South-East Asia Regional Conference on Epidemiology

22 | <strong>South</strong>-<strong>East</strong> <strong>Asia</strong> <strong>Regional</strong> <strong>Conference</strong> on Epidemiology
to search for cases of smallpox, or rumours of smallpox, from house to house, in markets, or public
gatherings, and then to initiate containment activity by targeted vaccination.
In all countries that still had smallpox, intensified search was conducted using recognition cards
for children or adults who had the disease. Investigators recorded names and addresses, information
on movements, isolated infected patients and conducted ring vaccination. Towards the end, in many
countries, a reward was given in order to find every last case, because if one could find the last case
of clinical smallpox, that meant that one had found the last case of infection. The containment activity
with smallpox vaccine was very well adapted. It was a heat-stable vaccine which could be carried
at temperatures up to 40o C for up to two or three weeks. It was very easy to administer through
a bifurcated needle by making punctures in the skin. In 1977, the last case of smallpox in nature
occurred in Somalia. The last known case of smallpox occurred in the United Kingdom in 1978 in
a laboratory in Birmingham, where a medical historian and librarian working in G block became
infected with smallpox, went home and infected her mother and father. Just 30 years ago, in 1980,
smallpox was certified as eradicated from the globe.
In 1970, just as smallpox was being eliminated from many African countries, a nine- year-old boy
in the Democratic Republic of the Congo, which was then Zaire, developed an infection that looked
very much like smallpox. In fact, at that time it was thought to be smallpox. Specimens were sent to
the laboratory but it turned out to be human monkeypox, which had been first identified in 1958 among
laboratory monkeys in Copenhagen. There was great concern at that time about human monkeypox
because it was a disease that looks very similar to smallpox and because it caused death. Some studies
were done between 1970 and 1980 showing that 72% of these cases had a contact with an animal
in nature. The disease was traced to children picking up dead squirrels or rodents. Three per cent of
those children transmitted it to their mothers and others. Between 1970 and 1996, three generations
of transmission, and a case-fatality rate of 10%, was observed. Monkeypox was found to be sporadic
in West and Central Africa. Primary cases over the age of 15 years were very rare, and secondary and
tertiary cases were mainly in unvaccinated parents or siblings. It turned out that smallpox vaccination
does protect against human monkeypox disease.
In 1980, it became clear that monkeypox was not such a rare disease. Was monkeypox rising due to
smallpox eradication? Humans who had been vaccinated against smallpox appeared to be protected,
but smallpox vaccination had been discontinued after the certification of smallpox eradication.
Reservoir of monkeypox virus was present in nature in rodents and monkeys. There were sporadic
breaches in the species barrier between rodents and humans. Only secondary and tertiary transmission,
however, had been observed in outbreaks among unvaccinated contacts. The question was whether
the decrease in transmission of human monkeypox after entry into human populations was due to
its attenuation with human passage or due to herd immunity from smallpox vaccination campaigns?
Also, did monkeypox pose a problem to eradication? Could it eventually replace smallpox? In order
to determine answers to these questions, a series of surveys were carried out throughout West Africa.
These surveys covered children under 15 years of age, who did not have a smallpox vaccination scar,
to see whether they had any facial scarring —which is a sign of human monkeypox—and to check
whether their serum had antibodies for orthopox virus. The study included 10 653 children with no
smallpox vaccination scars. They were examined and their blood specimens were obtained. None of
them had serum antibodies to orthopox virus, i.e. the monkeypox virus. The outcome was that no
replacement epidemiology was occurring; hence, smallpox would remain eradicated.
However, in 1996, there was a major outbreak of human monkeypox in the Democratic Republic of
the Congo, which had 511 suspected cases of the disease (Fig.1). It continued to appear over several
months. The virus was examined genetically and was found to be quite stable. It had not mutated in
any way from other viruses collected in the D. R. Congo and other places throughout Africa that had
earlier experienced human monkeypox outbreaks. But the epidemiology of the outbreak was quite