Pox viruses - a multilayered biosecurity challenge
Monkeypox – what’s in a name?
In this article, you will learn about the disease smallpox, and the virus that causes it. You will see that there are many viruses that are related to smallpox and that many of these occur in animals and can be spread to humans. You will also learn about zoonotic diseases. There are many fascinating, and worrying, aspects of smallpox and its virus relatives.
Smallpox was a human disease that has been eradicated from human populations. This has been one of the greatest global public health successes. It was achieved through immunisation. Smallpox was a horrendous and devastating disease. It was caused by the variola virus. The variola virus comes from a family of viruses called the Poxviridae. Even though it’s been eradicated, there are some stocks of viral specimens kept by some countries.
Infection by smallpox started with a strong fever and tiredness. The disease then progressed to a rash which was mainly on the face, arms and legs. The rash turned into liquid and then pus-filled sores. These eventually dried up and fell off, leaving scarring. It killed as many as 30% of people who were infected – that is, it had a case fatality rate of 30%, which is very high compared with most infectious diseases.
Interestingly, the last human case of the disease was the result of a laboratory accident in 1978 in England, which led to the virus being accidentally released. The virus was declared eradicated in 1979.
Pox viruses related to the smallpox virus have long circulated in animal populations. Examples are cowpox which occurs in cattle and monkeypox which occurs in monkeys. In fact, cowpox was used for the original smallpox vaccine by Edward Jenner in 1796. Since smallpox was eradicated, several outbreaks of animal pox have occurred in humans through zoonotic transmission. Zoonotic diseases are diseases that can be transmitted from animals to humans.
Because smallpox was eradicated, humans no longer receive the smallpox vaccine. The vaccine may have prevented some of the cases of animal pox infections that now occur in humans.
Monkeypox is a virus that is closely related to smallpox, but it occurs in monkeys. There are some important aspects of zoonotic diseases that are highlighted by the example of monkeypox. Humans can be infected by monkeypox, and it can cause a severe illness similar to smallpox-like infection.
A resurgence in monkeypox virus infections in humans has been identified in the Democratic Republic of Congo in Africa. This resurgence has occurred despite taking into account the growth in the country’s population size. Exposure to the virus often comes from hunting monkeys. One reason people are more susceptible to the disease now is that they are no longer being vaccinated against smallpox. The smallpox vaccine prevents 81% of monkeypox infections in those who are vaccinated. This is called cross-protection.
You might ask why smallpox vaccine is no longer used to prevent these monkeypox and other zoonotic pox infections? Unfortunately, the smallpox vaccine, in rare cases, can cause serious, and in even rarer cases, life threating reactions. This risk is considered too great to allow routine use of the vaccine.
Another feature of many viruses that is of great concern is that they constantly change because of genetic evolution. That means that new patterns of disease from existing viruses can occur at any time. There is concern that this is happening to animal pox viruses.
After reading this article, discuss your answers to the following questions in the comments section below:
- What could happen if monkeypox became easily transmitted between humans?
- How could we control an outbreak of human to human monkeypox?
© UNSW Sydney