South-East Asia Regional Conference on Epidemiology

Emerging and re-emerging vector-borne
diseases in <strong>Asia</strong>
Duane J. Gubler
There has been a dramatic global re-emergence of epidemic vector-borne diseases in the past 30
years. Many of the diseases that were effectively controlled in the middle part of the 20th century
have re-emerged and new pathogens have emerged, both of which are causing major epidemics of
disease. Most of the newly recognized diseases are caused by zoonotic pathogens. These animal
pathogens have probably been infecting people for thousands of years in rural areas, but now have the
opportunity to infect more people in urban settings.
The parasitic vector-borne diseases are not as important as some of the others in terms of causing
epidemic disease. Malaria is the most important vector-borne disease, but 95 per cent of the global
malaria burden is in Africa. Most countries in <strong>Asia</strong> have done a very good job of controlling malaria,
although in some areas there may be local problems. The re-emergence of leishmaniasis in India and
African trypanosomiasis in Africa are also important.
Of the bacterial diseases, plague is the most important, with natural foci occurring in <strong>Asia</strong>, the
Americas and Africa. However, most of the human plague reported in the last 15 years has come
from Africa. The enzootic sites in <strong>Asia</strong> include China, Viet Nam, Indonesia and India. The 1994
plague epidemic in Surat, India, illustrated the importance of this disease, being the first infectious
disease epidemic impacted by globalization. It was a surprise epidemic at the time because for 28
years there were no reported human plague cases in India; the last human case had occurred in 1966.
Unfortunately, both the clinical and laboratory diagnoses were confused, causing lack of confidence
in the public health system. When pneumonic plague cases were finally reported, it created panic,
and resulted in a mass exodus from the city of Surat. Within days, there were reports of cases of
plague in other Indian cities, from which people were flying around the world. The international health
regulations were implemented, and a number of airlines stopped flying to and from India. The global
airline industry, for the first time in history, was partially shut down for about two weeks. The actual
outbreak was relatively small, with less than 50 cases, and as a result it should have been a relatively
unimportant, local public health event. Instead, it became a media event, an epidemic of panic that
turned into a global public health emergency, causing an estimated US$3 billion economic loss to the
economy of India. On a global scale, the loss was about US$6 billion. In today’s money that does not
seem to be too much, but in 1994 that was a lot of money. This epidemic was a wake-up call because,
for the first time in modern history, it was realized that epidemic infectious diseases could move
very rapidly via modern transportation. This was reinforced by the severe acute respiratory syndrome
(SARS) epidemic nine years later.
Epidemics of louse-borne typhus and louse-borne relapsing fever have occurred in Africa, diseases
that had not been seen since World War II. In the temperate zones, lyme disease has become an
important emergent disease.