Assessing the impact of house screening and ivermectin administration to cattle on residual malaria transmission using entomological indicators in southwest Ethiopia: a cluster randomised control trial
Background: Malaria is a severe disease affecting millions of lives in the world. Despite the comprehensive coverage and scaled-up use of ITNs and IRS, which changed malaria epidemiology, malaria transmission continues. The behavioural variability of the malaria mosquito, human night-time activities exposed to the bite of the malaria mosquito, the effectiveness of ITN and IRS depend on the insecticides, and other reasons maintain the residual malaria transmission in the community. Pushing the mosquitoes outdoors and pulling them to the animals treated with ivermectin could be a complementary intervention to reduce the transmission of indoor and outdoor residual malaria.
Study area, design, and data collection methods: The study will be conducted in 14 Kebeles endemic to malaria located close to the southern Rift Valley Lakes, Abaya, and Chamo in the Arba Minch Zuria and Mirab Abaya districts. A cluster-randomised controlled trial design will be applied in 60 clusters with four arms (15 clusters each). One arm will be intervened by house screening, the second arm with ivermectin cattle treatment, the third arm will receive both house screening and cattle treatment, and the fourth arm will receive bed nets as a control. The human night hours activities, which may expose people to the bite of malaria mosquitoes, will be assessed using direct observation and questionnaires. The malaria mosquito collection will be conducted using Centers for Disease Control and Prevention (CDC) light traps, pyrethrum spray catches (PSC), pit shelter, and human landing catch (HLC).
Objectives
- To determine whether house screening and ivermectin cattle treatment reduce indoor and outdoor mosquito density
- To assess whether house screening and ivermectin cattle treatment affect the blood meal feeding patterns of mosquitoes
- To assess whether house screening and ivermectin cattle treatment reduce the gametocyte positivity rate in freshly fed mosquitoes
- To assess the human biting patterns of malaria mosquitoes in control and intervention arms
- To assess the human night hours activities and sleeping patterns contributing to residual malaria transmission.
Peer-reviewed publications
Conference presentations
2023 Annual Meeting American Society of Tropical Medicine and Hygiene
2023 Senuph Annual Scientific Conference
Publications
Eligo, N., et al. (2026). “Molecular xenomonitoring for identifying Plasmodium parasites and blood meal sources of mosquitoes in malaria endemic villages adjacent to the southern Rift Valley Lakes, South Ethiopia.” Sci Rep.
Detecting Plasmodium parasite DNA and host blood meals in the abdomens of fed mosquitoes enables timely decisions for effective malaria control. Hence, this study aimed to detect the Plasmodium parasite DNA and identify sources of blood meals in the abdomens of freshly fed Anopheles mosquitoes in South Ethiopia. A cross-sectional entomological survey was conducted in 12 malaria-endemic Kebeles near the southern Rift Valley Lakes, Abaya and Chamo, as a baseline for a trial evaluating house screening and/or ivermectin treatment for domestic animals to control malaria. Four hundred sixteen houses were selected for the Centers for Disease Control and Prevention (CDC) light trap collections. The mosquito species were identified using morphological and molecular methods. The polymerase chain reaction (PCR) technique was employed for the detection of Plasmodium parasite DNA and blood source identification. Plasmodium vivax (2.0%; 9/446) and P. falciparum (0.2%; 1/446) were detected in the abdomens of mosquitoes. Out of 446 tested Anopheles specimens, 85% (378/446) fed on six vertebrate hosts, while 15% (68/446) tested negative for these hosts. Goat blood was the most common, accounting for 67% (299/446), followed by human blood (23%; 102/446). Cow blood was identified in 19% (84/446) of the fed mosquitoes, while dog blood was present in 13% (57/446). Chicken and pig blood accounted for < 1% of blood meal sources. The overall human blood meal index was 23%, including mixed blood meal sources. Anopheles arabiensis was the most prevalent species, comprising 85% (380/446) of the nine Anopheles species identified, followed by An. pharoensis 7% (33/446) and An. tenebrosus 3% (13/446). Detecting Plasmodium parasites in the mosquitoes’ abdomens can enhance preparedness for malaria control. Anopheles mosquitoes obtain blood from various sources, with goats being the most common, followed by humans. Interventions targeting these mosquitoes may prioritise animal sources.