Tuesday, December 22, 2020

Epidemiology of HD

 Leprosy Mailing List – December 21 ,  2020 

 

Ref.:  (LML) Epidemiology of HD 

 

From:  Joel Almeida, London and Mumbai 


 Dear Pieter and colleagues, 

Understanding unexpected successes and unexpected failures is very helpful in achieving major epidemiological impact. Some field programmes achieved 16% to 90% real annual decline in new cases, while others showed a disappointing impact (0% to 3% real annual decline). The underlying epidemiology can be summarised as below. This might encourage great colleagues in endemic countries to implement increasingly effective interventions. 


Fig. 1 The neglected multitude of previously treated anergic patients maintains transmission despite all other efforts. 16% to 20% / year real decline in new cases is available from repeated skin camps with competent clinicians to diagnose subtle LL signs + MDT (prolonged for high BI patients to prevent reinfection/recurrence).(1-3)  90% / year real decline in new cases is available by adding repeated mass multi-drug administration to suppress bacilli in sub-clinical disease or missed cases, alongside skin camps and MDT.(4) By contrast, fixed duration MDT for LL patients failed to sustain a rapid decline,(5) with patients who had a high initial BI showing a significant risk of recurrent disease after even 24 months of MDT.(6) 

 


 

Fig. 2 Only a very small fraction of the population has genetically linked(7-10) anergy to HD bacilli, with consequently low ID50s. ID50 is the dose of bacilli sufficient to infect 50% of individuals of a given description. 

  


Fig. 3 Nearly all HD patients are non-infectious, for practical purposes. Transmission is almost exclusively by unrecognised LL or previously treated LL patients with recurrent disease, whose nasal discharge can contain up to tens of millions of viable bacilli per day.(11) 

Reliable epidemiology is like a reliable map. It is better than driving blindfolded. Further, our understanding keeps improving as clues from the front-lines are unearthed by great colleagues. Endemic countries need the elbow room to sustain and spread the successes they have demonstrated in exemplary programmes. 

 

Joel Almeida 

 

References 

 

1.    Tonglet R, Pattyn SR, Nsansi BN et al. The reduction of the leprosy endemicity in northeastern Zaire 1975/1989 J.Eur J Epidemiol. 1990 Dec;6(4):404-6 reviewed in: 23a. Almeida J. Reducing transmission in poor hyperendemic areas - evidence from Uele (DRC). LML 29 Nov 2019  

2.      Norman G, Bhushanam JDRS, Samuel P. Trends in leprosy over 50 years in Gudiyatham Taluk, Vellore, Tamil Nadu. Ind J Lepr 2006. 78(2): 167-185. reviewed and analysed further in: 20a Almeida J. Karigiri, India: How transmission rapidly was reduced in a low-income population LML 29 October 2020 

3.        Li HY, Weng XM, Li T et al. Long-Term Effect of Leprosy Control in Two Prefectures of China, 1955-1993. Int J Lepr Other Mycobact Dis. 1995 Jun;63(2):213-221. reviewed & analysed further in: 22a. Almeida J. What really happened in Shandong? LML 16 Nov 2019 

4.         WORKSHOP ON THE PREVENTION OF LEPROSY, POHNPEI, FEDERATED STATES OF MICRONESIA. 25-27 MAY 1999 sponsored by the Sasakawa Memorial Health Foundation Tokyo, Japan and the Western Pacific Regional Office of the World Health Organization. Int J Lepr, 67 (4) (SUPPLEMENT) 

 5.         Scheelbeek PFD, Balagon MVF, Orcullo FM et al. A retrospective study of the epidemiology of leprosy in Cebu: an eleven-year profile. PLoS Negl Trop Dis. 2013 Sep 19;7(9):e2444. doi: 10.1371/journal.pntd.0002444. eCollection 2013. 

6.         Balagon MF, Cellona RV, dela Cruz E et al. Long-Term Relapse Risk of Multibacillary Leprosy after Completion of 2 Years of Multiple Drug Therapy (WHO-MDT) in Cebu, Philippines. American Journal of Tropical Medicine and Hygiene, 2009; 81, 5: 895-9. reviewed and analysed further in 19a. Almeida J Recurrence rate among MB patients following RFT. LML 2 June 2019.  

7.         Gaschignard J, Grant AV, Thuc NV, Orlova M, Cobat A, Huong NT, et al. Pauci- and Multibacillary Leprosy: Two Distinct, Genetically Neglected Diseases. PLoS Negl Trop Dis 2016; 10(5): e0004345. https://doi.org/10.1371/journal.pntd.0004345 

8.         Chakravarti MR, Vogel F. A twin study on leprosy Georg Thieme Publishers, Stuttgart, Germany; 1973.

9.          Cambri G, Mira MT. Genetic Susceptibility to Leprosy—From Classic Immune-Related Candidate Genes to Hypothesis-Free, Whole Genome Approaches. Front. Immunol., 20 July 2018 | 
https://doi.org/10.3389/fimmu.2018.01674

10.          Sartori PVU, Penna GO, Bührer-Sékula S et al. Human Genetic Susceptibility of Leprosy Recurrence. Scientific Reports 2020; 10: Article number: 1284 

11.          Davey TF, Rees RJ. The nasal dicharge in leprosy: clinical and bacteriological aspects. Lepr Rev. 1974 Jun;45(2):121-34. 

PS. In medical exams someone from our college was asked, "What is the function of the muscle spindle?" The classmate replied "Sir, that is not well understood." 
The examiner shot back, "By whom, Sir? By the world at large or just by you?" 

In the epidemiology of HD, despite whatever might remain to be discovered, it seems wise to recognise and apply the knowledge already available. 

 

 


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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