MALARIA: Arm-in-cage testing of natural human-derived mosquito repellents

20 August 2010
Background
Individual human subjects are differentially attractive to mosquitoes and other biting insects. Previous investigations have demonstrated that this can be attributed partly to enhanced production of natural repellent chemicals by those individuals that attract few mosquitoes in the laboratory. The most important compounds in this respect include three aldehydes, octanal, nonanal and decanal, and two ketones, 6-methyl-5-hepten-2-one and geranylacetone [(E)-6,10-dimethylundeca-5,9-dien-2-one]. In olfactometer trials, these compounds interfered with attraction of mosquitoes to a host and consequently show promise as novel mosquito repellents.
Methods
To test whether these chemicals could provide protection against mosquitoes, laboratory repellency trials were carried out to test the chemicals individually at different concentrations and in different mixtures and ratios with three major disease vectors: Anopheles gambiae, Culex quinquefasciatus and Aedes aegypti.
Results
Up to 100% repellency was achieved depending on the type of repellent compound tested, the concentration and the relative composition of the mixture. The greatest effect was observed by mixing together two compounds, 6-methyl-5-hepten-2-one and geranylacetone in a 1:1 ratio. This mixture exceeded the repellency of DEET when presented at low concentrations. The repellent effect of this mixture was maintained over several hours. Altering the ratio of these compounds significantly affected the behavioural response of the mosquitoes, providing evidence for the ability of mosquitoes to detect and respond to specific mixtures and ratios of natural repellent compounds that are associated with host location.
Conclusion
The optimum mixture of 6-methyl-5-hepten-2-one and geranylacetone was a 1:1 ratio and this provided the most effective protection against all species of mosquito tested. With further improvements in formulation, selected blends of these compounds have the potential to be exploited and developed as human-derived novel repellents for personal protection.
http://www.malariajournal.com/content/9/1/239

MALARIA: Yellow Fever Mosquito Shows Up in Northern Europe

In the latest display of mosquitoes' predilection for modern travel, entomologists have found a small colony of the tropical species Aedes aegypti—also known as the yellow fever mosquito—in the Netherlands. The insects were found on and near two facilities of a company that imports used tires and presumably originated in the hot southern part of the United States. Aedes aegypti is an important vector not just of yellow fever but also of two other viral diseases, dengue and chikungunya.
http://www.sciencemag.org/cgi/content/summary/329/5993/736

MALARIA: Reducing Plasmodium falciparum Malaria Transmission in Africa: A Model-Based Evaluation of Intervention Strategies

Background. Half the world’s population is at risk of malaria, and every year nearly one million people—mainly children living in sub-Saharan Africa—die from this mosquito-borne parasitic disease. Most malarial deaths are caused by Plasmodium falciparum, which is transmitted to people by mainly night-biting Anopheles mosquitoes. When infected mosquitoes feed on people, they inject sporozoites, a parasitic form that replicates inside human liver cells. After
a few days, the liver cells release ‘‘merozoites,’’ which invade red blood cells where they replicate rapidly before bursting out and infecting more red blood cells. This increase in the parasitic burden causes malaria’s characteristic fever.
Infected red blood cells also release ‘‘gametocytes,’’ which infect mosquitoes when they take a blood meal. In the mosquito, the gametocytes multiply and develop into sporozoites, thus completing the parasite’s life cycle.
Malaria can be prevented by spraying the insides of houses (where most anopheles species feed and rest) with insecticides (indoor residual spraying, IRS) and by sleeping under bed nets that have been treated with long-lasting
insecticides (long-lasting insecticide nets, LLINs). Mass screening and treatment (MSAT) with effective antimalarial drugs can also reduce malaria transmission.
Why Was This Study Done? Early attempts to eradicate malaria (reduce its global incidence to zero) in the 1950s reduced the incidence of malaria to zero in some countries (malaria elimination) and greatly reduced malarial illnesses and
deaths in others (malaria control). However, this eradication program was aborted in the 1970s in part because of emerging drug and insecticide resistance. Recently, the advent of artemisinin-based combination therapies and new insecticides and the prospect of a malaria vaccine have renewed interest in
controlling, eliminating, and ultimately eradicating malaria.
Consequently, in September 2008, the Roll Back Malaria Partnership launched the Global Malaria Action Plan, which aims to reduce malaria deaths to near zero by 2015. But are the currently available tools for reducing malaria transmission
sufficient to control and eliminate malaria in Africa, the continent where most malaria deaths occur? In this study, the researchers use a new mathematical model of P. falciparum transmission to investigate this question.
What Did the Researchers Do and Find? The researchers’ P. falciparum transmission model consists of ‘‘compartments’’ through which individuals pass as they become infected with parasites, develop immunity, become
infectious to mosquitoes, and so on. The researchers used published data about parasite prevalence (the proportion of the population infected with parasites) and about relevant aspects of mosquito, parasite, and human biology, to
estimate the chances of an individual moving between compartments. Finally, they used the model to explore the impact over 25 years of increased coverage of LLINs, IRS, and MSAT, and of a future vaccine on malaria transmission in six
representative African settings. In a low-transmission setting, 80% coverage with LLINs reduced the parasite prevalence to below 1% in all age groups. In two moderate-transmission settings, LLIN scale-up alone failed to reach this target but the addition of IRS and MSAT drove the parasite prevalence below 1%. However, this combination of interventions did not control malaria in a moderate-transmission setting in which a mosquito species that bites and rests outside houses contributes to malaria transmission. Finally, in two hightransmission
settings, parasite prevalence could be driven below 1% only by setting unrealistic coverage targets for existing interventions.
What Do These Findings Mean? This new mathematical model greatly simplifies the complex dynamics of malaria transmission and includes several assumptions about which there is considerable uncertainty. The findings of this study are not, therefore, firm predictions of the future of malaria control in specific settings. Nevertheless, they suggest that it should be possible to make large reductions in malaria transmission and the associated disease burden in Africa over the next 25 years using currently available tools. Specifically, in regions where transmission is low or moderate and mosquitoes mainly feed indoors, it should be possible to reduce parasite prevalence to less than 1% provided a sustained intervention program is achieved. Importantly, however, these findings suggest that in regions where malaria transmission is high or where mosquitoes rest and bite outside houses, new approaches will be needed to control and eliminate malaria.

http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1000324

MALARIA: Malaria Entomology Revitalized in Zambia

A successful vector control program needs to do more than just spray houses and distribute mosquito nets. It must also have the ability to monitor mosquito populations and their response to vector control measures. The field of malaria entomology was in decline in Zambia for many years, but it attracted renewed interest owing to increased investment in malaria control efforts and interest in malaria elimination. The Ministry of Health, with support from PMI and others, is building entomologic capability to support vector control measures. "In former times, we had entomology technicians in the district who carried out local surveys," reminisces Dr. Cecilia Shinondo, Senior Entomologist and Malaria Specialist for the PMI-supported Health Systems Strengthening Project. "Today these categories of staff have virtually disappeared, but we are rebuilding capacity in entomology by training university students and district environmental health staff."

The National Malaria Control Center's insectary for rearing mosquitoes was recently refurbished with support from PMI. The insectary's small laboratory is now a center of activity, where students learn to identify and analyze mosquitoes (including dissections) to determine if they carry malaria parasites and changes in population survivorship to monitor the effectiveness of vector control programs. Heaters whirr, and a humidifier emits a steamy vapor. Small mesh cages filled with live adult mosquitoes line the shelves, and water-filled dishes in orderly rows contain larvae and pupae. The goal is to establish a colony of mosquitoes that will be used for training and to monitor the quality and duration of insecticides used in IRS and for ITNs and as a control group for insecticide resistance studies routinely conducted before and after the IRS programs. The painstaking work is paying off, and soon the insectary will have sufficient stock to support training and quality control monitoring for Zambia's vector control programs.
http://www.pmi.gov/news/voices/zambia_entomology.html

MALARIA: Trapping mosquitoes using milk products as odour baits in western Kenya

Traps baited with milk products pose good prospects for replacing the unethical man landing catches in sampling and surveillance of disease-spreading mosquitoes, especially the malaria vector An. funestus. Image: A gourd used in making African traditional milk cream used in trapping mosquitoes.
http://www.parasitesandvectors.com/

Angola: malaria statistics

Luanda – The co-ordinator of the Programme of Combat to Malaria, Filomeno Fortes, said this Monday in Luanda that the country registered 3.1 million cases of malaria during the year 2009, which resulted in 8,000 deaths.
The official was speaking about the situation of malaria in Angola and the national strategic plan in a forum about the role of journalists in the fight against malaria.
He said that the transmission of the disease in not uniform, having added that the central Benguela province was the most endemic of the country's 18 provinces with 28 percent of the cases of 2009.
According to the physician, Angola has two of the most violent species of mosquito of the world, the giant anopheles mosquito and the anopheles spontaneous mosquito, which can adapt to various circumstances living inside and outside residences and can also feed from animal blood.
Angola wants to control and reduce the disease until 2015 and eradicate the disease until the year 2030.
To reach this goal, the Ministry of Health aims at reducing the cases of malaria by 60 percent, by the year 2012, and cover 80 percent of children below the age of five and pregnant women with malaria.
The treatment of pregnant women through quick tests, the use of mosquito nets and an integrated control are the objectives of the Health Ministry.
In 2008, the country registered 3.45 million cases of malaria.
http://www.portalangop.co.ao/motix/en_us/noticias/saude/2010/3/16/Over-three-million-cases-malaria-recorded-2009,948c30cc-e77b-4cd2-a313-28ef2b708793.html