Influenza Virus—Host Co-evolution. A Predator-Prey Relationship?

Influenza virus continues to cause yearly seasonal epidemics worldwide and periodically pandemics. Although influenza virus infection and its epidemiology have been extensively studied, a new pandemic is likely. One of the reasons influenza virus causes epidemics is its ability to constantly antigenically transform through genetic diversification. However, host immune defense mechanisms also have the potential to evolve during short or longer periods of evolutionary time. In this mini-review, we describe the evolutionary procedures related with influenza viruses and their hosts, under the prism of a predator-prey relationship

On the Stability Property of the Infection-Free Equilibrium of a Viral Infection Model

The dynamics of a viral infection model with nonautonomous lytic immune response is studied from the perspective of dying out of the disease. With the help of the theory of exponential dichotomy of linear systems, we give a new proof about the global asymptotic stability of the infection-free equilibrium for the case R0=1. The result improves and complements one of the results of Wang et al. (2006)

Host-Parasite Interactions Within Food Webs

Parasitism is one of the most common life history strategies employed in nature, yet the effects of parasites are often thought to be minimal, and the vast majority of studies fail to consider parasites and their effects on host organisms. This is likely a problem, as the magnitude of parasite-mediated effects on their hosts can be quite large. Additionally, the effects of parasites are known to extend beyond the host to affect other species interactions. I used a series of approaches to gain a more integral understanding of host-parasite interactions by studying (1) the effects of parasites on biotic interactions that hosts engage in, (2) how biotic interactions such as predation and competition can affect host immune defense, and (3) how abiotic and biotic factors within the local environment affecting the host can further mediate parasitism dynamics. Specifically, in Chapter 1 I conducted a phylogenetically informed meta-analysis of the effects of parasites on species interactions (i.e., predation, competition, mutualism, and reproduction). I found that despite a strong overall negative effect on species interactions, the effects of parasites surprisingly ranged from being strongly beneficial to strongly deleterious on host species interactions. In Chapter 2 I used larval damselflies and their dominant fish predator to test how cascading effects of predators on host competitive interactions and resource acquisition affected a critical component of damselfly immune function, the phenoloxidase (PO) cascade. I found that neither direct density-mediated effects, indirect, trait-mediated effects, nor combined effects of predators via natural selection affected total PO activity. Instead, PO levels increased with resource availability, implying resource limitation. Finally, in Chapter 3 I used two field experiments and a detailed observational study to investigate how host, abiotic, and biotic factors within the local environment affected the relationships between damselfly (Enallagma spp.) hosts and their water mite (Arrenururs spp.) ectoparasites. I found that parasitism was species-specific and did not vary with host density or host condition (i.e., immune function). Instead, parasitism was largely predicted by abiotic factors (i.e., pH). Collectively, my results indicate that parasites are key players in the complex web of species interactions that compose food webs. Furthermore, host-parasite interactions are mediated by many of the same ecological factors as other species interactions, which has implications for parasitism dynamics within ecological communities. Future studies of food webs must incorporate parasites into their experimental and theoretical designs, and future studies of host-parasite interactions must expand beyond the focal relationship and consider the ecology of both the host and parasite

Inclusion Body Disease: pathogenesis, routes of transmission, husbandry procedures and diagnostic flow

openThe purpose of the assay is to compare distinct IBD causative agents considered etiological, underlying the possible correlations with the Reptarenaviruses; analyzing also the diverse clinical signs. A possible routes of transmission's review, will be, then connected with a short profile of the critical husbandry details that enhance the infection risks.The purpose of the assay is to compare distinct IBD causative agents considered etiological, underlying the possible correlations with the Reptarenaviruses; analyzing also the diverse clinical signs. A possible routes of transmission's review, will be, then connected with a short profile of the critical husbandry details that enhance the infection risks

Infectious Diseases in Yellowstone’s Canid Community

Each summer Yellowstone Wolf Project staff visit den sites to monitor the success of wolf reproduction and pup rearing behavior. For the purposes of wolf monitoring, Yellowstone National Park (YNP) is divided into two study areas, the northern range and the interior, each distinguished by their ecological and physiographical differences. The 1,000 square kilometer northern range, characterized by lower elevations (1,500–2,200 m), serves as prime winter habitat for ungulates and supports a higher density of wolves than the interior (20–99 wolves/1,000 km2 versus 2–11 wolves/1,000 km2). The interior of the park encompasses 7,991 square kilometers, is higher in elevation, receives higher annual snowfall, and generally supports lower densities of wolves and ungulates

The epidemiology of Rabies in domestic ruminants in Botswana

Rabies is a fatal viral disease of world-wide significance affecting warm blooded species, including humans, and is of major concern in Botswana. The objectives of the research reported in this thesis were to: determine the distribution of rabies in domestic ruminants in Botswana; identify risk factors associated with the disease in cattle; and assess the knowledge, attitudes and practices (KAP) of farmers in a high-risk area. Data on cases diagnosed by the Botswana National Veterinary Laboratory between 2000 and 2010 were analysed. An average of 35 cases per year was detected in ruminants during this study period. There was a strong positive correlation between the number of cases in ruminants and jackals (r = 0.78, p < 0.005), as well as in cattle and goats (r = 0.96, p < 0.0001). Cases of rabies (340) in ruminants were concentrated in the northern part of Botswana (88.7% of all cases). The North East District had the highest proportion of affected ruminants (0.029%) and 77.6% of these cases were in the peri-urban villages clustered around Francistown. Livestock from farms in peri-urban villages (OR 10.6; 95% CI 4.2, 26.9), free-roaming livestock (OR 3.1), dogs attacking livestock (OR 3.1) and the presence of herding dogs (OR 4.5) were all significantly associated with a history of rabies in ruminants in a multivariable logistic regression model. Farmers who could name at least one clinical sign of rabies in cattle were 5.7 times (95% CI 3.1, 10.5) more likely to have reported a case of rabies than those not knowing any clinical signs; however most farmers knew the clinical signs of rabies in dogs. This highlights the need for further education on the disease, including methods to recognise and control it in the farming community, as well as in the general public. It is concluded that management and husbandry factors, along with environmental factors associated with the presence of canids, results in the disease being a problem in Botswana. Implementation of appropriate education, along with regular vaccination programmes of all dogs, should help minimise the impact of the disease on the community in Botswana

The paradox of tolerance: parasite extinction due to the evolution of host defence.

Host defence against parasite infection can rely on two broad strategies: resistance and tolerance. The spread of resistance traits usually lowers parasite prevalence and decreases selection for higher defence. Conversely, tolerance mechanisms increase parasite prevalence and foster selection for more tolerance. Here we examine the potential for the host to drive parasites to extinction through the evolution of one or other defence mechanism. We analysed theoretical models of resistance and tolerance evolution in both the absence and the presence of a trade-off between defence and reproduction. In the absence of costs, resistance evolves towards maximisation and, consequently, parasite extinction. Tolerance also evolves towards maximisation but the positive feedback between tolerance and disease prevents the disappearance of the parasite. On the contrary, when defence comes with costs it is impossible for the host to eliminate the infection through resistance, because costly resistance is selected against when parasites are at low prevalence. We uncover that the only path to disease clearance in the presence of costs is through tolerance. Paradoxically, however, it is by lowering tolerance -and hence increasing disease-induced mortality- that extinction can occur. We also show that such extinction can occur even in the case of parasite counter-adaptation. Our results emphasise the importance of tolerance as a defence strategy, and identify key questions for future research

Temporal and Spatial Distribution of Cetacean Strandings Focusing On The Bottlenose Dolphin (Tursiops Truncatus) with a Synthesis of Potential Causes

A comprehensive review of the literature and a quantitative statistical analysis of that information are presented. A total of 6,015 cetaceans stranded at 36 locations from 24 peer reviewed articles published between 1999 and 2014 are documented, with the two most common stranding locations being the Canary Islands - accounting for 49 of the total cetacean stranding events - and Cape Cod - accounting for 31 of total cetacean stranding events. The documented cetacean stranding events included 805 for bottlenose dolphins (Tursiops truncatus) at a total of ten locations from 11 peer reviewed articles. When all single stranding events are eliminated and the collected data is analyzed, there are more documented stranding events of bottlenose dolphins than of any other cetacean species in the peer-reviewed literature. Using data collected from the Marine Mammal Stranding Network for the Southeast United States, a Chi-Square goodness of fit test is used to determine whether the number of bottlenose dolphin strandings is significantly different from the causes of strandings or causes of death categories. The analyses conclude that there is no significant difference among the categories of strandings or death. The general life history of the bottlenose dolphin is presented with special emphasis on its behavior and social structure, which are thought to affect stranding event frequencies. Various populations of bottlenose dolphins are also explored. The capstone concludes with a synopsis of speculated causes for stranding events and a synthesis discussion of stranding causes