Case of the Month

November / December 2018

Case presentation

Max Winkler, SASTM

In March 2018 a patient presented to a health care facility in Hout Bay, Cape Town after having been bitten by a large male brown fur seal at the local harbour earlier that day. He had travelled with his wife from the northern suburbs of Cape Town to spend the afternoon sightseeing and eating fish and chips at the picturesque local fishing harbour. After lunch they decided to take a stroll along the quay and while walking along the quayside he noticed a local resident feeding fish to a large male fur seal. This practice is common amongst residents, who entice visitors to feed the seals and then charge the tourists a small fee. According to the patient, the fur seal reared up and bit him on the inner aspect of his right thigh as he was walking past the animal.

What is the distribution of the fur seal in South Africa?

Seals, including fur seals, are members of the pinniped family with the most notable distinguishing feature being the presence of external ears in fur seals and internal hidden ears in true seals. In South Africa, brown fur seals are the predominant species of pinniped found along our coastline and their habitat extends from Cape Cross in Namibia to Port Elizabeth in the Eastern Cape where they breed on rocky outcrops and small offshore island. Near the base of sentinel peak in Hout bay on a small rocky island off the coast (Seal Island) there is a large breeding colony of brown fur seals. These seals often visit the local harbour to forage for fish and sun themselves on the quay. The majority of bites (n=8) have occurred in the harbour on the quayside involving a tourist and local seal “tamer” trying to entice visitors to take photos and feed the seals for a small fee. However there have also been some incidents of minor bites and scratches involving swimmers (n=2) during organized snorkeling tours to Seal Island where snorkelers can interact and swim with the seals in their natural habitat.

Clinical findings

When he arrived at the medical facility, a large puncture wound on the inner aspect of his right thigh was noted. The wound was 4-5 cm in diameter and extended through the superficial layers into the deep tissues and muscle bed of the right thigh. No neurological or vascular deficits were found distally. Although the wound was bleeding profusely at the time of presentation, his blood pressure was stable and he showed no signs of hypovolaemia. The patient is known with type 2 diabetes and is currently well controlled on oral medication. He has no other co-morbidities or allergies of note.

What soft tissue infection, specific to seals, must be considered in a bite of this nature?

Wounds sustained in the marine environment are at risk of developing atypical bacterial infections and require different management and treatment to standard animal bites. Seal bites are no different and can be the source of “seal” or “spekk” finger which was once a common hand infection amongst sealers and hunters who had been exposed to seals while hunting or after they had been working with seal pelts or meat in the early 20th century. In the second half of the 20th century the majority of “seal finger” cases involved veterinarians and researchers who had been handling seals during the course of their work (1).

If a possible “seal finger” infection is suspected, what is the recommended first line antibiotic for the treatment of this condition?

The typical presentation of “seal finger” is the development of a progressive soft tissue swelling and erythema surrounding the site of inoculation which normally occurs within the first 3-4 days after the bite has occurred. If left untreated this infection spreads to the surrounding tissues and can cause severe swelling, local erythema and discomfort; in advanced cases it can involve adjacent bones and joints. The majority of cases responded poorly to treatment with first line antibiotics such as most beta-lactams. In 1991 mycoplasma was first identified as the most likely causative organism after Mycoplasma phocacerebrale was isolated from the wound of a seal trainer and the seal that bit him (2).

High dose tetracyclines are currently recommended for the treatment of mycoplasma infections including “seal finger”. It is thought that the lack of a cell wall in these organisms affects the efficacy of the beta-lactam antimicrobials. Quinolones, as a class, are considered to be effective against other mycoplasma species and can be considered as possible alternative to tetracyclines.

What are the possible long-term complications of this infection?

There are numerous reports of severe complications as a result of incorrectly treated cases of “seal finger”. These complications include decreased joint mobility in the affected joint, eventually leading to ankyloses and severe pain which may require surgical arthrodesis or even amputation of the affected joints.

Which other soft tissue infections, apart from “seal finger” can cause a similar clinical presentation post seal bite and exposure to sea water and should be considered in the differential diagnosis?

  • Cellulitis: this soft tissue infection is a common complication of most animal bites and is generally caused by gram positive organisms such as Streptococcus and to a lesser degree Staphylococcus. This should always be high on your list of differential diagnoses in the majority of cases and it would normally respond well to a standard beta-lactam antibiotic.
  • Erysipeloid: this soft tissue infection is caused by the Erysipelothyrix rhusiopathae organism and is found in the soil, fish, poultry and birds and can contaminate bite wounds. It typically causes severe local erythema and swelling and may have systemic complications such as endocarditis. The causative organism is easy to culture and identify and responds well to beta-lactam antibiotics.
  • Atypical mycobacterium: this soft tissue infection is caused by Mycobacterium marinum and should always be considered in any wound with a history of exposure to the marine environment. It also causes progressive swelling and erythema at the inoculation site, however the disease course is more insidious in onset and symptoms take longer to develop. All the Mycobacterium species are difficult to culture and identify using standard laboratory techniques and they do not respond well to first line antibiotics such as beta-lactams.
  • Vibrio infections: this soft tissue infection is caused by Vibrio vulnificus and may present with a severe, rapidly progressive soft tissue infection after exposure to sea water and should all be considered in any bite or soft tissue injury from a marine organism. Vibrio infections are commonly seen after exposure to warm, shallow coastal water and can lead to a severe necrotizing fasciitis often needing extensive surgical debridement. This infection has never been described post seal bite and the water temperature where our seal bite cases occurred is likely too cold to harbor this pathogen.
Final diagnosis

The diagnosis in this case is straight forward: a deep wound on the inner thigh after being bitten by a local brown fur seal. Although there was no further differential diagnosis to consider at the time of presentation, it is important to monitor for complications and possible wound sepsis at the bite site at follow-up visits. Seal bites are at high risk of infection since multiple organisms have been found in the mouths and bites of seals. For this reason the patient was placed on prophylactic antibiotics to prevent secondary soft tissue infections.

Management and clinical course

The edges of the wound were infiltrated with xylocaine, cleaned and irrigated with chlorohexidine and iodine disinfectants. The ragged wound edges were debrided and haemostasis was achieved. Due to the severity and depth of the wound surgical closure was necessary; this was achieved with interrupted chromic sutures for the deeper layers and interrupted nylon sutures to close the skin. A pressure dressing was applied to the wound and tetanus vaccine was given in the left deltoid. The patient was discharged on a course of Amoxicillin-Clavulanic acid 1g BD and Doxycycline 100mg BD for seven days. The wound healed without any further complications.

A number of fur seal bites have been treated at this facility over the course of 2018, with ten recorded cases to date. Seven of these were severe wounds which required suturing and prophylactic antibiotic cover.

Have there been any local cases of “seal finger” infections described in the literature?

In the literature, the only reference to possible local cases, was personal communication with seal researchers who had encountered possible infections after exposure to fur seals in South Africa and New Zealand (3). However, there have been confirmed reports of three “seal finger” infections in South African researchers who were bitten while working with Ross seals in Antarctica in 1982 who developed an infection highly suggestive of “seal finger” after being exposed to tissue from seals during dissection of seal carcasses (4).

Should rabies or tetanus post exposure prophylaxis for a seal bite be given?

Although Clostridium tetani has not been found amongst seals, this bacterium is present in the marine environment and for this reason tetanus vaccination is recommended for all marine injuries due to the possible risk of exposure to infection.

The risk of rabies exposure is extremely rare amongst seals. There has only been a single recorded case of rabies in a ringed seal in Norway in 1981 during an outbreak amongst arctic foxes on the mainland (5). Therefore rabies prophylaxis is not recommended in this instance.


  1. White CP, Jewer DD. Seal finger: A case report and review of the literature. Can J Plast Surg. 2009;17(4):133–5.
  2. Baker AS, Ruoff KL, Madoff S. Isolation of Mycoplasma species from a patient with seal finger. Clin Infect Dis. 1998 Nov;27(5):1168–70.
  3. Cawthorn MW. Seal finger and mycobacterial infections of man from marine mammals: occurence, infection and treatment. Conservation Advisory Science Notes No. 102, Department of Conservation. Wellington, 1994.
  4. Panagis K, Apps P, Knight M. Seal Finger: occurence in Antarctica. S Afr J Antarct Res. 1982;12:49.
  5. Odegaard OA, Krogsrud J. Rabies in Svalbard: infection diagnosed in arctic fox, reindeer and seal. Vet Rec. 1981 Aug 15;109(7):141–2.

Figure 1) photo of tourist interacting with an adult male fur seal in Hout Bay

Figure 2, 3) Seal bite wounds that were treated in the Hout Bay facility

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