Category Archives: infectious disease

SteriPEN, convenient or worthless?

Clean water is of utmost importance, whether you’re backcountry hiking, camping, or travelling abroad. And there are many ways to disinfect water, including chemical tablets, mechanical filters, simply boiling, and ultraviolet light. And while we know that UV light from the sun works with enough contact time, does a handheld UV light work well enough to be safe?

They’ve been around since the late 90s, but decreases in size and cost have made them more popular recently. They are lighter than ceramic filters, don’t require heating and then cooling the water, and they don’t leave a funky taste in the water after use. And while you can go to SteriPENs’s website and see a bunch of articles they sponsored showing how awesome they are, it’s nice that an independent group has finally looked into their effectiveness.

One of the things the article points out is that UV light is bacteriostatic, not bacteriocidal. Their DNA is damaged, so they can’t reproduce or cause infection (probably), but the water is disinfected, not sterile. Also, while still effectively treated by UV light, viruses and spores require much higher doses to be inactivated.

They tested the function against of the SteriPEN against water bottles contaminated with Escherichia coli, Staphylococcus aureus, and the spore of Geobacillus stearothermophilus. Using 1 L bottles in 3 different styles (wide mouth reusable, narrow mouth reusable, and disposable narrow mouth bottles), they either agitated as per the instructions for the device, or let the water remain calm. For wide mouth containers, you can stir. With narrow mouth bottles, you need to plug the mouth with the pen and invert and shake. However, knowing that many people don’t do this, they also did a test by simply stirring the narrow mouth bottle as well. They also measured the spectrum emitted by the device during use.

Used correctly the SteriPEN works pretty well. Bacteria counts were reduced more than 99.99%, but spores were only reduced 99.57% on average. If you don’t agitate the water, this drops to 94.2% on average. The SteriPEN does emit its maximal intensity of UV at 254nm, which is the most efficient wavelength for bacterial DNA. And in a bottle made of glass, PET, or metal, there’s no risk of UV injury to the user, as it’s all blocked. However, in a big open-topped pot, there’s a risk of UV emission that could be hazardous to the eyes. Thankfully, the device won’t turn on if not immersed in water.

Therefore it is ok to use a SteriPEN to disinfect your water, as long as you’re doing it right. You’ve got to agitate the water, not just put it in and let it sit there. These authors also didn’t test against viruses, but the manufacturer does have data, and since this paper replicates some of their other results, it’s not unreasonable to state that it likely works against those as well.

Downsides are a few. 4 AA batteries only gives you 100 cycles and the bulb is pretty fragile, so pack extras. It doesn’t filter out toxins, and turbid water decreases efficacy, so you might night a filter anyway. This particular device has 2 settings, 90s of light for 1L containers, 48s for 0.5L ones, so you’ll need to make sure you have it set for the correct size as well. Finally, it doesn’t keep the water disinfected forever, so be aware that the water can become contaminated again and require re-treatment.

Drinking water treatment with ultraviolet light for travelers – Evaluation of a mobile lightweight system
And it’s FOAMed!

Komodo dragons: Myth vs Reality

The Komodo dragon is a creature that inspires fear and mysticism in many. It’s got all the characteristics of a good monster movie: only found on rare tropical islands, large, and possessing magical saliva that can kill. First identified by the west in 1910 by Dutch sailors, they reported the lizards could spit fire and reached 7m in length. In reality the lizard can only get up to 3m and can weigh 70kg, and none have been identified as either breathing or spitting fire.

Komodo dragon (Varanus komodoensis), Komodo National Park, Indonesia

This review comes after a zoo worker was bitten on the hand by a small Komodo dragon. She had transient hypotension, and a retained tooth on xray. This was not removed, and after loose approximation (Ed. note: never do this), she was discharged on antibiotics. Thankfully the tooth came out on its own, and she did not develop a deep space infection. After this case report, the authors decided to do a literature review, knowing that it would help them get published.

Many of us are taught in school that Komodo dragon saliva is a possibly venomous, potentially fatal concoction of particularly virulent bacteria, including E. Coli, Staphylococcus, Streptococcus, and Pasteurella. These bacteria live in the rotting flesh that they leave in their mouth. But what is that based on?

It turns out, not much. The “facts” we have in textbooks, zoos, and medical literature are based on one guy’s book written in 1981. While Walter Auffenberg was the Jane Goodall of Komodo dragons, moving to the island and studying them in their natural habitat, his results haven’t been widely reproducible. And, more importantly, komodos don’t carry rotting flesh in their mouth. They fastidiously clean their teeth and gums. Now, perhaps the water buffalo does die of sepsis after being bitten, but if it does, it’s because it runs into murky water with fresh wounds, and not from bacteria in the mouth of the lizard. So, the “bacteria as venom” concept is just as dead in the water as the buffaloes.

So what about the venom aspect? The author of that study (Fry) was able to identify glands in the lower jaw that could potentially be venom glands. Furthermore, the extract of those glands does in fact contain proteins that inhibit blood clotting similar to snake venom. However, there isn’t any evidence that the venom actually affects the prey or is secreted in any significant amount during bites. The teeth lack venom grooves present in every other venomous animal (including the shrew). On the plus side, the author did come up with the “grip, rip, and drip” model of lethality from komodos.

Then why do animals die after being bitten by a large, reptilian predator? For the same reasons they die after being bitten by any large animal. Direct trauma, blood loss, and hypovolemic shock (and by eating).

Our findings are also in accord with the view that the killing technique of V. komodoensis is broadly similar to that of some sharks and Smilodon fatalis (saber cat). Despite obvious anatomical differences, these unrelated predators kill or are thought to have killed (respectively) large prey by using relatively weak bite forces amplified by sharp teeth and postcranial input.

They have strong neck muscles and serrated teeth, so after they bite they pull away, tearing holes in the prey that then bleeds to death. Is it possible that venom can increase this bleeding? Sure, but it’s also possible that it doesn’t.

So then why did this patient become hypotensive? Likely a vasovagal response. And given that the bite was on the hand, it’s appropriate to put the patient on antibiotics. But maybe we can finally stop propagating the magical thinking associated with komodo dragons.

Bitten by a Dragon

Further enjoyable reading
National Geographic
A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus