By Mary Hearty
With Africa accounting for nine out of ten malaria cases globally, the continent is turning to gene drive technology to control the disease. This is according to a decision made by African leaders at the 29th Summit of Heads of States and Governments of the African Union held in Addis Ababa.
There are 3500 to 4000 mosquito species worldwide and 837 of the species are in Africa, with only 3 species transmitting malaria in sub-Saharan Africa.
Speaking during a virtual conference by the African Union Development Agency (AUDA-NEPAD) , Dr Abdoulaye Diabate, Head of Medical Entomology and Parasitology at the Research Institute in health Sciences in Burkina Faso who presented on Gene Drive for Malaria Control and Elimination in Africa said that two options for genetic control of mosquito-borne infectious diseases identified were population suppression and population replacement.
“Population suppression involves releasing of modified mosquitoes into the population, and this can cause transient or permanent suppression. With the population replacement method, modified mosquitoes released into the population can lead to the spread of a gene that blocks malaria transmission,” the Medical Entomologist stated.
Further, he highlighted that a lot of challenges are met in the pathway of gene drive testing to the field including risk management, public acceptance, legal and ethical issues, and technical issues, emphasizing: “The safety issue is the one vital aspect that may not be easily fixed. One can gather more data, lobby for political report, and build capacity but, if we cannot provide a plan that considers safety, then the effort is really dead.”
Combating malaria using the gene drive approach was conducted in three phases; the first phase is known as the sterile male self-limiting; then the second one will be the self-limiting male bias; and the final phase will be self-sustaining male bias.
“The sterile male self-limiting construct means that you have genetically modified (GM) male mosquito. And if you release it to the field, they will mate with local fertile female mosquitoes but they will have no progeny. No progeny means that the genetic material of interest cannot be transmitted to the next generation within the environment, that is, female fertility will be reduced or bias sex ratio towards male will be increased,” he explained.
The medical entomologist said that in 2016, they carried out the sterile male self-limiting construct in Burkina Faso, whereby the genetic material of the GM mosquitoes and those of the local mosquitoes in the country was tested in the laboratory.
Thereafter, they got authorization from the National Agent for Bio-Security for field testing. Besides, he affirmed that t it is very important that the technical aspect of the technology involves the stakeholder engagement.
This is by communicating with the community to sensitize them on what this technology is about so that they can know what we are doing. For instance, Burkina Faso has a population of 20 million people and potentially, all of them are our stakeholders, he said.
“We started from the community all the way to the highest level of engagement in the county, which included regional and national authorities such as Ministry of Research, Health Environment, the Parliament, the religious authority, the media, and social civil society. We simplified key messages all the way to the complex ones hence, we observed transparency.
We used visual type of communication at the community level, and also we had an open day where the villagers were able to see the GM mosquito, and ask questions,” he narrated.
The release was done in 2019 but the work started in 2012 (seven years down the line). He explained:
“It took that long because the technology developed is not just about science. There is more to this technology than just science. You really need to take your time, go to the community and make sure that people can clearly understand what you are doing to ensure transparency before you can move to the next step.”
The release was done with a self-limiting sterile male construct so no gene has been released so far because the objective of the release was to collect meaningful scientific information that will inform the next step.
Moreover, it did not intend to have an epidemiological impact on malaria or to suppress mosquito populations, and they wanted to build capacity to handle, manipulate and release GM mosquitoes.
Scientific objective of the release was to assess the ability of released males to participate to swarms. Secondly, they wanted to estimate the daily survival rate of male mosquitoes of the sterile male strain in the field. Thirdly, they wanted to understand their dispersal within and from the release village.
“So, in July 2019, we released the mosquitoes and the consecutive days, we were in the field collecting back these mosquitoes and every moth we would do a regular monitoring up to one year,” he said.
Dr. Diabate added: “We have released about 14850 specimen mosquitoes and about 6428 were GM mosquitoes. Overall, we have collected back 527 mosquitoes, representing about 3.6 percent of recapture rate, which was beyond the recapture rate of most medical entomology studies in West or East Africa at one or two percent.”
With the GM mosquitoes, the recaptured rate was 27 percent. Also, they did PCR test with the mosquitoes in the lab to determine whether they are GM mosquitoes or not after collection.
With regards to net dispersal distance based on GPS recapture locations, the minimum dispersal distance was 50 m while the maximum was 500m. Meaning the mosquitoes could not fly very far from the village where they were released.
Other studies that have been done in and beyond Burkina Faso on the net dispersal distance among these mosquitoes indicate about 550m maximum, that is, in East and West African countries.
In terms of survival rate, the study indicated 80 percent daily survival rate of 100,000 mosquitoes and 60 percent of 100,000 GM mosquitoes too.
Therefore, the study indicated that the assessment of the release was successful.
During the conference, Dr Diabate focused on the first phase as he revealed that the last two phases are yet to be started. “We have completed the phase one and submitted it to the national security for evaluation. If they approve it, hopefully we will get to the second phase,” he said.
Dr Prosper Chaki, Research Scientist and Director of Pan-African Mosquito Control Association during the meeting mentioned that some of the challenges that need to be addressed include; weak capacity; no standardized best practices; weakness in routine programmatic vector surveillance control; and decision making is still outside driven.
In terms of data and politics, Dr Chaki said that there is weak local capacity for data processing, analysis and interpretation; inequities in analytical capacity; and operational research are not locally driven.
According to survey done on human capacity and infrastructure for vector borne diseases research and control, there are 112 institutions and 362 individual entomologists in 35 countries which participated in the survey. 30 of the institutions were universities, 21 Ministries of Health, 19 National Research Centres, 16 National Malaria Control Programmes, and 11 Non-Governmental Organizations.
Therefore, he emphasized on the need to strengthen local capacity for malaria surveillance and elimination in Africa; promote and invest in locally-driven operational research; invest in infrastructure such as data collection tools, insectaries and laboratories, and data processing infrastructure.