Development, validation, and utilization of a competitive enzyme-linked immunosorbent assay for the detection of antibodies against Brucella species in marine mammals

Serological Detection of Marine Origin Brucella Exposure in Two Alaska Beluga Stocks

Simple Summary

Brucellosis, the disease caused by Brucella bacteria, is of emerging concern in marine-mammal populations worldwide due to its potential link to reproductive failure, yet is less well-studied than in terrestrial animals, such as cattle. To understand Brucella exposure and disease in two populations of beluga, in Bristol Bay and the eastern Chukchi Sea, Alaska, USA, this study screened animals for the presence of antibodies against the bacterium (serology), as well as tested for the direct presence of bacterial DNA or bacterial growth from tissue samples. More than half of all animals tested, from both populations, were positive for the presence of antibodies, providing evidence of exposure to Brucella. Few animals, however, were positive for the direct detection of Brucella DNA and none resulted in successful bacterial growth, suggesting a lack of active clinical disease. The high rate of exposure in these populations supports the need for long-term monitoring of beluga populations, particular those that are threatened or endangered, such as the Cook Inlet belugas.

Abstract

Among emerging threats to the Arctic is the introduction, spread, or resurgence of disease. Marine brucellosis is an emerging disease concern among free-ranging cetaceans and is less well-studied than terrestrial forms. To investigate marine-origin Brucella sp. exposure in two beluga stocks in Alaska, USA, this study used serological status as well as real-time polymerase chain reaction (rtPCR) and bacterial culture. In total, 55 live-captured–released belugas were tested for Brucella exposure in Bristol Bay (2008–2016) and 112 (8 live-captured; 104 subsistence-harvested) whales were tested in the eastern Chukchi Sea (2007–2017). In total, 73% percent of Bristol Bay live captures, 50% of Chukchi Sea live captures, and 66% of Chukchi Sea harvested belugas were positive on serology. Only 10 of 69 seropositive belugas were rtPCR positive in at least one tissue. Only one seropositive animal was PCR positive in both the spleen and mesenteric lymph node. All animals tested were culture negative. The high prevalence of seropositivity detected suggests widespread exposure in both stocks, however, the low level of rtPCR and culture positive results suggests clinical brucellosis was not prevalent in the belugas surveyed. Continued detection of Brucella exposure supports the need for long-term monitoring of these and other beluga populations.

CEREBROSPINAL FLUID SAMPLING IN A BOTTLENOSE DOLPHIN (TURSIOPS TRUNCATUS) UNDER GENERAL ANESTHESIA

Brucella ceti, associated with neurobrucellosis, has been isolated from cerebrospinal fluid (CSF) of postmortem cetaceans. A 106-kg, stranded female bottlenose dolphin (Tursiops truncatus) presented with serum antibodies to Brucella spp. via competitive enzyme-linked immunosorbent assay and fluorescence polarization assay. Polymerase chain reaction (PCR) and culture of whole blood, bronchoalveolar fluid, and rectal, nasal, and genital swabs for Brucella spp. were consistently negative. Serial computed tomography revealed mild focal dilatation of brain ventricles. CSF sampling was warranted to exclude neurobrucellosis. Sedation was achieved with 30 mg diazepam (0.28 mg/kg) orally 2.5 hours prior to arrival in hospital, followed by 5.3 mg midazolam (0.05 mg/kg) intramuscularly, and anesthetic induction with 2.5 mg midazolam (0.02 mg/kg) and 200 mg propofol (2 mg/kg) administered slowly intravenously, followed by intubation and maintenance on sevoflurane using controlled mechanical and apneustic anesthesia ventilation. The atlanto-occipital joint was opened by flexing the upper cervical region with the animal in left lateral recumbency. A 20-ga × 6-inch spinal needle was advanced into the cisterna magna using radiographic guidance. CSF was collected successfully with no neurological deficits appreciable on recovery. Brucella spp. was not identified via PCR or culture. This represents the first report of an antemortem CSF tap in a cetacean.

Comparative Health Assessments of Alaskan Ice Seals

Bearded (Erignathus barbatus), ringed (Pusa hispida), spotted (Phoca largha), and ribbon (Histriophoca fasciata) seals rely on seasonal sea-ice in Arctic and sub-Arctic regions. Many aspects of the biology and physiology of these seals are poorly known, and species-typical health parameters are not available for all species. Such information has proven difficult to obtain due to the challenges of studying Arctic seals in the wild and their minimal historic representation in aquaria. Here, we combine diagnostic information gathered between 2000 and 2017 from free-ranging seals, seals in short-term rehabilitation, and seals living in long-term human care to evaluate and compare key health parameters. For individuals in apparent good health, hematology, and blood chemistry values are reported by the source group for 10 bearded, 13 ringed, 73 spotted, and 81 ribbon seals from Alaskan waters. For a smaller set of individuals handled during veterinary or necropsy procedures, the presence of parasites and pathogens is described, as well as exposure to a variety of infectious diseases known to affect marine mammals and/or humans, with positive titers observed for Brucella, Leptospira, avian influenza, herpesvirus PhHV-1, and morbillivirus. These data provide initial baseline parameters for hematology, serum chemistries, and other species-level indicators of health that can be used to assess the condition of individual seals, inform monitoring and management efforts, and guide directed research efforts for Alaskan populations of ice-associated seals.

BRUCELLA PINNIPEDIALIS IN GREY SEALS ( HALICHOERUS GRYPUS) AND HARBOR SEALS ( PHOCA VITULINA) IN THE NETHERLANDS

Brucellosis is a zoonotic disease with terrestrial or marine wildlife animals as potential reservoirs for the disease in livestock and human populations. The primary aim of this study was to assess the presence of Brucella pinnipedialis in marine mammals living along the Dutch coast and to observe a possible correlation between the presence of B. pinnipedialis and accompanying pathology found in infected animals. The overall prevalence of Brucella spp. antibodies in sera from healthy wild grey seals ( Halichoerus grypus; n=11) and harbor seals ( Phoca vitulina; n=40), collected between 2007 and 2013 ranged from 25% to 43%. Additionally, tissue samples of harbor seals collected along the Dutch shores between 2009 and 2012, were tested for the presence of Brucella spp. In total, 77% (30/39) seals were found to be positive for Brucella by IS 711 real-time PCR in one or more tissue samples, including pulmonary nematodes. Viable Brucella was cultured from 40% (12/30) real-time PCR-positive seals, and was isolated from liver, lung, pulmonary lymph node, pulmonary nematode, or spleen, but not from any PCR-negative seals. Tissue samples from lung and pulmonary lymph nodes were the main source of viable Brucella bacteria. All isolates were typed as B. pinnipedialis by multiple-locus variable number of tandem repeats analysis-16 clustering and matrix-assisted laser desorption ionization-time of flight mass spectrometry, and of sequence type ST25 by multilocus sequence typing analysis. No correlation was observed between Brucella infection and pathology. This report displays the isolation and identification of B. pinnipedialis in marine mammals in the Dutch part of the Atlantic Ocean.

Application of real-time quantitative PCR assays for detecting marine Brucella spp. in fish

Brucella ceti and Brucella pinnipedialis have been documented as occurring in marine mammals, and B. ceti has been identified in 3 naturally acquired human cases. Seroconversion and infection patterns in Pacific Northwest harbor seals ( Phoca vitulina richardii) and North Atlantic hooded seals ( Cystophora cristata) indicate post-weaning exposure through prey consumption or lungworm infection, suggesting fish and possibly invertebrates play an epizootiologic role in marine Brucella transmission and possible foodborne risk to humans. We determined if real-time quantitative PCR (qPCR) assays can detect marine Brucella DNA in fish DNA. Insertion sequence (IS) 711 gene and sequence type (ST)27 primer-probe sets were used to detect Brucella associated with marine mammals and human zoonotic infections, respectively. First, DNA extracts from paired-species fish (containing 2 species) samples were tested and determined to be Brucella DNA negative using both IS 711 and ST27 primer-probe sets. A representative paired-species fish DNA sample was spiked with decreasing concentrations of B. pinnipedialis DNA to verify Brucella detection by the IS 711 primer-probe within fish DNA. A standard curve, developed using isolated DNA from B. pinnipedialis, determined the limit of detection. Finally, the IS 711 primer-probe was used to test Atlantic cod ( Gadus morhua) DNA extracts experimentally infected with the B. pinnipedialis hooded seal strain. In culture-positive cod tissue, the IS 711 limit of detection was ~1 genome copy of Brucella. Agreement between culture and PCR results for the 9 positive and 9 negative cod tissues was 100%. Although a larger sample set is required for validation, our study shows that qPCR can detect marine Brucella in fish.

Seroprevalence of Brucella antibodies in harbor seals in Alaska, USA, with age, regional, and reproductive comparisons

Populations of harbor seal Phoca vitulina in the Gulf of Alaska have dramatically declined during the past 4 decades. Numbers of seals in Glacier Bay, in southeast Alaska, USA, have also declined despite extensive protection. Causes of the declines and slow recovery are poorly understood. Brucellosis is a zoonotic disease that adversely affects reproduction in many domestic species. We measured the seroprevalence of Brucella antibodies in 554 harbor seals in 3 Alaska locations: Prince William Sound (PWS), Glacier Bay (GB), and Tracy Arm Fords Terror (TAFT) Wilderness Area. Objectives included testing for regional, sex, age, and female reproductive state differences in Brucella antibody seroprevalence, persistence in titers in recaptured seals, and differences in titers between mother seals and their pups. Overall, 52% of adults (AD), 53% of subadults (SA), 77% of yearlings (YRL), and 26% of <5 mo old pups were seropositive. Matched mother-pup samples were consistent with dependent pups acquiring maternal passive immunity to Brucella. Results show higher seroprevalence (64%) for AD and SA seals in the depressed and declining populations in PWS and GB than in TAFT (29%). Lactating females were less likely to be seropositive than other AD females, including pregnant females. Further research is needed to seek evidence of Brucella infection in Alaskan harbor seals, identify effects on neonatal viability, and assess zoonotic implications for Alaska Natives who rely on harbor seals for food.

INFECTIOUS DISEASE AND TOXICOLOGICAL MONITORING OF STRANDED PACIFIC HARBOR SEALS (PHOCA VITULINA RICHARDSI) IN COOK INLET AS SURROGATES FOR MONITORING ENDANGERED BELUGAS (DELPHINAPTERUS LEUCAS)

  Pacific harbor seals ( Phoca vitulina richardsi) and belugas ( Delphinapterus leucas ) eat many of the same prey species, occupy the same geographic area, and demonstrate site fidelity in Cook Inlet, Alaska. Although most direct research involving the critically endangered belugas is currently prohibited, studying harbor seals may provide important information about this beluga population. In recent years, harbor seal populations in Alaska have declined for unknown reasons. As part of its stranding program, the Alaska SeaLife Center (ASLC) managed 59 cases of live and dead stranded harbor seals from Cook Inlet between 1997 and 2011. Animals were screened for a variety of diseases and contaminants of concern. Animals were negative by serology to the following diseases: avian influenza, canine distemper virus, dolphin morbillivirus, porpoise morbillivirus, Leptospira canicola, L. grippotyphosa, L. pomona, Neospora caninum , Sarcocystis neurona , and Toxoplasma gondii . Positive titers were found against Brucella spp., phocine distemper virus, seal herpesvirus-1, L. bratislava, L. hardjo, and L. icterohemorrhagiae. All titers were stable or declining except in one animal with an increasing titer for seal herpesvirus-1. Fecal pathogen screenings identified normal flora as well as stable or declining low levels of potentially pathogenic and opportunistic bacteria, though most were of little concern for seal health. In most animals, toxicology screening showed that the majority of tested contaminants were below detectable limits. The level of evidence of exposure to pathogens of concern was low in harbor seals. Although the infectious disease burden and contaminant levels in belugas in Cook Inlet cannot be definitively determined without direct testing, pathogen and contaminant exposure is expected to be similar to that found in harbor seals in this region, as the harbor seals and belugas share the habitat and food resources.

SURVEY FOR INFECTIOUS DISEASE IN THE SOUTH AMERICAN FUR SEAL (ARCTOCEPHALUS AUSTRALIS) POPULATION AT PUNTA SAN JUAN, PERU

The Peruvian population of the South American fur seal ( Arctocephalus australis ) is a distinct evolutionarily significant unit that is endangered. One of the largest rookeries for this species in Peru is located within the Punta San Juan marine protected area (15°22'S, 75°12'W). To better understand the current health status of this population, exposure to 10 pinniped pathogens was evaluated in adult female fur seals (n=29) via serology and polymerase chain reaction (PCR) techniques in November 2010. The results suggest this population is naïve to canine and phocine distemper viruses (serum neutralization test), five Leptospira interrogans serovars (microscopic agglutination test), and Brucella canis (card test). Indirect fluorescent antibody testing for Toxoplasma gondii , Neospora caninum , and Sarcocystis neurona was also uniformly negative. PCR testing of nasal swabs using previously described Mycoplasma spp. primers was positive in 37.9% (11/29) of samples. One animal was positive via card test for Brucella abortus , whereas 53.7% (15/28) were positive or suspect using a marine Brucella competitive enzyme-linked immunosorbent assay. Antibody to phocine herpesvirus-1 (PHV-1) was identified in 85.7% (24/28) of the sampled population by serum neutralization testing. Overall, exposure to Mycoplasma spp., Brucella spp., and PHV-1 was observed, but results demonstrated low to no exposure to many key pinniped pathogens. The expansion of human populations, agriculture, and industry along the Peruvian coast may lead to increased pathogen exposure from human, domestic, and wild animal sources. The naïve nature of this key population of South American fur seals raises concerns about potential risk for disease outbreaks.

Diagnosis and successful treatment of a lung abscess associated with Brucella species infection in a bottlenose dolphin (Tursiops truncatus)

This brief communication describes the clinical presentation, antemortem diagnosis, and successful treatment of a pulmonary abscess associated with a Brucella sp. in a 27-yr-old female bottlenose dolphin (Tursiops truncatus). Ultrasound revealed a 3-cm diameter hypoechoic mass deep to the pleural lining in the left lung field. Multiple ultrasound-guided fine-needle aspirates were performed and tested for bacterial and fungal etiology. All cultures were negative, but the infectious agent was identified by MicroSEQ analysis in two samples and confirmed with real-time polymerase chain reaction (PCR) amplification using known Brucella sp. primers. Amikacin was infused into the abscess and was followed by an oral doxycycline and rifampin protocol. Follow-up diagnostic imaging, including radiographs and computed tomography, revealed a resolved lesion with minimal mineralization within the affected lung fields. Brucellosis should be considered for pulmonary disease in dolphins, and personnel who interact with marine animals should use caution to prevent zoonotic brucellosis.

Assay dependence of Brucella antibody prevalence in a declining Alaskan harbor seal (Phoca vitulina) population

Background

Brucella is a group of bacteria that causes brucellosis, which can affect population health and reproductive success in many marine mammals. We investigated the serological prevalence of antibodies against Brucella bacteria in a declining harbor seal population in Glacier Bay National Park, Alaska.

Results

Prevalence ranged from 16 to 74 percent for those tests detecting antibodies, indicating that harbor seals in Glacier Bay have been exposed to Brucella bacteria. However, the actual level of serological prevalence could not be determined because results were strongly assay-dependent.

Conclusions

This study reinforces the need to carefully consider assay choice when comparing different studies on the prevalence of anti–Brucella antibodies in pinnipeds and further highlights the need for species- or taxon-specific assay validation for both pathogen and host species.

A multiplex real-time polymerase chain reaction assay with two internal controls for the detection of Brucella species in tissues, blood, and feces from marine mammals

Brucellosis has emerged as a disease of concern in marine mammals in the last 2 decades. Molecular detection techniques have the potential to address limitations of other methods for detecting infection with Brucella in these species. Presented herein is a real-time polymerase chain reaction (PCR) method targeting the Brucella genus–specific bcsp31 gene. The method also includes a target to a conserved region of the eukaryotic mitochondrial 16S ribosomal RNA gene to assess suitability of extracted DNA and a plasmid-based internal control to detect failure of PCR due to inhibition. This method was optimized and validated to detect Brucella spp. in multiple sample matrices, including fresh or frozen tissue, blood, and feces. The analytical limit of detection was low, with 95% amplification at 24 fg, or an estimated 7 bacterial genomic copies. When Brucella spp. were experimentally added to tissue or fecal homogenates, the assay detected an estimated 1–5 bacteria/µl. An experiment simulating tissue autolysis showed relative persistence of bacterial DNA compared to host mitochondrial DNA. When used to screen 1,658 field-collected marine mammal tissues in comparison to microbial culture, diagnostic sensitivity and specificity were 70.4% and 98.3%, respectively. In addition to amplification in fresh and frozen tissues, Brucella spp. were detected in feces and formalin-fixed, paraffin-embedded tissues from culture-positive animals. Results indicate the utility of this real-time PCR for the detection of Brucella spp. in marine species, which may have applications in surveillance or epidemiologic investigations.

Detection of Francisella tularensis-specific antibodies in patients with tularemia by a novel competitive enzyme-linked immunosorbent assay

A novel competitive enzyme-linked immunosorbent assay (cELISA) was developed and evaluated for detection of antibodies against Francisella tularensis in humans. The assay is based on the ability of serum antibodies to inhibit the binding of monoclonal antibodies (MAbs) directed against F. tularensis lipopolysaccharide antigens. The assay was evaluated using serum samples of tularemia patients, inactivated F. tularensis-immunized rabbits, and F. tularensis-infected mice. Antibodies against F. tularensis were successfully detected in serum samples of tularemia patients as well as the immunized and infected animals. The cELISA method was compared to indirect ELISA (iELISA) and the commonly used microagglutination test (MA) using serum samples of 19 tularemia patients and 50 healthy individuals. The sensitivity and specificity of cELISA were 93.9 and 96.1%, respectively, in comparison to the iELISA. MA was less sensitive than cELISA with a sensitivity and specificity of only 81.8 and 98.0%, respectively. A high degree of correlation (R(2) = 0.8226) was observed between cELISA and iELISA results. The novel cELISA developed in this study appears to be highly sensitive and specific for serodiagnosis of human tularemia. The potential of the MAb-based cELISA to be used in both human and animal samples emphasizes its usefulness for serological survey of tularemia among multiple animal species.

Brucella ceti and brucellosis in cetaceans

Since the first case of brucellosis detected in a dolphin aborted fetus, an increasing number of Brucella ceti isolates has been reported in members of the two suborders of cetaceans: Mysticeti and Odontoceti. Serological surveys have shown that cetacean brucellosis may be distributed worldwide in the oceans. Although all B. ceti isolates have been included within the same species, three different groups have been recognized according to their preferred host, bacteriological properties, and distinct genetic traits: B. ceti dolphin type, B. ceti porpoise type, and B. ceti human type. It seems that B. ceti porpoise type is more closely related to B. ceti human isolates and B. pinnipedialis group, while B. ceti dolphin type seems ancestral to them. Based on comparative phylogenetic analysis, it is feasible that the B. ceti ancestor radiated in a terrestrial artiodactyl host close to the Raoellidae family about 58 million years ago. The more likely mode of transmission of B. ceti seems to be through sexual intercourse, maternal feeding, aborted fetuses, placental tissues, vertical transmission from mother to the fetus or through fish or helminth reservoirs. The B. ceti dolphin and porpoise types seem to display variable virulence in land animal models and low infectivity for humans. However, brucellosis in some dolphins and porpoises has been demonstrated to be a severe chronic disease, displaying significant clinical and pathological signs related to abortions, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings, and death.

Comparison of GD2 binding capture ELISA assays for anti-GD2-antibodies using GD2-coated plates and a GD2-expressing cell-based ELISA

Two assay methods for quantification of the disialoganglioside (GD2)-specific binding activities of anti-GD2 monoclonal antibodies and antibody immunofusion proteins, such as ch14.18 and hu14.18-IL2, were developed. The methods differed in the use of either microtiter plates coated with purified GD2 or plates seeded with GD2-expressing cell lines to bind the anti-GD2 molecules. The bound antibodies were subsequently detected using the reactivity of the antibodies to an HRP-labeled anti-IgG Fc or antibodies recognizing the conjugate IL-2 part of the Hu 14.18IL-2 fusion protein. The bound HRP was detected using reagents such as orthophenylene diamine, 2, 2'-azinobis [3-ethylbenzothiazoline-6-sulfonic acid] or tetramethylbenzidine. The capture ELISA using GD2-coated plates was developed earlier in assay development and used to demonstrate assay specificity and to compare lot-to-lot consistency and stability of ch14.18, and Hu14.18 IL-2 in clinical development. During this study, we found a number of issues related to plate-to-plate variability, GD2 lot variability, and variations due to GD2 storage stability, etc., that frequently lead to assay failure in plates coated with purified GD2. The cell-based ELISA (CbELISA) using the GD2 expressing melanoma cell line, M21/P6, was developed as an alternative to the GD2-coated plate ELISA. The results on the comparability of the capture ELISA on GD2-coated plates and the cell-based assay show that both assays give comparable results. However, the cell-based assay is more consistent and reproducible. Subsequently, the anti-GD2 capture ELISA using the GD2-coated plate was replaced with the CbELISA for product lot release testing and stability assessment.

Brucella sp. vertebral osteomyelitis with intercurrent fatal Staphylococcus aureus toxigenic enteritis in a bottlenose dolphin (Tursiops truncatus)

A previously beach-stranded, juvenile, male, bottlenose dolphin (Tursiops truncatus) was diagnosed with vertebral osteomyelitis of unknown etiology. Antemortem serological testing suggested past or current Brucella sp. infection; however, this could not be confirmed prior to death despite multiple isolation attempts from aspirates, blood, and biopsies. Systemic antibiotics were administered for over a year to control the suspected infection; however, the animal succumbed peracutely to infection by a highly pathogenic, enterotoxin-secreting Staphylococcus sp. Gross necropsy findings included a fistulous tract leading to locally extensive osteomyelitis of a coccygeal vertebra with sequestra and osteophytes from which a Brucella species was isolated. Histopathological examination of intestine revealed pseudomembranous enteritis with a uniform population of intraluminal Gram-positive cocci. Staphylococcus aureus was isolated in pure culture from the intestine and tested positive for the staphylococcal enterotoxin A gene by polymerase chain reaction analysis. Serum taken shortly before death had endotoxin and elevated antibody titers to staphylococcal enterotoxin A when compared to samples collected during a period of apparent good health 18 months earlier. The isolation of a pyrogenic toxin superantigen-producing staphylococcal isolate, clinical signs, and diagnostic findings in this animal resembled some of those noted in human toxic shock syndrome. The present case highlights the clinical challenges of treating chronic illnesses, complications of long-term antibiotic use, and promotion of pathogenic strains in cases of prolonged rehabilitation of marine mammals.