Early Diagnosis of Leprosy
Dr. P. Klatser
Leprosy is an infectious djsease in which symptoms are mainly determined by the host and the clinical presentation may vary within wide limits. Leprosy may have an acute, but usually a chronic onset, the latter developing insidious. Mycobacterium leprae may be present in enormous numbers without its host showing any clinical signs and symptoms. The disease may thus be in an advanced state before any abnormalities are evident in the patient. Nevertheless, the diagnosis of leprosy is a key element in the control of this disease which is entirely based on timely detection followed by adequate treatment of patients.
Because of the lack of a single independent 'gold standard" for diagnosis, it is mainly on clinical symptoms. For a relatively short period of time laboratory techniques had been introduced but have now been abandoned in most places where leprosy is still endemic.
There are a number of findings that may be interpreted as an illustration of the present failure of diagnosis. In 1997 still 5.4% Of the global new leprosy cases presented with visible disability grade 2; it was 11.3% for the 8 countries with the highest endemicity.
Assuming that the development of disability takes several years, it illustrates under-diagnosis in many situations. Thus, leprosy control programmes face the problem of many leprosy cases remaining undetected, as may be evidenced by the large number of patients found in the leprosy elimination campaigns (LEC) . Clearly, there is a need for an objective, easy-to-use diagnostic test. More so, because in the post-elimination era, leprosy will be a rare disease, with specific knowledge available at the central level and much less at the periphery. Over the past years several tests for diagnostic purposes have been described. Most of these tests got little appreciation from leprosy control programmes for reasons that were not always clear.
Several studies have shown that serology with PGL-I is very useful in identifying persons at high risk of developing MB disease, the main source of infection. A simple dipstick assay that can be used in the field is now available. Serological selection of high risk groups as a means of early diagnosis and elimination of sources of infection makes sense, more so now that preliminary evidence indicates that chemoprophylactic treatment of seropositive contacts decreases their antibody titre. It has often been argued that intervention limited to contacts only deals with a small proportion of the problem, because the majority of incident patients appear among the so-called non-contacts. We now know that the vast majority of new patients, almost 80%, can be associated to contact with another leprosy patient, whereby the type of contact is not limited to household relationships, but also includes neighbour and social relationships. This concept shows similarities with the 'Stone-in-the-Pond' principle describing tuberculosis transmission in concentric circles around a patient. This principle can be translated into a valuable and sustainable tool for
leprosy control programmes and elimination campaigns by focusing case detection and health promotion activities not only on household contacts but also on at least neighbours of leprosy cases.
