Review of research on hookworms (Uncinaria lucasi Stiles, 1901) in northern fur seals (Callorhinus ursinus Linnaeus, 1758)

First Report of Uncinaria hamiltoni in Orphan Eastern Mediterranean Monk Seal Pups in Greece and Its Clinical Significance

The Mediterranean monk seal (Monachus monachus) is classified by the IUCN as “endangered,” with a global population estimated to number fewer than 800 individuals. Our understanding of the biology and health status of the species is still limited, rendering every medical case a challenge for conservationists and veterinary clinicians. Although studying and managing disease in wild marine hosts is complex and challenging, studying and mitigating the effects of any disease to the Mediterranean monk seal is of utmost importance for conservation. The aim of this study was to document for the first time the presence of the hookworm Uncinaria hamiltoni in rehabilitated Mediterranean monk seal pups in Greece. A detailed examination protocol was followed for all pups that live-stranded over 30 years in 22 different locations, including physical, parasitological, and other examinations. Hookworms (adults and/or eggs) were detected in all the fecal samples, from all animals. Molecular identification using MtDNA (COI) and ribosomal DNA (D2/D3 28S and internal transcribed spacer [ITS] regions) identified the nematode species as Uncinaria hamiltoni. The clinical impacts and the benefits of anthelmintic treatment as a tool for the conservation management of the species are discussed.

Topical ivermectin is a highly effective seal 'spot-on': A randomised trial of hookworm and lice treatment in the endangered Australian sea lion (Neophoca cinerea)

The Australian sea lion (Neophoca cinerea) is an endangered and declining otariid species, with a high rate of pup mortality associated with endemic hookworm (Uncinaria sanguinis) infection a suspected contributor to this decline. Injected ivermectin is an effective treatment for Uncinaria sp. in otariids, with optimal outcomes achieved by the early treatment of pups prior to disease development. This randomised controlled trial evaluated the effectiveness of the novel use of a topical ivermectin formulation against hookworm infection and lice (Antarctophthirus microchir) infestation, in comparison with injected ivermectin. During the 2017 breeding season at Dangerous Reef, South Australia, pups ≤ 70 cm in standard length (≤ 2 weeks of age; n = 85) were randomised to single dose topical (500 μg/kg spot-on; n = 27) or injected (200 μg/kg subcutaneous; n = 29) ivermectin treatment groups, or to an untreated control group (n = 29). Topical ivermectin was highly effective for U. sanguinis elimination, and not significantly different to the injected formulation (estimated effectiveness 96.4% and 96.8%, respectively; P > 0.05). Its application resulted in an 81.6% reduction and 62.7% additional clearance for A. microchir infestation by 15-24 days post-treatment, compared with untreated control pups (also not significantly different to injected ivermectin; 83.1% and 59.4%, respectively; P > 0.05). Treatment with either ivermectin formulation significantly ameliorated increases in inflammatory markers detected in the blood of untreated control pups - peripheral blood eosinophil counts (persisting to 36-41 days post-recruitment P < 0.05) and increased plasma protein concentrations (15-24 days post-recruitment; P < 0.05). Further, an initial short-term decrease in body condition in the control group was not observed in either of the treatment groups. This study demonstrates that topical ivermectin is an effective antiparasitic treatment in N. cinerea. It offers an alternative administration method for ivermectin delivery to a young pup cohort in this species, and an alternative, minimally invasive management tool for species conservation.

Review of metazoan parasites of the northern fur seal (Callorhinus ursinus) and the analysis of the gastrointestinal helminth community of the population on St. Paul Island, Alaska

The northern fur seal (NFS), Callorhinus ursinus (Mammalia: Otariidae), is a marine mammal species included into the IUCN Red List as the vulnerable species which population is dramatically declining. A significant amount of parasitological data collected previously and our recent data allowed us to clarify the list of NFS metazoan parasites and to perform a comprehensive analysis of the gastrointestinal helminth community. Gastrointestinal tracts from 756 NFSs (3- to 4-year-old males) were collected during the annual Aleut subsistence harvests in July-August of 2011-2014 from five separate rookeries on St. Paul Island, Alaska. Totally, 27,625 specimens of helminths and approximately 1000 nasal mites were collected and identified. Detailed analysis of the previously published and newly obtained data revealed 32 species of metazoan parasites, including trematodes (6 species), cestodes (4), nematodes (9), acanthocephalans (9) and arthropods (4). The gastrointestinal helminth community of newly studied NFSs comprised 19 species including trematodes (4), cestodes (3), nematodes (5) and acanthocephalans (7). Temporal changes in the helminth community structure were small but statistically significant. Gastrointestinal helminth infracommunities comprised from 1 to 10 species (average of 4). Small but significant correlation was found between the abundances of acanthocephalans (Corynosoma similis and C. strumosum), nematodes (Contracaecum osculatum, Pseudoterranova spp.) and cestode Diphyllobothrium tetrapterum.

Host Population Expansion and the Genetic Architecture of the Pinniped Hookworm Uncinaria lucasi

The long-term fidelity of pinniped hosts to their natal rookery site suggests the genetic architecture of their Uncinaria spp. hookworms should be strongly structured by host breeding biology. However, historical events affecting host populations may also shape parasite genetic structure. Sequences of the mitochondrial cytochrome c oxidase 1 (COI) gene of 86 Uncinaria lucasi individuals were obtained to assess genetic variation and structure of nematodes from 2 host species (68 hookworms from northern fur seals; 18 hookworms from Steller sea lions) and rookeries from 3 widely separated geographic regions: the western Bering Sea and Sea of Okhotsk, eastern Bering Sea, and the eastern Pacific Ocean. High COI haplotype (h = 0.96-0.98) and nucleotide (π = 0.014) diversity was found. The haplotype network showed a star-shaped pattern with a large number of haplotypes separated by few substitutions. The network did not show separation of U. lucasi by geographic region or host species. Fst values between U. lucasi individuals representing geographic regions showed no differentiation, consistent with the absence of genetic structure. At face value, this lack of genetic structure in U. lucasi suggests high gene flow but could also be explained by recent (post-glacial) population expansions of northern fur seals and their hookworms.

Parasitism Elicits a Stress Response That Allocates Resources for Immune Function in South American Fur Seals (Arctocephalus australis)

Parasites can cause chronic stress in some animal species, and this type of stress response has been associated with adverse consequences for the host. In order to know whether parasitism elicited a stress response associated with decreased host fitness, hookworm (Uncinaria sp.) infection was studied in a colony of South American fur seals (Arctocephalus australis) in which hookworms infect nearly all pups born in a reproductive season. A parasite-free group was generated by treating a subset of pups with an antiparasitic drug before they developed patent hookworm infection. Stress and metabolic hormones, energy balance, and humoral and cellular immune parameters were measured in this group and hookworm-infected pups. Hookworms elicited a marked increase in plasma cortisol levels in fur seal pups. These hookworm-infected pups were able to maintain constant glucose levels, despite losing body mass over the course of infection potentially because of increased protein catabolism. Infected pups were able to mount an effective immune response against the parasite and eliminated hookworms from the intestine, recovering partial body mass lost as a result of hookworm infection at the end of the study period. As shown in previous studies, adequate glucose levels are critical for proper T lymphocyte reactivity, and it is possible that, through activation of a stress response, energy can be readily available for immune response against the parasite contributing to early recovery from infection. Although there are potential fitness costs to mounting a sustained stress response, these could also be adaptive and promote survival during critical life-history stages.

The contrasting hidden consequences of parasitism: Effects of a hematophagous nematode (Uncinaria sp.) in the development of a marine mammal swimming behavior

Parasites are an important part of ecosystems, playing a critical role in their equilibrium. However, the consequences of parasitism beyond the direct effects associated with disease and mortality are not completely understood. This gap in knowledge is in part due to the difficulties to isolate the effect of single parasite species on physiological and behavioral traits in natural systems.The South American fur seal (Arctocephalus australis)-hookworm (Uncinaria sp.) interaction offers an ideal system to overcome these difficulties and study the behavioral and physiological effects of parasites in their hosts.Hookworms cause stunted growth and anemia in pinniped pups, which could affect early life active behaviors such as swimming. The aim of this study was to determine the effects of hookworms (Uncinaria sp.) on the development of swimming capabilities in A. australis through physiological and ethological analyses.Higher parasite burden was associated with reduced growth rates and lower blood hemoglobin concentrations, whereas scaled body mass and blood hemoglobin levels had an important positive effect on the water activity of the pups. However, antihookworm treatment did not affect the level of water activity of the pups, and pups with high hookworm burden increased their time budget in water. This was probably related to lower maternal attendance in heavily parasitized pups, leaving these pups more time to perform water activities. Therefore, pups with heavy hookworm burden, despite having decreased growth rates and blood hemoglobin concentrations, compensated for their handicap in physiological traits related to swimming by spending more time in the water.This work offers new insights to understand the contrasting effects of parasites on aquatic organisms, and the compensatory mechanisms employed by infected animals to avoid the worst consequences of parasitism.

The life history strategy of a fur seal hookworm in relation to pathogenicity and host health status

The strategies that parasites use to exploit their hosts can lead to adverse effects on human and animal populations. Here, we describe the life cycle, epidemiology, and consequences of hookworm (Uncinaria sp.) disease in South American fur seals (Arctocephalus australis), and propose that hookworm adaptation to fur seal life history traits has led to maximizing transmission at high levels of parasite-induced anemia and mortality. Fur seal pups acquire hookworms during their first days of life through their mothers' colostrum and most adult hookworms are expelled from the pups' intestine 30-65 days later. This gives hookworms little time to feed and reproduce. However, despite reaching high within-host densities, female hookworms do not decrease egg output, therefore pups with high hookworm burden contribute disproportionately to parasite egg shedding. These heavily infected pups also suffer severe anemia and high levels of hookworm-induced mortality. Alternative strategies to maximize total egg shedding and/or transmission, such as increased environmental survival of larval stages or avoidance of clearance, have not been developed by this hookworm. We propose that fur seal hookworms exploit a live fast-die young life history strategy, which translates to the highest levels of host anemia and mortality recorded among hookworms.

The population genetics of parasitic nematodes of wild animals

Parasitic nematodes are highly diverse and common, infecting virtually all animal species, and the importance of their roles in natural ecosystems is increasingly becoming apparent. How genes flow within and among populations of these parasites - their population genetics - has profound implications for the epidemiology of host infection and disease, and for the response of parasite populations to selection pressures. The population genetics of nematode parasites of wild animals may have consequences for host conservation, or influence the risk of zoonotic disease. Host movement has long been recognised as an important determinant of parasitic nematode population genetic structure, and recent research has also highlighted the importance of nematode life histories, environmental conditions, and other aspects of host ecology. Commonly, factors influencing parasitic nematode population genetics have been studied in isolation, such that an integrated view of the drivers of population genetic structure of parasitic nematodes is still lacking. Here, we seek to provide a comprehensive, broad, and integrative picture of these factors in parasitic nematodes of wild animals that will be a useful resource for investigators studying non-model parasitic nematodes in natural ecosystems. Increasingly, new methods of analysing the population genetics of nematodes are becoming available, and we consider the opportunities that these afford in resolving hitherto inaccessible questions of the population genetics of these important animals.

Immune-mediated hookworm clearance and survival of a marine mammal decrease with warmer ocean temperatures

Increases in ocean temperature are associated with changes in the distribution of fish stocks, and the foraging regimes and maternal attendance patterns of marine mammals. However, it is not well understood how these changes affect offspring health and survival. The maternal attendance patterns and immunity of South American fur seals were assessed in a rookery where hookworm disease is the main cause of pup mortality. Pups receiving higher levels of maternal attendance had a positive energy balance and a more reactive immune system. These pups were able to expel hookworms through a specific immune mediated mechanism and survived the infection. Maternal attendance was higher in years with low sea surface temperature, therefore, the mean hookworm burden and mortality increased with sea surface temperature over a 10-year period. We provide a mechanistic explanation regarding how changes in ocean temperature and maternal care affect infectious diseases dynamics in a marine mammal.

Pinnipediae

This chapter reviews common diseases of pinnipeds, including species in the Otariidae (fur seals and sea lions), Phocidae (true seals), and Odobenidae (walrus) families. Much of the knowledge on pathologic conditions of pinnipeds comes from necropsies of stranded animals and those housed in captivity. As such, disease knowledge is biased toward species frequently housed in zoos and aquaria, those that strand more commonly, or those in which free-ranging populations are more easily accessible. Though historically systematic evaluations of wild populations have rarely been accomplished, in the past 10 years, with advances in marine mammal medicine and anesthesia, biologists and veterinarians more frequently completed live animal health field investigations to evaluate health and disease in free-ranging pinniped populations.

The diversity and impact of hookworm infections in wildlife

Hookworms are blood-feeding nematodes that parasitize the alimentary system of mammals. Despite their high pathogenic potential, little is known about their diversity and impact in wildlife populations. We conducted a systematic review of the literature on hookworm infections of wildlife and analyzed 218 studies qualitative and quantitatively. At least 68 hookworm species have been described in 9 orders, 24 families, and 111 species of wild mammals. Black bears, red foxes, and bobcats harbored the highest diversity of hookworm species and Ancylostoma pluridentatum, A. tubaeforme, Uncinaria stenocephala and Necator americanus were the hookworm species with the highest host diversity index. Hookworm infections cause anemia, retarded growth, tissue damage, inflammation and significant mortality in several wildlife species. Anemia has been documented more commonly in canids, felids and otariids, and retarded growth only in otariids. Population- level mortality has been documented through controlled studies only in canines and eared seals although sporadic mortality has been noticed in felines, bears and elephants. The main driver of hookworm pathogenic effects was the hookworm biomass in a population, measured as prevalence, mean burden and hookworm size (length). Many studies recorded significant differences in prevalence and mean intensity among regions related to contrasts in local humidity, temperature, and host population density. These findings, plus the ability of hookworms to perpetuate in different host species, create a dynamic scenario where changes in climate and the domestic animal-human-wildlife interface will potentially affect the dynamics and consequences of hookworm infections in wildlife.

Hookworm Infection in South American Fur Seal ( Arctocephalus australis) Pups

Tissues of South American fur seal pups naturally infected with hookworms ( Uncinaria sp) were examined. Hookworm infection was found in nearly all pups examined (132/140, 94%), and hookworm enteritis with secondary bacteremia was considered the cause of death in 46 (35%) pups. Common findings in these pups included severe hemorrhagic enteritis and numerous (mean intensity = 761.8) hookworms in the jejunum. Hookworms were recovered from the abdominal cavity in 12 of 55 pups (22%) examined through peritoneal wash; these pups had an average of 1343.3 intestinal hookworms and marked fibrinohemorrhagic peritonitis. In all pups that died as a consequence of hookworm infection, the intestinal villi were short, blunt, and fused, and there were variable numbers of free and intrahistiocytic gram-negative bacteria in submucosal hookworm feeding tracks, mesenteric lymph nodes, spleen, blood vessels, and liver sinusoids. Pups that died of causes unrelated to the hookworm infection (trauma) had hookworm feeding tracks confined to the apical portions of the mucosa, and moderate to marked catarrhal eosinophilic enteritis. The number of hookworms was negatively correlated with intestinal villous length and number of leukocytes in the intestine. Pups with hookworm peritoneal penetration had nematodes with little or no blood in the hookworm intestine, suggesting that lack of food for the nematode could be associated with peritoneal penetration. Findings suggest that the initial burden of larval infection, the level of the host tissue response, or a combination determine the number of nematodes in the intestine, the severity of hookworm tissue damage, and pup mortality.

Parasitological examination of northern elephant seal (Mirounga angustirostris) pups for presence of hookworms (Uncinaria spp.) on San Miguel Island, California

Necropsy and extensive parasitological examination of dead northern elephant seal (NES) pups was done on San Miguel Island, California, in February, 2015. The main interest in the current study was to determine if hookworms were present in NESs on San Miguel Island where two hookworm species of the genus Uncinaria are known to be present - Uncinaria lyonsi in California sea lions and Uncinaria lucasi in northern fur seals. Hookworms were not detected in any of the NESs examined: stomachs or intestines of 16 pups, blubber of 13 pups and blubber of one bull. The results obtained in the present study of NESs on San Miguel Island plus similar finding on Año Nuevo State Reserve and The Marine Mammal Center provide strong indication that NES are not appropriate hosts for Uncinaria spp. Hookworm free-living third stage larvae, developed from eggs of California sea lions and northern fur seals, were recovered from sand. It seems that at this time, further search for hookworms in NESs would be nonproductive.

The cestode community in northern fur seals (Callorhinus ursinus) on St. Paul Island, Alaska

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Three species of cestodes were found in northern fur seals (Callorhinus ursinus).

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Prevalence and intensity of cestodes collected from five haul-outs were studied.

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Ecology and maturity of cestodes were analyzed.

The diversity and ecology of cestodes from the northern fur seals, Callorhinus ursinus (NFS), were examined using newly collected material from 756 humanely harvested subadult males between 2011 and 2014. NFSs were collected from five different haul-outs on St. Paul Island, Alaska. A total of 14,660 tapeworms were collected with a prevalence of 98.5% and intensity up to 107 cestodes per host (mean intensity 19.7 ± 16.5 SD). Three species of tapeworms were found: Adenocephalus pacificus (Diphyllobothriidea) was the most prevalent (prevalence 97.4%), followed by Diplogonoporus tetrapterus (49.7%), and 5 immature specimens of Anophryocephalus cf. ochotensis (Tetrabothriidea) (0.5%). Most of the cestodes found in the NFS were immature (69.7%). However, only 0.9% of cestodes were in larval (plerocercoid) stages. The species composition, prevalence and intensity of cestodes from these NFSs were not statistically different between the five separate haul-outs. Significant increases in the intensity of NFS infections were observed during the study period.

Long-term survival and reproductive success of New Zealand sea lions (Phocarctos hookeri) treated with ivermectin as pups

Context Hookworms (Uncinaria spp.) are a common parasite of neonatal fur seals and sea lions around the world and may contribute to decreased pup growth and survival. Removal of these parasitic burdens by administration of the anthelmintic ivermectin has been trialled in New Zealand (NZ) sea lion (Phocarctos hookeri) pups at Sandy Bay, Enderby Island, with initial benefits in growth and survival reported. Long-term effects, however, are not known. Aims To determine the impact of ivermectin treatment administered in the first month of life, on long-term survival and fecundity in a sample of NZ sea lion pups. Methods For a sample of treated and control pups born between 2002 and 2004, resighting data to 2012 was assessed with the Cox proportional hazards analysis to evaluate survival to maturity and fecundity. Key results Sample size was a limiting factor as juvenile survival was very low, but a trend of improved survival was observed in the ivermectin-treated group. Year of birth was significant due to the effects of a bacterial epizootic in the first year of the trial. Reproductive rate was not significantly different between groups. Conclusions The effect of disease and parasitism on the survival of NZ sea lions is apparent, contributing to early pup mortality, with potentially wider-ranging implications for juvenile survival and beyond. Implications Further research is warranted to investigate anthelmintic treatment of NZ sea lion pups as a safe and effective management tool to improve survival and recruitment in declining populations.

Unexpected absence of genetic separation of a highly diverse population of hookworms from geographically isolated hosts

The high natal site fidelity of endangered Australian sea lions (Neophoca cinerea) along the southern Australian coast suggests that their maternally transmitted parasitic species, such as hookworms, will have restricted potential for dispersal. If this is the case, we would expect to find a hookworm haplotype structure corresponding to that of the host mtDNA haplotype structure; that is, restricted among geographically separated colonies. In this study, we used a fragment of the cytochrome c oxidase I mitochondrial DNA (mtDNA) gene to investigate the diversity of hookworms (Uncinaria sanguinis) in N. cinerea to assess the importance of host distribution and ecology on the evolutionary history of the parasite. High haplotype (h=0.986) and nucleotide diversity (π=0.013) were seen, with 45 unique hookworm mtDNA haplotypes across N. cinerea colonies; with most of the variation (78%) arising from variability within hookworms from individual colonies. This is supported by the low genetic differentiation co-efficient (GST=0.007) and a high gene flow (Nm=35.25) indicating a high migration rate between the populations of hookworms. The haplotype network demonstrated no clear distribution and delineation of haplotypes according to geographical location. Our data rejects the vicariance hypothesis; that female host natal site fidelity and the transmammary route of infection restrict hookworm gene flow between N. cinerea populations and highlights the value of studies of parasite diversity and dispersal to challenge our understanding of parasite and host ecology.

Acanthocephalans in northern fur seals (Callorhinus ursinus) and a harbor seal (Phoca vitulina) on St. Paul Island, Alaska: species, prevalence, and biodiversity in four fur seal subpopulations

Monitoring studies of acanthocephalans in northern fur seals (Callorhinus ursinus Linnaeus, 1758) (NFSs) and a harbor seal (Phoca vitulina Linnaeus, 1758) were performed on St. Paul Island, Alaska, in July-August 2011. Gastrointestinal tracts of 105 humanely harvested NFS subadult males (SAMs) (3-4 years old) were collected during the annual Aleut subsistence harvest at four haul-out areas (HOAS): Lukanin (n = 26 NFSs), Polovina (n = 28), Gorbatch (n = 30), and Morzhovyi (n = 21). One gastrointestinal tract collected from a harbor seal (about 3-4 years old) found dead at Morzhovyi HOAS was also examined. The total prevalence of infection in NFSs with acanthocephalans was 29.52 % with variations from 7.69 % to 47.62 % between the four different HOAS. Eight acanthocephalan species of two genera-Corynosoma Lühe, 1904 (Corynosoma strumosum, Corynosoma alaskensis, Corynosoma cameroni, Corynosoma semerme, Corynosoma similis, Corynosoma validum, and Corynosoma villosum), and Bolbosoma Porta, 1908 (Bolbosoma nipponicum)-were found in the NFSs and a harbor seal. This is a new record of C. alaskensis for the NFSs. Short biological notes of the species found are presented. Differences in species composition as well as in prevalence of acanthocephalans parasitizing NFSs were observed in subpopulations from four different HOAS on St. Paul Island. The highest biodiversity of acanthocephalans and infection were found in subpopulations on Polovina and Morzhovyj HOAS, the lowest was on Lukanin HOAS. From 3.2 % (for C. validum) to 19.4 % (for C. villosum) of NFSs were infected by one acanthocephalan species; two species were found in 22.6 %; three in 9.7 %; and four in 3.2 %. Further studies of NFS parasites are necessary to follow the trends in parasitic infection rates and diversity in NFS population on the Pribilov Islands and for monitoring the influence of various ecological factors on NFS populations in Alaska.

Parasitological examination for presence of hookworms (Uncinaria spp.) in northern elephant seals (Mirounga angustirostris) at Año Nuevo State Reserve, California (2012)

Northern elephant seals (Mirounga angustirostris Gill, 1866), inhabiting rookeries on the mainland of Año Nuevo State Reserve in central California, were investigated in 2012 for presence of hookworms (Uncinaria spp.). Material collected and examined for hookworms included: blubber (n = 15), stomach and intestines (n = 21) from dead pups; feces from the rectum of weaned pups (n = 23); sand containing apparent feces in areas of weaned pups (n = 28) and sand without apparent feces in areas of weaned pups (n = 54); milk from females (n =23) at 5 days and about 23 to 26 days postpartum; and placenta from one female. Evidence of hookworm presence was not detected in any of the samples examined. Possible reasons why hookworms were not found in northern elephant seals on the mainland of Año Nuevo State Reserve are discussed.