A new in vitro bioassay system for discovery and quantitative evaluation of mosquito repellents

Authors: ALI, ABBAS - University Of Mississippi; Cantrell, Charles; KHAN, IKHLAS - University Of Mississippi

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2017
Publication Date: 5/24/2017
Publication URL: http://handle.nal.usda.gov/10113/5700685
Citation: Ali, A., Cantrell, C.L., Khan, I. 2017. A new in vitro bioassay system for discovery and quantitative evaluation of mosquito repellents. Journal of Medical Entomology. 54(5):1328-1336. doi:10.1093/jme/tjx100.
DOI: https://doi.org/10.1093/jme/tjx100

Interpretive Summary: Mosquitoes are vectors of many pathogens that cause human diseases. Although prevention and control of immature stages is the best method to control mosquitoes, repellents play a significant role in reducing the risk of these diseases by preventing mosquito bites. The In vitro K & D bioassay system is commonly used for screening of natural products against mosquitoes for biting deterrent activity. This K & D bioassay is very useful for high throughput screening programs but the size of the chamber where females are exposed to the treatment may be too small to provide adequate space for the females to fly away from the treated organdy if desired. Hence the data is not always comparable with in vivo bioassays. In vivo human arm-based bioassay systems are also used to test repellent activity of compounds and mosquito repelling compositions. In vivo bioassays involve the use of human subjects and are often difficult, complicated and time consuming. Additionally, there is a risk of allergies and inconsistency of data because of variable response of mosquitoes to individual subjects. In this paper, we are reporting an Ali and Khan (A & K) large cage in-vitro bioassay system that can effectively be used to quantitatively measure the repellent activity of chemicals and compositions against mosquitoes.

Technical Abstract: Mosquitoes are vectors of many pathogens that cause human diseases. Although prevention and control of immature stages is the best method to control mosquitoes, repellents play a significant role in reducing the risk of these diseases by preventing mosquito bites. The In vitro K & D bioassay system is commonly used for screening of natural products against mosquitoes for biting deterrent activity. This K & D bioassay is very useful for high throughput screening programs but the size of the chamber where females are exposed to the treatment may be too small to provide adequate space for the females to fly away from the treated organdy if desired. Hence the data is not always comparable with in vivo bioassays. In vivo human arm-based bioassay systems are also used to test repellent activity of compounds and mosquito repelling compositions. In vivo bioassays involve the use of human subjects and are often difficult, complicated and time consuming. Additionally, there is a risk of allergies and inconsistency of data because of variable response of mosquitoes to individual subjects. In this paper, we are reporting an Ali and Khan (A & K) large cage in-vitro bioassay system that can effectively be used to quantitatively measure the repellent activity of chemicals and compositions against mosquitoes. The A &K system consists of a 30 × 30 × 30 cm aluminum cage with metal screens and one side modified to replace metal screens with a transparent acrylic sheet. A blood box containing a removable feeding device consisting of 1, 3 × 4 cm or a 7.5 x 4 cm rectangular reservoir was attached to the transparent side of the cage through a 120 × 35 mm slit. The top of the blood box had a sliding door used to expose the females to the treatment while performing the bioassay. The space between the sliding door and the feeding device is such that it can distinguish between the feeding and non-feeding females when the door is closed after 1 min exposure of females to the treatment. Many natural compounds with known repellency and DEET (N,N-diethyl-meta-toluamide) were tested in this bioassay. MED value of DEET (11.7 µg/cm2) from A & K bioassay falls in the range of the in vivo bioassay (9 - 23 µg/cm2). Undecanoic acid, thymol and geranic acid with MED values of 2.9, 5.9 and 5.9 µg/cm2 in the A & K bioassay were active at about 5-8 times lower dose than in the in vivo bioassay. Methyl eugenol and (-)-trans-p-menthane-3,8 diol (trans-PMD) with MED values of 5.9 and 11.7 µg/cm2 were active at 4 times lower dose in A & K bioassay than in in vivo cloth patch bioassay. In general, the natural compounds work at 4-8 times lower dosages in the A & K bioassay as compared to in vivo, cloth patch bioassay. Comparison between 12 cm2 and 30 cm2 treated area in A & K bioassay indicated that the MED values at 30 cm2 was 1-2 times higher than at 12 cm2.