DEET

Re the DEET, I think of things this way:- the only 100% way to ensure you
don't get malaria is to not get bitten (i.e. there's definitely reports out
there about travellers who took all of their tablets religiously and still
got malaria)...so, the DEET is the most important thing. Yes, it's toxic -
they used to spray it on malarial areas to kill mosquitoes - so, if it can
kill mosquito cells, it can kill human cells. However, I used the tropical
strength version liberally on my body when I was in Thailand and sparingly
on my face, but making sure I covered all areas of the face (I'm not sure if
this is true but I think the skin of the face is thinner than on the body
and hence, I assumed that there was more chance that it might penetrate into
my blood).
I was also strict about the use of mosquito coils in my room (bought them
when I got to Thailand), always had the fan on (harder for mosquitoes to
land), slept with some light clothes on so that some areas of the body were
always covered, and used a fine mosquito net to cover my bed that was
impregnated with "permethrin" (which is also a recognized carcinogen) and
that I bought back in Australia. You can also spray your clothing with
Permethrin - "treated clothing will effectively repel mosquitoes for more
than one week even with washing and field use" (Reference 1 at end of
email)...I chose not to do that though - just didn't like the idea of
spraying my clothes with this stuff.

What's the strength of DEET to consider getting? I used tropical strenght
RID because that's what was in the www.traveldoctor.com.au shop at the time
, which, if I remember correctly, was about 30% too. It's sticky and gluggy
and if you get it on to plastic, it will melt the plastic! (I kid you
not...oh, it also melts spandex and rayon).

However, the principle of DEET is that the higher the % formulation, the
longer the protection. It's generally felt that the effectiveness of DEET
reaches a plateau at 50% concentrations. To be sure of getting a few hours
protection though, you need to use the 30% version (e.g. the 25% version
provided less than 90% protection two hours after repellent application
against one strain of mozzie in field testing...Reference 2 at end of
email).

So, it's DEET yeah? Well...there is now an alternative. It's called Picardin
- it's odorless, does not feel sticky when applied, and does not damage
clothing. But...from what I know it's only available commercially in
Australia as the 9.3% formulation (based on this Choice article from 2005:
Reference 3). Here's what the report said: " The 9.3% picaridin formulation
provided greater than 95% protection for only two hours. In daytime tests, a
20% controlled-release deet formulation (Sawyer, 20% deet) provided greater
than 95% protection for six hours, and both 19.2% picaridin and the US Army
extended-duration repellent formulation (which contains 33% deet in a
polymer) provided greater than 95% protection for eight hours" (Reference
4).
So, if the 19.2% formulation is available then I would snap that one up and
use it instead of the DEET...but if you can only get the 9.3% formulation
then I'd go for the >/30% DEET instead.
Do you know anyone in the armed forces? Maybe they'd be able to get you some
"Autan Repel Army 20" which is the brandname for the 19.2% solution.

REFERENCES:
1) TI Effects of weathering on fabrics treated with permethrin for
protection against mosquitoes.
AU Gupta RK; Rutledge LC; Reifenrath WG; Gutierrez GA; Korte DW Jr
SO J Am Mosq Control Assoc 1989 Jun;5(2):176-9.

Permethrin-impregnated and untreated fabrics were evaluated for their
toxic and repellent effects against Anopheles stephensi and Aedes aegypti
after both types of fabrics were subjected to accelerated weathering for 9
weeks, under a simulated wet/tropical environment. The toxic (knockdown)
effect of permethrin-impregnated fabrics against both species of mosquitoes
diminished rapidly after 1 week compared to the repellent effect. After 6
weeks of weathering, the remaining low amounts of permethrin provided fair
protection from mosquito bites; however, no knockdown was observed at those
levels. Permethrin-treated fabric was effective in providing protection from
mosquito bites and appears to be a means of attenuating both the nuisance
effects and, possibly, disease transmission by mosquitoes.

AD Letterman Army Institute of Research, Presidio of San Francisco, CA
94129-6800.


2) J Med Entomol. 1996 Jul;33(4):511-5.
Laboratory and field evaluation of deet, CIC-4, and AI3-37220 against
Anopheles dirus (Diptera: Culicidae) in Thailand.Frances SP, Klein TA,
Hildebrandt DW, Burge R, Noigamol C, Eikarat N, Sripongsai B, Wirtz RA.
Department of Entomology, Armed Forces Research Institute of Medical
Sciences, Bangkok, Thailand.

Laboratory and field tests of the repellents diethyl methylbenzamide (deet),
1-(3-Cyclohexen-1-yl-carbonyl)-2-methylpiperidine (AI3-37220), and
(2-hydroxymethylcyclohexyl) acetic acid lactone (CIC-4) were conducted
against Anopheles dirus Peyton & Harrison, the principal malaria vector in
Thailand. In the laboratory, An. dirus was more sensitive to CIC-4 than
either AI3-37220 or deet. The duration of protection provided by each
repellent in laboratory tests increased with higher concentrations of
repellents and when exposed in cages containing fewer mosquitoes. A field
study in Chanthaburi Province, southeastern Thailand, during November 1993
tested 25% (wt:wt) ethanol solutions of each repellent against An. dirus. In
contrast to the laboratory experiments, protection provided by AI3-37220 was
significantly better than either deet or CIC-4 and there was no significant
difference between deet and CIC-4. Protection provided by deet and CIC-4
fell to below 95% 2 h after repellent application, whereas AI3-37220
provided > 95% protection for 4 h. The protection provided by all repellents
fell to < or = 65% 7 h after repellent application.

3)
http://choice.com.au/viewarticleasonepage.aspx?id=105015&catId=100281&tid=100008&p=1

4) J Med Entomol. 2002 May;39(3):541-4. Links
Field evaluation of repellent formulations against daytime and nighttime
biting mosquitoes in a tropical rainforest in northern Australia.Frances SP,
Van Dung N, Beebe NW, Debboun M.
Australian Army Malaria Institute, Enoggera, Queensland, Australia.

Field trials to compare repellent formulations containing either picaridin
or deet against rainforest mosquitoes in northern Queensland, Australia,
were conducted. Three repellents were compared at night: 9.3% picaridin and
19.2% picaridin (Autan Repel and Autan Repel Army 20, respectively, Bayer,
Sydney, Australia) and 35% deet in a gel (Australian Defense Force [ADF]).
During the day, the following three repellents were compared: 19.2%
picaridin, 20% deet in a controlled release formulation (Sawyer Controlled
Release Deet), and 33% deet in a polymer formulation (U.S. Army Extended
Duration Topical Insect and Arthropod Repellent [EDTIAR]). The predominant
mosquito species collected was Verrallina lineata (Taylor), with smaller
numbers of Ochlerotatus kochi (Donitz), Anopheles farauti s.s. Laveran,
Ochlerotatus notoscriptus (Skuse), and Coquilletidia xanthogaster (Edwards).
In nighttime tests, 19.2% picaridin provided >94.7% protection for at least
9 h, and ADF deet provided >95% protection for 7 h. The 9.3% picaridin
formulation provided >95% protection for only 2 h, and provided 60%
protection at 9 h. In daytime tests, Sawyer 20% deet provided >95%
protection for 6 h, and both 19.2% picaridin and U.S. Army EDTIAR provided
>95% protection for 8 h. In both nighttime and daytime tests 19.2%
picaridin provided similar or better protection than deet formulations.