DISEASES

Comprehensive review of the diseases of Australian pin­nipeds is covered in Barnes et al. (2008) and Ladds (2009). More recent literature is reviewed here.

7.1 Infectious diseases

Several recent serosurveys in Southern Hemisphere pin­niped species have increased our understanding of the epizootiology and incidence of infectious diseases in free- ranging populations.

7.1.1 Protozoal diseases

a. Toxoplasma gondii

Serosurveys of Australian fur seals, Antarctic fur seals, Weddell seals, crabeater seals and Ross seals did not detect antibodies against T. gondii (Lynch et al. 2011c; Tryland et al. 2012). However, antibodies (titres >1:25) against T. gondii were detected in 13.3% of Antarctic pin­nipeds tested by Rengifo-Herrera et al. (2012). Those authors postulated that exposure to T. gondii might have occurred outside Antarctica.

b. Giardia duodenalis

Delport et al. (2014) screened 271 faecal samples from Australian sea-lions using PCR targeting the 18S rRNA of Giardia. The presence of G. duodenalis assemblage AI and B in Australian sea-lions was considered a strong indicator of transmission from terrestrial mammals to the marine environment.

7.1.2 Nematodiasis

Hookworm infection is a recognised cause of morbidity and mortality in free-ranging otariid seal pups (Marcus et al. 2014b). Ramos et al. (2013) found that hookworms (Uncinaria sp.) in Australian fur seals, long-nosed fur seals and Australian sea-lions were genetically similar. Marcus et al. (2014a) studied the host-parasite-environ­ment relationship of the Australian sea-lion and the hookworm U. sanguinis, and determined that it is a sig­nificant agent of disease in pups and could play a role in population regulation in this species. Ivermectin (200 μg/ kg SC, 500 pg/kg spot-on) is highly effective at eliminat­ing U. sanguinis in Australian sea-lion pups and iver­mectin treatment had a positive effect on clinical health parameters (Marcus et al.

7.1.3 Viral disease

Phocine distemper virus (PDV) infection is a major infec­tious disease risk for pinnipeds worldwide, but PDV epi­zootics have not been confirmed in Southern Hemisphere seals. Tryland et al. (2012) found no serological evidence of exposure to PDV in Weddell, Ross and crabeater seals in Antarctica, and Lynch et al. (2011c) found no evidence of population exposure to morbilliviruses in Australian fur seals in Bass Strait.

7.1.4 Bacterial diseases

a. Brucella

Positive antibody titres to Brucella spp. have been reported in a large number of marine mammal species in the North­ern Hemisphere and in Weddell seals, southern elephant seals, Ross seals, crabeater seals, leopard seals, Australian sea lions, Australian fur seals and long-nosed fur seals (McFarlane 2009; Lynch et al. 2011c; Tryland et al. 2012; Jensen et al. 2013). In 2007, pinniped and cetacean isolates were named as new species within the genus Brucella: B. pinnipedialis and B. ceti (Foster et al. 2007). The potential impact of infection in pinnipeds is unknown, but Brucella spp. cause abortion in terrestrial species and cetaceans.

Lynch et al. (2011c) detected an overall Brucella spp. antibody prevalence of 57% in female Australian fur seals in Bass Strait, but found that there was significant varia­tion between 2007 (74%) and 2008 (53%). The prevalence of active infection was thought to be low compared with antibody prevalence. There is no conclusive evidence that Brucella spp. cause abortion in Australian fur seals (Lynch et al. 2011a).

b. Coxiellosis

Coxiella burnetti is an emerging wildlife disease and Gardner et al. (2022b) reported 10.6% to 40.9% prevalence following examination of placental tissue and aborted foetuses from two Australian fur seal colonies in Bass Strait. The organism appears not to be an Australian ter­restrial genotype, but rather is a marine-specific genotype (Gardner et al.

c. Nocardiosis

Nocardia spp. have caused pyogranulomatous lesions in free-ranging and managed marine mammals, including phocid seals (St Leger et al. 2009). There has been one reported case of pulmonary disease in a free-ranging leop­ard seal and two reported cases of systemic nocardiosis in zoo-housed leopard seals (Shrubsole-Cockwill et al. 2010).

d. Tuberculosis

Mycobacterium pinnipedii has been isolated from cases of tuberculosis (TB) in zoo-housed or free-ranging Austral­ian sea-lions, long-nosed fur seals, Australian fur seals, Antarctic fur seals and a subantarctic fur seal. Infection is predominately associated with granulomatous lesions in the lung, lymph nodes, pleurae, spleen and peritoneum; however, there have been cases of disseminated disease (Cousins et al. 2003; Barnes et al. 2008; Ladds 2009; Boardman et al. 2014). Clinical signs are non-specific and include weight loss, exercise intolerance and dyspnoea. Coughing may not be a prominent clinical sign (Kiers et al. 2008).

Mycobacterium pinnipedii infection has been reported in cattle in NZ and transmission of infection from free- ranging pinnipeds was suspected. In all cases, cattle had access to seals via beach grazing areas or waterways con­necting directly with the ocean (Loeffler et al. 2014). In managed animal populations, interspecific transmission of disease has also been recorded (Jurczynski et al. 2011). The prevalence of M. pinnipedii in free-ranging pinni­peds in Australian waters is unknown. Antibodies to M. tuberculosis complex were not detected in serum samples collected between 2007 and 2009 from 104 free-ranging adult female Australian fur seals (Lynch et al. 2011c). Otariid seals have been the source of zoonotic infection with M. pinnipedii.

Serologic tests have improved the capacity for ante­mortem diagnosis. Two antibody detection tests validated for use in elephants, multiantigen print immunoassay (MAPIA) and ElephantTB STAT-PAK® assay (Chembio Diagnostic Systems, Inc., Medford, NY, USA), have been used in a range of other species, including pinnipeds. A new-generation test for rapid point-of-care TB serodiag- nosis in elephants (DPP® VetTB Assay for Elephants, Chembio Diagnostic Systems) has also been evaluated in pinnipeds.

Jurczynski et al. (2012) examined 14 South American sea-lions (Otaria byronia) with suspected M. pinnipedii infection. The authors used a range of antemortem diag­nostic methods, including sputum sample microscopy/ Ziehl-Neelsen staining, PCR and culture, STAT-PAK® assay, MAPIA, DPP® VetTB assay and diagnostic imaging (CT scans were used to detect calcification of lymph nodes). Molecular typing was also used to identify the M. pinnipedii strains involved to determine strain origin. A case series subsequently described in a zoo-based colony held in New Zealand recommended a similar diagnostic approach for in-contact animals: two tracheobronchial lavages (for Ziehl-Neelsen staining, Mycobacterium tuber­culosis complex PCR, and mycobacteria culture), two DPP VetTB assays (taken at least 8 wk apart), and at least one CT scan (Chatterton et al.

One female South American sea-lion that had serocon- verted within the previous 6 mo was treated using a combi­nation of rifampicin 7.5 mg/kg PO sid, isoniazid 5 mg/kg PO sid and myambutol 15 mg/kg (Jurczynski et al. 2012). Post-treatment testing showed no evidence of active infec­tion up to the time of publication.

7.2 Non-infectious diseases

7.2.1 StarvationZexhaustion

Veterinarians may be asked to assess lone seals that have hauled out in urban coastal locations. These animals may come ashore to rest, but will also come ashore following injury/entanglement or disease, or because they are starv­ing (Barnes et al. 2008). An assessment of body condition is an important part of the clinical assessment. Muscle wasting around the lumbar spine and pelvis is an impor­tant feature. Ribs, lumbar vertebrae, pelvic bones and all bony prominences will become more evident as body condition declines (Fig. 45.3). In addition, in phocids a

Fig. 45.3. An emaciated, juvenile Australian fur seal (Arctocephalus pusillus doriferus). When viewed from behind, muscle wasting around pelvis and spine are clearly visible and ribs can be seen.

Fig. 45.4. An emaciated sub-adult southern elephant seal (Miroungaleonina). In phocid seals, loss of fat and muscle around the neck and shoulders often exaggerates the appearance of the head.

prominent neckline is indicative of poor body condition (Fig. 45.4).

Most Australian fur seals are born from mid-Novem- ber to mid-December and long-nosed fur seals from late December to early January (Kirkwood and Goldsworthy 2013). During December-February, there is high pup mortality. Compromised pups may appear on beaches near breeding colonies because of starvation (e.g. mater­nal inexperience), injury and disease. During summer storms, large numbers of pups may wash off low-lying colonies and drown (P Shaughnessy pers.

Along the Victorian coast, reports of juvenile Austral­ian fur seals mostly occur between November and Janu­ary (R McIntosh pers. comm.). In NSW and south-east Qld, juvenile long-nosed fur seals are more frequently reported during the winter (L Vogelnest, D Blyde and D March pers. comm.). In general, sightings of leopard seals in Australian waters occur from July to October, with a peak in August-September.

In otariid seals, weaning and transition to independ­ence occurs between 9 and 12 mo of age and the period following this transition is also associated with higher mortality rates. ‘Weanling’ otariid seals will haul out on land because they are starving and exhausted. Traumatic injury and/or parasitism may be a consequence of or fur­ther contribute to debility.

Of 28 leopard seals that were sighted in NSW during 1972-2003, 86% were determined to be less than 3 yr old and the majority observed on Australian beaches were in poor body condition when compared with those in Ant­arctica (Gray et al. 2009). Dispersal of leopard seals into

Fig. 45.5. Pulp width:tooth width (primary vertical axis) ratio and standard lengths (secondary vertical axis) of long-nosed fur seals (Arctocephalus forsteri) with previously estimated ages. Ages were estimated by analysing growth layer groups in post-canine teeth cementum. Pulp width:tooth width ratio was determined by measuring pulp width and tooth width of the left maxillary canine tooth on dental radiographs taken using the bisecting angle technique. Note that the pulp width:tooth width trend line is not statistically significant and is displayed as a guide only (K O'Connor pers. comm.). Standard length predictions for males and females are adapted from McKenzie et al. (2007), additional data K O'Connor and J McKenzie, data analysis by K O'Connor.

temperate regions is thought to be influenced by resource availability, particularly krill, which is thought to be more heavily utilised by juvenile leopard seals.

Accurate identification of species and age class is essential when making a clinical assessment of any young seal, as age will influence the course of action and prog­nosis. The prognosis is poor for milk-dependent pups and emaciated or severely injured seals older than 18 mo. Malnourished juvenile otariids (10-18 mo old) may be reported as being orphaned pups, but they are no longer milk-dependent. Definitive differentiation between pups and juveniles is via the teeth. The lower canines of Aus­tralian fur seal pups (up to 10 mo old) are approximately the same length as their incisors and post-canines; the lower canines of juveniles are at least twice the length of their other teeth (Kirkwood and Goldsworthy 2013). Ageing animals >10 mo old is more difficult. In long­nosed fur seals, use of dental radiographs to determine the pulp width:tooth width ratio may prove a useful technique for age determination of young seals (O’Connor and Vogelnest 2016) (Fig. 45.5).

When pinnipeds are present on beaches, any decision to intervene must be considered carefully, in consultation with the relevant government wildlife agency (State of NSW and Department of Planning, Industry and Envi­ronment 2021; State of NSW and Department of Planning and Environment 2023). Pinnipeds in good body condi­tion with normal behaviour or minor injuries may simply have hauled out to rest and should be monitored. Deaths of emaciated young pinnipeds are considered natural mortality events and in remote areas, such animals are likely to die undiscovered or be deliberately left undis­turbed by wildlife authorities. In urbanised coastal areas, there is greater public exposure and concern, and an imperative to protect beached pinnipeds from harassment by humans and domestic pets. Intervention to euthanase weak, poorly responsive, injured or emaciated pinnipeds is appropriate on welfare grounds. A decision to rescue and rehabilitate those with poor body condition and/or significant but treatable injuries must be carefully consid­ered. For most species, there is little conservation benefit from rehabilitation and release of individuals from large or expanding free-ranging populations. The care of pin­nipeds requires specialised facilities, specialist caretakers and a regular food supply, and sub-adult and adult otariids can be dangerous and difficult to manage. Strict biosecu­rity is required while the animal is in care to minimise risk of exposure to novel pathogens to which the free- ranging population may be naive. Habituation to people during rehabilitation may occur, with the potential to contribute to the issue of ‘problem seals’ once released. These seals may aggressively beg for food around jetties and fish-cleaning stations (although free-ranging seals may also be attracted to these areas simply because they are fed there). Further detail on intervention criteria is provided in policy and procedure documents produced by relevant state government agencies (e.g. State of NSW and Department of Planning, Industry and Environment 2021; State of NSW and Department of Planning and Environ­ment 2023). Little is known about the impacts and likely success of rescue and rehabilitation in Australian pin­niped species.

7.2.2 Anthropogenic trauma

Plastic has replaced natural fibres in the fishing industry over the past 40 yr and its widespread use has resulted in considerable quantities of fishing debris in the oceans.

Fig. 45.6. Juvenile Australian fur seal (Arctocephalus pusillus doriferus) with a monofilament fishing line entanglement. Exploratory behaviour is common in young seals and may lead to entrapment in synthetic materials. This results in severe laceration as the seal grows. Photo: Troy Muir

Fig. 45.7. Deep, full-thickness laceration following entanglement in a single loop of monofilament fishing line: sub-adult Australian fur seal (Arctocephaluspusillus doriferus).

Pinniped entanglements are largely associated with aban­doned, lost or dumped fishing gear, including trawl nets, monofilament lines and packing straps.

There does not appear to be a significant population level consequence of entanglement affecting Australian fur seals in Vic. (Lawson et al. 2015); however, entanglement in marine debris and fisheries by-catch poses a significant threat to Australian sea-lion populations (Goldsworthy et al. 2010). Even in the absence of population affects, there are clear welfare concerns associated with entanglement of individual animals (Figs 45.6 and 45.7). Entanglement has a multitude of consequences, including severe laceration/ wounds, strangulation, amputation and increased drag and restricted movement of the animal leading to exhaus­tion, starvation or drowning (Byard and Machado 2019).

In Tas., Australian and long-nosed fur seals have nega­tive interactions with aquaculture industry operations. Protocols have been developed to manage problem seals and include use of deterrents (such as bean bag projectiles and oleoresin capsicum spray) and sedation of seals for removal from fish cages and relocation (DPIPWE 2002).

7.2.3 Other trauma

Trauma from conspecific aggression was the major cause of pup mortality in Australian sea-lions at Seal Bay Con­servation Park, SA (McIntosh and Kennedy 2013). In southern Australia, pinnipeds are predated by white sharks (Charcaradon charcarias). Shaughnessy and Goldsworthy (2016) examined bodies of four free-ranging Australian sea-lions on a breeding colony off the coast of

Table 45.2. Clinical features of otariid keratitis

SA and concluded that the animals had died following lightning strike.

7.2.4 Ophthalmic disease

Ophthalmic disease is common in free-ranging and managed pinnipeds. Recent studies have described two major clinical presentations: progressive keratitis and lens-associated disease, including cataracts and lens luxation.

Although corneal and lens disease occur in both free- ranging and pinnipeds in managed care, there is a higher prevalence in pinnipeds under human care (Miller et al. 2013). Keratopathy can affect phocid and otariid seals in managed care. Colitz et al. (2010a) reviewed the ophthal­mic health of 113 otariid seals housed in managed care and found that 64.6% of animals were affected by pro­gressive keratitis. Lesions could be quiescent or active and three stages of development were described (Table 45.2, Plates 45.3-45.5).

A study of 111 Northern Hemisphere pinnipeds housed in managed care determined that 15.3% of ani­mals had dual diagnoses of lens luxation and cataract, and 34.2% had cataracts alone (Colitz et al. 2010b). Cata­racts and lens luxations have been observed in pinnipeds in managed care in Australia, including subantarctic fur seals, Australian fur seals, long-nosed fur seals and Aus­tralian sea-lions.

The apparent inability of pinnipeds to induce corneal neovascularisation as part of normal corneal healing has been implicated in their high incidence of ocular pathol­ogy. There is ongoing investigation into the neovasculari- sation response and the components of the angiogenic pathway in pinnipeds (Linnehan et al. 2013).

Exposure to ultraviolet (UV) radiation appears to be an important factor in development of keratopathy in pinni­peds in managed care. Studies suggest that doses of UVB radiation above the maximum tolerable dose will disrupt the normal orderly cell shedding process and homeostatic equilibrium of the corneal epithelium. In humans, the most common acute ocular effect of environmental UV radiation is photokeratitis and chronic exposure to UV radiation may play a significant contributory role in the development of several ocular diseases including keratitis and cataracts (Newkirk et al. 2007). Chronic corneal dis­ease contributes to subclinical or clinical uveitis, and uvei­tis can potentiate cataract formation (Colitz et al. 2010b).

Features of pinniped enclosure design and husbandry that appear important for prevention of UV damage include:

• Correct installation of shade structures - even when present, these may not provide complete shade and animals may display a preference for sunny areas in the enclosure.

• Minimising local surface reflection - paint colour used in pools must be dark and colours used in areas surrounding the pool should not be brightly painted or highly reflective.

• Reducing ‘sky fish’ during feeding - wild pinnipeds rarely gaze skyward and look downward into dark waters when hunting; however, seals in managed care are often fed from above (Colitz et al. 2010a; Gage 2012).

In closed water systems, oxidizing agents such as chlo­rine, ozone and bromine are used for disinfection, reduc­tion of growth of unwanted bacteria or algae and to improve water clarity. These agents may themselves cause damage to corneal tissues when in high concentrations. Additionally, oxidising agents will combine with dissolved organic material to produce intermediate compounds that may also damage ophthalmic tissues. These intermediate compounds are less commonly measured, so their con­centration and identification may be unknown (Latson 2009; Gage 2012). Anecdotally, pinnipeds maintained in natural seawater seem to have a lower incidence of oph­thalmic disease, when compared with those maintained in closed/semi-closed water systems (L Vogelnest pers. comm.; D Esson pers. comm.).

Veterinarians managing pinnipeds held in managed care must become familiar with water quality and life support system components, so that any risk factors for development of ophthalmic disease can be identified and addressed. Compliance parameters for closed or semi­closed water systems used to hold pinnipeds have been published (NSW DPI 2008) and detailed descriptions of life support systems and management of water quality are available (e.g. Mohan and Aiken 2004).

A case study reported by Gomes et al. (2020) describes chronic keratitis in a female long-nosed fur seal held in managed care that was held in a closed water system. Response to therapies (including oral NSAID, oral doxycy­cline, episcleral cyclosporine implants and superficial ker­atectomy) was transient and limited. Clinical resolution occurred following modification of the pool’s life support system: by removing more organic matter before applica­tion of ozone in the system, the production of disinfection by-products (intermediate compounds) was reduced.

Corneal trauma may also result from debris in pool water, fighting or other abrasive injury (Gage 2012). At one rehabilitation facility, corneal ulceration was most frequently attributed to trauma (Simeone et al. 2017).

A wide range of topical therapies has been used to manage keratitis and other ocular pathologies in pinni­peds. Application will be difficult unless animals are trained to accept ophthalmic preparations. Additionally, seals need to remain out of water for 15-20 min after application to ensure adequate absorption. Strong blepha­rospasm appears to be a feature of corneal disease in otariid seals and may be either a response to pain or irri­tation or a protective response (L Vogelnest pers. comm.). In some cases, seals will hold the affected eye firmly closed even when corneal disease appears not to be severe. Response to systemic analgesics and anti-inflammatory therapy may be poor and the eye may remain closed for long periods, making it difficult to examine and/or treat. Application of topical local anaesthetic drops along the eyelids (e.g. 0.5% proparacaine hydrochloride, wait 10 min for effect) may facilitate examination of the cornea (L Vogelnest pers. comm.).

Episcleral cyclosporine implants deliver therapeutic levels of cyclosporine to the cornea. These allow a low dose to be released to the eye for an extended period of time, without reliance on patient compliance. Silicone matrix cyclosporine implants have been used to treat keratopathy in pinnipeds in managed care, including Australian fur seals, long-nosed fur seals, Australian sea­lions and subantarctic fur seals (Colitz et al. 2016).

Oral doxycycline (10 mg/kg bid) is secreted in the tear film and will reduce matrix metalloproteinase activity and promote corneal epithelialisation. Oral administra­tion of doxycycline at 10 mg/kg and 20 mg/kg PO sid resulted in concentrations in plasma and tears of northern elephant seals likely to be clinically effective for treatment of bacterial ulcerative keratitis and ocular surface inflam­mation (Freeman et al. 2013). Subconjunctival antibiotic poloxamer gels, containing enrofloxacin 2%, were as effective as oral doxycycline for treating superficial cor­neal ulceration in California sea-lions (Simeone et al. 2017). Systemic anti-inflammatory drugs (carprofen 2-4.4 mg/kg PO sid or meloxicam 0.1 mg/kg PO/IM sid), tramadol (0.5-4 mg/kg PO sid-tid) and sustained-release buprenorphine (0.12 mg/kg SC q 72 hr) have been used to manage ocular pain in pinnipeds (C Colitz pers. comm., Simeone et al. 2017).

Antioxidants may protect ophthalmic tissues against photo-oxidative stress. Marine mammal antioxidant sup­plements are commercially available (Eye-SEA™, Animal Necessity, LLC, NY, USA).

7.3 Syndromes of uncertain aetiology

7.3.1 Gestational failure in Australian fur seals

Gibbens et al. (2010) detected a 31% difference between rates of pregnancy and rates of birth in free-ranging Australian fur seals and suggested that a substantial number of females aborted fetuses before parturition. Brucella spp. infections in terrestrial mammals are a well-recognised cause of abortion and Lynch et al. (2011a) found inflammatory lesions in fetal tissues that sug­gested the involvement of infectious agents in some instances of gestational failure. However, failure to detect or isolate Brucella spp. by molecular means from fetal tissues did not support the involvement of that pathogen. Gibbens and Arnould (2009) studied pup production in a colony of Australian fur seals in Vic. and proposed that reproductive failure is a physiological outcome related to interannual variation in food availability. It is not yet known if infection with Coxiella burnetti is contributing to reduced pup production seen in this species (Gardner et al. 2022b).

7.3.2 Alopecia affecting Australian fur seals in north-western Bass Strait

Since 1989, an alopecic syndrome has been recognised in free-ranging Australian fur seals in Bass Strait colonies (Lynch et al. 2011b). The syndrome is characterised by bilaterally symmetrical loss of guard hairs over the dorsal thorax. In severe cases, this extends over much of the back and head. The syndrome primarily affects juvenile females and the highest prevalence of disease was noted at a large breeding colony on Lady Julia Percy Is., in north-western Bass Strait. Disease was also present in nearby colonies.

Thermographs from affected seals confirmed greater heat loss from alopecic areas than from normally furred regions of the body and alopecic juveniles had a lower mean body condition index compared with unaffected juveniles.

There were compositional differences between the hair of affected and unaffected animals that suggested affected seals had suboptimal hair strength. Higher toxin levels in affected seals suggested consumption of prey items con­taining higher levels of pollutants. A preliminary study of animals from Lady Julia Percy Is. has indicated that there are significantly greater concentrations of dioxin-like pol­ychlorinated biphenyls in tissues from alopecic seals, when compared with tissues from unaffected seals (Taylor et al. 2018).

ACKNOWLEDGEMENTS

I thank Stephen Jackson for clarification on taxonomy; and David Blyde, Carmen Colitz, Douglas Esson, Duan March, Rebecca McIntosh, Hayley Newman, Katelyn O’Connor, Peter Shaughnessy, Dayle Tyrrell and Larry Vogelnest for information they provided for this chapter.