Comparative Ecology of Bartonella and Brucella Infections in Wild Carnivores

Biological Characteristics

Bartonella and Brucella bacteria share some biological characteristics, yet there are evident differences in their adaptations to their animal reservoirs. Infections caused by bacteria of both taxonomic groups can lead to a long-lasting bacteremia with ability to invade specific mammalian cells and survive inside them. Via analogous mechanisms, the specialized secretion system (T4SS) works as a molecular syringe to inject effector molecules into their target cells (18, 19). Bartonella and Brucella modulate their gene expression to adapt to the different environments during the infectious process (20, 21). The VirB systems of Bartonella and Brucella are associated with distinct groups of effector proteins that collectively mediate interactions with host cells (19).

Bartonella bacteria infect endothelial cells and seed into the bloodstream, colonizing erythrocytes which provide a persistence niche for the bacteria. The ability of these bacteria to exploit their reservoir hosts with diminished morbidity and to cause a high level of bacteremia justifies the definition of “elegant hemotrophic parasites” given by Birtles (22) to bartonellae. In incidental hosts, Bartonella infections can cause various clinical manifestations commonly without high-level bacteremias (21). In contrast to Bartonella, Brucella bacteria invade and multiply within mammalian host's macrophages and placental trophoblasts (18, 19, 23). Although bacteremia is common during brucellosis, data on duration and mechanisms of Brucella persistence in animal blood are limited.

Transmission of Bartonella and Brucella Bacteria

The persistence of Bartonella bacteria in red blood cells optimizes transmission of these bacteria by blood-sucking arthropods. High prevalence and long-term bacteremia in reservoir mammals and adaptation to specific vectors seem to be the common strategy of bartonellae for transmission and host diversity (24). Many described Bartonella species are vector-borne bacteria transmitted by fleas, sand flies, lice, and biting flies depending on the bacteria species involved and their vertebrate reservoirs (24, 25). Experimental studies demonstrated louse and flea transmission of B. henselae and B. quintana (26–28). Some investigators provided evidence of potential role of ticks and mites in transmission of Bartonella species, but debates continue on their role of as vectors (25, 29). A 2008 study by Cotté et al. (30) showed that Ixodes spp. ticks are capable of transmitting B. henselae via salivary contents, but Telford and Wormser (31) found no convincing evidence that ticks were vectors of Bartonella species. Molecular detection of Bartonella spp. in terrestrial leeches (Haemadipsa rjukjuana) by Kang et al. (32) opens up a discussion of the pathogen transmission by land leeches.

Transcutaneous transmission of Bartonella via animal bites and scratches during hunting, as well as through butchering or handling wild meat is another possibility (33). Cat scratch disease, caused by B. henselae is the best-documented example of direct animal-to-human transmission of a Bartonella species by scratch or bite inoculation (14). Finkelstein et al. (27) showed that B. henselae can remain viable in flea feces for over 72 hours. Therefore, transmission potentially can occur via inoculation of B. henselae from infected flea feces into the skin via open wounds. Suspected Bartonella alsatica transmission from wild rabbits to humans, presumably occurring during hunting and butchering, was reported in patients with endocarditis or lymphadenitis in France (34, 35). Suspected dog bite transmission of B. vinsonii to a human was reported based upon serological evidence (36). There is little information on possible vertical transmission of bartonellae in animals. However, Bartonella species were isolated from the embryos and neonates of naturally infected cotton rats (Sigmodon hispidus) and white-footed mice (Peromyscus leucopus) (37). Experimental inoculation of B. henselae to adult female cats was accompanied by decreased conception or failure to maintain pregnancy (38). Considering the extensive animal reservoirs and the large number of insects that have been implicated in the transmission of Bartonella species, animal exposure to these organisms may be more substantial than is currently believed.

Transmission of Brucella occurs mainly via close contact with placenta, aborted fetuses, fetal fluids, reproductive tract discharges, and secretions (7). Infected dogs intermittently shed low concentrations of bacteria in seminal fluids and nonestrus vaginal secretions. Postabortion vaginal fluids contain a high level of bacteria and are a source of infection for other dogs (39). In addition, dogs can shed the bacteria in the saliva, nasal secretions, and urine (40). Studies suggest that the concentration of Br. canis in urine is higher in male than female dogs; this difference is attributed to urine contamination with seminal fluid (41). However, the role of urine as a source of infection is not fully understood (39).

There is a widely accepted perception that absence of transmission of Brucella species via arthropod vectors is the most essential difference in ecology of these bacteria compared to the Bartonella species. We found a number of rarely cited publications on either detection of Brucella species in arthropods or experimental studies designed to verify a possibility of vector transmission of these bacteria. Although detection of Brucella in arthropods collected from different sources does not often directly relate to carnivores, such information can help interpret potential mechanisms of bacterial transmission. The invasion of Brucella into erythrocytes and its persistence in blood suggest a possibility for transmission by bloodsucking arthropods in nature (42). Although Brucella may be found in erythrocytes, these bacteria exhibit strong tissue tropism and replicate within vacuoles in macrophages, dendritic cells, and placental trophoblasts. Evidence that Brucella species can be spread among animals by arthropods is very limited. Some Russian authors argued that parasitic arthropods, especially ticks, could preserve Brucella in nature and transmit them within a population from one animal to another (43, 44). Rementsova (43) listed 20 observations of Brucella detection in ticks. Experiments in Russia reported that both ixodid and argasid ticks were infected with Brucella at different phases of their development and could transmit the pathogen to uninfected animals during bloodsucking (43). Brucella in ticks retained their virulence even after 2 years (43). More recently, Neglia et al. (45) detected Br. abortus DNA and RNA in different stages of development of the sucking louse (Haematopinus tuberculatus).

Alimentary transmission is important for Brucella as proved by experimental studies in wild carnivores. Scanlan et al. (46) infected gray foxes with Br. abortus in dog food. Seven of eight foxes became seropositive. Neiland and Miller (47) infected six beagle dogs, two wolves (Canis lupus), one black bear (Ursus americanus), and two grizzly bears (Ursus arctos horribilis) with a strain of Br. suis biovar 4 isolated from a sled dog from Alaska. Their experiments demonstrated that canids and ursids are susceptible to the infection via intraperitoneal inoculation and through oral mucous membranes. During acute stages of the infection, Brucella congregated in these species in high numbers in lymph nodes and distributed throughout the body. Importantly, Brucella invaded salivary glands and probably also mammary glands and kidney, thus providing conditions for shedding the bacteria in saliva, milk, and urine. The authors reported reproductive failure during infection in wolves, but were not confident that the failure was a consequence of the infection (47). Morton (48) experimentally infected foxes with Br. suis biovar 4 and observed that the incidence of positive titers, positive cultures, and shedding of bacteria was related to the number of Brucella organisms experimentally fed to the animals. Lowest doses did not produce infection. Highest doses produced positive titers and cultures.

Tests on rats showed transmission of Br. abortus biovar 1 from infected male to uninfected female rats resulted from sexual intercourse (49). Vertical transmission of Br. abortus caused sterility in pregnant mice (50); Wang et al. (51) documented vertical transmission of Br. melitensis on a pregnant mouse model. Guzman-Verri et al. (52) cited the more likely modes of transmission of Br. ceti to be through sexual intercourse, maternal feeding, aborted fetuses, placental tissues, vertical transmission from mother to the fetus or through fish or helminth reservoirs.

Brucellae have high viability and can survive in the environment for 3–21 days in spring-summer and for 151–233 days in winter-fall seasons. Brucellae maintain viability in carcasses (muscles, internal organs, and lymph nodes) at −7.2° to 38.4°C for 1–12 months (53). Long-term survival of Br. microti in soil was described and, thus, soil might act as a reservoir of infection (54).

General Prevalence Pattern

Overall, prevalence of Bartonella infections in carnivores was higher compared to Brucella infections. In the studies of over two Feliformia animals, the highest prevalence was registered by culture in bobcats [37%, 7/19, (55)], by IFA in bobcats again [74%, (56)], and by PCR of blood in Iberian lynx [33.3%, 10/30, (57)]. In studies of over two Caniformia animals, the highest Bartonella prevalence was registered by culture in gray foxes [49%, 26/53, (58)], by IFA in coyotes [89%, 48/53, (58)], and by PCR of blood in raccoons [43%, 16/37, (59)]. A very high overall prevalence of antibodies to B. henselae (95%) was detected among Brazilian free-ranging felids (60) (Table 1). As expected, the number of seropositive animals was usually higher than the numbers of culture or PCR positive individuals from the same study. Thus, of the 54 lions from South Africa, 5.2% were positive by culture, 3.7% were PCR positive for Bartonella DNA, and 17% had Bartonella antibodies (62). A study on golden jackals in Iraq found 14.5% of animals positive by PCR and 40.4% (23/57) by IFA (86).

Age and Gender Pattern

Prior studies usually show no statistical difference in prevalence by age or gender in felines (61, 69, 79). However, Chomel et al. (17) found antibody prevalence for B. henselae to increase with age in pumas in California. In contrast, Rotstein et al. (79) found antibody prevalence higher in Florida panthers under 2 years of age (40%) compared to panthers over 2 years of age (13%).

Geographic Pattern

Prevalence of B. henselae antibodies in mountain lions and bobcats varied significantly between different states of the U.S. (17). Mountain lions from Arizona, California, and Texas were more likely to be seropositive for B. henselae (26.7–40.0%) than pumas from the Northwest and Mountain states (0–11.8%) (17). In California, the highest prevalence in bobcats was from the coastal range (37.5%), while the highest prevalence in pumas was from Southern California and Sierra Nevada (17). The reported pattern was similar to the geographic distribution of Bartonella infection in domestic cats. It has been demonstrated that in cat populations (stray or pets), prevalence of infection was demonstrated to vary considerably with an increasing gradient from cold climates (0% in Norway) to warm and humid climates (68% in the Philippines) (14). In the U.S., prevalence of B. henselae antibodies in pet cats varied significantly with the highest average prevalence in the southeastern United States, Hawaii, coastal California, the Pacific Northwest, and low prevalence in Alaska, the Rocky Mountain-Great Plains region, and the Midwest (113). Comparing wild felids at four sites in California and Colorado, Bevins et al. (68) noted that seroprevalence varied considerably, but in almost all cases, it was higher in warmer and more humid California than in Colorado. For mountain lions, suburban land use predicted increased exposure to Bartonella species in southern California (114).

Seasonal Pattern

Studies have yielded conflicting evidence about the seasonality of B. vinsonii subsp. berkhoffii infection in coyotes. First, Chang et al. (91) reported that the prevalence of Bartonella antibodies was highest in summer (42%) and lowest in spring (29%), whereas a geographically more restricted study conducted in coastal central California, U.S., by the same authors found the highest seroprevalence in winter (100%) and the lowest in summer (62%) (90). Investigating antibody prevalence in 239 coyotes from northern California, Beldomenico et al. (89) identified some environmental factors associated with the seropositivity. In that study, prevalence of antibodies against B. vinsinii subsp. berkhoffii was 44% in the summer, 40% in the spring, 27% in the winter, and 19% in the fall. The authors noticed that Bartonella seropositivity was associated with higher precipitation and proximity to the coast. In addition, coyotes seropositive for B. vinsonii subsp. berkhoffii were more likely to be seropositive for tick-borne agents Anaplasma phagocytophilum and mosquito-vectored Dirofilaria immitis (89). Interestingly, California Zoo felids of the genus Felis were found almost three times more likely to be seropositive for B. henselae than animals belonging to the genera Panthera and Acinonyx (69).

General Pattern

Eighty-nine percent of Brucella studies of wild carnivores were conducted by serological and bacteriological methods, but no reports were found on culturing Brucella from representatives of suborder Feliformia. Only a few wild felid species (lion, jaguar, and bobcat), mongooses, and spotted hyena were serologically positive. Apart from one bobcat that had antibodies against Br. canis (115), the rest of seropositive Feliformia animals had antibodies against Br. abortus. We have to be cautious with the claim about presence of specific antibodies in this paper, as well in many other reports, because Br. abortus suspensions can also detect Br. melitensis. The highest seroprevalence was registered in white-tailed mongoose [33.3%, 1/3, (116)]. In evident contrast to Feliformia animals, prevalence of Brucella in various Caniformia species varied greatly, with many reporting high prevalences of positive antibody titeres. Antibodies to Brucella species were recorded in 40% of coyotes (117), 42% of wolves (118), 43% of black-backed jackals (116), 50% of Arctic foxes and 40% of red foxes (48), 64% of grizzly bears (119), 28% of Asian sea otters (120), 23% of California sea lions (121), and 74% of Australian seals (122). Brucella was cultured from 30.8% of wolves (123) (Table 2).

Age Pattern

We could find information on age dependence only in marine Brucella. In the 2018 study on gray and harbor seals, Kroese et al. (212) noted remarkable age-dependent prevalence of Br. pinnipedialis in both serology and in the investigation of the tissues from stranded animals. The PCR positivity was 84% (26/31) in juveniles compared to 57% (4/7) in adults and Br. pinnipedialis was cultured only from juveniles and not from adults in that study. Similar age dependence was shown in harbor seals by Miller et al. (169) and Ewalt et al. (229). Nymo et al. (206) noted the age-dependent prevalence of anti-Brucella antibodies in hooded seals. Pups (<1 mo old) had a substantially lower probability of being seropositive (4/159, 2.5%) than yearlings (6/17, 35.3%), suggesting that exposure may occur post-weaning, during the first year of life. For seals over 1 year old, the mean probability of being seropositive decreased with age, with no seropositives older than 5 years, indicating loss of antibody titer with either chronicity or clearance of infection (206).

Bartonella Species in Wild Feliformia Animals

Wild Feliformia animals mostly carry the same Bartonella species as domestic cats, namely B. henselae (types I and II), B. koehlerae, and B. clarridgeiae (234). The same species were detected in feral cats from Georgia, U.S. (59). In Africa, free-ranging lions were found infected with B. henselae type II and B. koehlerae subsp. koehlerae and Namibian cheetah with a strain that clustered between B. henselae and B. koehlerae and was considered a new subspecies of B. koehlerae (61, 63). In Japan, B. henselae was found in Iriomote leopard cats and B. clarridgeiae DNA was detected in Tsushima leopard cats (74, 82).

In a study on free-ranging mountain lions and bobcats from California, U.S., Chomel et al. (55) described new Bartonella strains, which were similar to but different from B. henselae and B. koehlerae, and named them B. koehlerae subsp. boulouisii and B. koehlerae subsp. bothieri. Phylogenetic analysis based on comparison of four genetic markers revealed two clusters: one with five strains obtained from bobcats and another with three strains obtained from mountain lions indicating a degree of host-speciation of these strains (55). In Brazil, sequencing analysis revealed a Bartonella strain close to but different from B. henselae and B. koehlerae in wild-born captive margay (Leopardus wiedii) (235).

Other Bartonella species were detected in fleas collected from wild felids. For example, Bartonella alsatica was found in one of six rabbit fleas Spilopsyllus cuniculi collected from a European wildcat (F. silvestris) in Spain (65). This Bartonella species is usually associated with rabbits and possibly fleas were infected or they contained blood meal from infected rabbits, as S. cuniculi is normally found on European rabbits (Oryctolagus cuniculus). A different situation has been reported by López-Pérez et al. (67) regarding a genetic variant obtained from a flea (Pulex simulans) collected from a bobcat (L. rufus) in northwestern Mexico. This variant had ITS sequence 99.1% similar to a strain previously isolated from another bobcat from California, U.S., but distant from all other Bartonella genotypes.

Bartonella Species in Wild Caniformia Animals

In the studies, Caniformia animals were found to carry B. henselae, B. clarridgeiae, B. vinsonii subsp. berkhoffii, B.rochalimae, B. washoensis, and B. bacilliformis. In an investigation of wild carnivores from Colorado, U.S., Bai et al. (77) identified two Bartonella species, B. vinsonii subsp. berkhoffii and B. rochalimae. Striped skunks exclusively carried B. rochalimae, while coyotes, red foxes, and raccoons were infected with either or both Bartonella species. Bartonella rochalimae DNA was found in a wolf (C. lupus) in northern Spain (64). Investigating wild canids along with stray dogs throughout Iraq, Chomel et al. (86) identified a novel strain of Bartonella, which was named Candidatus B. merieuxii, in six jackals (Canis aureus). By three genetic markers, the “jackal” strain was aligned most closely with B. bovis and the other ruminant Bartonella species. Sequences closely related to Candidatus Bartonella merieuxii later were found in three jackals and one red fox (V. vulpes) in Israel (85). Besides this strain, B. rochalimae and B. rochalimae-like were found in five jackals and one fox, and one jackal harbored B. vinsonii subsp. berkhoffii (85).

Kehoe et al. (87) documented the presence of three Bartonella species in heart valves and/or spleen of free-ranging coyotes from northern California, U.S. Partial DNA sequencing showed that aortic valves from 8 (53%) of 15 coyotes were B. vinsonii subsp. berkhoffii positive, B. rochalimae DNA was amplified from the spleen of one coyote, and B. henselae DNA was amplified from the mitral valve of another coyote. By sequence analyses, four coyotes were infected with B. vinsonii subsp. berkhoffii genotype I, three with genotype II, and one with genotype III (87).

Two species of Bartonella, a novel Bartonella clarridgeiae-like bacterium and B. vinsonii subsp. berkhoffii, were isolated from rural dogs and gray foxes in northern California (58). Two B. henselae sequences detected in the spleen of raccoon dogs in Korea matched the strain Houston-1 and by ITS sequences were 99.8% similar to a strain found in dogs in China (94). Northern and Southern sea otters were found IFA positive for B. washoensis (107, 108). The authors also detected B. bacilliformis by PCR in heart valves of both species. A strain close to B. washoensis was detected by PCR in Japanese marten (95). Chinnadurai et al. (109) detected a novel strain in river otters by PCR with a sequence matched a strain previously described in Southern flying squirrel. In the Netherlands, harbor seals were found to carry a strain 97% similar to B. grahamii (112).

Family Felidae

Family Viverridae

The most common species are civets and genets widely distributed in South and Southeast Asia, Africa, and Southern Europe. The first evidence suggesting that civets can host Bartonella came from a description of a human cat scratch disease case reported in 2001 in Japan. In the case, a patient scratched by a masked palm civet (Paguma larvata) developed fever and inguinal lymphadenopathy with a high antibody titer (1:1,024) to B. henselae (237). Later, Sato et al. (82) cultured B. henselae from blood of one of 50 masked palm civets collected in Chiba Prefecture of Japan. The level of bacteremia was high (7,000 bacteria per 1 mL of blood). Importantly, the multi-locus sequence type detected from the isolated strain revealed a unique genotype. Though the prevalence of Bartonella in cats in Chiba prefecture was 5%, the same genotype had never been found in any B. henselae strains from cats from the same and other prefectures (82). Bartonella DNA was detected in another Viverridae species, the common genet (Genetta genetta). Conducting molecular detection of vector-borne pathogens in wild carnivores in natural parks and adjacent residential areas in Barcelona, Spain, Millán et al. (83) identified B. clarridgeiae in tissues of two of 34 (6%) common genets, but ticks collected from genets were free of Bartonella DNA. In another study conducted in Northern Spain (Basque County), Gerrikagoitia et al. (64) did not detect Bartonella DNA in 13 common genets tested. Márquez et al. (65) also found no Bartonella DNA in 18 fleas S. cuniculi collected from 10 common genets in Andalusia, Spain.

Reports of Brucella testing among viverrids are nearly nonexistent. No Brucella antibodies were found in two common genets (G. genetta) and three Cape genets (G. tigrina) from eastern Africa tested by tube agglutination test (116, 136).

Family Herpestidae

Mongooses is the common name for the weasel-like small carnivores that live in southern Asia, Africa, and southern Europe, and are introduced to some other areas. We have information about Bartonella in one species of this genus—the small Asian mongoose (Herpestes javanicus). Sato et al. (82) isolated B. henselae from 15.9% (10/63) of small Asian mongooses from Okinawa prefecture, Japan. Based on multi-locus sequence analysis, they identified four types of B. henselae strains cultured from mongooses (82). Jaffe et al. (81) tested small Asian mongooses in Grenada and found 32% (54/167) of the animals IFA positive and 35% (18/51) PCR positive for B. henselae. The only additional report of investigation of mongooses was from testing a single Egyptian mongoose (Herpestes ichneumon) in Algeria and the PCR test was negative (80).

There is a report of antibodies against Br. abortus in one white-tailed mongoose (Ichneumia albicauda) (33%, 1/3) and one banded mongoose (Mungos mungo) (100%, 1/1) in Tanzania (116).

Family Hyaenidae

The family contains four species of hyenas and phylogenetically belongs to the suborder Feliformia despite the dog-like appearance of these animals. The only available report on testing hyenas for Bartonella is from a molecular survey of 19 spotted hyenas (Crocuta crocuta) from two sites in Zambia with no positive results (70).

Serological observation of 15 spotted hyenas from Tanzania resulted in detection of antibodies against Brucella in four out of 15 (27%) animals (116). In the prior study, Sachs and Staak (135) found Brucella species exposure in two out of four hyenas in Tanzania. Another serological study did not detect Brucella antibodies in two spotted hyenas from the Kruger National Park in South Africa (131).

Family Canidae

Family Ursidae

We found research on Bartonella and Brucella in three bear species, namely black bear (U. americanus), brown bear (U. arctos), and polar bear (U. maritimus). Bartonella DNA was not detected in seven black bears from Colorado, U.S. (77). All other research was focused on Brucella in bears (119, 147, 148, 179, 180, 182–185). Despite high seroprevalence levels for Br. abortus antibodies in all investigated bear species, we could not find any report on successful isolation of Brucella from these animals. Serological tests of 61 black bears for Br. canis by Bronson et al. (178) were negative.

Family Mephitidae

Twelve skunks of two species, the hooded skunk (Mephitis macroura) and the striped skunk (M. mephitis), from Colorado, U.S., and Mexico were found infected with B. rochalimae and one skunk from Mexico was infected with B. vinsonii subsp. berkhoffii (67, 77).

Antibodies against B. abortus were found in 8.7% of striped skunks and 3.9% of western spotted skunks (Spilogale gracilis) from California, U.S. (127).

Family Procyonidae

The common raccoon (Procyon lotor) has a natural range from southern Canada to Panama. Of 37 raccoons trapped on St. Simon Island in Georgia, U.S., 12 were positive for B. henselae and one for B. koehlerae (59). Interestingly, raccoons from the western regions of the U.S. carried different species of Bartonella. Henn et al. (88) isolated B. rochalimae from 11 of 42 raccoons from California, and Bai et al. (77) found 11 of 186 raccoons from Colorado PCR positive for B. rochalimae and three for B. vinsinii subsp. berkhoffii. All 977 raccoons from Japan, where it is an introduced species, were PCR negative for Bartonella (95).

Two Brucella strains cultured from raccoons from Alabama were identified as Br. abortus biovar 1 (126, 177). Raccoons seropositive to Brucella species were found in California, Alabama, Florida, and Texas in the U.S. (115, 126–128). None of 63 raccoons from Nebraska, U.S., had antibodies to Br. canis (139). In South Korea, Brucella DNA was found in blood (1/9) and tissues (2/5) of introduced raccoons (172). Three (8.8%) of 34 brown-nosed coatis (Nasua nasua), which also belong to family Procyonidae, were serologically positive for Brucella in the Brazilian Pantanal (149).

Family Mustelidae

Mustelidae is the largest family in the order Carnivora. Many terrestrial species of this genus were tested for Bartonella, including the beech marten (Martes foina), pine marten (M. martes), Japanese marten (M. melampus), American badger (Taxidea taxus), stoat (Mustela erminea), Japanese weasel (M. itatsi), least weasel (M. nivalis), Siberian weasel (M. sibirica), American mink (M. vison), European polecat (M. putorius), and ferret (M. putorius furo) (Table 1). However, out of 16 mustelid species tested for Bartonella DNA, only two cultures were obtained: one from a Japanese badger (Meles anakuma) and another from a Japanese marten (95). The isolate from the marten was close to Bartonella washoensis, a species typically found in squirrels, suggesting that it could have potentially “jumped” from a squirrel to its natural predator. The isolate from the Japanese badger was unique, with the closest match being to B. clarridgeiae and B. rochalimae (95). Bartonella clarridgeiae or related sequences were also detected in a beech marten and in European badgers, all from Spain (64, 83).

In North Carolina, U.S., Chinnadurai et al. (109) revealed a novel Bartonella species in 19 (29%) of 65 tested river otters (Lontra canadensis). Bartonella infection was detected in 45% (23/51) and 10% (3/30) of heart valves of northern and southern sea otters (Enhydra lutris kenyoni and E. l. nereis), respectively, by PCR (108). Analysis of the Bartonella ITS region identified two Bartonella species in those animals: a novel species closely related to Bartonella washoensis and Candidatus B. volans, whereas another genotype was molecularly identical to B. henselae. Sera from 50% of necropsied and 34% of presumed healthy, live-captured northern sea otters and in 16% of necropsied southern sea otters contained antibodies against Bartonella species (107).

Antibodies against Brucella species were detected in the American badger (Taxidea taxus), American mink (Neovison vison), European mink (Mustela lutreola), Eurasian otter (Lutra lutra), wolverine (Gulo gulo), and northern, southern and Asian sea otters (Enhydra lutris keyoni, lutris, nereis) from Europe, Asia, North and South Americas (11, 124, 125, 127, 174). We found only one report of successful culturing of Brucella (Br. abortus) from terrestrial mustelids (farmed European mink) and only one report of PCR detection of Brucella DNA in tissues of Asian badger (Meles leucurus) (172, 240). Similar to Bartonella, sea otters carry different species of Brucella than terrestrial mustelids. Investigating rectal swab samples of Asian sea otters (E. l. lutris) from Russia (168) found DNA of three Brucella species (Br. abortus, Br. melitensis, and Br. pinnipedialis). Miller et al. (169) isolated marine Brucella from a southern sea otter (E. l. nereis) with osteolytic lesions that was stranded on the central California coast. Antibodies to Brucella were detected in Northern sea otters (E. l. keyoni) from Alaska in the U.S. and Russia (120).

Families Phocidae, Otariidae, and Odobenodae

There is only one report on the identification of Bartonella in any of the pinnipeds, including walruses, eared seals, and true seals. Morick et al. (112) tested spleen samples and seal lice (Echinophtirius horridus) collected from seven harbor seals (Phoca vitulina). One spleen of 48 tissue samples and one of six lice pools were positive. The Bartonella species identified in the spleen and lice were found to be identical to each other by two genetic loci. One genetic marker identified the genotype as B. henselae, while another marker indicated 97% sequence similarity with B. grahamii.

In contrast to Bartonella, there is abundant evidence of Brucella infections in various species of the clade Pinnipedia. In family Phocidae (true seals), cultures of Brucella species were obtained from hooded seals (Cystophora cristata), gray seals (Halichoerus grypus), ringed seal (Phoca hispida), harp seal (Pagophilus groenlandicus), and harbor seal (Ph. vitulina) (170, 171, 206, 208, 214, 223, 224, 226, 231, 233). All identified cultures from true seals were Br. pinnipedialis. Serological evidence of Brucella was reported from investigation of even more species of true seals, including the bearded seal (Erignathus barbatus), ribbon seal (Histriophoca fasciata), leopard seal (Hydrurga leptonyx), Weddell seal (Leptonychotes weddellii), crab-eater seal (Lobodon carcinophaga), southern elephant seal (Mirounga leonina), Hawaiian monk seal (Neomonachus schauinslandi), Ross seal (Ommatophoca rossii), and several species of the genus Phoca.

In the family Odobenidae (walruses), Nielsen et al. reported serological prevalence of 12% (7/59) in 1996 and 3% (5/170) in 2001 in Atlantic walrus (Odobenus rosmarus rosmarus) from Canada; however serological tests of 40 Pacific walruses (O. r. divergens) from Alaska by Calle et al. (211) showed no antibodies to Brucella species

There are multiple reports of Brucella antibodies in fur seals and sea lions of the family Otariidae—nine species of the genera (Arctocephalus, Callorhinus, Eumetopias, Neophoca, Phocarctos, and Zalophus) (Table 2).

Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.