Distinguishing epidemic waves from disease spillover in a wildlife population

Serengeti lions frequently experience viral outbreaks. In 1994, one-third of Serengeti lions died from canine distemper virus (CDV). Based on the limited epidemiological data available from this period, it has been unclear whether the 1994 outbreak was propagated by lion-to-lion transmission alone or involved multiple introductions from other sympatric carnivore species. More broadly, we do not know whether contacts between lions allow any pathogen with a relatively short infectious period to percolate through the population (i.e. reach epidemic proportions). We built one of the most realistic contact network models for a wildlife population to date, based on detailed behavioural and movement data from a long-term lion study population. The model allowed us to identify previously unrecognized biases in the sparse data from the 1994 outbreak and develop methods for judiciously inferring disease dynamics from typical wildlife samples. Our analysis of the model in light of the 1994 outbreak data strongly suggest that, although lions are sufficiently well connected to sustain epidemics of CDV-like diseases, the 1994 epidemic was fuelled by multiple spillovers from other carnivore species, such as jackals and hyenas.     

Endemic infection can shape exposure to novel pathogens: Pathogen co‐occurrence networks in the Serengeti lions

Pathogens are embedded in a complex network of microparasites that can collectively or individually alter disease dynamics and outcomes. Endemic pathogens that infect an individual in the first years of life, for example, can either facilitate or compete with subsequent pathogens thereby exacerbating or ameliorating morbidity and mortality. Pathogen associations are ubiquitous but poorly understood, particularly in wild populations. We report here on 10 years of serological and molecular data in African lions, leveraging comprehensive demographic and behavioural data to test if endemic pathogens shape subsequent infection by epidemic pathogens. We combine network and community ecology approaches to assess broad network structure and characterise associations between pathogens across spatial and temporal scales. We found significant non‐random structure in the lion‐pathogen co‐occurrence network and identified both positive and negative associations between endemic and epidemic pathogens. Our results provide novel insights on the complex associations underlying pathogen co‐occurrence networks.     

Dynamics of a multihost pathogen in a carnivore community

1. We provide the first theoretical analysis of multihost disease dynamics to incorporate social behaviour and contrasting rates of within- and between-group disease transmission. 2. A stochastic susceptible-infected-recovered (SIR) model of disease transmission involving one to three sympatric species was built to mimic the 1994 Serengeti canine distemper virus outbreak, which infected a variety of carnivores with widely ranging social structures. The model successfully mimicked the erratic and discontinuous spatial pattern of lion deaths observed in the Serengeti lions under a reasonable range of parameter values, but only when one to two other species repeatedly transmitted the virus to the lion population. 3. The outputs from our model suggest several principles that will apply to most directly transmitted multihost pathogens: (i) differences in social structure can significantly influence the size, velocity and spatial pattern of a multihost epidemic; and (ii) social structures that permit higher intraspecific neighbour-to-neighbour transmission are the most likely to transmit disease to other species; whereas (iii) species with low neighbour-to-neighbour intraspecific transmission suffer the greatest costs from interspecific transmission.     

A possible new piroplasm in lions from the Republic of South Africa

A small piroplasm was detected in blood smears from lions (Panthera leo) in the Kruger National Park (KNP; Republic of South Africa) during 1991/1992. The parasite was identified provisionally as Babesia felis, but sera from these lions tested negative to B. felis antigen in the indirect immunofluorescent antibody test (IFAT). Blood from an infected lion was subsequently subinoculated into a domestic cat and two leopards in an attempt to identify the parasite. A lion also was infected with B. felis (from a cat). Serum samples collected from these animals were tested against B. felis, the KNP small piroplasm, and Cytauxzoon felis antigen in the IFAT. The serological results indicate that the KNP small piroplasm isolated from the lion is probably a distinct species from B. felis and C. felis.     

Anthropogenic causes of the western Steller sea lion Eumetopias jubatus population decline and their threat to recovery

• 1 The western Steller sea lion Eumetopias jubatus population has experienced a chronic decline since the 1960s. The causes are likely multifactorial and a combination of anthropogenic and natural factors. A draft revised recovery plan for the Steller sea lion has been published by the US National Marine Fisheries Service, listing both anthropogenic and natural factors that may have contributed to the observed decline or which may be a threat to the recovery of the western Steller sea lion population. The purpose of this review is to consider the anthropogenic threats to this stock.
• 2 Anthropogenic sources of mortality include fisheries competition resulting in nutritional stress, mortality incidental to commercial fisheries (i.e. fisheries by‐catch), subsistence hunts, legal and illegal shooting, commercial hunts, anthropogenic‐related contamination, and research‐induced mortalities.
• 3 We present evidence that the following anthropogenic factors likely contributed to the decline of the western Steller sea lion population over the last 40 years: (i) mortality incidental to commercial fisheries (i.e. by‐catch); (ii) commercial hunting of western Steller sea lions; and (iii) legal and illegal shooting; whereas the subsistence hunts for western Steller sea lions and mortality incidental to research were not likely to be contributors to the observed decline.
• 4 Further, we present evidence that the following can be excluded as significant anthropogenic threats to the recovery of the western Steller sea lion population: (i) mortality incidental to commercial fishing; (ii) legal and illegal shooting; (iii) commercial hunts of Steller sea lions; (iv) subsistence hunting; and (v) mortality incidental to research.
• 5 Competition with fisheries resulting in nutritional stress, and the potential impacts of contaminants, are two anthropogenic factors that should continue to be a priority for the various organizations currently doing research on this population.

     

Seasonal Diet and Prey Preference of the African Lion in a Waterhole-Driven Semi-Arid Savanna

Large carnivores inhabiting ecosystems with heterogeneously distributed environmental resources with strong seasonal variations frequently employ opportunistic foraging strategies, often typified by seasonal switches in diet. In semi-arid ecosystems, herbivore distribution is generally more homogeneous in the wet season, when surface water is abundant, than in the dry season when only permanent sources remain. Here, we investigate the seasonal contribution of the different herbivore species, prey preference and distribution of kills (i.e. feeding locations) of African lions in Hwange National Park, Zimbabwe, a semi-arid African savanna structured by artificial waterholes. We used data from 245 kills and 74 faecal samples. Buffalo consistently emerged as the most frequently utilised prey in all seasons by both male (56%) and female (33%) lions, contributing the most to lion dietary biomass. Jacobs’ index also revealed that buffalo was the most intensively selected species throughout the year. For female lions, kudu and to a lesser extent the group “medium Bovidae” are the most important secondary prey. This study revealed seasonal patterns in secondary prey consumption by female lions partly based on prey ecology with browsers, such as giraffe and kudu, mainly consumed in the early dry season, and grazers, such as zebra and suids, contributing more to female diet in the late dry season. Further, it revealed the opportunistic hunting behaviour of lions for prey as diverse as elephants and mice, with elephants taken mostly as juveniles at the end of the dry season during droughts. Jacobs’ index finally revealed a very strong preference for kills within 2 km from a waterhole for all prey species, except small antelopes, in all seasons. This suggested that surface-water resources form passive traps and contribute to the structuring of lion foraging behaviour.     

SEASONAL DISTRIBUTION OF STELLER'S SEA LIONS AT ROOKERIES AND HAUL-OUT SITES IN ALASKA

The Steller's sea lion population has declined by 60%-70% over much of Alaska since the late 1970s. Overlap in species composition and sizes of fishes consumed by sea lions and harvested by commercial fisheries, particularly during winter, has led to examination of potential interaction between commercial fisheries and Steller's sea lions. Abundance and distribution data for Steller's sea lions in Alaska were derived from aerial surveys conducted during the breeding season, mid-June to early July 1992, 1994, and 1996. To study winter distribution of sea lions, we conducted aerial surveys during March 1993, November-December 1994, and March 1999. We counted about one-half as many sea lions during winter surveys compared to the breeding-season surveys. Numbers of sea lions at rookery sites dropped off considerably during winter, whereas numbers at haul-out sites did not. We found little evidence of large-scale, seasonal movement, at least for the western stock of sea lions. Rather, differences between summer and winter distribution were primarily a function of sea lions dispersing to local haul-out sites during the winter. Terrestrial sites, both rookeries and haul-outs, clearly are important to Steller's sea lions during the entire year. Individual sites may be occupied year-round or only during particular times of year.     

A genetically distinct lion (Panthera leo) population from Ethiopia

Lion (Panthera leo) numbers are in serious decline and two of only a handful of evolutionary significant units have already become extinct in the wild. However, there is continued debate about the genetic distinctiveness of different lion populations, a discussion delaying the initiation of conservation actions for endangered populations. Some lions from Ethiopia are phenotypically distinct from other extant lions in that the males possess an extensive dark mane. In this study, we investigated the microsatellite variation over ten loci in 15 lions from Addis Ababa Zoo in Ethiopia. A comparison with six wild lion populations identifies the Addis Ababa lions as being not only phenotypically but also genetically distinct from other lions. In addition, a comparison of the mitochondrial cytochrome b (CytB) gene sequence of these lions to sequences of wild lions of different origins supports the notion of their genetic uniqueness. Our examination of the genetic diversity of this captive lion population shows little effect of inbreeding. Immediate conservation actions, including a captive breeding programme designed to conserve genetic diversity and maintain the lineage, are urgently needed to preserve this unique lion population.     

Neonatal mortality in New Zealand sea lions (Phocarctos hookeri) at Sandy Bay, Enderby Island, Auckland Islands from 1998 to 2005

As part of a health survey of New Zealand sea lions (Phocarctos hookeri) on Enderby Island, Auckland Islands (50 degrees 30'S, 166 degrees 17'E), neonatal mortality was closely monitored at the Sandy Bay colony for seven consecutive years. Throughout the breeding seasons 1998-99 to 2004-05, more than 400 postmortem examinations were performed on pups found dead at this site. The primary causes of death were categorized as trauma (35%), bacterial infections (24%), hookworm infection (13%), starvation (13%), and stillbirth (4%). For most pups, more than one diagnosis was recorded. Every year, two distinct peaks of trauma were observed: the first associated with mature bulls fighting within the harem and the second with subadult males abducting pups. In 2001-02 and 2002-03, epidemics caused by Klebsiella pneumoniae increased mortality by three times the mean in nonepidemic years (10.2%). The increased mortality was attributed directly to acute suppurative infection due to the bacterium and also to an increase in traumatic deaths of debilitated pups. Parasitic infection with the hookworm Uncinaria spp. was a common finding in all pups older than three weeks of age and debilitation by the parasite may have contributed to increased susceptibility to other pathogens such as Klebsiella sp. or Salmonella sp. This study provides valuable quantitative data on the natural causes of neonatal mortality in New Zealand sea lions that can be used in demographic models for management of threatened species.     

Pseudo‐nitzschia blooms,domoic acid,and related California sea lion strandings in Monterey Bay,California

Blooms of the toxin‐producing diatom Pseudo‐nitzschia commonly occur in Monterey Bay, California, resulting in sea lion mortality events. The links between strandings of California sea lions suffering from domoic acid (DA) toxicity, toxic cell numbers, and their associated DA concentration in Monterey Bay and in sea lion feces were examined from 2004 to 2007. While Pseudo‐nitzschia toxic cells and DA concentrations were detectable in the water column most of the time, they were often at low levels. A total of 82 California sea lions were found stranded in the Bay between 2004 and 2007 with acute or chronic signs associated with DA poisoning. The highest number with detectable DA in feces occurred in April 2007 and corresponded with the presence of a highly toxic bloom in the Bay. Higher DA levels occurred in feces from sea lions stranding with acute toxicosis and lower concentrations in feces of sea lions exhibiting signs of chronic DA poisoning or not exhibiting any neurologic signs. Results indicated that sea lions are likely exposed to varying levels of DA through their prey throughout the year, often at sublethal doses that may contribute to a continued increase in the development of chronic neurologic sequelae.     

OBSERVATIONS ON LIONS IN THE LAKE MANYARA NATIONAL PARK,TANZANIA

The lions of Lake Manyara National Park were observed for 1 1/4 years. About 0.4 lions/km² inhabited the park, a density nearly double that found in Nairobi National Park and Ngorongoro Crater. One group of lions occupied the southern half of the park; in the northern half, the range of two males included two distinct groups of lionesses each of which confined itself to its own area. The composition and changes in composition of each group are discussed. Buffalo were observed to kill a lion cub on three occasions, and elephant were seen to do so once. The lions' most important prey was buffalo, which comprised 62% of the kills, followed by zebra (18%) and impala (12%). Eighty-one per cent. of the buffalo killed were males. Lions were seen in trees on 2/3 of the occasions on which they were encountered. Possible reasons for tree-climbing are given.     

Critical thresholds in sea lice epidemics: evidence, sensitivity and subcritical estimation

Host density thresholds are a fundamental component of the population dynamics of pathogens, but empirical evidence and estimates are lacking. We studied host density thresholds in the dynamics of ectoparasitic sea lice (Lepeophtheirus salmonis) on salmon farms. Empirical examples include a 1994 epidemic in Atlantic Canada and a 2001 epidemic in Pacific Canada. A mathematical model suggests dynamics of lice are governed by a stable endemic equilibrium until the critical host density threshold drops owing to environmental change, or is exceeded by stocking, causing epidemics that require rapid harvest or treatment. Sensitivity analysis of the critical threshold suggests variation in dependence on biotic parameters and high sensitivity to temperature and salinity. We provide a method for estimating the critical threshold from parasite abundances at subcritical host densities and estimate the critical threshold and transmission coefficient for the two epidemics. Host density thresholds may be a fundamental component of disease dynamics in coastal seas where salmon farming occurs.     

Identification of Theileria buffeli/orientalis and Babesia bigemina in Apulian cattle using molecular techniques and study of changes in blood parameters

Recently several cases of theileriosis due to the haemoprotozoan Theileria buffeli/orientalis have been recorded in the Apulian region, Italy. In this area other tick-borne pathogens were usually identified such as Anaplasma marginale and Babesia bigemina. Outbreaks were recorded showing that these pathogens can be observed separately or in mixed infections. Sub-clinical cases and carrier animals were also previously identified. A lack of specific techniques could not rule out the presence of other haemoparasites such as T. annulata, B. divergens, B. bovis, Ehrlichia phagocytophila and E. bovis. Moreover little is known about the tick species involved in the dissemination of these diseases. Therefore more powerful techniques to specifically identify Theileria or Babesia species have been recently developed. A PCR technique and reverse line blotting (RLB) system to specifically identify six Theileria species and three Babesia species were used. T. buffeli/orientalis and B. bigemina were the only pathogens observed in the targeted animals. The authors also present some changes in blood parameters for the animals followed during this study.     

Babesia spp. identified by PCR in ticks collected from domestic and wild ruminants in southern Switzerland

Concurrent infections with vector-borne pathogens affected a cattle herd in Switzerland, and one of the pathogens was identified as Babesia bigemina, which had never been observed in this country before. Therefore, a survey of the occurrence of ruminant Babesia spp. and their tick vectors in Switzerland was conducted. A total of 2,017 ticks were collected from sheep, goats, cattle, and wild ruminants (deer, roe deer, and chamois) in southern parts of Switzerland and identified morphologically. The vast majority of the ticks (99.2%) were Ixodes ricinus, but 14 ticks from sheep and goats were identified as Dermacentor marginatus and two ticks from wild ruminants were identified as Hemaphysalis punctata. PCR analyses of 700 ticks revealed the presence of Babesia divergens (n = 6), Babesia sp. genotype EU1 (n = 14), and B. major (n = 2), whose suggested occurrence was confirmed in this study by molecular analysis, and the presence of novel Babesia sp. genotype CH1 (n = 4), which is closely related to B. odocoilei and to Babesia sp. genotype RD61 reported from North America. The identification of B. divergens and B. major in ticks collected from wild ruminants cast doubt on the postulated strict host specificity of these bovine Babesia species. Furthermore, the zoonotic Babesia sp. genotype EU1 was detected in ticks collected from domestic animals but was obtained predominantly from ticks collected from wild ruminants. More than one tick containing DNA of different Babesia spp. were collected from two red deer. Hence, the role of these game animals as reservoir hosts of Babesia spp. seems to be important but requires further investigation.     

Effects of wolf pack size and winter conditions on elk mortality

Elk (Cervus canadensis) are high-profile game animals for many states in the western United States, yet over the past several decades some populations have experienced a persistent and broad-scale decline in recruitment. Over this same period, gray wolves (Canis lupus) have become an integral component of many western landscapes and agencies are increasingly challenged to maximize hunting opportunities of ungulates via predator management while simultaneously ensuring wolf conservation. To better understand the implications of predator management on elk populations, we monitored survival of 1,244 adult female elk and 806 6-month-old calves from 29 populations distributed throughout Idaho, USA, from 2004 to 2016. We developed predictive models of mortality that related mortality risk to wolf pack size, winter conditions, and individual-level characteristics. Annual mortality rates (excluding harvest) for adult females and calves were 0.09 and 0.40, respectively. Calf mortality was predicted best with a model that included additive effects of chest girth at time of capture, mean size of surrounding wolf packs, and snow depth. Adult female mortality was predicted best with a model that included female age, mean size of surrounding wolf packs, and snow depth. Based on a sensitivity analysis, chest girth had the largest effect on risk of mortality for calves followed by pack size and snow depth. Other than the effect of senescence in the oldest (>15 yr) individuals, pack size and snow depth had the largest effect on risk of mortality for adult females. We estimated cause-specific mortality and predation was the dominant cause of known-fate mortalities for adult females (35% mountain lion [Puma concolor] and 32% wolf) and calves (45% mountain lion and 28% wolf), whereas malnutrition accounted for 9% and 10% of adult female and calf mortalities, respectively. Wolves preferentially selected smaller calves and older adult females, whereas mountain lions showed little preference for calf size or age class of adult females. Our study indicates managers can increase elk survival by reducing wolf pack sizes on surrounding winter ranges, especially in areas where, or during years when, snow is deep. Additionally, managers interested in improving over-winter calf survival can implement actions to increase the size of calves entering winter by increasing the nutritional quality of summer and early fall forage resources. Although our study was prompted by management questions related to wolves, mountain lions killed more elk than wolves and differences in selection of individual elk indicate mountain lions may have comparably more of an effect on elk population dynamics. Although we were unable to relate changes in mountain lion populations to elk survival in our study, future research should seek a better understanding of multi-predator systems, including how management of one predator affect others and ultimately how these interactions affect elk survival. © 2019 The Wildlife Society     

Desert bighorn sheep habitat selection,group size,and mountain lion predation risk

Bighorn sheep (Ovis canadensis) evolved for thousands of years in the presence of numerous predators, including mountain lions (Puma concolor). Bighorn sheep have presumably developed predator avoidance strategies; however, the effectiveness of these strategies in reducing risk of mountain lion predation is not well understood. These strategies are of increasing interest because mountain lion predation on bighorn sheep has been identified as a leading cause of mortality in some sheep populations. Therefore, we investigated how mountain lions affect both bighorn sheep habitat selection and risk of mortality in Arizona, USA. We used 2 approaches to investigate the predator-prey relationship between mountain lions and bighorn sheep. We fit 103 bighorn sheep (81 females and 22 males) with global positioning system radio-collars in 2 Arizona populations from 2013 to 2017, and used a negative binomial resource selection probability function to evaluate whether bighorn sheep selected for habitat features in accordance with presumed predator avoidance strategies, including terrain ruggedness, slope, topographic position, and horizontal obstruction, in 2 seasons (winter and summer). We then estimated how habitat features such as terrain ruggedness, slope, horizontal obstruction, and group size, influence the risk of mortality due to mountain lion predation using an Andersen-Gill proportional hazards model. Generally, both sexes selected areas with lower horizontal obstruction and intermediate ruggedness and slope, but selection patterns differed between seasons and sexes. The use of more rugged areas and steeper slopes decreased the risk of mortality due to mountain lion predation, consistent with presumed predator avoidance strategies. Increased group size decreased risk of bighorn sheep mortality due to mountain lion predation but this effect became marginal at approximately 10 individuals/group. We did not identify a relationship between horizontal obstruction and bighorn sheep mortality risk. Our findings can be used in habitat and population management decisions such as the prioritization of habitat restoration sites or selection of translocation sites. In addition, we suggest that augmentation of low-density bighorn sheep populations may reduce mountain lion predation risk by increasing group size, and that releasing large groups of bighorn sheep in population augmentation and reintroduction efforts may help to reduce mountain lion predation.     

STELLER SEA LION STATUS AND TREND IN SOUTHEAST ALASKA: 1979–1997

Steller sea lion (Eumetopias jubatus) numbers in the United States declined by about 75% over the past 20+ yr. They are classified, under the U. S. Endangered Species Act, as “threatened” in the eastern portion of their range and as “endangered” in the western portion. We analyzed trends in numbers of pup and non-pup Steller sea lions counted in Southeast Alaska between 1979 and 1997. Sea lion numbers, based on counts of pups on rookeries, increased by an average of 5.9% per year between 1979 and 1997. However, numbers of pups increased at a much slower rate (+ 1.7% per year) between 1989 and 1997. For counts of non-pup Steller sea lions we used models that controlled for the effects of date, time, and tide at the time of the survey to analyze trends. This technique reduced bias and increased precision of the resulting trend estimates. Numbers of sea lions were stable (+0.5%) between 1989 and 1996, based on counts of non-pups. We estimated the Southeast Alaska breeding population of Steller sea lions at about 19,000 animals of all ages in 1997, a level that is probably near the highest in recorded history.     

Accelerated phenology of blacklegged ticks under climate warming

The phenology of tick emergence has important implications for the transmission of tick-borne pathogens. A long lag between the emergence of tick nymphs in spring and larvae in summer should increase transmission of persistent pathogens by allowing infected nymphs to inoculate the population of naive hosts that can subsequently transmit the pathogen to larvae to complete the transmission cycle. In contrast, greater synchrony between nymphs and larvae should facilitate transmission of pathogens that do not produce long-lasting infections in hosts. Here, we use 19 years of data on blacklegged ticks attached to small-mammal hosts to quantify the relationship between climate warming and tick phenology. Warmer years through May and August were associated with a nearly three-week advance in the phenology of nymphal and larval ticks relative to colder years, with little evidence of increased synchrony. Warmer Octobers were associated with fewer larvae feeding concurrently with nymphs during the following spring. Projected warming by the 2050s is expected to advance the timing of average nymph and larva activity by 8–11 and 10–14 days, respectively. If these trends continue, climate warming should maintain or increase transmission of persistent pathogens, while it might inhibit pathogens that do not produce long-lasting infections.     

Projected effects of climate change on tick phenology and fitness of pathogens transmitted by the North American tick Ixodes scapularis

Ixodes scapularis is the principal tick vector of the Lyme borreliosis agent Borrelia burgdorferi and other tick-borne zoonoses in northeastern North America. The degree of seasonal synchrony of nymphal and larval ticks may be important in influencing the basic reproductive number of the pathogens transmitted by I. scapularis. Because the seasonal phenology of tick vectors is partly controlled by ambient temperature, climate and climate change could shape the population biology of tick-borne pathogens. We used projected monthly normal temperatures, obtained from the second version of the Canadian Coupled Global Climate Model (CGCM2) under emissions scenario A2 of the Intergovernmental Panel on Climate Change for a site in southern Ontario, Canada, to simulate the phenology of I. scapularis in a mathematical model. The simulated seasonal abundance of ticks then determined transmission of three candidate pathogens amongst a population of white-footed mice (Peromyscus leucopus) using a susceptible-infected-recovered (SIR) model. Fitness of the different pathogens, in terms of resilience to changes in tick and rodent mortality, minima for infection duration, transmission efficiency and particularly any additional mortality of rodents specifically associated with infection, varied according to the seasonal pattern of immature tick activity, which was different under the temperature conditions projected for the 2020s, 2050s and 2080s. In each case, pathogens that were long-lived, highly transmissible and had little impact on rodent mortality rates were the fittest. However, under the seasonal tick activity patterns projected for the 2020s and 2050s, the fitness of pathogens that are shorter-lived, less efficiently transmitted, and more pathogenic to their natural hosts, increased. Therefore, climate change may affect the frequency and distribution of I. scapularis-borne pathogens and alter their evolutionary trajectories.     

Protistan parasites as mortality drivers in cold water crab fisheries

From a historical perspective, several protistan taxa, including the recently re-aligned Microsporidia, have been associated with or identified as causes of mortalities in crustacean populations. Depending upon the host species, associated protistan prevalences could be as low as 5% or approach 100%. It has generally been assumed that reported prevalences translated directly into significant mortalities that could impact the distribution and abundance of affected populations. However, this assumption may be incorrect especially when the dynamics of host-pathogen-environment interactions are not entirely understood. We will discuss the presumed impact of several protistan pathogens on temperate and cold water commercial crab species. By using selected examples such as a ciliate in the Dungeness crab (Cancer magister) and Hematodinium sp. infections in North Pacific crabs, we will attempt to contrast differences between prevalence and mortality, acute and chronic infections/mortalities, age or size selectivity of affected population, and geographically restricted and widespread epizootics. We will also briefly discuss the potential impact of environmental changes such as climate change and ocean acidification on both host and protistan pathogen.