Infectious diseases have plagued humans before the dawn of civilisation. In the last few decades, after the discovery of penicillin, a large number of these diseases have been controlled or eliminated. However, infectious diseases have a tendency to recur in a different population or region than before. This phenomenon is termed as emerging infectious diseases (EID). Old infectious diseases re-emerge due to developed attributes like resistance or increased virulence (The Henry J Kaiser Family Foundation, 2014). One of the reasons is increased globalisation and environmental changes. This leads microbes to spread in new regions. Another reason is increasing drug resistance, making EIDs’ a grave concern (WHO Community, 2014).
What are emerging infectious diseases?
By the 1960-70s, mankind was successfully eliminating infectious diseases, including small pox, polio and plague. Around this time, global concern regarding EIDs’ rose. Since 1980, one to three “re-emerged” human infectious diseases have been identified every year. Their incidence cases have risen in number every year. These diseases affected different populations and more regions than in the past, such as Dengue fever and Ebola. Furthermore, some other disease pathogens had developed resistance to available treatments, especially antibiotics. A good example of this is multi-drug resistant tuberculosis, which affected 540,000 people in 2015, globally (WHO, 2016a). Also, the rapid spread and high mortality rates of HIV/AIDS in 1980s proved how vulnerable humans were to EIDs’ (The Henry J Kaiser Family Foundation, 2014). Typical causative pathogens and most common reasons for evolution of EIDs’ have been described in the figure below.
Consequently, EIDs’ can be classified broadly into four categories, based on their mode of evolution (Fauci and Morens, 2012; CDC, 2017a):
- Newly emerging infectious diseases: Diseases that are recognized in humans for the first time. Examples include HIV/AIDS, H1N1 and Bourbon virus (USA).
- Emerging disease in an area: Those that appear for the first time in an area, like Zika and Ebola in the West.
- Re-emerging infectious diseases: Diseases that have historically infected humans but re-appear after apparent control or eradication (West Nile virus and Dengue)
- Resistant pathogen based epidemics: Epidemics caused by pathogens that have become resistant to antibiotics (Carbapenem-resistant Enterobacteriacea).
Global prevalence of emerging infectious diseases
The most common pathogens causing diseases are communicable viruses. They are spread through inhalation, sexual exposure or direct contact to mucous membranes (e.g., HIV/AIDS, influenza viruses). Furthermore, bacteria and fungi are also responsible for epidemics in new areas. Infectious disease deaths globally by different modes of transmission include (World Health, 2013):
- Person to person – 65%
- Food/water/soil – 22%
- Vector based transmission – 13%
- Animal interactions – <1%.
It is estimated that communicable diseases are responsible for approximately 19% of the global deaths (WHO, 2016b). But EIDs’ have become more prevalent in the recent years. The most common examples include HIV outside the African continent and Zika across South America. In 2015, WHO recognised several emerging infectious diseases likely to cause havoc. These include Crimean Congo Haemorrhagic fever, Ebola, MERS, SARS, Nipah and Rift Valley fever. However, Zika spread quickly in South America in 2015 and later spread to North America too. Total number of affected countries were 48 by 2015.
Statistics show a growing global concern
EIDs’ like Influenza, Zika, Dengue and West Nile are leading to global chaos contributing to high mortality. Other EIDs’ include Yellow fever and Chikungunya (WHO, 2016). For instance, the 2009 pandemic of influenza A(H1N1) became a global threat in a short span of time and shocked the world. Therefore, strategies for developing new drugs as well as provision of vaccine for all countries has been prioritised. Another example is the large outbreaks involving a specific arbovirus and Chikungunya found in Eastern Africa and Indian Ocean islands. Subsequently, these diseases were found to have spread into Europe as well (De Cock et al., 2013).
Table below shows the global prevalence of EIDs’ and deaths caused so far:
Emerging Disease (Bacterial, Viral, Fungal, Parasitic)
First epidemic reported in (year and place)
Death toll (Latest/2017 status)
|1||Zika virus||76 countries of Africa, America, Europe and Asia||1947, Zika forest of Uganda. (Dick, Kitchen and Haddow, 1952)||Death is rare, but affects 25,000 children in US, every year.||
WHO and PAHO, (2017)
|2||Ebola virus||Africa||1976, northern Zaire and southern Sudan (Sanchez et al., 1995).||4 deaths out of 8 instances (2017), 44 deaths out of 66 in 2014||CDC, (2017b)|
|3||Dengue Virus||Carribean and Latin America,||Since 1950s, Philippines and Thailand (CDC, 2014)||500,000 cases, 22,000 death per year||CDC (2014)|
|4||HIV||Africa, USA, Asia||Early 1980s, Africa (CDC and NPIN, no date)||No deaths||PAHO and WHO, (2017)|
|H1N1 (Influenza)||USA, Asia||1976, Fort Dix, New Jersey (Gaydos et al., 2006)||Approx. 575,400, 2009||Gibbs, Armstrong and Downie (2009)|
|6||Middle East Respiratory Syndrome (MERS)||Saudi Arabia, UAE, Republic of Korea||2012 in Saudi Arabia||720 deaths out of 2067 confirmed cases||World Health Organization, (2017)|
Table: Geographical distribution and mortality of Emerging Infectious Diseases (EID)
Challenges posed by EIDs’ to public health
The recent instances of Ebola in the United States posed a threat at global levels. Such diseases continue to challenge the capacity of health systems and communities. Furthermore, the spread of infections generates stigma and fear among public (American Public Health Association, 2014). Incidentally, technological and scientific advances have improved outbreak detection and response in recent decades. However there are significant challenges that remain in addressing the diseases. Firstly, lack of basic public health surveillance interferes with effect EIDs’ diagnosis and treatment. Further, scientific, technological and political dialogue, intellectual property barriers, etc. obstruct research and development. Thus prevention measures and response tools against EIDs’ may fail (The Henry J Kaiser Family Foundation, 2014).
Future prospects of epidemiology strategies
Reportedly, a global shortage of trained health care workers persists. Epidemiological research, capacity and expertise in Africa is growing day by day. But they can have a greater impact on health if recommendations are implemented (Klipstein-Grobusch, Chirwa and Fonn, 2013). However, planning for doctors without a grand strategy for epidemiology is not going to help in eliminating EIDs’.
- Firstly, reporting is important for EID control. Assessing the impact of EIDs’ globally will improve political, financial, and research prioritisation. Consequently, more informed decision making and enhanced modelling can take place (Murray, Quam and Wilder-Smith, 2013). Epidemiological transitions mean that key health indicators (infants, toddlers, and maternal mortality rates) no longer provide insight into health. Therefore there is an urgent need for robust vital registration systems. Accurate reporting of cause-specific mortality rates across all life stages is also needed (De Cock et al., 2013). Therefore organizations like CDC, UN and WHO spread awareness and greatly help in combating communicable diseases.
- Secondly, development of Gold-kit to diagnose is an eminent step. Because it will relieve the complexity amongst genetically similar disease-causing viruses, bacteria etc., it can prevent misdiagnoses.
- Further, providing generic medicines may prove as a crucial step. Patenting a drug may benefit a company. However, making it generic will benefit the poor against EIDs’.
Control of emerging infectious diseases through statistical analysis
Emerging Infectious diseases that affect social life and economy should be controlled in time. Population growth and increased life expectancy in people with EIDs’ have changed the global health landscape. Therefore, organisations like WHO and CDC are striving to eradicate EIDs’. However, their efforts are insufficient as cheaper treatment for the common man is essential. Accordingly, generic medicines, health policies and diagnostic approach are a solution for EIDs’. Also, surveillance for major causes of disability and death, disease outcomes, and health systems globally are important. In the proceeding article, the importance of statistical analysis in epidemiological studies is explained. Insightful analysis can help humans combat such EIDs’ by predicting their outbreaks in advance.
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