Leprosy Mailing List – January 13, 2017
Ref.: (LML) Chemoprophylaxis in Leprosy
From: Joel Almeida, Mumbai and London
Two rounds of whole-population chemoprophylaxis with 3 drugs (rifampicin + ofloxacin + minocycline) had only a temporary impact on the incidence rate of leprosy on some small islands. (1) The incidence rate rose again subsequently. Therefore, hopes about sustainably reducing the incidence rate by chemoprophylaxis among contacts of index cases might well prove to be over-optimistic. This might remain so even if delays in diagnosis were shortened.
Further, visitors to the homes of Indian leprosy patients already treated with powerful bactericidal drugs (multi-drug therapy, MDT) show an increased risk of developing the disease, compared to the risk in the local population. (2) This remains true even after the patients have apparently been "cured" by MDT. This increase in risk might well be manifested in household contacts after the concentration of single-dose rifampicin in their blood has declined to non-therapeutic levels.
M. leprae, when dried in the Indian shade, remain viable for up to 5 months (3). M. leprae ingested by amoebae remain similarly viable for at least 8 months (4). If an individual with low specific immunity comes into contact with such M. leprae, replication can resume. The cycle of transmission could then be maintained indefinitely even if M. leprae do not replicate outside hosts.
The duration of extra-human survival may prove to be longer than 8 months, if more prolonged studies are undertaken. In Norway, a phenolic glycolipid specific to M. leprae was found in the environment decades after the last human case (5). It seems prudent to presume that dried M. leprae, which measure under 10 microns, can become airborne along with other dust. Single-dose chemoprophylaxis has only a transient effect, not offering sustained protection against such extra-human sources of infection.
A sustained reduction in the incidence rate of leprosy owing to chemoprophylaxis seems uncertain. Therefore, it seems wise to treat it as a fervent hope rather than a firm promise. Meanwhile, those newly developing the disease need protection from permanent disfigurement. This requires the rebuilding of leprosy expertise. Trained mobile workers need pro-actively to visit patients and monitor their nerve function, so that anti-inflammatory treatment can be started before permanent disfigurement sets in.
Over-optimistic hopes and promises have dealt blows to leprosy services in the past. Funding, talent and human resources have effectively been diverted away from leprosy. The narrative of interrupted transmission has been rich in promises but poor in outcomes. This has merely facilitated the spread of leprosy and its associated disfigurements. Such mistakes of over-optimism, and claims contradicted by evidence from India, need not be repeated.
Advocates of prophylaxis continue to shy away from demonstrating the eradication of leprosy from a small hyper-endemic island. The evidence gained, one way or another, would be invaluable. Let the demonstration convince everyone.
1) Diletto C, Blanc L, Levy L. Leprosy chemoprophylaxis in Micronesia. Lepr Rev. 2000 Dec;71 Suppl:S21-3; discussion S24-5.
2) P. Vijayakumaran et al. Does MDT Arrest Transmission of Leprosy to Household Contacts? Int. J. Lepr. (1998) 66(2): 125-130.
3) Desikan KV, Sreevatsa. Extended studies on the viability of Mycobacterium leprae outside the human body. Lepr Rev. 1995 Dec;66(4):287-95.
4) Wheat HW et al. Long-term Survival and Virulence of Mycobacterium leprae in Amoebal Cysts. PLoS Negl Trop Dis. 2014 Dec; 8(12): e3405
5) Kazda J, Irgens L, Kolk A. Acid fast bacilli found in sphangnum vegetation of coastal Norway containing Mycobacterium leprae specific phenolic glycolipid-I. Int J Lepr. 1990;58:353-357.
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