Category Archives: infectious disease

Want to repel mosquitoes?

Mosquitoes. Mozzies. Whatever name you want to use for them, they’re a nuisance to you when you’re outdoors. And even worse, if you are in certain areas, they can transmit a large number of serious diseases. So which repellent is best? While I covered botanical mosquito repellents previously, this review article examines the products most of us think of when someone mentions mozzie spray.

At 38 pages, this is no light read. It’s certainly more words on mosquitoes than I’ve ever read in one sitting. But it’s full of interesting information, both trivial and applicable. For instance, did you know that the US Army had the patent on DEET for a full 11 years before they allowed civilian use?

As detailed in the article, not only are there several species of mosquitoes, there are also several formulations of repellent, and even seemingly minor things such as local weather patterns that can affect how long any particular product will work. Something as simple as wearing dark clothing can attract biters as they are able to see you better. Carbon dioxide, lactic acid, carboxylic acids, and even sweat will also attract mosquitoes, as their olfactory receptors are keen on these smells.

Using specific search strings, the authors found 1417(!)articles between 2000 and 2012, and they further pared this down to 102 when they only included repellent efficacy on human skin. The main repellents studied were DEET, Insect Repellent 3535, Icaridin (Picaridin), and Citriodora. DEET, being the gold standard, is often what others are compared against.

So what should you use?

  • DEET 20-25%
  • IR3535 10-20%
  • Icaridin 10-20%
  • Citriodora 20-30% (cream)

If you want to repel mosquitoes, a high concentration DEET product (20-25%) has the greatest repellency against all species, and conveniently it lasts the longest. It is clearly the most effective at repelling Aedes spp. Of note, in their data, they found that going over 25% DEET doesn’t offer greater protection against Aedes spp., but it does have longer repellency against Anopheles spp. Of note, it also has the most side effects, up to and including neuro- and cardiotoxicity.

IR3535 at concentrations of 10-20% works against most mosquitoes, but puzzlingly loses some efficacy against Anopheles at higher concentrations. Icaridin is also effective at 10-20%. Using IR3535 or Icaridin is reasonable, especially if you want to wear anything that DEET can destroy, such as rayon, spandex, vinyl, plastic, or even leather. 

Citriodora (lemon scented eucalyptus extract) is useful when applied as a cream, but is ineffective when used as just the essential oil. Speaking of essential oils and other “natural repellents”, these authors actually looked at a fair amount of studies, and found that some really are effective. These include catmint oil and rosemary, among others. And to really mess with you, adding 5% vanillin to anything, synthetic or natural, makes it more effective. However, most are fairly volatile and short-lived. Sorry I couldn’t give you more ammo against certain Facebook users.

The authors also included tick (Ixodes) repellent efficacy in this article, but found the data wanting. DEET, IR3535, and Icaridin all seem effective, but it isn’t conclusive.

The efficacy of repellents against Aedes, Anopheles, Culex and Ixodes spp.-A literature review

How you wash your utensils matters

When you’re out in the wild for extended periods of time, you’re always reminded of the need to eat. Some get around this by only carrying pre-prepared foods. Others decide to cook, which inevitably leads to dirty dishes. Even if you make the grave sin of using disposable dishes and silverware, you still have to clean the larger containers you prepare the food in. And when somewhere between 1/3 and 3/4 of hikers end up with diarrhea, cleaning of these dishes is clearly important. 

If you’re car camping and have running water, you can go ahead and move on to another blog post. Fresh running potable water makes this job easy. But for those times when it isn’t available, you need to clean your utensils somehow. Many of us have been taught the 3 bowl system seen above, where you wash in the first bowl, rinse in the second, and disinfect in the third. It has similarities to the 3 sink systems many restaurants use. But does this mean it’s best?

To find out, a group of authors decided to test 18(!) different 3 bowl systems to see which actually reduced bacterial loads the most. They used porridge contaminated with E. coli, a practice I can’t recommend when camping. (They describe the contamination in excruciating detail, using 232 words). The authors trimmed the systems to 10 after finding 8 of them “wholly inadequate.” Describing each of the systems is needlessly complex, so here’s Table 1 from the article. Table 1

This doesn’t entirely explain their methods though. When they wrote “established”, they meant washing until visibly clean in first bowl, then using 2 and 3 just for rinsing and sanitizing, as it were. “Alternative” meant removing all easy food residue in bowl 1, then getting them visibly clean in bowl 2, and rinsing in bowl 3.

Their results weren’t entirely surprising. First they note that grease is only removed with detergent. Second, while systems D, F, G, and J were best for bacterial loads, E through I were easiest to use because you could see what you were washing easier in the cleaner bowl 2, and D-I where the ones that didn’t leave a disinfectant smell on the dishes when done. Putting this all together, the winner was system G in using the least bleach while still reducing coliform counts below measurable levels.

Of note, systems B and C are often what is used and taught for wilderness trips. This may be due to a real or perceived need to decontaminate the rinsing water, but the authors recommend using potable water for bowl 3. Otherwise you are left with a distinct disinfectant residue on your dishes that can be tasted at your next meal. More importantly, due to reduced contact time with the disinfectant (dunking takes less time than cleaning), they had higher coliform counts as well.

So there you have it. You can use the 3 bowl system, but not the way it’s been taught historically. You should have water and detergent in the first bowl, cleaning them mostly. Then continue cleaning until visibly clean in a second bowl of water with 10mL of bleach in it (5L:10mL water:bleach). Finally, rinse in potable water. In severely water restricted circumstances,  this system gives you the added benefit of still working when you remove the 3rd bowl, except for that disinfectant taste again. The authors do note that if an outbreak of diarrhea occurs at your campsite, consider increasing the bleach content of bowl 2 to 100mL.

Laboratory evaluation of the 3-bowl system used for washing-up eating utensils in the field.