In order to investigate the mode of spread in leprosy, I observed 32 years old female
with lepromatous leprosy (LL)-mother, primary case and her healthy family including
two sons (8 years old, 6 years old) and two daughters (4 years old, 1 year old) for 10
years. The 2nd son (6 years old)-secondary case-developed leprosy at the age of 16.
This observation leads to the following conclusions.
1. The 2nd son has lived with his mother for 16 years. His village was not an
endemic area for leprosy and there was no leprosy patient in his neighbourhood. His
mother was his only contact. I assume that made of spread of this disease is by
indirect or air borne contact rather than direct contact. The basis for this assumption is
that the mother’s duties as a farmer kept her away from her children most of the
time. And also the fact that the first son and the younger children ages 4 and 1 year
claimed most of her time.
2. The incubation period was estimated at a minimum of 5 years and 3 months
according to Ml positive period. However, considering BI positive period, it is minimum
of 4 years and 2 months and maximum 10 years and 11 months.
3. This case must have had the sub-clinical infection at the age of 12 since the small
hypopigmented patch was noticed on the buttock area and the Mitsuda reaction became
negative at that time. In spite of treatment with 25㎎ dapsone daily for 12 months and
BCG vaccination, he developed leprosy. This observation suggests that it took 50
months (4 years 2 months) to develops from the sub-clinical infection to the clinical
infection.
4. Since the 2nd son had low or absent CMI, he may have a genetic factor from his
mother predisposing him to leprosy.
5. When the members of families with lepromatous leprosy (LL) is examined, the
lepromin test and clinical examination should be performed. In the case of negative
Mitsuda reaction, they need long term follow-up and at the same time dapsone should
be given by mouth according to their weight for more than 1 year.
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