03 October 2010

Olive passes away unexpectedly

David Vaughan
Olive. Photograph by Karin Schwerm

David Vaughan is the Two Oceans Aquarium’s aquatic animal health researcher. He conducts research into various fish parasites and other health issues affecting aquatic animals at the Aquarium.

It is with much sadness that I write this article. Olive, our beloved 200kg giant short-tail stingray died suddenly, just before she was due to be released back into the exhibit after spending time in quarantine. Our curatorial team is devastated by her sudden and unexpected passing. Having seen her recover from various ailments in the past, but recently witnessing her final breath, I am left with many more questions than answers. 

In the beginning

Olive was caught in Struisbaai near Cape Agulhas in May 2008 and was a medical challenge from day one. She was caught by hook and line from a boat, but the hook pulled loose from her mouth and snagged her underside, just inside her left wing. This caused a significant tear, and upon her arrival at the Aquarium a veterinary surgeon was called in to stitch the wound. He was most intrigued and excited to have this opportunity. Olive was given a course of antibiotics to prevent secondary infection and remained in quarantine until she healed sufficiently and was ready for release into the I&J Predator Exhibit.

The tokolosh makes its appearance

After six happy months on display, interacting with divers and her adopted family, she contracted a Heterocotyle tokoloshei infection. The tokolosh worm is a monogenean flatworm parasite that attacks gill tissue. Monogeneans continuously produce microscopic eggs which are shed into the water and attach to debris where they embryonate and hatch as free-swimming larvae. They then actively seek out a new host to infect.

The tokolosh worm is species-specific, which means that it only infects one species, in this case short-tail stingrays. As a result, Olive’s infection increased while on display and it was decided to transfer her to the quarantine facility where the worm infection could be treated.

Details from a previous infection of the same worm provided us with the data necessary to design a new treatment programme, one that would allow us to break the lifecycle. A special drug called praziquantel, specifically used in the treatment of parasites, was administered orally while Olive was under anaesthetic. The drug was disguised in small gel capsules and placed inside pieces of food that were carefully inserted directly into her stomach.

This ensured that she obtained both the nutrition she needed and the correct oral dosage of the drug to ensure its efficacy.

The procedure was repeated to coincide with intervals of expected re-invasion by new worm larvae, determined by water temperature. Once Olive recovered and was eating on her own again, she was re-introduced into the exhibit.

The tokolosh returns

Approximately six months later she again became infected with H tokoloshei. After some thinking and investigating, I determined that some of the eggs that were produced in the I&J Predator Exhibit just prior to Olive’s move to quarantine had survived long enough to cause the re-infection after she returned.

The number of worms in the exhibit had slowly increased until Olive again began to show signs of distress.

Again she was moved to quarantine for treatment and an extended period of isolation from the exhibit to ensure that any remaining eggs in the system hatched and were removed from the exhibit before she was re-introduced. These eggs would therefore not pose a re-infection risk.

Once the worm larvae hatch, they are generally limited to only a few days in which to find a new host before they run out of energy reserves and die. The trick, however, is knowing how long the eggs will take to hatch, given the direct influence of temperature on the rate of embryonation. Temperature fluctuates seasonally and with weather patterns.

Photo courtesy Day Is Coming

Mysterious circumstances

Olive responded very well to her treatment and her extended stay in the 30 000-litre quarantine pool. On occasion, she would even come up to see who was looking at her and was happily eating by herself.

A week before her scheduled return to the I&J Predator Exhibit, however, she suddenly refused to eat. The following Monday the water in her pool took on a brownish opaque colour and further investigation of water samples determined that the colour of the water was produced by blood cells.

But why? She was anaesthetised and small amounts of blood could be seen flowing gently from her mouth and gill openings. This with no obvious signs of injury anywhere! More bizarre was that her blood was not clotting when it came into contact with seawater as sharks’ blood normally does. We immediately called in the vet to have a closer look and to give us his opinion while she was still anaesthetised.

The vet could not locate the source of the slow-diffusing bleeding and suggested that the blood had somehow lost its normal ability to clot. Normally, shark blood clots rapidly when it comes into contact with seawater, forming jelly-like lumps.

We realised that time was of the essence and that stopping the bleeding was our highest priority. Unfortunately Olive’s condition was, until now, unheard of. The vet suggested we try an intravenous injection of vitamin K1, a known blood-clotting agent that is usually given to newborn human babies immediately after birth. The problem was that we did not have a known dosage for stingrays, so a quick phone call was made to a specialist vet in Thailand, who suggested we use a mammalian dosage. Like a shot, the vet took off on foot toward Somerset Hospital to acquire some vitamin K1 from the maternity ward while our team remained with Olive.

After a short while, the vet returned with just enough ampoules of the vitamin necessary to treat Olive for a single application. I immediately administered the vitamin intravenously into the caudal vein at the base of her tail.

She was slowly brought out of anaesthesia and we increased the water flow and filtration in her pool. The next morning, Olive’s breathing had slowed down dramatically. After a few hours her breathing became less rhythmic and I watched sadly as she took her final breath. Although our entire team was devastated we needed to act quickly to perform a necropsy to determine the exact cause of death.

I contacted the director of the Provincial Veterinary Laboratory Service in Stellenbosch, Dr Tertius Gous, who was able to perform the necropsy for us. I took Olive’s body to the labs in Stellenbosch, where both doctors Gous and Gers were standing by. The examination was very thorough and the cause of death was determined as septicemia, the result of a bacterial infection that had originated in the reproductive system and had then become systemic.

Toxins caused by the infection in her bloodstream may have caused cell walls to rupture, resulting in the slow-diffuse bleeding that we saw. Of particular interest to us was that no parasites were found post-mortem, which was an indication of the success of her previous treatment.

Dr Gous suggested that her infection might have been contracted if there had been an abnormally high bacterial load in the water system, but this remains to be investigated. He concluded that septicemia kills exceptionally quickly and that we had done all we could to save her. This, at least, was a comfort to us all.

I am incredibly grateful to our team of dedicated individuals who once again showed such a high level of care and support for one of our animals. Particular mention must be made of Ruth Wright, who stayed up all night tending to Olive. Also, to the members of our technical team who adapted and balanced the entire water supply of the Aquarium to ensure that we could repeat anaesthetic procedures, and lower and re-fill Olive’s pool as and when needed. These people are the very reason why, despite adversity, we can still find inspiration.

Rest in peace, old girl, we will all miss you.

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