Laboratory infection rates and associated mortality of juvenile Chinook Salmon (Oncorhynchus tshawytscha) from parasitic copepod (Salmincola californiensis).

Pacific salmon (Oncorhynchus spp.) rearing in lakes and reservoirs above dams have been known to become heavily infected with an ectoparasitic copepod (Salmincola californiensis). Little is known about the factors that affect the parasite infection prevalence and intensity. However, previous research suggests that the parasite may negatively affect the fitness and survival of the host fish. The effect of water temperature, confinement and the density of the free-swimming infectious stage of S. californiensis, the copepodid, on infection prevalence and intensity was evaluated by experimentally exposing juvenile Chinook Salmon (O. tshawytscha). Infection rates observed in wild populations were achieved under warm water (15-16°C) and high copepodid density (150-300/L) treatment conditions. Infection prevalence and intensity were also significantly higher in larger fish. During the infection experiment, 4.5% of infected fish died within 54 days with mortality significantly related to copepod infection intensity. The potential for autoinfection was compared to cross-infection by cohabitation of infected fish with naïve fish. Previously infected fish had significantly greater infection intensity compared with naïve fish, indicating that infected fish can be reinfected and that they may be more susceptible than naïve fish.

A participatory surveillance of marsh deer (Blastocerus dichotomus) morbidity and mortality in Argentina: first results.

BACKGROUND: In an era of unprecedented socio-ecological changes, managing wildlife health demands high-quality data collection and the engagement of local communities. Blastocerus dichotomus, the largest South American deer, is Vulnerable to extinction mainly due to habitat loss. Diseases have been recognised as a potential threat, and winter mortality has been historically described in marsh deer populations from Argentina. Field difficulties have, however, prevented in-depth studies of their health status. RESULTS: Between May 2014 and April 2017, we investigated marsh deer morbidity and mortality in the two largest populations in Argentina. We collected data by means of a passive surveillance system that involved a network of researchers, field partners (veterinarians, park rangers, and local community), and decision makers. We sampled marsh deer during as well as outside mortality events. A total of 44 marsh deer with different body condition scores were evaluated. We obtained haematology and biochemistry values from animals with good body condition score. Marsh deer with poor body condition had a high burden of the ticks Amblyomma triste and Rhipicephalus microplus. Vector-borne agents such as Theileria cervi, Trypanosoma theileri, Trypanosoma evansi, Ehrlichia chaffeensis, Anaplasma platys, Anaplasma odocoilei, Anaplasma marginale, and Candidatus Anaplasma boleense were also found. Haemonchus spp., Ostertagia spp., and Trichostrongylus spp. were the most frequent gastrointestinal parasites in deer with poor body condition. A Multiple Correspondence Analysis reinforced a possible association of winter period with lower body score condition, high tick loads, infection with E. chaffeensis, and presence of harmful gastrointestinal parasites. CONCLUSIONS: Our approach allowed the establishment of a participatory surveillance network of marsh deer morbidity and mortality in Argentina. We report and analyse the first data obtained opportunistically within the framework of this network, providing information on the infectious and parasitic agents in marsh deer populations. The occurrence of Fasciola hepatica and Leptospira interrogans serovar pyrogenes is reported for the first time in wild marsh deer from Argentina. Our data will be useful to improve the interpretation of future mortality events. The field implementation of a surveillance network is key to a holistic approach to wildlife diseases.

Disease mortality in domesticated animals is predicted by host evolutionary relationships.

Infectious diseases of domesticated animals impact human well-being via food insecurity, loss of livelihoods, and human infections. While much research has focused on parasites that infect single host species, most parasites of domesticated mammals infect multiple species. The impact of multihost parasites varies across hosts; some rarely result in death, whereas others are nearly always fatal. Despite their high ecological and societal costs, we currently lack theory for predicting the lethality of multihost parasites. Here, using a global dataset of >4,000 case-fatality rates for 65 infectious diseases (caused by microparasites and macroparasites) and 12 domesticated host species, we show that the average evolutionary distance from an infected host to other mammal host species is a strong predictor of disease-induced mortality. We find that as parasites infect species outside of their documented phylogenetic host range, they are more likely to result in lethal infections, with the odds of death doubling for each additional 10 million years of evolutionary distance. Our results for domesticated animal diseases reveal patterns in the evolution of highly lethal parasites that are difficult to observe in the wild and further suggest that the severity of infectious diseases may be predicted from evolutionary relationships among hosts.

Causes of death in goats in Rio Grande do Sul state, Brazil: analysis of 322 cases (2000-2016) / Causas de morte em caprinos diagnosticadas no estado do Rio Grande do Sul: análise de 322 casos (2000-2016)

The diagnosis of the cause of death in goats submitted to necropsy from January 2000 to December 2016 by Setor de Patologia Veterinária from the Universidade Federal do Rio Grande do Sul was reviewed. Epidemiological features, such as the breed, sex and age, in addition to the clinical and pathological features were evaluated. During this period, 322 goats were necropsied, in which a conclusive diagnosis was obtained in 290 (90%) goats. Goats that were part of other experimental study were excluded from this study. From these 290 cases, 167 (57.6%) corresponded to diseases of infectious origin and toxinfectious diseases, while 123 (42.4%) were classified as non-infectious conditions. Infectious diseases included 55 cases of bacterial origin, 59 cases with parasitary involvement, 14 cases of viral origin, and 39 toxinfectious cases. Non-infectious conditions were grouped into metabolic diseases (44 cases), plants or chemical substances poisoning (36), mineral and nutritional deficiencies (20), and neoplasms and developmental disorders (5). In the remaining 18 cases, a conclusive diagnosis was obtained, however the conditions did not fit into those criteria and were classified as "others". The age range of the goats in this study was from 1 day-old to 10 years-old. Most of the goats were females (201), while 121 were males. Affected breeds included Boer, Saanen, Anglo-Nubian, Toggenburg and mixed breeds. Parasitic, infectious and toxin-infectious diseases were the main cause of deaths, especially haemonchosis, pleuropneumonia, eimeriosis and enterotoxemia. Among the non-infectious conditions, metabolic disorders, especially rumen acidosis, pregnancy toxemia and urolithiasis, were directly related to the management employed in the property. Plant poisoning diagnosis was also highlighted with locally present plants, such as Sida carpinifolia, as the most important.(AU)

Foram revisadas as causas de morte de caprinos submetidos ao exame de necropsia no período compreendido entre janeiro de 2000 e dezembro de 2016 pelo Setor de Patologia Veterinária da Universidade Federal do Estado do Rio Grande do Sul, Brasil. Avaliaram-se os dados epidemiológicos relacionados à raça, sexo e idade, assim como as alterações macroscópicas e microscópicas observadas. Durante esse período, foram recebidos para necropsia 322 caprinos, nos quais em 290 casos (90%) foi obtido o diagnóstico conclusivo. Caprinos destinados à experimentação animal foram excluídos deste estudo. Do total de 290 casos, 167 (57,6%) corresponderam a enfermidades de origem infecciosa e toxi-infecciosa, enquanto 123 (42,4%) em causas não infecciosas. Entre as doenças infecciosas foram contabilizados 55 casos de origem bacteriana, 59 casos com envolvimento parasitário, 14 casos de origem viral, e 39 casos toxi-infecciosos. As doenças de caráter não infeccioso foram agrupadas em doenças metabólicas (44 casos), intoxicações por plantas ou substâncias tóxicas (36), deficiências minerais e nutricionais (20), neoplasias e distúrbios no desenvolvimento (5). Dezoito casos com diagnóstico conclusivo, mas que não se enquadravam nestas classificações foram agrupadas como "outros". A faixa etária dos caprinos neste estudo variou de um dia a 10 anos. A maior parte dos animais eram fêmeas (201), enquanto 121 eram machos. As raças dos caprinos necropsiados neste período incluíram Boer, Saanen, Anglo-Nubiano, Toggenburg e sem raça definida (SRD). As enfermidades de origem parasitárias, infecciosas e toxi-infecciosas, especialmente hemoncose, eimeriose, pleuropneumonias e a enterotoxemia acarretaram o maior número de mortes. Das causas não infecciosas, distúrbios metabólicos, como acidose lática ruminal, toxemia da prenhez e urolitíase, estiveram diretamente relacionadas com o manejo empregado nas propriedades. Evidenciou-se também a importância do diagnóstico de intoxicações por plantas relevantes da região, como Sida carpinifolia.(AU)

Causes of mortality and morbidity in free-ranging mustelids in Switzerland: necropsy data from over 50 years of general health surveillance.

BACKGROUND: Although mustelids occur worldwide and include a wide range of species, little is known about the diseases affecting them. Mustelids have regularly been submitted for post mortem investigation in the framework of the program for general wildlife health surveillance in Switzerland, which has been in place for nearly 60 years. We performed a retrospective analysis of the necropsy reports on mustelids submitted to the diagnostic service of the University of Bern. The aims of this study were to present an overview of the causes of mortality and morbidity observed in these carnivores, to assess differences among species, to assess changes in disease detection over the study period, and to describe the pathology of selected diseases. RESULTS: Five hundred and sixty-six reports from 1958 to 2015 were analyzed. Most animals were stone martens (Martes foina, 46%) and badgers (Meles meles, 44%); the remaining species were polecats (Mustela putorius, 4.7%), pine martens (Martes martes, 2%), stoats (Mustela erminea, 1.4%), weasels (Mustela nivalis, 0.8%) and otters (Lutra lutra, 0.3%). Infectious diseases (n = 262) were frequent and were mostly bacterial or viral; non-infectious conditions (n = 169) were less common and were mostly traumatic or due to metabolic disorders. The most frequent diagnoses included distemper (75% were badgers), amyloidosis (96% were martens), bacterial respiratory infections (all mustelids), biting lice (badgers only) and pulmonary and gastro-intestinal helminths (all species). Less frequent diseases included histoplasmosis (badgers only), aspergillosis, toxoplasmosis, hepatozoonosis, and sarcoptic mange. Lesions due to infection with distemper virus were primarily appreciated in the respiratory tract and central nervous system; they presented species-specific characteristics such as necrosis in the ependyma in badgers and absence of syncytia in stone martens. Amyloidosis in martens was multisystemic in most cases and included both AA and AL amyloidosis; the main macroscopic change was severe splenomegaly. CONCLUSION: Infectious diseases were the most frequent causes of morbidity and mortality of mustelids, with marked species-specific differences. Lung and skin were the most commonly affected organs. Contagious diseases such as canine distemper, sarcoptic mange and rabies in mustelids showed a similar temporal pattern as in red foxes (Vulpes vulpes), suggesting pathogen spillovers from foxes to mustelids.

Descriptions of Mikrocytos veneroïdes n. sp. and Mikrocytos donaxi n. sp. (Ascetosporea: Mikrocytida: Mikrocytiidae), detected during important mortality events of the wedge clam Donax trunculus Linnaeus (Veneroida: Donacidae), in France between 2008 and 2011.

BACKGROUND: Microcell parasites are small intracellular protozoans mostly detected in molluscs and can be associated with mortalities. In 2010 and 2011, strong increases in mortality events were reported in different wild beds of the wedge clam Donax trunculus Linnaeus, along the Atlantic coast of France and the presence of potential pathogens, including microcells, was investigated. METHODS: Clams collected in different beds showing mortality were examined by histology. Based on histological observations, confirmatory analyses were carried out, including transmission electron microscopy (TEM) and molecular characterization. RESULTS: Histological analyses revealed the presence of small protozoans similar to microcell parasites in different tissues of Donax trunculus, particularly in muscular and connective tissues. TEM examination confirmed the intracellular localization of the protozoans. Moreover, the lack of haplosporosomes and mitochondria suggested that the observed parasites belong to the genus Mikrocytos Farley, Wolf & Elston, 1988. Mikrocytos genus-specific PCR and in situ hybridization results supported the microscopic observations. Sequence fragments of the 18S rRNA gene shared 75-83% identity with the different Mikrocytos spp. described previously, including Mikrocytos mackini Farley, Wolf & Elston, 1988 and M. boweri Abbott, Meyer, Lowe, Kim & Johnson, 2014. Phylogenetic analyses confirmed that the microcell parasites observed in Donax trunculus in France belong to the genus Mikrocytos and suggest the existence of two distinct species. CONCLUSIONS: Based on morphological, ultrastructural, molecular data and host information, the two microcell parasites detected in Donax trunculus belong to the genus Mikrocytos and are distinct from previously described members of this genus. This is the first report of Mikrocytos spp. found in France and infecting the clam Donax trunculus. Mikrocytos veneroïdes n. sp. was detected in different wild beds and Mikrocytos donaxi n. sp. was detected only in Audierne Bay.

MORTALITY TRENDS IN NORTHERN SEA OTTERS ( ENHYDRA LUTRIS KENYONI) COLLECTED FROM THE COASTS OF WASHINGTON AND OREGON, USA (2002-15).

During 2002-15 we examined the causes of mortality in a population of northern sea otters ( Enhydra lutris kenyoni). Beachcast sea otters were collected primarily from the US coast of Washington. Although there are no permanent sea otter residents in Oregon, several beachcast otters were collected from the Oregon coast. Infectious diseases were the primary cause of death (56%) for otters we examined. Sarcocystosis was the leading infectious cause of death (54%) and was observed throughout the study period. Some infectious diseases, such as morbilliviral encephalitis and leptospirosis, were documented for a limited number of years and then not detected again despite continued testing for these pathogens in necropsied animals. Trauma was the second most common cause of death (14%) during the study period. The continued stable growth of the Washington population of otters suggests they are able to tolerate current mortality rates.

A pan-European epidemiological study reveals honey bee colony survival depends on beekeeper education and disease control.

Reports of honey bee population decline has spurred many national efforts to understand the extent of the problem and to identify causative or associated factors. However, our collective understanding of the factors has been hampered by a lack of joined up trans-national effort. Moreover, the impacts of beekeeper knowledge and beekeeping management practices have often been overlooked, despite honey bees being a managed pollinator. Here, we established a standardised active monitoring network for 5 798 apiaries over two consecutive years to quantify honey bee colony mortality across 17 European countries. Our data demonstrate that overwinter losses ranged between 2% and 32%, and that high summer losses were likely to follow high winter losses. Multivariate Poisson regression models revealed that hobbyist beekeepers with small apiaries and little experience in beekeeping had double the winter mortality rate when compared to professional beekeepers. Furthermore, honey bees kept by professional beekeepers never showed signs of disease, unlike apiaries from hobbyist beekeepers that had symptoms of bacterial infection and heavy Varroa infestation. Our data highlight beekeeper background and apicultural practices as major drivers of honey bee colony losses. The benefits of conducting trans-national monitoring schemes and improving beekeeper training are discussed.

Detecting and quantifying parasite-induced host mortality from intensity data: method comparisons and limitations.

Parasites can significantly impact animal populations by changing host behaviour, reproduction and survival. Detecting and quantifying these impacts is critical for understanding disease dynamics and managing wild animal populations. However, for wild hosts infected with macroparasites, it is notoriously difficult to quantify the fatal parasite load and number of animals that have died due to disease. When ethical or logistical constraints prohibit experimental determination of these values, examination of parasite intensity and distribution data may offer an alternative solution. In this study we introduce a novel method for using intensity data to detect and quantify parasite-induced mortality in wildlife populations. We use simulations to show that this method is more reliable than previously proposed methods while providing quantitative estimates of parasite-induced mortality from empirical data that are consistent with previously published qualitative estimates. However this method, and all techniques that estimate parasite-induced mortality from intensity data alone, have several important assumptions that must be scrutinised before applying those to real-world data. Given that these assumptions are met, our method is a new exploratory tool that can help inform more rigorous studies of parasite-induced host mortality.

Study of the distribution of active caspase-3-positive cells in turbot, Scophthalmus maximus (L.), enteromyxosis.

Enteromyxosis caused by Enteromyxum scophthalmi is one of the parasitizations with a higher economic impact on turbot, Scophthalmus maximus (L.), aquaculture. This myxosporean produces severe catarrhal enteritis with abundant inflammatory infiltrates in the lamina propria-submucosa (LP), epithelial detachment and leucocyte depletion of the lymphohaematopoietic organs. Some advances made on the pathogenesis pointed to a role of apoptosis in the enteromyxosis. Therefore, the main aim of this work was to employ the TUNEL assay and the anti-(active caspase-3) immunohistochemical assay to detect apoptotic cells in both healthy and E. scophthalmi-infected turbot in order to establish the presence and distribution of apoptotic cells during development of the disease. More apoptotic cells located within the gastrointestinal epithelium were observed in the initial stages of the infection in E. scophthalmi-infected turbot compared with non-infected turbot. As the infection progressed, a higher degree of apoptosis occurred in the epithelium of folds heavily parasitized. In the severely infected turbot, apoptosis was also found among the leucocytes of the intestinal inflammatory infiltrates. Moreover, the number of active caspase-3-positive cells in the lymphohaematopoietic organs tended to increase with disease severity. In view of the results, increased apoptosis in the epithelium may favour the scaling that occurs during enteromyxosis and cell death of leucocytes in the intestinal LP, contributing to leucocyte depletion in severe cases.

Enteromyxum leei infection in parrotfish, Sparisoma cretense: histopathological, morphological and molecular study.

Enteromyxum leei (Myxozoa) has been identified as the aetiological agent of morbidity and mortality in captive feral parrotfish, Sparisoma cretense held at the facilities of Cretaquarium, the public aquarium of the Hellenic Centre for Marine Research in Crete. The parasite caused substantial mortality to the parrotfish exceeding 60% over a period of 3.5 months. Here we describe the course of disease, the effects of the parasite on the host based on histopathological observations and we provide morphological and molecular data on the parasite.

Neospora caninum is a cause of perinatal mortality in axis deer (Axis axis).

Neospora caninum is a worldwide distributed protozoan that may cause neuromuscular disease in dogs and reproductive failure in domestic and wild ruminants. One axis fawn (Axis axis) and four neonates from the same deer herd died at a zoo in Argentina within a four-month period. The fawn presented with dilatation of the anal sphincter at birth and incontinence, developed weakness and ataxia and died at 14 days of age. At necropsy, a mega formation of the distal large intestine was observed. Microscopically, non-suppurative encephalitis, suppurative bronchopneumonia, fibrin necrotic enteritis and degenerative changes in the liver were observed in hematoxilin and eosin-stained tissue sections, and thick-walled N. caninum-like cysts were observed in fresh brain samples. Serologic studies for N. caninum revealed an IFAT titer of 1:6400 in the fawn and 1:25, 1:400, 1:3200 and 1:6400 in the neonates. N. caninum DNA was detected in brain samples from the fawn and from one neonate by PCR, and the parasite was isolated in vitro from the fawn' brain after passage through gerbils (Meriones unguiculatus) and gamma-interferon knock-out mice. N. caninum DNA obtained from the fawn, neonate and isolated parasites showed the same microsatellite pattern. This suggests a common infection source for both animals. The diagnosis of N. caninum infection was confirmed, suggesting its association with perinatal mortality in captive axis deer. To the best of our knowledge, this is the first report of clinical disease associated to N. caninum infection in axis deer and of isolation of the parasite from this wild ruminant species.

Mass-mortality in green striped tree dragons (Japalura splendida) associated with multiple viral infections.

In spring 2011, high mortality in association with skin lesions, systemic haemorrhages and necrosis occurred in a group of green striped tree dragons (Japalura splendida) which were imported from southwestern China via Florida to Germany. Infections with various endoparasites were diagnosed in coprological examinations. Different antiparasitic and antibiotic treatments over a period of three months did not reduce the mortality rate. The remaining animals were therefore euthanased and submitted for additional testing. Predominant findings in pathological examination were granulomatous and necrotising inflammation of the skin, vacuolar tubulonephrosis of the distal renal tubules, hyperaemia and liver necrosis. Eosinophilic intranuclear and basophilic intracytoplasmic inclusion bodies were detected in the liver. Virological testing (PCR and virus isolation methods) demonstrated the presence of ranavirus, adenovirus and invertebrate iridovirus.

Molecular crosstalk between a chemical and a biological stressor and consequences on disease manifestation in rainbow trout.

The aim of the present study was to examine the molecular and organism reaction of rainbow trout, Oncorhynchus mykiss, to the combined impact of two environmental stressors. The two stressors were the myxozoan parasite, Tetracapsuloides bryosalmonae, which is the etiological agent of proliferative kidney disease (PKD) and a natural stressor to salmonid populations, and 17ß-estradiol (E2) as prototype of estrogen-active chemical stressors in the aquatic environment. Both stressors, the parasite and estrogenic contaminants, co-exist in Swiss rivers and are discussed as factors contributing to the decline of Swiss brown trout populations over the last decades. Using a microarray approach contrasting parasite-infected and non-infected rainbow trout at low or high estrogen levels, it was observed that molecular response patterns under joint exposure differed from those to the single stressors. More specifically, three major response patterns were present: (i) expression responses of gene transcripts to one stressor are weakened by the presence of the second stressor; (ii) expression responses of gene transcripts to one stressor are enhanced by the presence of the second stressor; (iii) expression responses of gene transcripts at joint treatment are dominated by one of the two stressors. Organism-level responses to concurrent E2 and parasite treatment - assessed through measuring parasite loads in the fish host and cumulative mortalities of trout - were dominated by the pathogen, with no modulating influence of E2. The findings reveal function- and level-specific responses of rainbow trout to stressor combinations, which are only partly predictable from the response to the single stressors.

Relationship between temperature and Ceratomyxa shasta -induced mortality in Klamath River salmonids.

Water temperature influences almost every biological and physiological process of salmon, including disease resistance. In the Klamath River (California), current thermal conditions are considered sub-optimal for juvenile salmon. In addition to borderline temperatures, these fish must contend with the myxozoan parasite Ceratomyxa shasta , a significant cause of juvenile salmonid mortality in this system. This paper presents 2 studies, conducted from 2007 to 2010, that examine thermal effects on C. shasta -induced mortality in native Klamath River Chinook ( Oncorhynchus tshawytscha ) and coho ( Oncorhynchus kisutch ) salmon. In each study, fish were exposed to C. shasta in the Klamath River for 72 hr and then reared in the laboratory under temperature-controlled conditions. The first study analyzed data collected from a multi-year monitoring project to asses the influence of elevated temperatures on parasite-induced mortality during the spring/summer migration period. The second study compared disease progression in both species at 4 temperatures (13, 15, 18, and 21 C) representative of spring/summer migration conditions. Both studies demonstrated that elevated water temperatures consistently resulted in higher mortality and faster mean days to death. However, analysis of data from the multi-year monitoring showed that the magnitude of this effect varied among years and was more closely associated with parasite density than with temperature. Also, there was a difference in the timing of peak mortality between species; Chinook incurred high mortalities in 2008 and 2009, whereas coho was greatest in 2007 and 2008. As neither temperature nor parasite density can be easily manipulated, management strategies should focus on disrupting the overlap of this parasite and its obligate hosts to improve emigration success and survival of juvenile salmon in the Klamath River.

Ceratomyxa shasta genotypes cause differential mortality in their salmonid hosts.

Ceratomyxa shasta is a myxozoan parasite of salmonid fish. In natural communities, distinct genotypes of the parasite are associated with different salmonid hosts. To test the hypothesis that genotypes of C. shasta cause differential mortality, the polychaete host was experimentally infected with different parasite genotypes. Genotype I was obtained from Chinook salmon, Oncorhynchus tshawytscha, and genotype II from either coho salmon, O. kisutch, or rainbow trout, O. mykiss, We then challenged four salmonid strains: Chinook and coho salmon that occur in sympatry with the parasite and allopatric Chinook salmon and rainbow trout. Parasite genotype I caused mortality only in Chinook strains, although mortality in the allopatric strain also occurred from exposure to genotype II. A second experiment demonstrated that genotype II could be separated into two biotypes based on differential mortality in rainbow trout and coho salmon. These differential patterns of mortality as a result of infection by certain genotypes of C. shasta support field observations and suggest a co-evolutionary relationship between these parasites and their hosts.

Density of the waterborne parasite Ceratomyxa shasta and its biological effects on salmon.

The myxozoan parasite Ceratomyxa shasta is a significant pathogen of juvenile salmonids in the Pacific Northwest of North America and is limiting recovery of Chinook (Oncorhynchus tshawytscha) and coho (O. kisutch) salmon populations in the Klamath River. We conducted a 5-year monitoring program that comprised concurrent sentinel fish exposures and water sampling across 212 river kilometers of the Klamath River. We used percent mortality and degree-days to death to measure disease severity in fish. We analyzed water samples using quantitative PCR and Sanger sequencing, to determine total parasite density and relative abundance of C. shasta genotypes, which differ in their pathogenicity to salmonids. We detected the parasite throughout the study zone, but parasite density and genetic composition fluctuated spatially and temporally. Chinook and coho mortality increased with density of their specific parasite genotype, but mortality-density thresholds and time to death differed. A lethality threshold of 40% mortality was reached with 10 spores liter(-1) for Chinook but only 5 spores liter(-1) for coho. Parasite density did not affect degree-days to death for Chinook but was negatively correlated for coho, and there was wider variation among coho individuals. These differences likely reflect the different life histories and genetic heterogeneity of the salmon populations. Direct quantification of the density of host-specific parasite genotypes in water samples offers a management tool for predicting host population-level impacts.

The sea louse Lepeophtheirus acutus (Caligidae, Siphonostomatoida, Copepoda) as a pathogen of aquarium-held elasmobranchs.

Lepeophtheirus acutus Heegaard, 1943 (Caligidae, Siphonostomatoida, Copepoda), was collected from or observed on four of six elasmobranch species held at Burgers' Zoo (Arnhem, The Netherlands). Circumstantial evidence suggested that a zebra shark, Stegostoma fasciatum (Hermann), from the wild carried the infection into the facility, where copepods reproduced and colonized additional hosts. Copepods typically attached on and about the eyes, in the mouth and occasionally about the cloaca and on the claspers. Severe ocular lesions were associated with infections on zebra sharks, a grey reef shark, Carcharhinus amblyrhynchos (Bleeker), whitetip reef sharks, Triaenodon obesus (Rüppell), and giant shovelnose ray, Rhinobatos typus Bennett, while blacktip reef sharks, Carcharhinus melanopterus (Quoy & Gaimard), and blacktip sharks, Carcharhinus limbatus (Valenciennes), living in infested aquaria showed no sign of infection. Water treatments using trichlorfon were considered primarily responsible for the eradication of copepods from hosts and infested aquaria. This case is the first report of a copepod infection being closely associated with disease and death of an aquarium-held elasmobranch. Given its ability to infect a wide variety of elasmobranchs and promote life-threatening lesions on some hosts, L. acutus should be considered a dangerous pathogen of captive elasmobranchs.

Mortality of coho salmon (Oncorhynchus kisutch) associated with burdens of multiple parasite species.

Multiple analytical techniques were used to evaluate the impact of multiple parasite species on the mortality of threatened juvenile coho salmon (Oncorhynchus kisutch) from the West Fork Smith River, Oregon, USA. We also proposed a novel parsimonious mathematical representation of macroparasite distribution, congestion rate, which (i) is easier to use than traditional models, and (ii) is based on Malthusian parameters rather than probability theory. Heavy infections of Myxobolus insidiosus (Myxozoa) and metacercariae of Nanophyetus salmincola and Apophallus sp. occurred in parr (subyearlings) from the lower mainstem of this river collected in 2007 and 2008. Smolts (yearlings) collected in 2007-2010 always harboured fewer Apophallus sp. with host mortality recognised as a function of intensity for this parasite. Mean intensity of Apophallus sp. in lower mainstem parr was 753 per fish in 2007 and 856 per fish in 2008, while parr from the tributaries had a mean of only 37 or 13 parasites per fish, respectively. Mean intensity of this parasite in smolts ranged between 47 and 251 parasites per fish. Over-dispersion (variance to mean ratios) of Apophallus sp. was always lower in smolts compared with all parr combined or lower mainstem parr. Retrospective analysis based on smolt data using both the traditional negative binomial truncation technique and our proposed congestion rate model showed identical results. The estimated threshold level for mortality involving Apophallus sp. was at 400-500 parasites per fish using both analytical methods. Unique to this study, we documented the actual existence of these heavy infections prior to the predicted mortality. Most of the lower mainstem parr (approximately 75%) had infections above this level. Heavy infections of Apophallus sp. metacercariae may be an important contributing factor to the high over-wintering mortality previously reported for these fish that grow and develop in this section of the river. Analyses using the same methods for M.insidiosus and N. salmincola generally pointed to minimal parasite-associated mortality.