Viability ofMycobacterium lepraewithin the gut ofAedes aegyptiafter they feed on multibacillary lepromatous patients: a study by fluorescent and electron microscopes

Abstract

Summary 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 fe male Aedes aegyp ti were allowed to feed on bacilliferous leprosy patients, while in the control experiments mosquitoes were fed on a glucose-water-lepromin mixture containing dead M. leprae. The insects were sacrified 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: I, fluorescent staining technique; 2, by a light microscope using acid-fast staining technique; and 3, also by scanning as well as transmission electron microscopes. AFB were fo und 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 fu rther 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 fo und 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 ' fo llowing a blood meal. However the possibility of transmission of the illness into humans by mosquito bites seemed to be remote,

Transmission of viableMycobacterium lepraebyAedes aegyptifrom lepromatous leprosy patients to the skin of mice through interrupted feeding

“…The percentage of red coloured solid bacteria increased steadily from the second day onwards. The survival of M. leprae for up to 4 days in the gut of mosquitoes has been reported earlier by Saha et al 5 Out of 20 smears made from 12 suckling mouse skin extracts and examined for AFB, 17 smears were fo und positive with a bacillary count of up to 59 per skin smear. In the 20 smears examined for fluorescing bacilli (viable and non-viable) 18 smears were found positive with bacillary count ranging up to 57 per skin smear.…”

“…aegyp ti were established in the laboratory under sterile conditions according to the method described by Saha et al 5 Laboratory reared 5-to 8-day-old Ae. aegyp ti adult females starved overnight were allowed to feed for 40 to 140 seconds on the skin lesions of LL patients (with a Bacillary Index of 3 to 4 on the Dharmendra scale)6 using inverted glass tubes with mouths covered with cotton net cloth.…”

Experimental Infection of Rhodnius prolixus (Hemiptera, Triatominae) with Mycobacterium leprae Indicates Potential for Leprosy Transmission

“…There are several reports on mosquitoes capacity to carry M . leprae from one mammal to another through biting [ 18 ], being able to maintain its cell wall morphology inside their digestive tract for until four days [ 19 ], as the only viability parameter used on that moment. To verify if M .…”

“…Literature data estimates M . leprae viability inside mosquitoes through cell wall integrity accessed by microscopy for short periods of time from two [ 17 ] to 3 days [ 19 ]. On the other hand, longer observation periods in A .…”

Long-term Survival and Virulence of Mycobacterium leprae in Amoebal Cysts

“…Currently, the possibility of transmission by the respiratory aerosol route has gained considerable interest [39] . Other means such as transmission through insects [40] [41] has been considered but there has not been any substantial evidence supporting that claim. The possibility of discharge of M. leprae from the nasal mucosa begs the question of how the discharged organism remains viable in between hosts.…”