Plague in South-East Asia: A brief historical summary and present geographical distribution

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The paper presents a historical background and a summary of the situation of plague in South-East Asia. South-East Asia contributes at present over 90% of the total world incidence of plague. Two small outbreaks in Nepal can be considered as accidental in a wild plague focus due to intimate sharing of habitat by both man and rodents. No cases of human plague occurred in Thailand in the last 17 years (Fig. 6). In Indonesia the disease has been active again in a previously infected area after a silent period of 7 years (Fig. 5). In Burma and South Viet-Nam it continued to be active since its introduction almost 70 years ago (Figs. 7, 8, 9 and 10). Occasional increases in incidence due to new entrants in the areas in which zootic maintenance of plague is possible, and intermittent silent periods, are less evident in those two countries. The question whether the foci are “true” or not is rather academic if large numbers of cases in humans are observed year after year for 70 years. The facility with which it has spread in Viet-Nam in the last few years due to the state of war and consequent profound disturbances of the human and zootic habitats, should not obscure the fact that plague is neither new nor unexpected and that in 7 provinces (out of which 5 are coastal) the disease in humans occurred with perseverance and regularity. In others, quiescent periods are not unusual. The dispersal beyond the as yet not precisely defined “plague areas” might be temporary and plague might again retract to more limited areas ∗ ∗ The incomplete data gathered during the second world war and after and the change of names of towns and provinces have made the persistence of plague less evident to an external observer. . However, at present it continues to occur in 33 out of 46 provinces and autonomous towns of the Republic of Viet-Nam in spite of tremendous antiflea dustings and vaccination campaigns. The transformation of the habitats in such a way as to eliminate the opportunity for an epizootic maintenance is still a very distant hope. Studies of plague ecology in this part of the world are rare and are sensu stricto only starting now. Obviously, many questions could not have been answered at the time when infection was widely spread, when it involved a large portion of the country and large numbers of people. Also a certain historical perspective is necessary for this appraisal. The question of the existence of foci, that is to say of the true “natural” foci in South-East Asia has not been solved yet. It may be that the occurrence of plague in areas described are the last remnants of a slowly disappearing infection after the last pandemic, which started 70 years ago, which is in ecological terms, a very short period. The question of the nature of the foci will therefore be answered only after complex ecological studies have been carried out involving the pathogen, vector and host, and their dynamics and mutual relationship have been understood. While these studies are, no doubt, extremely important in order to assess the state of periodicity, the persistence and the future of the plague situation, there are many pressing practical public health problems which now require full attention.