BY ALAZAR SHIFERAW
Researchers argue that although tremendous efforts in financing and coverage of malaria control have been made, the disease has continued to be public health threat not only in Ethiopia but also at global level. Hence, assessing the entomological nature of Anopheles mosquitoes; species composition, longevity, behavior and infectivity rates among others are highly essential.
According to the World Health Organization (WHO), only certain species of mosquitoes of the Anopheles genus, only females of those species can transmit malaria. However, in Ethiopia, to gain better insight into the geographic range of Anopheles stephensi, carrying out further research conducts; mosquito surveys in different locations throughout Ethiopia is very important. Researchers believe the effort should center on malaria prone areas of the country. Both rural and urban surveys are needed, particularly to investigate the role that livestock presence plays in Anopheles stephensi abundance.
Besides, according to some literatures, the impacts of inter annual climate fluctuations on vector-borne diseases, especially malaria, have received considerable attention in the scientific literature. These effects can be significant in semi-arid and high-elevation areas such as the highlands of East Africa. Because cooler temperature and seasonally dry conditions limit malaria transmission. Many previous studies have examined short-term lagged effects of climate on malaria but fewer have explored the possibility of longer-term seasonal effects, it added.
Recently, the International Centre of Insect Physiology and Ecology (ICIPE) said that it has generated new evidence of the immense threat posed by a highly destructive invasive plant, known scientifically as Parthenium hysterophorus, towards the probable escalation of malaria incidents in East Africa.
In a study published on 20th July 2021, the Center demonstrates that the weed, which has aptly earned the alias of ‘famine weed’ due to its phenomenal adverse impact on people’s health, agriculture, livestock and the environment, has contrastingly favorable effects on Anopheles mosquitoes, which transmit the malaria parasite. Also, the researchers note the possibility of exploiting the Parthenium-mosquito relationship to control the insects.
“In general, mosquitoes lay their eggs in standing water. However, we have established that Parthenium releases from its roots, chemicals known as terpenes that have a distinct blend of mosquito-attractive fragrances. When these chemicals leak into stagnant water, they enhance its attractiveness as an egg laying site for mosquitoes, in comparison to plain water,” explains Prof. Baldwyn Torto, Head, ICIPE Behavioural and Chemical Ecology Unit (BCEU).
“As our research further demonstrates, this preference has major implications on the ability of mosquitoes to survive and thrive. The Parthenium root chemicals enable mosquito larvae to emerge two to three days earlier, and they also extend the lifespan of the adult mosquitoes arising from the contaminated breeding sites to a week longer than normal, thus boosting their chances to bite people and transmit the malaria parasite,” said.
He further said that these findings are especially significant considering that Parthenium – a native of North and South America and one of the world’s most devastating invasive plants – is widely spread across East Africa including in flooding-prone malaria endemic zones. Parthenium aggressively colonises its invaded regions, killing other plants and reducing crop yields. It also produces a highly toxic compound called parthenin that causes dermatitis, hay fever and asthma in people, poisons animals and contaminates meat and dairy products in livestock that has fed on it.
In 2015, ICIPE published a seminal study that made the first global connection between Parthenium and mosquitoes. The research demonstrated that the weed is a preferred nectar source for Anopheles mosquitoes and it can sustain these insects by extending their lifespan even in the absence of a blood meal from people. Moreover, female Anopheles mosquitoes that feed on Parthenium survive longer, accumulate substantial energy reserves and they are capable of laying more eggs. Importantly, the researchers found that parthenin does not have the same toxic effect on adult female mosquitoes as it does on people and animals, indicating that the insects can tolerate and possibly detoxify themselves of the compound.
“Our recent findings present a silver lining in that the chemical fragrances found in the roots of Parthenium could be used as a bait in combination with traps, to selectively capture pregnant female mosquitoes seeking egg laying sites,” explains Trizah Milugo, a Kenyan student who conducted the study as part of her PhD research based within the ICIPE BCEU. “We also noted that only half of the eggs deposited in water containing these chemicals hatched. We singled out parthenin as being responsible for the low egg hatch rate, meaning that female mosquitoes can compensate the cost of exposing their juveniles to plant toxins for improved survival as adults.”
“Globally, invasive species are considered one of the most important perils to nature due to their severe impact on many socio-economic aspects,” notes Dr. Segenet Kelemu, ICIPE Director General & CEO, “Africa is one of the most susceptible regions, with a long and diverse list of such menace. Therefore, ICIPE has prioritized the management of invasive species as a key area of focus.”
In addition to the Centre’s invasive species initiatives, ICIPE and partners have developed a Strategy for Managing Invasive Species in Africa (2021 – 2030), which focuses on a three-stage approach of prevention, early detection and control. It also dealt with a ‘One Health’ focus to tackle the cross-cutting impact on human, animal, plant and environmental health, according to the International Centre of Insect Physiology and Ecology. Our mission is to help alleviate poverty, ensure food security, and improve the overall health status of peoples of the tropics, by developing and disseminating management tools and strategies for harmful and useful arthropods, while preserving the natural resource base through research and capacity building.
New insights into malaria vectors, edited by Sylvie Manguin said that Anopheles mosquitoes are involved in the transmission of human malaria and its devastating consequences in endemic countries worldwide. In 2010 alone, malaria was a cause for an estimated 660,000 deaths. As the study of Anopheles species and populations is a key element for reaching the goal of malaria elimination, an enormous amount of information has accumulated over the past century, and together in recent decades with the advent of novel technologies the acquisition of new knowledge has accelerated even further.
The Ethiopian Herald August 6/2021
