Page 67 - Journal of Special Operations Medicine - Fall 2016

Prevention not absorbed through the skin as readily as the alco-
hol-based DEET, which garners an improved side-effect
18
Vaccines profile. On the other hand, alcohol-based DEET loses
An effective vaccine would be beneficial to military almost all of its ability to prevent cercarial penetration
7
personnel. However, this appears to be years away. when exposed to water. However, it may have a role
The World Health Organization reports that there is postexposure. Because the cercariae must travel through
one vaccine for S. haematobium and two vaccines for the skin to the circulatory system, alcohol-based DEET
17
S. mansoni currently in clinical trials. With these still applied shortly after exposure may kill the cercariae be-
in the trial phase, other preventative measures must be fore they can enter the bloodstream. One study of 15
instituted now. travelers showed that the use of this method resulted in
no new schistosomal infections despite an average of 47
Education hours of freshwater exposure. 8
One preventative measure is education on freshwater
avoidance, but this achieves mixed results. In one retro- DEET is fairly ubiquitous at deployed sites in Africa,
spective study, travelers receiving a written and/or ver- making this a very practical approach to preventing this
bal brief were more likely to bathe in fresh water than disease. Education on its use with regard to schistoso-
10
were those who had not been briefed. The Belgian mil- miasis is the only missing piece.
itary reviewed personnel returning from the Democratic
Republic of Congo and found that despite premission Chemotherapy
briefings on schistosomiasis, 94 (47.7%) of 197 person- Artemisinin derivatives have been used as a preventative
nel reported recreational freshwater exposure during medication against schistosomiasis in high-risk individ-
12
5
their tour. While education did not solve the problem uals. They are effective against juvenile schistosomes
12
in the Belgian military, it was more successful in the less than 21 days old. Dosing of the derivative artesu-
US Peace Corps. After noticing that more than 25% of nate at 6mg/kg every 2 to 4 weeks by mouth is effective
12
their personnel returned with positive schistosomiasis as prophylaxis against all Schistosoma species. The
serology, they started an educational intervention. This derivative artemether is commonly used as treatment
consisted of a 30-minute lecture solely on schistoso- against malaria, making it dual purpose in endemic ar-
12
miasis at the beginning and midpoint of their tour as eas. However, this approach could allow selection of
well as increased emphasis during one-on-one contact artemether-resistant Plasmodium falciparum, leading
12
with healthcare providers. They also advised freshwater to more dangerous malarial infections.
avoidance and vigorous toweling after freshwater con-
tact. After 2 years, their seropositive rate was reduced Praziquantel is the drug of choice for treatment of schis-
to 5% to 7%. Despite these promising results, it must tosomiasis, but it cannot be used as a preventative or
be mentioned that 74% of Peace Corp volunteers still postexposure chemoprophylaxis, as it is only effective
16
swam in freshwater. Education does not appear to against the adult form of schistosoma. 12
change people’s habits while traveling in Africa.
Topicals Screening
Since we are unlikely to change habits with education,
we must find ways to mitigate the risk for someone while History and Physical Examination
in freshwater. This is even more important as military Medical dogma tells providers to screen patients with a
missions may require freshwater exposure. In the Bel- history and physical examination; however, schistoso-
gian military study, 51.3% of exposures were mission miasis is an infection where this mantra fails. There is
requirements. Fortunately, there are simple ways to do little value asking for answers other than a simple yes or
5
this. Wearing a dry suit, toweling after exposure, and no about freshwater exposure. In a retrospective study
applying topical N,N-diethyl-meta-toluamide (DEET) of travelers by Whitty et al., only 18.3% of patients
10
all decrease infection rates. 5,7,9,16,18 complaining of symptoms tested positive for schisto-
somiasis, compared with 15.8% of patients without
DEET kills Schistosoma cercariae at concentrations as symptoms. In the same study, 282 patients revealed an
18
low as 7.5%. There are currently two formulations abnormality on physical examination, but none tested
for DEET: liposomal and alcohol based. The liposo- positive for schistosomiasis. History and physical ex-
10
mal DEET is imbedded in a fatty structure, feels oily amination do not meaningfully contribute to the diag-
on the skin when applied, and is highly water resistant. nosis of schistosomiasis. 5,10,13 This can be seen in Figure
Liposomal formulations of 20% DEET remain >90% 3, which is a visual depiction of the sensitivity and speci-
efficacious in preventing cercarical penetration after 1 ficity of the screening methods discussed. The width of
hour of washing with water. The liposomal DEET is the bar represents the range of data found.
7

Schistosomiasis in Nonendemic Populations 49