Viability of Mycobacterium leprae within the gut of Aedes aegypti after they feed on multibacillary lepromatous patients: A study by fluorescent and electron microscopes

Abstract

This paper describes the viability of Mycobacterium leprae within the gut of mosquitoes after they have bitten bacilliferous lepromatous patients. In the test experiments prestarved female Aedes aegypti were allowed to feed on bacilliferous leprosy patients, while the control experiments mosquitoes were fed on a glucose-water-lepromin mixture containing dead M. leprae. The insects were sacrificed for 7 consecutive days, their guts were dissected out and excreta were collected. These preparations were mounted and examined for acid-fast bacilli (AFB) by: 1, fluorescent staining technique; 2, by a light microscope using acid-fast staining technique; and 3, also by scanning as well as transmission electron microsopes. AFB were found in the gut and also in excreta but more abundantly in the earlier days after blood meal. The fluorescent staining technique showed that AFB within the gut of mosquitoes became non-viable (red stain) after 4 days of blood meals. It also demonstrated multiplication of the viable bacilli (green stain) during early days. It was further observed that most of the solid bacilli quickly became granular and non-viable (red stain). Ultrastructural studies confirmed these findings and demonstrated membrane bound dividing bacteria within the gut of the insects mostly within 72 h after a blood meal. No such cell-division was found in the gut of mosquitoes artificially fed on the glucose-water-lepromin mixture. These data together with light microscopic findings lend support to the transient multiplication of viable M. leprae within the gut of the mosquitoes after the bacilli were taken up from the circulation of lepromatous patients at least during the early period following a blood meal. However the possibility of transmission of the illness into humans by mosquito bites seemed to be remote, because of the short viable time, quick fragmentation and elimination of the ingested bacteria from the gut of the insects.