4,963 research outputs found
Multi-country field trials comparing wash-resistance of PermaNet and conventional insecticide-treated nets against anopheline and culicine mosquitoes.
No full textInsecticide-treated bednets (ITNs) are commonly used as a means of personal protection from malaria transmission by anopheline mosquitoes (Diptera: Culicidae). Long-lasting insecticidal nets (LLINs) have special treatments intended to remain effective after many washes. The present trials assessed the efficacy and wash-resistance of several production batches of PermaNet (polyester net coated with polymer resin containing pyrethroid insecticide deltamethrin 55 mg ai/m2) against malaria vectors in Pakistan, Iran and Tanzania compared to ITNs conventionally treated with alphacypermethrin 15 or 20 mg ai/m2, or deltamethrin 25 or 50 mg ai/m2. Insecticidal efficacy of the nets before and after repeated washing (using W.H.O. recommended and traditional local washing procedures) was monitored through contact bioassays with Anopheles and by experimental hut and outdoor platform tests. Local washing regimes gradually reduced the insecticidal efficacy of conventionally treated nets, but they were not exhausted, even after 21 washes. Using a more rigorous laboratory washing method, insecticide was more readily stripped from conventionally treated nets. PermaNet retained high efficacy after 21 washes, giving more than 97% mortality of Anopheles in contact bioassays with 3-min exposure. Using the more sensitive bioassay criterion of 'median time to knockdown', PermaNet showed no loss of insecticidal activity against Anopheles after washing repeatedly in 2 out of 6 trials; whereas in a further three trials knockdown activity of PermaNet and conventional ITNs declined at comparable rates. Higher mortality levels of Anopheles in contact bioassays did not always translate to superiority in experimental hut or enclosed platform trials. In only one of four comparative field trials did PermaNet out-perform conventional ITNs after washing: this was in the trial of PermaNet 2.0--the product with improved quality assurance. Because PermaNet and conventionally treated nets were both quite tolerant of local washing procedures, it is important in field trials to compare LLINs with conventional ITNs washed an equivalent number of times. Our comparison of PermaNet 2.0 against conventionally treated deltamethrin nets (CTDN) in Pakistan demonstrated superior performance of the LLIN after 20 washes in phase I and phase II bioassays, and this was corroborated by chemical assays of residual deltamethrin. Although PermaNet 2.0 has received WHOPES interim recommendation for malaria control purposes, its performance should be monitored in everyday use throughout its lifespan in various cultural settings to assess its durability and long-term effectiveness for malaria prevention and control. As many millions of conventionally treated nets are already in routine use, and these will require regular re-treatment, programme strategies should be careful to preserve the effectiveness of ITNS before and after establishing the reliability of LLINs in long-term use
Factors affecting the rotational use of insecticides for the management of resistance in mosquitoes
No full textThe
rotation
of
the
use
of
chemically
unrelated
insecticides
has
been
advocated
to
delay
the
build
up
of
resistance.
To
examine
this
concept
in
the
laboratory,
Anopheles
albimanus
and
Culex
guinquefasciatus
were
subjected
to
two
kinds
of
rotational
selection
which
may
be
referred
to
as
short
term
pre-planned
rotation
and
"opportunistic"
rotation.
No
difference
was
observed
between
these
two
methods
in
term
of
the
time
for
each
resistance
level
to
reach
5Q%.
The
effectiveness
of
selection
for
resistance
depends
on
the
protection
conferred
by
resistance
genes
and
this
was
tested
by
laboratory
releases
of
the
DDT
resistant
and
susceptible
homozygotes
and
heterozygotes
of
An.
gambiae
into
DDT
sprayed
and
unsprayed
miniature
huts.
All
the
genotypes
were
killed
with
freshly
applied
DDT
but
survivors
were
observed
from
month
2,
3
and
5
onwards
for
RR,
RS
and
SS
genotypes,
respectively.
Persistence
of
DDT
on
the
sprayed
wall
and
roof
of
the
mud
hut
was
studied
by
bioassays
and
biochemical
assays
on
scrapings
from
the
wall
and
roof.
Linkage
between
resistance
genes
could
effect
the
rotational
use
of
insecticides.
No
linkage
was
found
between
propoxur
and
dieldrin
resistance
genes
by
combining
bioassay
and
biochemical
methods.
As
a
preparation
for
a
field
studies
in
Malaysian
field
collected
Aedes
aegypti
and
Culex
guinguefasciatus
larvae
were
selected
with
temephos
and
Bti.
Cx
guinguefasciatus
responded
to
temephos
selection
but
Ae.
aegypti
did
not
respond
to
temephos
and
neither
species
responded
to
Bti
selection.
~
Caged
adults
were
exposed
to
thermal
fogging
in
the
field.
The
partially
resistant
Cx
guinguefasciatus
strain
hardly
survived
any
better
than
susceptible
strains.
Resistant
and
susceptible
larvae
were
exposed
to
water
samples
from
containers
which
had
been
treated
with
temephos
sand
granules.
100%
mortality
was
obtained
for
all
the
strains
up
to
week
6.
Resistant
Culex
started
to
survive
at
week
7
but
susceptibles
did
not
do
so
until
week
ten.
The
prospects
for
the
various
proposed
strategies
for
resistance
management
are
discussed
Effects of sublethal doses of pyrethroids on malaria vectors
No full textPyrethroids are currently the most widespread class of insecticide in public health use,
although their future may be limited by resistance. The present study investigates the
effects of these compounds on mosquitoes, other than mortality immediately after
exposure.
Longevity of both male and female An. gambiae was found to be significantly
curtailed following sublethal exposure to the most commonly used pyrethroids,
permethrin, deltamethrin and lambda-cyhalothrin. There was no direct effect observed on
fecundity. Irritancy on direct contact with all 3 compounds was recorded, particularly
with permethrin. Evening host-seeking flight activity was greatly reduced, and when
females were treated with permethrin before release into a flight chamber, significantly
fewer flew to a host to feed.
Experiments investigating Plasmodium yoelii and P. falciparum development in the
Asian vector An. stephensi revealed that sublethal exposure to pyrethroids inhibited
development of oocysts in the midgut. Similar experiments using organochlorine,
organophosphate and carbamate insecticides found no effect.
Radio-labeled permethrin was traced inside the blood meal following exposure.
However, none of the 3 pyrethroids were found to have a direct anti-malarial activity on
cultured gametocytes. Likewise, permethrin did not affect exflagellation of P. yoelii.
Time course experiments determined that for the reduction in oocysts there was a critical
period of between 18 and 48 hours after the infective feed. Permethrin was not found to
inhibit trypsin activity in assays, and the levels of trypsin in the midgut of blood fed
treated and untreated females was not found to differ in a manner which could explain
reduced infection rates.
It is clear that sublethal exposure of mosquitoes can lead to a wide range of
potentially important effects in terms of the impact of pyrethroids in malaria vector control
Mutations in dhfr in Plasmodium falciparum infections selected by chlorproguanil-dapsone treatment.
No full textTreatment with the novel antifolate drug combination chlorproguanil-dapsone effectively cleared asymptomatic Plasmodium falciparum infections in 246 (93.5%) of 263 children in the Usambara Mountains of Tanzania during the course of a 2-week follow-up. Samples from 71 recurrent infections, collected over a 9-week follow-up, showed selection for parasites with the triple mutant Ile(51)-Arg(59)-Asn(108) in dihydrofolate reductase. There was no selection for mutations in dihydropteroate synthetase, the target enzyme of dapsone. Search for complete identity in the highly polymorphic genes coding for merozoite surface proteins 1 and 2 in parasite samples collected before and after treatment indicated that the majority of recurrent parasitemias were new infections. These observations on selection in Tanzania and the lack of selection reported from a less endemic area suggest that the active metabolite of chlorproguanil, which has a short half-life in the blood, may persist in the liver, where it exerts selective pressure on growing preerythrocytic stages
An experimental hut evaluation of Olyset nets against anopheline mosquitoes after seven years use in Tanzanian villages.
No full textBACKGROUND: Long-lasting insecticidal nets (LLINs) are advocated by WHO for protection against malaria. Of the three brands of LLINs currently approved by WHO, Olyset(R) is the only one currently granted full recommendation. With this type of LLIN, the insecticide (permethrin) is incorporated into the polyethylene fibre during manufacture and diffuses from the core to the surface, thereby maintaining surface concentrations. It has not been determined for how long Olyset nets remain protective against mosquitoes in household use. METHODS: Examples of Olyset nets, which had been in use in Tanzanian villages for seven years, were tested in experimental huts against naturally entering Anopheles gambiae and Anopheles funestus mosquitoes. Performance was compared with new Olyset nets, conventionally treated ITNs (either newly treated with alphacypermethrin or taken from local villages after 1.5 years of use) and untreated nets. All nets were artificially holed except for the seven-year Olyset nets, which had developed holes during prolonged domestic use. RESULTS: Anopheles funestus and An. gambiae in NE Tanzania are susceptible to pyrethroids. The new Olyset nets caused high mortality against An. funestus (73.9%) and An. gambiae (62.7%) in experimental huts. The seven-year Olyset nets caused 58.9% mortality against An. funestus and 40.0% mortality against An. gambiae. The freshly treated alphacypermethrin nets also caused high mortality against An. funestus (70.6%) and An. gambiae (72.0%); this decreased to 58.4% and 69.6% respectively after 1.5 years of use. The new Olyset nets inhibited blood-feeding by 40-50%. The 7 year Olyset nets showed no feeding inhibition over that shown by the untreated nets. The alphacypermethrin treated nets failed to inhibit blood-feeding after 1.5 years of use. However iHhhdn laboratory tunnel tests samples of all types of treated net including the 7 year Olyset inhibited blood-feeding by more than 95%. CONCLUSION: After seven years of use Olyset nets were still strongly insecticidal. Mosquito mortality decreased by only 20-35% over this period. However, Olyset would not provide personal protection after seven years unless it was in good condition and all holes fully repaired
Importance of asymptomatic malaria and its infectivity to Anopheles mosquitoes in Mae Hong Son Province, Thailand
No full textThis study aimed to record the prevalence of asymptomatic malaria and the
development of malaria parasites in laboratory-bred Anopheles minimus mosquitoes
fed on the blood of people with or without malaria symptoms. The intention was to
identify where the main reservoir of infection was maintained. The study was
conducted in three cantons in Muang district, Mae Hong Son Province, Northwest
Thailand.
Chapter 3 describes studies of epidemiology of malaria in this area, based on
two cross-sectional surveys of populations in villages and people who visited a
malaria clinic. A questionnaire was conducted in the local languages by trained
interviewers, to identify people suffering from fever.
The parasite prevalence was 0.7% of all the surveyed populations. The
prevalence of slide positivity among males was significantly higher than females. All
those with positive slides who had a body temperature >37.4°C reported fever. Some
without measured body temperature >37.4°C also reported fever. Those people may
have had fever a few hours previously. Contrary to expectation P. falciparum
infections did not cause fever more than P. vivax infections. The prevalence of
asymptomatic malaria was 47.1 % among those who were slide positive which
corresponded to about 0.5% of the interviewed population. From the Clinic, 101
patients with malaria infection were interviewed. More than half of the infections
had high parasitaemia.
When people thought they had malaria, the malaria clinic and the hospital
facilities were most commonly used, with the largest number going to the Clinic. A
significantly higher malaria prevalence was found in the people who reported not
having any form of mosquito protection. More than 99% stated that they owned
mosquito nets, but only 44% of the nets had been treated with insecticide.
2 Chapter 4 reports a study of the infectiousness of malaria patients to An.
minimus. Direct feedings were conducted on adults >15 years old and who gave their
consent. All of these people had blood slides positive for P. falciparum or P. vivax
and had been located from the village surveys (n = 28) or the Clinic (n = 92). After
feeding, the mosquitoes were held for 7-9 days and then dissected and examined for
oocysts. Feeding on about 40% of human subjects yielded some mosquitoes with
oocysts. There was a significantly lower probability of infection with P. falciparum
than P. vivax. Symptomatic or non-symptomatic people with parasites were equally
able to infect mosquitoes. There was a significant association of probability of
mosquito infection with presence of observable gametocytes, but there were some
individuals without observable gametocytes who infected mosquitoes.
PCR on 58 subjects with negative slides showed that 30% were positive for
P. falciparum, but none yielded oocysts after mosquito feeding. PCR was also used
to identify the parasite species in the mosquito's gut. The results revealed that none
of the donors with visible P. falciparum infections carried cryptic P. vivax infections
which could yield P. vivax positivity in mosquitoes fed on them.
The occurrence of some cases with undetectable gametocytes who could
infect mosquitoes suggests the question "Do gametocytes selectively enter the
mosquito's proboscis during blood feeding"? However, a small study showed that
the gametocyte density in the mosquito blood meals did not differ significant from
that in the corresponding finger pricks, indicating that gametocytes do not selectively
enter a mosquito's proboscis. The occurrence in some cases of high oocyst counts in
mosquitoes fed on blood with no observable gametocytes remains unexplained.
From the results, on infection of mosquitoes by different categories of people
an attempt was made to estimate the number of people in the catchment area of the
Clinic who were reservoirs of infection. On the basis of the number of patients
visiting the Clinic per day, it was concluded that the main reservoir of infection for
mosquitoes was not in patients feeling ill enough to be motivated to come to the
Clinic. The present study suggests that directing anti-gametocyte drugs to all feverish
3 patients in the villages could have a major impact on the reservoir of infection.
However, in Thailand there have not yet been reports on the infectivity of the
gametocytes in mosquitoes after treatment of patients with gametocytocidal drugs
(e. g. primaquine or artesunate). Such studies are strongly recommende
Coniopteryx Curtis 1834
No full textGenus Coniopteryx Curtis, 1834 Type species: Coniopteryx (Coniopteryx) tineiformis Curtis, 1834 Coniopteryx has a worldwide distribution. Considering the new species herein described, this genus includes 222 species in six subgenera (Coniopteryx s. str., Holoconiopteryx, Metaconiopteryx, Protoconiopteryx, Scotoconiopteryx, and Xeroconiopteryx), with sixteen species recorded in Mexico (cf., Sziráki 2011, 2015; Martins & Amorim 2016).Published as part of Sarmiento-Cordero, Mariza Araceli & Contreras-Ramos, Atilano, 2019, Two new species and a key to the dustywings of Mexico (Neuroptera, Coniopterygidae), pp. 551-563 in Zootaxa 4671 (1) on page 554, DOI: 10.11646/zootaxa.4671.4.6, http://zenodo.org/record/345050
Experimental hut evaluation of bednets treated with an organophosphate (chlorpyrifos-methyl) or a pyrethroid (lambdacyhalothrin) alone and in combination against insecticide-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes.
No full textBACKGROUND: Pyrethroid resistant mosquitoes are becoming increasingly common in parts of Africa. It is important to identify alternative insecticides which, if necessary, could be used to replace or supplement the pyrethroids for use on treated nets. Certain compounds of an earlier generation of insecticides, the organophosphates may have potential as net treatments. METHODS: Comparative studies of chlorpyrifos-methyl (CM), an organophosphate with low mammalian toxicity, and lambdacyhalothrin (L), a pyrethroid, were conducted in experimental huts in Côte d'Ivoire, West Africa. Anopheles gambiae and Culex quinquefasciatus mosquitoes from the area are resistant to pyrethroids and organophosphates (kdr and insensitive acetylcholinesterase Ace.1R). Several treatments and application rates on intact or holed nets were evaluated, including single treatments, mixtures, and differential wall/ceiling treatments. RESULTS AND CONCLUSION: All of the treatments were effective in reducing blood feeding from sleepers under the nets and in killing both species of mosquito, despite the presence of the kdr and Ace.1R genes at high frequency. In most cases, the effects of the various treatments did not differ significantly. Five washes of the nets in soap solution did not reduce the impact of the insecticides on A. gambiae mortality, but did lead to an increase in blood feeding. The three combinations performed no differently from the single insecticide treatments, but the low dose mixture performed encouragingly well indicating that such combinations might be used for controlling insecticide resistant mosquitoes. Mortality of mosquitoes that carried both Ace.1R and Ace.1S genes did not differ significantly from mosquitoes that carried only Ace.1S genes on any of the treated nets, indicating that the Ace.1R allele does not confer effective resistance to chlorpyrifos-methyl under the realistic conditions of an experimental hut
Zoophilic and anthropophilic behaviour in the Anopheles gambiae complex
No full textThe work included in this thesis
arose
from
a
long-standing interest in the
possible
use of genetic control for one of
the
most
important
malaria
vectors
in
Africa, Anopheles
gambiae sensu stricto. It was hoped that the
genes
involved in
animal
biting in the
sibling
species Anopheles quadriannulatus
could
be
exploited
by
crossing
with
An. gambiae s. s.
and using the fertile female hybrids for
successive
backcrosses to
An. gambiae s. s..
It
was
envisaged that this method could
be
used
in
an attempt to
produce
a mosquito
stock
that is
harmless to humans because it is
zoophilic
but
with
the
genetic
background
of
An. gambiae s. s. so that there would
be
no
barriers to
cross-mating
in the
wild.
The innate
host preference of mosquitoes can
be determined in the laboratory
using
an olfactometer,
or in the field using baits. Host-selection patterns
in
nature
are often affected
by
external
factors, which may or may not mask the
host
preference
of the
mosquito
species
in
question (discussed in section 1.3).
The main aim of this work was
to investigate the
host
preferences
of
the two
most
behaviourally diverse members of
the
Anopheles
gambiae
complex
(An. gambiae s. s. and An. quadriannulatus) and to attempt
to
modify
the
anthropophilic
host
preference
of
An. gambiae s. s. by hybridisation experiments
with the
zoophilic
An. quadriannulatus.
The behaviour of these two sibling species
was
assessed
in
an olfactometer
by testing
a
range of odours. Anopheles gambiae s. s.
behaved
as expected
and was
attracted
to
human
odours. However, the behaviour of
An. quadriannulatus
was
somewhat
unexpected
and
a
large proportion also selected human odour.
Therefore
an outdoor
host-choice
experiment
was performed and confirmed
the
olfactometer
findings. A
standardised
bioassay
was
developed to evaluate the behaviour of
mosquitoes
resulting
from the
crossing
experiments. Human and cow skin washings
were
prepared
and
tested.
Cow
skin washing
combined with carbon dioxide and
tested
against
a
control
of
clean air
was then
chosen
to
evaluate the behaviour of hybrids and
backcrossed
mosquitoes
in the
olfactometer.
Three
backcrosses to both An. gambiae s. s.
and
An. quadriannulatus
were
performed,
which
showed extreme stability of the anthropophilic
trait.
A field
study
in
Ethiopia investigated
the host preference of An. quadriannulatus species B
and suggested
that this
species
is
more zoophilic than its sibling species
An. arabiensis
but is
also attracted
to
humans.
The
impact of these findings on our current
understanding
of the
behaviour
of members of
the
Anopheles gambiae complex is discussed
Creating an "enabling environment" for taking insecticide treated nets to national scale: the Tanzanian experience.
No full textINTRODUCTION: Malaria is the largest cause of health services attendance, hospital admissions and child deaths in Tanzania. At the Abuja Summit in April 2000 Tanzania committed itself to protect 60% of its population at high risk of malaria by 2005. The country is, therefore, determined to ensure that sustainable malaria control using insecticide-treated nets is carried out on a national scale. CASE DESCRIPTION: Tanzania has been involved for two decades in the research process for developing insecticide-treated nets as a malaria control tool, from testing insecticides and net types, to assessing their efficacy and effectiveness, and exploring new ways of distribution. Since 2000, the emphasis has changed from a project approach to that of a concerted multi-stakeholder action for taking insecticide-treated nets to national scale (NATNETS). This means creating conditions that make insecticide-treated nets accessible and affordable to all those at risk of malaria in the country. This paper describes Tanzania's experience in (1) creating an enabling environment for insecticide-treated nets scale-up, (2) promoting the development of a commercial sector for insecticide-treated nets, and (3) targeting pregnant women with highly subsidized insecticide-treated nets through a national voucher scheme. As a result, nearly 2 million insecticide-treated nets and 2.2 million re-treatment kits were distributed in 2004. CONCLUSION: National upscaling of insecticide-treated nets is possible when the programme is well designed, coordinated and supported by committed stakeholders; the Abuja target of protecting 60% of those at high risk is feasible, even for large endemic countries
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