphibian species in Kihansi Gorge and the adjacent Udagaji Gorge, but not in any toads collected prior to this. Following the population decline, the remnant spray toad population gradually disappeared over a nine-month period. We demonstrate how demographic and behavioral attributes predisposed the spray toads to chytridiomycosis, due to B. dendrobatidis infection, and how epidemic disease could have been exacerbated by altered environmental conditions in the spray wetlands. Our results show that chytridiomycosis was the proximate cause of extinction in the wild of N. asperginis. This represents the first known case of extinction by disease of an amphibian species in Africa. A captive breeding program in the US and Tanzania ensures the survival of the species and a reintroduction program is underway. However, we caution that chytridiomycosis remains an existing threat that requires a comprehensive mitigation strategy before the desired conservation outcome of an established population of repatriated toads can be achieved.

The effect of the acanthocephalan Pomphorhynchus laevis upon the respiration of its intermediate host, Gammarus pulex

Parasitology ◽  
1974 ◽  
Vol 68 (2) ◽  
pp. 271-284 ◽  
Author(s):  
A. E. Rumpus ◽  
C. R. Kennedy
Keyword(s):  
Oxygen Consumption ◽  
Oxygen Uptake ◽  
Host Population ◽  
Gammarus Pulex ◽  
Multiple Infections ◽  
Pomphorhynchus Laevis ◽  
Respiration Rates ◽  
Physiological Processes ◽  
Stage Of Development ◽  
Host Parasite

The respiration rates of individual Gammarus pulex infected by larval Pomphorhynchus laevis were investigated with particular reference to the stage of development of the host and parasite and to the water temperature. At 20°C the oxygen consumption of Gammarus of all sizes was reduced by an average of 19·3 % by the presence of cystacanths of the parasite, but was unaffected by the presence of acanthellae. It is considered that the small size of this larval stage, in relation to that of its host, is responsible for the failure to detect an effect. Multiple infections did not exert any greater effect upon host respiration than single cystacanths, nor did it appear that the parasite had different effects upon hosts of different sexes. At 10°C no significant differences were observed between the respiration rates of infected and uninfected gammarids. The parasite was probably still depressing the host respiration rate at this temperature, but the oxygen uptake of G. pulex is so low that the differences between infected and uninfected individuals were too small to be detected. The parasite has a direct effect upon the physiological processes of the host, but neither the mechanism of this nor the reasons for the different effects found in different host-parasite systems are yet understood. Despite the pronounced effect of P. laevis on respiration of individual hosts, its effect upon the oxygen consumption of a natural host population is small since only a small proportion of the population carries infections and water temperatures remain below 10°C for over half the year.

Population variation in the metabolic response of deer mice to infection with Capillaria hepatica (Nematoda)

2001 ◽  
Vol 79 (4) ◽  
pp. 554-561 ◽  
Author(s):  
Shawn Meagher ◽  
Timothy P O'Connor
Keyword(s):  
Cold Stress ◽  
Metabolic Response ◽  
Host Population ◽  
Population Variation ◽  
Deer Mice ◽  
Negative Consequences ◽  
Capillaria Hepatica ◽  
Generation Times ◽  
Stress Maximum ◽  
Host Parasite

The effects of parasites on their hosts can vary among host populations, but few studies have examined geographic variation in host-parasite interactions. We examined the effects of Capillaria hepatica (Nematoda) infection on deer mice (Peromyscus maniculatus gracilis) from two different populations. Specifically, we measured the basal metabolic rate (BMR), cold-stress maximum oxygen consumption (MRpeak), metabolic scope (MRpeak/BMR), and thermogenic endurance of infected and uninfected mice from one population with, and a second population without, a history with C. hepatica. Infection had no effect on BMR, but did have effects on cold-stress measures. A previous study documented a significant relationship between survival and MRpeak in wild deer mice; hence, the effects of infection on the parameters that we measured could influence fitness. Only mice that had no historical association with C. hepatica displayed negative consequences of infection, which suggests that the historical host population has evolved mechanisms to cope with infection. Models of the evolution of virulence should include evolutionary responses of both hosts and parasites, particularly when systems involve macroparasites that have long generation times.

scholarly journals Modelling the amphibian chytrid fungus spread by connectivity analysis: towards a national monitoring network in Italy

2021 ◽  
Author(s):  
Andrea Costa ◽  
Lorenzo Dondero ◽  
Giorgia Allaria ◽  
Bryan Nelson Morales Sanchez ◽  
Giacomo Rosa ◽  
...  
Keyword(s):  
Batrachochytrium Dendrobatidis ◽  
National Level ◽  
Monitoring Network ◽  
Electric Circuit ◽  
Population Declines ◽  
Climate Data ◽  
Landscape Permeability ◽  
National Monitoring ◽  
Climatic Scenarios ◽  
Amphibian Chytrid Fungus

AbstractThe emerging amphibian disease, Batrachochytrium dendrobatidis (Bd), is driving population declines worldwide and even species extinctions in Australia, South and Central America. In order to mitigate effects of Bd on amphibian populations, high-exposed areas should be identified at the local scale and effective conservation measures should be planned at the national level. This assessment is actually lacking in the Mediterranean basin, and in particular in Italy, one of the most relevant amphibian diversity hotspots in the entire region. In this study, we reviewed the available information on Bd in Italy, and conducted a 5-year molecular screening on 1274 individual skin swabs belonging to 18 species. Overall, we found presence of Bd in 13 species and in a total of 56 known occurrence locations for peninsular Italy and Sardinia. We used these occurrence locations and climate data to model habitat suitability of Bd for current and future climatic scenarios. We then employed electric circuit theory to model landscape permeability to the diffusion of Bd, using a resistance map. With this procedure, we were able to model, for the first time, the diffusion pathways of Bd at the landscape scale, characterising the main future pathways towards areas with a high probability of Bd occurrence. Thus, we identified six national protected areas that will become pivotal for a nationally-based strategic plan in order to monitor, mitigate and possibly contrast Bd diffusion in Italy.

scholarly journals Prevalence of Gastrointestinal Parasitic Infections and Assessment of Deworming Program among Cattle and Buffaloes in Gampaha District, Sri Lanka

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Nayana Gunathilaka ◽  
Dimuthu Niroshana ◽  
Deepika Amarasinghe ◽  
Lahiru Udayanga
Keyword(s):  
Parasitic Infection ◽  
Parasite Prevalence ◽  
Parasitic Infections ◽  
Infection Prevalence ◽  
Digenetic Trematodes ◽  
Linear Modelling ◽  
Cattle Management ◽  
Veterinary Surgeon ◽  
Effect Of Treatment ◽  
The Difference

Gastrointestinal (GI) parasitic infection is a serious issue in cattle management. The effects of GI parasites may vary with age, sex of cattle, nutritional condition, and severity of infection. Prevalence of GI parasites among cattle population in Gampaha District has not been studied and there is no published study available. A total of 45 farms rearing cattle were selected randomly in three areas, namely, Kelaniya, Ganemulla, and Welisara, under three Veterinary Surgeon Divisions (VSD) in Gampaha District (Mahara, Gampaha, and Welisara). Freshly voided cattle fecal samples were collected randomly from the selected farms during March 2017–December 2017. Out of 163 cattle and buffaloes examined, 13.39% (n=22) were positive for eggs of one or more species of GI parasites. The prevalence of parasitic infection was higher in buffaloes (31.25%, 5/16) as compared to that of cows (11.56%, 21/147), but the difference was not significant (P >0.05). Hookworms (Bunostomum spp.), whipworms (Trichuris spp.), digenetic trematodes (Paramphistomum spp.), cestodes (Moniezia spp.), and oocysts of protozoans (coccidians) were found during the study. The nontreated animals indicated the highest percentage of parasitic infections accounting for 46.67% (n= 14), followed by partially treated individuals (15.15%, n= 5). GI parasite prevalence in males was higher when compared to that of females, but the difference was nonsignificant (P >0.05). General Linear Modelling (GLM) revealed that the effect of treatment status was significantly associated with the prevalence of GI parasites. The calves and yearlings had the highest rate of GI parasitic infections. The highest infection rate was observed at Kelaniya, followed by Welisara. Future investigations are necessary to evaluate the economic impact of GI parasites in the study areas.

scholarly journals Proteomic Analysis of Leishmania donovani Membrane Components Reveals the Role of Activated Protein C Kinase in Host-Parasite Interaction

Pathogens ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 1194
Author(s):  
Sandeep Verma ◽  
Deepak Kumar Deep ◽  
Poonam Gautam ◽  
Ruchi Singh ◽  
Poonam Salotra
Keyword(s):  
Membrane Proteins ◽  
Protein C ◽  
Leishmania Donovani ◽  
Parasitic Infection ◽  
Activated Protein C ◽  
Host Cells ◽  
Filamin A ◽  
Related Factors ◽  
Interacting Protein ◽  
Host Parasite

Visceral leishmaniasis (VL), mainly caused by the Leishmania donovani parasitic infection, constitutes a potentially fatal disease, for which treatment is primarily dependent on chemotherapy. The emergence of a resistant parasite towards current antileishmanial agents and increasing reports of relapses are the major concerns. Detailed research on the molecular interaction at the host-parasite interface may provide the identification of the parasite and the host-related factors operating during disease development. Genomic and proteomic studies highlighted several essential secretory and cytosolic proteins that play vital roles during Leishmania pathogenesis. The aim of this study was to identify membrane proteins from the Leishmania donovani parasite and the host macrophage that interact with each other using 2-DE/MALDI-TOF/MS. We identified membrane proteins including activated protein C kinase, peroxidoxin, small myristoylated protein 1 (SMP-1), and cytochrome C oxidase from the parasite, while identifying filamin A interacting protein 1(FILIP1) and β-actin from macrophages. We further investigated parasite replication and persistence within macrophages following the macrophage-amastigote model in the presence or absence of withaferin (WA), an inhibitor of activated C kinase. WA significantly reduced Leishmania donovani replication within host macrophages. This study sheds light on the important interacting proteins for parasite proliferation and virulence, and the establishment of infection within host cells, which can be targeted further to develop a strategy for chemotherapeutic intervention.

Conservation biology of marine fishes: perceptions and caveats regarding assignment of extinction risk

2001 ◽  
Vol 58 (1) ◽  
pp. 108-121 ◽  
Author(s):  
Jeffrey A Hutchings
Keyword(s):  
Population Size ◽  
Extinction Risk ◽  
Population Decline ◽  
Empirical Support ◽  
Marine Fishes ◽  
Marine Biodiversity ◽  
Population Declines ◽  
High Fecundity ◽  
Reproductive Rates ◽  
Biological Extinction

Quantitative criteria used to assign species to categories of extinction risk may seriously overestimate these risks for marine fishes. Contemporary perception is that marine fishes may be less vulnerable to extinction than other taxa, because of great natural variability in abundance, high fecundity, rapid population growth, and an intrinsically high capability of recovering from low population size. Contrary to perception, however, there appears to be generally little theoretical or empirical support for the hypotheses that marine fish are more likely to experience large reductions in population size, to produce unusually high levels of recruitment, to have higher reproductive rates, or to recover more rapidly from prolonged population declines than nonmarine fishes. Although existing population-decline criteria may not accurately reflect probabilities of biological extinction, they do appear to reflect the converse-population recovery. Insufficient support for contemporary perceptions of their susceptibility to extinction, coupled with caveats associated with the assignment of extinction risk, suggest that significant increases in the population-decline thresholds used to assign marine fishes to at-risk categories would be inconsistent with a precautionary approach to fisheries management and the conservation of marine biodiversity.

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