109
eggs. Mosquitoes lay their eggs in or near water because the eggs need to be covered
with water when they hatch. Ponds, marshes, pools, puddles, rain barrels, bird baths and
clogged gutters are common places for mosquitoes to lay eggs. There is recent evidence
that some species prefer particular types of water over others. Water containing leaves
appears to be a favorite of the Aedes aegypti mosquito the microbes and their fatty acids
and methyl ester waste products found on the leaves attract this species.10
Diseases
Mosquito-borne diseases include malaria Japanese, California, eastern equine, western
equine, St Louis and Venezuelan encephalitis dengue and dengue hemorrhagic fever Rift
Valley fever yellow fever elephantiasis and Chikungunya fever. As mentioned earlier,
the pathogens that cause these diseases are transmitted by injection of saliva into suscepti-
ble hosts by female mosquitoes needing protein from a blood meal to develop their eggs.11
Mosquitoes are responsible for diseases in more than 700 million people each year.12
Malaria alone kills three million annually, including one child every 30 seconds. In the
US, arboviruses (arthropod-borne viruses) transmitted by mosquitoes continue to cause
sporadic outbreaks of eastern equine encephalitis, western equine encephalitis, St. Louis
equine encephalitis and La Crosse encephalitis. Eastern equine encephalitis is the most
lethal of the mosquito-borne encephalitides. The infection first became evident in the
suburbs of Boston in 1938, but the virus had been isolated from horses five years earlier.
In 1999, West Nile virus was discovered in the New York City area where 62 people were
infected. The virus has now been detected in 27 states, and is expected to spread unabated
across the US.13
Repellents
Protection from mosquito bites is best achieved by avoiding infected habitats, wear-
ing protective clothing and using insect repellent. In many circumstances, however,
applying repellents to the skin may be the only feasible way to protect against insect
bites.14 The best-known and most widely used chemical insect repellent is N,N-diethyl-
3-methylbenzamide (formerly N,N-diethyl-m-toluamide), thus the name DEET. DEET
was developed in 1953 and is the gold standard based on its excellent human use safety
record. The mechanism of action, however, has remained a mystery. Just recently, several
researchers have discovered that DEET blocks odorant receptors in the nervous system of
insects, masking odors that would ordinarily attract mosquitoes.15
DEET inhibits receptors for three compounds in human sweat, and these recep-
tors and others work in combination with a co-receptor, a protein called OR83b. This
information can be used to screen other compounds in hopes of finding one that is more
effective.16 Work has been done on a series of 34 promising N-acylpiperidine repellent
candidates. The repellency assays used on these chemicals were same as those that led
to discovery of DEET. Early results indicate that some candidates are equivalent to, or
better than, DEET in duration of protection.17 Until new products are available, consum-
ers should be aware that DEET’s efficacy has been compared to a number of alternative
repellent products available in the US and DEET-based products provided complete
protection for the longest duration.18 The complete protection times correlated positively
with the concentration of DEET in the repellent. The formulation containing 4.75% pro-
vided an average of 88.4 minutes of complete protection from mosquito bites, whereas
23.8% protected for an average of 301.5 minutes. The study cited shows that DEET-based
products can be depended upon for long-lasting repellent effects, but they are not perfect.
DEET may be washed off by perspiration or rain, and its efficacy decreases dramatically
with rising outdoor temperatures.19 DEET is also a plasticizer, capable of dissolving watch
crystals, frames of eyeglasses and some synthetic fabrics.20
Mosquitoes—the Mysterious Scourge
eggs. Mosquitoes lay their eggs in or near water because the eggs need to be covered
with water when they hatch. Ponds, marshes, pools, puddles, rain barrels, bird baths and
clogged gutters are common places for mosquitoes to lay eggs. There is recent evidence
that some species prefer particular types of water over others. Water containing leaves
appears to be a favorite of the Aedes aegypti mosquito the microbes and their fatty acids
and methyl ester waste products found on the leaves attract this species.10
Diseases
Mosquito-borne diseases include malaria Japanese, California, eastern equine, western
equine, St Louis and Venezuelan encephalitis dengue and dengue hemorrhagic fever Rift
Valley fever yellow fever elephantiasis and Chikungunya fever. As mentioned earlier,
the pathogens that cause these diseases are transmitted by injection of saliva into suscepti-
ble hosts by female mosquitoes needing protein from a blood meal to develop their eggs.11
Mosquitoes are responsible for diseases in more than 700 million people each year.12
Malaria alone kills three million annually, including one child every 30 seconds. In the
US, arboviruses (arthropod-borne viruses) transmitted by mosquitoes continue to cause
sporadic outbreaks of eastern equine encephalitis, western equine encephalitis, St. Louis
equine encephalitis and La Crosse encephalitis. Eastern equine encephalitis is the most
lethal of the mosquito-borne encephalitides. The infection first became evident in the
suburbs of Boston in 1938, but the virus had been isolated from horses five years earlier.
In 1999, West Nile virus was discovered in the New York City area where 62 people were
infected. The virus has now been detected in 27 states, and is expected to spread unabated
across the US.13
Repellents
Protection from mosquito bites is best achieved by avoiding infected habitats, wear-
ing protective clothing and using insect repellent. In many circumstances, however,
applying repellents to the skin may be the only feasible way to protect against insect
bites.14 The best-known and most widely used chemical insect repellent is N,N-diethyl-
3-methylbenzamide (formerly N,N-diethyl-m-toluamide), thus the name DEET. DEET
was developed in 1953 and is the gold standard based on its excellent human use safety
record. The mechanism of action, however, has remained a mystery. Just recently, several
researchers have discovered that DEET blocks odorant receptors in the nervous system of
insects, masking odors that would ordinarily attract mosquitoes.15
DEET inhibits receptors for three compounds in human sweat, and these recep-
tors and others work in combination with a co-receptor, a protein called OR83b. This
information can be used to screen other compounds in hopes of finding one that is more
effective.16 Work has been done on a series of 34 promising N-acylpiperidine repellent
candidates. The repellency assays used on these chemicals were same as those that led
to discovery of DEET. Early results indicate that some candidates are equivalent to, or
better than, DEET in duration of protection.17 Until new products are available, consum-
ers should be aware that DEET’s efficacy has been compared to a number of alternative
repellent products available in the US and DEET-based products provided complete
protection for the longest duration.18 The complete protection times correlated positively
with the concentration of DEET in the repellent. The formulation containing 4.75% pro-
vided an average of 88.4 minutes of complete protection from mosquito bites, whereas
23.8% protected for an average of 301.5 minutes. The study cited shows that DEET-based
products can be depended upon for long-lasting repellent effects, but they are not perfect.
DEET may be washed off by perspiration or rain, and its efficacy decreases dramatically
with rising outdoor temperatures.19 DEET is also a plasticizer, capable of dissolving watch
crystals, frames of eyeglasses and some synthetic fabrics.20
Mosquitoes—the Mysterious Scourge