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Geographic Distribution

Fig. 34.1. Geographic distribution of leprosy.

In 1996 there were, for the first time in human history, less than 1 million registered patients being treated for leprosy (WHO, Epidemiological Record, 1996) and over 90% of these were receiving multidrug treatment in the hope that drug resistance would not develop. In India a vaccine has been developed to boost treatment. Over 8 million patients have been cured in the last decade, which must have prevented 1-2 million deformities. The decline in leprosy is remarkable; nevertheless, there are probably more than 300,000 patients not being treated, and over half a million cases are diagnosed each year: there are at least 1-2 million people who have deformities from leprosy (Fig. 34.1). The highest prevalence is in India and tropical Africa and South America, excluding Chile. It still occurs frequently in Southeast Asia, the Philippines, southern China and southern Malaysia, Indonesia and some of the South Pacific islands, and perhaps in Russia. In 1992 there were over 6,000 known patients in the southern United States and the Hawaiian Islands. That year there were 174 new cases in the United States, of whom 90% were immigrants. However, they are no threat to the local inhabitants. About one-third, or perhaps more, of the remaining leprosy patients worldwide suffer from disabilities which are specific to the disease.

Epidemiology

In all countries the social stigma of leprosy until recently has meant that patients were only found by active searching and the examination of every person in reservoir areas. The fear of the disease was also heightened in any country where leper colonies or sanatoria were the method of treatment; the establishment of outpatient clinics has encouraged patients to come forward voluntarily. Unfortunately, there are still many rural areas where the availability of a complete cure is unknown (WHO). In endemic areas leprosy occurs in about 6% of spouses; in high endemic areas, exposure rates, as measured by serology, may be as high as nearly 60% in household contacts and about 30% in those without known contact. The type of leprosy varies widely but overall susceptibility is not affected by race, ethnicity or nutrition. In endemic areas, cases are clustered about foci of villages or families, whereas in epidemics no particular foci can be identified. The frequency of infection peaks in the second decade and rises again from 30 to 60 years. There is no doubt that prolonged physical contact with an "open" and infectious patient carries an increased risk of the disease. Overcrowding and poor hygiene are common in endemic areas but whether these are of significance is undecided.

The exact mode of transmission is unknown; no vector has been recognized. Although the bacillus has been found in a variety of insects, it is uncertain whether they can transmit the disease to humans. Cases have been recorded where transmission has occurred through tattooing and also by contaminated intradermal injections. Droplet infection and dermal contact are known to transmit the infection and nasal secretions are a probable route. It has been suggested that, as paranasal sinus involvement is quite common, this is a reservoir for the infection. This is not accepted by all authorities.

When this book was first written, it was believed that leprosy did not occur naturally in any host other than man, but it has now been found in wild armadillos, from which it may be transmitted. Naturally acquired leprosy has been found in a chimpanzee from West Africa. Epidemiological information suggests that there is a nonhuman source of transmission and it is probable that this is either animals or soil, but so far (2000) this has not been established.

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