Juan Antonio Raga

Emerging infectious diseases in cetaceans worldwide and the possible role of environmental stressors.

We reviewed prominent emerging infectious diseases of cetaceans, examined their potential to impact populations, re-assessed zoonotic risk and evaluated the role of environmental stressors. Cetacean morbilliviruses and papillomaviruses as well as Brucella spp. and Toxoplasma gondii are thought to interfere with population abundance by inducing high mortalities, lowering reproductive success or by synergistically increasing the virulence of other diseases. Severe cases of lobomycosis and lobomycosis-like disease (LLD) may contribute to the death of some dolphins. The zoonotic hazard of marine mammal brucellosis and toxoplasmosis may have been underestimated, attributable to frequent misdiagnoses and underreporting, particularly in developing countries and remote areas where carcass handling without protective gear and human consumption of fresh cetacean products are commonplace. Environmental factors seem to play a role in the emergence and pathogenicity of morbillivirus epidemics, lobomycosis/LLD, toxoplasmosis, poxvirus-associated tattoo skin disease and, in harbour porpoises, infectious diseases of multifactorial aetiology. Inshore and estuarine cetaceans incur higher risks than pelagic cetaceans due to habitats often severely altered by anthropogenic factors such as chemical and biological contamination, direct and indirect fisheries interactions, traumatic injuries from vessel collisions and climate change.

Marine debris ingestion in loggerhead sea turtles, Caretta caretta, from the Western Mediterranean

Marine debris represents an important threat for sea turtles, but information on this topic is scarce in some areas, such as the Mediterranean sea. This paper quantifies marine debris ingestion in 54 juvenile loggerhead sea turtles (Caretta caretta) illegally captured by fishermen in Spanish Mediterranean waters. Curved carapace length was measured, necropsies were performed and debris abundance and type was recorded. Different types of debris appeared in the gastrointestinal tract of 43 turtles (79.6%), being plastics the most frequent (75.9%). Tar, paper, Styrofoam, wood, reed, feathers, hooks, lines, and net fragments were also present. A regression analysis showed that the volume of debris increased proportionally to the size of the turtles. The high variety of debris found and the large differences in ingestion among turtles indicated low feeding discrimination of this species that makes it specially prone to debris ingestion. Our data suggest that more severe control of litter spills and greater promotion of environmental educational programmes are needed in the Western Mediterranean.

Diet of the bottlenose dolphin ( Tursiops truncatus ) in the western Mediterranean Sea

The stomach contents of 16 bottlenose dolphins Tursiops truncatus (Cetacea: Odontoceti) stranded in the Spanish Mediterranean coast were examined. Remains and size of prey were analysed and correlated with the ecological characteristics and behavioural patterns of this dolphin. Fish and cephalopods represented the main diet components, and hake Merluccius merluccius was the most important prey. The food habits were considered as mainly demersal according to the characteristics of the prey. The study suggested ontogenic and sexual differences in feeding behaviour based on diet composition and hake size. The potential causative factors, particularly as they relate to dolphin social structure, are discussed.

An insight into the epidemiology of dolphin morbillivirus worldwide

Serum samples from 288 cetaceans representing 25 species and originating from 11 different countries were collected between 1995 and 1999 and examined for the presence of dolphin morbillivirus (DMV)-specific antibodies by an indirect ELISA (iELISA) (N = 267) or a plaque reduction assay (N = 21). A total of 35 odontocetes were seropositive: three harbour porpoises (Phocoena phocoena) and a common dolphin (Delphinus delphis) from the Northeastern (NE) Atlantic, a bottlenose dolphin (Tursiops truncatus) from Kent (England), three striped dolphins (Stenella coeruleoalba), two Rissos dolphins (Grampus griseus) and a bottlenose dolphin from the Mediterranean Sea, one common dolphin from the Southwest (SW) Indian Ocean, three Frasers dolphins (Lagenodelphis hosei) from the SW Atlantic, 18 long-finned pilot whales (Globicephala melas) and a bottlenose dolphin from the SW Pacific as well as a captive bottlenose dolphin (Tursiops aduncus) originally from Taiwan. The presence of morbillivirus antibodies in 17 of these animals was further examined in other iELISAs and virus neutralization tests. Our results indicate that DMV infects cetaceans worldwide. This is the first report of DMV-seropositive animals from the SW Indian, SW Atlantic and West Pacific Oceans. Prevalence of DMV-seropositives was 85.7% in 21 pilot whales from the SW Pacific and both sexually mature and immature individuals were infected. This indicates that DMV is endemic in these animals. The same situation may occur among Frasers dolphins from the SW Atlantic. The prevalence of DMV-seropositives was 5.26% and 5.36% in 19 common dolphins and 56 harbour porpoise from the NE Atlantic, respectively, and 18.75% in 16 striped dolphins from the Mediterranean. Prevalence varied significantly with sexual maturity in harbour porpoises and striped dolphins; all DMV-seropositives being mature animals. The prevalence of seropositive harbour porpoise and striped dolphins appeared to have decreased since previous studies. These data suggest that DMV is not endemic within these populations, that they are losing their humoral immunity against the virus and that they may be vulnerable to new epidemics.

Cetacean Morbillivirus: Current Knowledge and Future Directions

We review the molecular and epidemiological characteristics of cetacean morbillivirus (CeMV) and the diagnosis and pathogenesis of associated disease, with six different strains detected in cetaceans worldwide. CeMV has caused epidemics with high mortality in odontocetes in Europe, the USA and Australia. It represents a distinct species within the Morbillivirus genus. Although most CeMV strains are phylogenetically closely related, recent data indicate that morbilliviruses recovered from Indo-Pacific bottlenose dolphins (Tursiops aduncus), from Western Australia, and a Guiana dolphin (Sotalia guianensis), from Brazil, are divergent. The signaling lymphocyte activation molecule (SLAM) cell receptor for CeMV has been characterized in cetaceans. It shares higher amino acid identity with the ruminant SLAM than with the receptors of carnivores or humans, reflecting the evolutionary history of these mammalian taxa. In Delphinidae, three amino acid substitutions may result in a higher affinity for the virus. Infection is diagnosed by histology, immunohistochemistry, virus isolation, RT-PCR, and serology. Classical CeMV-associated lesions include bronchointerstitial pneumonia, encephalitis, syncytia, and lymphoid depletion associated with immunosuppression. Cetaceans that survive the acute disease may develop fatal secondary infections and chronic encephalitis. Endemically infected, gregarious odontocetes probably serve as reservoirs and vectors. Transmission likely occurs through the inhalation of aerosolized virus but mother to fetus transmission was also reported.

Effects of the gill parasite Zeuxapta seriolae (Monogenea: Heteraxinidae) on the amberjack Seriola dumerili Risso (Teleostei: Carangidae)

Zeuxapta seriolae (Monogenea: Heteraxinidae) infection was associated with important mortalities of amberjacks (Seriola dumerili) reared in tanks in the experimental facilities of the Spanish Institute of Oceanography (Western Mediterranean) during the period 1998–2000. Fish infested by this parasite presented characteristics similar to those described for Seriola quinqueradiata parasitized by Heteraxine heterocerca in Japan. All dead amberjacks had high parasite abundance (mean abundanceFS.D.=686.7F125.4) and egg strings entangled in gills. The parasitological analysis of 17 live amberjacks collected from the infested tanks showed that 41.2% of fish harboured Z. seriolae with intensities ranging between 5 and 731 parasites per fish. No apparent relationship was observed between the abundance of the parasite and the condition factor (rS=0.175, n=17, p>0.5). However, the haematocrit values were significantly lower in the fish infested with monogeneans. The relationship between parasite abundance and haematocrit values was negative and statistically significant (rS=0.625, n=17, p<0.01). The light and scanning electron microscope studies of affected gills revealed that the parasites attached to the host grasping one or two lamellae with each clamp of the haptor, which led to lamellar synechiae, lamellar clubbing and disruption of epithelial and vascular structures. A mild to moderate epitheliocystis infection was also

The effects of inbreeding on mortality during a morbillivirus outbreak in the Mediterranean striped dolphin (Stenella coeruleoalba)

Between 1990 and 1992, Mediterranean striped dolphins ( Stenella coeruleoalba ) suffered high mortality due to a morbillivirus epidemic. Ten highly variable microsatellite markers were used to assess the population structure of a sample of these stranded animals and to assess the genetic consequences of the epizootic on present stocks. We found little evidence of population structure within the Mediterranean, but distinct separation between this and the North Sea (Atlantic) population, the latter also showing greater genetic diversity. Using a genetic measure of inbreeding, we found that dolphins dying early in the outbreak were significantly more inbred than those dying later. Within 10 years of the end of the epidemic, the level of inbreeding among stranded dolphins had returned to its pre-outbreak levels. However, on average all stranded animals showed elevated levels of inbreeding, suggesting that animals dying from disease may venture towards the shore more than those dying of old age. Our results imply an important role for inbreeding in the dynamics of disease spread and that, in marine mammal research, caution should be exercised when inferring demographic parameters from stranded specimens.

Serological evidence of Brucella species infection in odontocetes from the south Pacific and the Mediterranean

Sera from 58 odontocetes taken in fisheries off Peru in 1993 to 1995 and from 24-cetaceans stranded along the Spanish coast of the Mediterranean in 1997 to 1999 were tested for the presence of Brucella species antibodies in competitive and indirect ELISAS (cELISA and iELISA). Among the animals from Peru, 21 of 27 (77.8 per cent) Lagenorhynchus obscurus, three of six Delphinus capensis, one of two inshore and two of three offshore Tursiops truncatus and five of 20 (25 per cent) Phocoena spinipinnis were positive in the cELISA. Brucella species antibodies were also observed in two of 16 (12.5 per cent) Stenella coeruleoalba and in one of two T truncatus from the Mediterranean. These data provide the first evidence for the presence of cetacean brucellae in the south Pacific Ocean and the Mediterranean Sea.

Genetic differentiation in the striped dolphin Stenella coeruleoalba from European waters according to mitochondrial DNA (mtDNA) restriction analysis

We used mitochondrial DNA (mtDNA) restriction analysis to study genetic variation in 98 striped dolphins (Stenella coeruleoalba) stranded on coasts from different European countries and from animals caught by fisheries. A total of 63 different restriction sites was mapped after digestion of mtDNA with 15 restriction endonucleases that yielded a total of 27 haplotypes. No haplotype was shared between Mediterranean and Atlantic areas. All the analyses indicate the existence of two different populations with a very limited gene flow across the Strait of Gibraltar.

Living Together but Remaining Apart: Atlantic and Mediterranean Loggerhead Sea Turtles (Caretta caretta) in Shared Feeding Grounds

Juvenile loggerhead sea turtles (Caretta caretta) from Atlantic nesting populations migrate into the western Mediterranean, where they share feeding grounds with turtles originating in the Mediterranean. In this scenario, male-mediated gene flow may lead to the homogenization of these distant populations. To test this hypothesis, we genotyped 7 microsatellites from 56 Atlantic individuals sampled from feeding grounds in the western Mediterranean and then compared the observed allele frequencies with published data of 112 individuals from Mediterranean nesting beaches. Mediterranean populations were found to be genetically differentiated from the Atlantic stock reaching the western Mediterranean (F(st) = 0.029, P < 0.001); therefore, the possible mating events between Atlantic and Mediterranean individuals are not sufficient to homogenize these 2 areas. The differentiation observed between these 2 areas demonstrates that microsatellites are sufficiently powerful for mixed stock analysis and that individual assignment (IA) tests can be performed in combination with mitochondrial DNA (mtDNA) analysis. In a set of 197 individuals sampled in western Mediterranean feeding grounds, 87% were robustly assigned to Atlantic or Mediterranean groups with the combined marker, as compared with only 52% with mtDNA alone. These findings provide a new approach for tracking the movements of these oceanic migrants and have strong implications for the conservation of the species.