Smallpox is an extremely contagious disease characterized by fever, vesicular and pustular rash, and a high mortality rate. A milder form (smallpox) would be caused by the same virus.
The global eradication of smallpox was officially announced in 1989, which is one of the greatest feats of modern medicine. There was no re-emergence of smallpox in the 1980s. If this pattern continues, the disease that was once responsible for 10% of all deaths in the world would become a disease primarily of historical interest.
Although smallpox has disappeared as a topic in medical textbook editions, it was wise to continue to be prepared to recognize them and prevent their spread if they reappeared as an endemic, epidemic, or pandemic. Some cases are currently being reported around the world, which is of concern to public health authorities.
The oropharynx of infected patients is the main source of virus spread. Contacts are infected by inhaling the virus, which enters the respiratory tract and multiplies there, probably in macrophages. The virus is transmitted to the circulation in macrophages, and from there to regional lymph nodes. Reproduction occurs in the lymphatic organs, and there is secondary viremia.
The virus localizes to small blood vessels in the dermis, leading to capillary dilation, endothelial swelling, and mononuclear cell infiltration. Epidermal cells increase in size and intraepidermal vesicles form on the skin and mucous membranes. The vesicles burst, forming shallow ulcerations, while the epidermal cells increase in size and expand into the chorion.
Viral infection stimulates cytotoxic T-cell responses, neutralizing antibodies, and interferon production. Such responses limit virus replication and induce prolonged immunity if the patient recovers. Smallpox is likely to be more severe in immunocompromised patients, especially those with T-cell deficiency.
Smallpox was described in Asia during the 1st century AD and in Europe and Africa around 700 AD. The infection was transmitted to Central, South and North America during the 16th and 17th centuries. Endemic smallpox was eradicated in the United States in 1926, and smallpox in 1940. Eradication was slower in Asia, Africa, and certain regions of America. The last case of smallpox occurred in Somalia (Africa) in October 1987.
The last known case occurred a year later in Birmingham (England), in September 1979, and was the result of a laboratory accident. There was no re-emergence of smallpox during the 1980s. The ability to eradicate this disease, through an effective worldwide vaccination program, seems to be essentially related to the fact that man is the only known reservoir of the smallpox virus.
That there was no asymptomatic carrier, which facilitated control. And that early diagnosis and prevention of the disease or modification of its evolution was possible by rapid vaccination of contacts.
In temperate climates, endemic smallpox occurred in winter and spring. It was basically a disease of children and young people. The prevalence of unvaccinated family contacts was approximately 58%, compared with 4% of those vaccinated. In general, patients were in a serious condition and were bedridden, which limited their transfer to direct contact with family.
Index cases rarely infected more than five patients, more often those sharing the same rooms. Transmission intervals were two to three weeks, and new cases occurred in the community or geographic region over many months. The theme continues in the next issue from Tuesday.
* The author specializes in general surgery and digestive health.
Note: The opinions contained in this column do not necessarily reflect the opinion of CORREIO DE CARAJÁS.