The Human Loving Diseases: Poliovirus and Small Pox | Part II

All microbes and pathogens can die or be killed, so why is it that every disease in the world has not been destroyed? Because, a disease evolves and grows. And as we invent new techniques to eradicate the virus, the virus also develops to resist the new techniques. However, if all the correct tools and apparatuses were available, all diseases could be eradicated.

Epidemiologists have identified three factors to decide the ease with which a disease can be eradicated. There needs to be an effective vaccine available to interrupt transmission of the agent. So that, more people are not infected, successfully breaking the chain of infection. Diagnostic tools need to be available to detect and identify the levels of infection that can lead to transmission so that epidemiologists can build a database of transmission pathways and virus locations. And humans must be the only reservoir for the virus. But, these factors are not quintessential. They are only a small checklist that helps scientists to determine feasibility of eradication.

A short comparison between a disease that has already been eradicated (smallpox) and a disease which we hope to eradicate (polio) may help in our understanding of such factors. 

Smallpox Polio
An acute infection
An acute infection
Humans are the only reservoir
Humans are the only reservoir
Immunization interrupts virus transmission
Immunization interrupts virus transmission

An acute infection:

Acute diseases come on rapidly, and are accompanied by distinct symptoms that require urgent or short-term care, and the patient gets better once they are treated. Meaning, that the person infected can only transmit the virus for a limited amount of time. The distinct symptoms allow health officials to easily and effectively diagnose patients and track the transmission pathway in different communities. The harder it is to diagnose the disease, the harder it will be to eradicate the disease.

Humans are the only reservoir:

Most diseases can be transmitted between insects, animals, and plants. In these cases, the pathogen exists in a species that serves as a ‘reservoir’ for future infections for other species. One of the things that makes polio and smallpox eradicable is the fact that humans are the only reservoir. No poliovirus or smallpox has been found to exist and spread among animals. If we eradicate polio in every human being, then the polio virus would cease to exist.

Immunization interrupts virus transmission:

Vaccination generates herd immunity and that is the key to extermination of a disease. Herd immunity occurs when a significant amount of the population is protected through vaccination against a particular virus, making it difficult for the virus to continue to spread. It is important to reach herd immunity to protect those who can’t get vaccinated, like immune-compromised children. Once a person is immunized, he can no longer transmit the disease. Limiting the pathogen geographically, allowing epidemiologists to focus their efforts.

By the comparison and explanations of these factors, it may help you in identifying future microbes which can be feasibly eradicated. We must now focus our attention on polio.

Read Next: The First Step: Identification and Prevention | Part III

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