8 Most Deadly Infectious Outbreaks of 20th Century

Twenty years of the 21st century have already passed, and the vulnerability of the world towards the known and unknown diseases still exists.^[2] Although medical science has achieved immense success and made breakthrough advancements in recent times, there still exists the fear of dangerous and deadly diseases, which can cause tremendous devastation. In fact, with the increasing population across the world, changing climatic conditions, globalization, and many other factors, the vulnerability of the world may be expanded due to the occurrence of a significant pandemic manifold.

Diseases such as Ebola virus disease, Yellow fever (YF), Plague, Tuberculosis (TB), Zika, H1N1, Cholera, COVID-19, etc., caused a severe epidemic condition that had affected thousands of people worldwide. Subsequently, other diseases whose transmittance was due to a vector or a carrier were identified as significant causes of disease in both humans and animals. As the source and the nature of these diseases became more transparent to the scientists, the preventive measures and control were becoming highly effective ways of controlling the disease transmission. It was possible due to the discovery and development of various new insecticides, drugs, and vaccines. By the end of the 70s, the major vector-borne diseases had been controlled effectively in most parts of the world, and those that were not yet controlled were targeted for more intensive programs using new vaccines, drugs, and insecticides.^[1]

Numerous factors affect the severity and transferability of these diseases in the 21st century. These are as follows:-

• Changing Lifestyles: The enhanced inter-connectivity of people both nationally and internationally, or increased contacts between animals and people due to several other factors, has become inevitable. The changing preferences of people regarding food, clothing, geographical location for habitation, etc. have caused changes in the way things used to be earlier, leading to increased contact with lethal pathogens acting as causative agents for new deadly diseases.^[2]
• Climate Change: Changes in global temperature cause environmental changes leading to growth, multiplication, and spread of numerous pathogenic strains of already known and existing microbes, which results in the rise of such deadly diseases.
• Globalization: Increased trade among countries leading to migration of both people and goods has posed a higher risk of transmittance of diseases from one country to another. ^[2]
• Growing Population: Increasing the number of people who ultimately compete against each other for the limited resources imposing a burden on Mother Earth. Invariably they tend to become refugees or economic migrants who tend to live in pathetic conditions. It often increases the risk of the spread of such diseases.^[2]
• Limited Access To Healthcare/Poor Healthcare Systems: This has contributed to increased virulence of the viruses globally. The casualties caused due to such inadequate healthcare systems in different parts of the world increase the mortality rate and lead to increased suffering of the poor and disadvantaged people.^[2]

1. H5N1: The highly pathogenic Asian H5N1 influenza virus that was first detected in Guangdong in the People’s Republic of China (China) in 1996 is unique in having spread to humans and other mammalian species. This virus has not transmitted between any mammalian species, but the continued spread and evolution of these viruses in domestic poultry across Eurasia present a continuing severe threat. These viruses have killed over 60% of the people who have come in contact either directly or indirectly. H5N1 infections are unique due to multiple evolutions. These viruses were found in their epicenter in southern China.^[7]
2. H1N1: The H1N1 pandemic virus is a newly emergent human influenza A virus that is closely related to several currently circulating pig viruses in the ‘classic North American’ and ‘Eurasian’ swine influenza virus. The first-ever reported case of H1N1 in humans was seen in April 2009. According to the statistics, the H1N1 virus spread to 168 countries and overseas territories.^[8]
3. MERS-CoV: MERS-CoV (Middle East Respiratory Syndrome Coronavirus) was first identified and reported to WHO in September 2012. Up to the data of January 23, 2015, WHO has confirmed 956 cases of MERS-CoV infection, out of which at least 351 deaths were confirmed. These cases were related to people traveling or residing in nine countries: Saudi Arabia, the United Arab Emirates, Qatar, Jordan, Oman, Kuwait, Yemen, Lebanon, and Iran.^[9]
4. Ebola: One of the most widespread and deadliest diseases in the world, the Ebola virus disease outbreak started in West Africa in 2013 and lasted until 2016. Liberia, Sierra Leone, and Guinea were among the worst affected countries. Significant loss of life and damages both socially and in economic aspects were seen during this epidemic. The Guinea reported the first-ever case of infection in 2013. The disease took over hundreds of lives with a fatality rate of more than 70%.
5. Zika: In 1947, a study of yellow fever found the first isolation of a novel virus, from the blood of a sentinel rhesus macaque that had been placed in the Zika Forest of Uganda. Zika virus remained latent for nearly 70 years; then, within just one year, it was introduced into Brazil from the Pacific Islands. It became the first significant infectious disease that was responsible for causing human congenital disabilities. It led to the creation of a global Public Health Emergency of International Concern by the World Health Organization (WHO).^[10]
6. Yellow Fever: Yellow Fever (YF), caused by a virus commonly called Yellow Fever Virus, was the first-ever virus to be isolated and was shown for the first time to be transmitted by an arthropod. While there has been increased transmittance activity in both Africa and the Americas, the outbreaks have been limited in nature.^[1]
7. Tuberculosis (TB): One of the most ancient and deadly diseases affecting humankind globally, it has damaged human communities since the beginning of civilization. It is counted as one of the most devastating infectious diseases in the 21st century. A report released by the World Health Organization has estimated that 1.45 million have died due to Tuberculosis, with 9 million incident cases and 14 million prevalent cases. Nevertheless, TB is a curable disease that has been effectively controlled in many parts of the world since the middle of the 20th century.^[3]
8. COVID-19: In December 2019, reports came out from the central city in Wuhan, China, that a novel coronavirus is causing many pneumonia cases. Since that day, things have changed drastically. The World Health Organization, on 11 March 2020, declared coronavirus as a pandemic.^[11] The deadly virus has affected more than 213 countries worldwide and has taken a toll on human lives. It has affected more than 28 million (as of 11 September, 2020) people worldwide. According to the Worldometer data, more than 20 million have recovered, yet 914,168 have succumbed to the virus.^[12] Therefore, researchers are pushing forward to develop the vaccines and treatments to slow down the pandemic’s impact as soon as possible.

The coronavirus pandemic is more than merely a health crisis and affects livelihoods and economies at their core. While the pandemic’s impact varies from country to country, it has increased unemployment, poverty, and inequalities globally. Economies across the globe are decreasing day by day.^[13] Currently, 170 research teams are racing to develop an effective and safe vaccine for the deadly virus.^[14] Considering the global threat to livelihoods and economies, scaling up research for finding effective treatment and prevention of SARS-Cov-2 is urgently needed.

1. GAVI: It is an international organization that was created in the year 2000 to improve the accessibility of novel and underused vaccines.^[2] It serves on the Leadership Council of the Decade of Vaccine (DoV) Collaboration and provides critical expertise.^[4]
2. GLVP: (Global Vaccine Action Plan) It is a unique effort with an unprecedented emphasis on gathering country-led ownership and input. It aims to create a transformational plan to stimulate discovery, development, and delivery of lifesaving vaccines.^[4]
3. GOARN: (Global Outbreak Alert and Response Network) It is a technical collaboration of institutions and networks across the globe that provide human as well as technical resources to identify and confirm the outbreaks of international importance rapidly. ^[2] It responds to requests from member states for assistance and outbreak management.^[5]
4. IHR: (International Health Regulations) It is an international law that came into force in the year 2005, which aims at helping the countries to work together to save lives and livelihoods caused by the spread of devastating diseases across the world.^[2] Since 1948, WHO has been responsible for the implementation of IHR by its member states. These regulations were intended to enhance the international use of epidemiological principles to detect, reduce, or eliminate sources from which the infection spreads. ^[5]
5. PIP: (Pandemic Influenza Preparedness) It aims at bringing together the member states and WHO to implement a global approach pandemic influenza preparedness and response. [2] This framework was developed with expertise from clinical, organizational and public health ethics. This framework includes both substantive and procedural elements for the Pandemic Influenza Planning to be more ethical and suitable in the current scenario. ^[6]
6. GPHIN: (Global Public Health Information Network) It is a web-based electronic system developed by Health Canada and WHO which scans the web to identify suspected outbreaks, which are then actively followed up with affected countries to verify the existence of the disease.^[5]

Apart from the above mentioned international collaborations, WHO has established several international networks for specific disease threats, naming them as Specialized Surveillance Networks e.g., FluNet for influenza, RabNet for rabies, Global Salm-Surv for salmonellosis and DengueNet for Dengue.^[5]

In conclusion, the most deadly diseases in the 21st century have not only affected the lives and the well being of the people across the world. They have resulted in the death and devastation of millions of people, also showing a negative impact on the growth of the affected countries.

In light of the effects above of these deadly diseases, various initiatives and collaborations have taken place to curb and control their spread and mitigate the possible impact that these diseases impose on the lives of people and the growth of the nations affected. The World Health Organization (WHO) has taken the responsibility to rid the country off of these deadly infections to help the countries to grow and help them manage such pandemic and endemic conditions.

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