Leprosy Mailing List – May 10, 2017
Ref.: (LML) Preventive measures for leprosy
From: Joel Almeida, London and Bombay
Dear Pieter,
Esteemed colleagues on LML might be interested in this response to a thought-provoking recent article.
Reference: Laura Gillini, Erwin Cooreman, Tanya Wood, Venkata Rao Pemmaraju, Paul Saunderson. Global practices in regard to implementation of preventive measures for leprosy. PLOS NTD. Published: May 4, 2017. https://doi.org/10.1371/journal.pntd.0005399
The authors state, "active case-finding activities have been reduced and it is likely that a significant number of incident cases are not being detected." This guess seems reasonable.
Most incident cases of leprosy are transient and self-healing. A permanent marker of disease can help indicate the underlying trend in the true incidence rate of all leprosy cases, even if transient cases are missed. Permanent physical damage, in the form of visible deformities, is such a marker. In India, the incidence rate of cases with visible deformity at diagnosis has doubled in the decade since 2005 (1). This strongly suggests a rising trend in the incidence rate of leprosy in India. India has well over half the world's new cases of leprosy.
The authors' hopes regarding post-exposure prophylaxis seem over-optimistic even by their own account of the epidemiology. If the infection spreads largely before treatment of the index case is started, then belated and truncated treatment of household contacts is unlikely to reduce the incidence rate. Even if it delays the onset of clinical signs in household contacts for a couple of years.
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. (2) 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.(3) 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 (4). M. leprae ingested by amoebae remain similarly viable for at least 8 months (5). 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 (6). 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. This has merely facilitated the spread of leprosy and its associated disfigurements. Such mistakes of over-optimism need not be repeated.
Joel Almeida
References
1) Central Leprosy Division, Government of India. NLEP Newsletter October–December 2016, Vol. 1, issue 5
2) Diletto C, Blanc L, Levy L. Leprosy chemoprophylaxis in Micronesia. Lepr Rev. 2000 Dec;71 Suppl:S21-3; discussion S24-5.
3) P. Vijayakumaran et al. Does MDT Arrest Transmission of Leprosy to Household Contacts? Int. J. Lepr. (1998) 66(2): 125-130.
4) Desikan KV, Sreevatsa. Extended studies on the viability of Mycobacterium leprae outside the human body. Lepr Rev. 1995 Dec;66(4):287-95.
5) Wheat HW et al. Long-term Survival and Virulence of Mycobacterium leprae in Amoebal Cysts. PLoS Negl Trop Dis. 2014 Dec; 8(12): e3405
6) 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.
LML - S Deepak, B Naafs, S Noto and P Schreuder
LML blog link: http://leprosymailinglist.blogspot.it/
Contact: Dr Pieter Schreuder << editorlml@gmail.com
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