Monthly Archives: December 2013

Piranha attacks

Attribution: Andrewself at en.wikipedia.org

Jaw of the piranha

70 people were injured in a piranha attack in Argentina on Christmas Day. While nobody was killed, one can imagine the panicked atmosphere present as bathers who were simply trying to cool off were suddenly involved in a fish biting frenzy. The question is, what sequence of events led to this happening? The media has implicated hot weather and fisherman waste as the inciting factors. Other authors have discussed similar attacks in the literature, and implicate damming of streams and rivers causing ideal spawning grounds for piranhas. These spawning grounds can then coexist with recreational areas, and this leads to the fish being in close proximity to people.

There is a large amount of folklore surrounding piranhas and their behavior. What is important to note is that the bites are typically defensive, and the fish are not feeding on humans (or other large mammals typically).  The documented cases of piranhas eating humans involve people dying of other causes, then being eaten by the fish. The defensive nature of piranha bites is evident in that the most are single bites that are of a warning behavior. That bite can pack a punch, as one study demonstrated that piranhas bite up to three times harder than alligators proportionally.

This bite is typically circular and crater-like in nature, and damages skin and underlying tissues. The majority of these bites are on the lower extremities, which is not surprising. Most need minimal first aid, but occasionally bites can amputate digits or cause severe bleeding. They do not seem to need prophylactic antibiotics, but can rarely become infected with pathogenic bacteria, so the wound needs monitoring.

As far as mass attacks go, they typically occur during the major spawning seasons for piranha. They also occur most often when large numbers of people are in the water, and at shallow dammed sites. Because dammed sites can allow spawning year round, and allow larger groups of people to recreate together the attacks can be more common and larger in size. Thus, it seems that the attacks are fairly predictable, and not something that should cause paranoia.

Piranha attacks in dammed streams used for human recreation in the State of São Paulo, Brazil
http://www.ncbi.nlm.nih.gov/pubmed/21085879
Mega-Bites: Extreme jaw forces of living and extinct piranhas (Serrasalmidae)
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3526859/
Piranha attacks on humans in southeast Brazil: epidemiology, natural history, and clinical treatment, with description of a bite outbreak.
http://www.ncbi.nlm.nih.gov/pubmed/14719860

How long can we delay recompression?

Decompression sickness is the clinical constellation of symptoms that result from gas bubbles that form after going from a high pressure environment to a lower pressure environment. Classically, it was discovered in caisson workers, but today most of the cases are due to diving. The bubbles are not from the oxygen that is required for the diver to breathe at depth, but from the inert gases mixed with it to prevent oxygen poisoning.

Neutral Buoyancy Laboratory

Source: Mike Renland

Symptoms can be varied, from muscle and joint pain, to itching, to fatigue, to neurologic deficits and more. Current teaching is to refer all patients with suspected decompression sickness to facilities with hyperbaric treatment facilities as soon as possible. With more and more people flying to distant locales to dive, people are presenting with decompression illness days later. This isn’t necessarily a new phenomenon, as this article is from 1984.

It’s a case series, and only 3 patients at that. They presented to hyperbaric centers at 7, 5, and 3 days after symptoms started, respectively. All had neurological involvement. All also had complete resolution of their symptoms after appropriate treatment, at least until their one year followup.

So is there a consensus on how to treat patients who have delayed presentation? Not that I could find. The authors recommend titrating according to patient response. That isn’t particularly helpful, but all of the patients in this series were treated with US Navy Treatment Table 6.  Per the article, there have been successful treatments as far as 10 days out from symptom onset. As always, you can contact the Diver’s Alert Network at +1-919-684-9111 for help with managing your patient.

Delayed treatment of serious decompression sickness
http://www.ncbi.nlm.nih.gov/pubmed/3977150