Infectious diseases were responsible for the largest global burden of premature death and disability until the end of the twentieth century, when that distinction passed to noncommunicable diseases. Over the previous centuries, global pandemics of infectious diseases, such as smallpox, cholera, and influenza, periodically threatened the survival of entire populations. At least as early as the late 1800s, improved living conditions (such as better sanitation and piped water supplies), particularly in high-income countries (HICs), began to drive down the infectious disease burden.
By the mid-twentieth century, safe, effective, and affordable vaccines and the increasing availability of antibiotics had further reduced the toll of infectious diseases in HICs. Not until the second half of the twentieth century did largescale efforts begin to better control infectious diseases in low- and middle-income countries (LMICs), where the infectious disease burden was greatest and highly varied. These efforts included a global commitment to immunize the world’s children against the major infections for which vaccines are available and global campaigns to control malaria and diarrheal disease. The International Health Regulations of the World Health Organization (WHO) represent a key agreement among 196 countries to implement metrics and measures to detect and control outbreaks of infectious diseases and to prevent pandemics (World Health Assembly 2005).
Global under-five mortality fell by almost two-thirds (from 14 per cent to 5 per cent) between 1970 and 2010 (Norheim and others 2015). In 1980, smallpox, responsible for 300 million–500 million deaths in the twentieth century, was declared to be the first disease eradicated from the planet following a global immunization campaign led by the WHO. Wild Poliovirus has been eliminated from all but three countries (Afghanistan, Nigeria, and Pakistan) and currently is the focus of a major eradication programme.
The decline of the vaccine-preventable diseases has contributed to a recognition of the potential for using vaccines to prevent other infectious diseases, including human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS), tuberculosis (TB), malaria, hepatitis C, and a variety of neglected tropical diseases (NTDs). Hepatitis B and C substantially increase the risk of death from cirrhosis and liver cancer. The effect of viral hepatitis is significant. Indeed, an important recent study (Stanaway and others 2015) found that viral hepatitis led to an estimated 0.9 million deaths in 1990 (including hepatitis-caused deaths from cirrhosis and liver cancer). Furthermore, this number has been increasing rapidly—to an estimated 1.5 million deaths in 2013—despite the fact that hepatitis B is a vaccine-preventable disease and that hepatitis B and C are both treatable.
Emerging pandemic viral infections remain a constant threat, many entering the human population from contact with animals. The most recent such infections include SARS (severe acute respiratory syndrome), MERS (Middle East respiratory syndrome), and Ebola and Zika viruses (Madhav and others 2018) as well as, perennially, influenza and chikungunya infections. Compared with antibiotics to treat bacterial infections, relatively few antiviral drugs have been developed to treat these emerging viral infections. Therefore, the most important intervention is to break the chain of transmission. A global increase in antibiotic-resistant bacteria includes a small but growing number that are resistant to most or essentially all of the available antimicrobials.
Spectacular progress has been made in reducing mortality from most infectious diseases. For example, in low-income countries (LICs) from 2000 to 2010, the number of deaths before age 70 years from HIV/AIDS, TB, and malaria fell by 46 per cent, 35 per cent, and 36 per cent, respectively (Norheim and others 2015). Rapid progress was also reported in other country income groups. However, if the death rates of 2010 remain static, about 5.1 million people will still die in 2030 from these three conditions and from other communicable diseases, many of which are concentrated in LMICs. In contrast, mortality in HICs from these conditions (except for HIV/AIDS) will be relatively small, although major pandemics of other pathogens are not predictable. Hence, infectious diseases will remain a major threat to humankind, especially in LMICs, requiring vigilance, surveillance, and new interventions of all types.
3 KEY STEPS TO REDUCE RISK OF FUTURE EPIDEMIC
1. Surveillance of wildlife for high-risk pathogens
2. Surveillance and risk reduction in people at high risk of contact with wildlife
3. Surveillance of wildlife for high-risk pathogens and biosecurity of the wildlife trade and animal markets
OVERCOME 4 CHALLENGES TO ACHIEVE PROGRESS IN FIGHT AGAINST INFECTIOUS DISEASES
1. Focusing and Targeting of Intervention Strategies
2. Scale-Up of Interventions against Major Infectious Diseases
3. Integration of Services More Effectively across Disease Areas
4. Development of New Technologies— Drugs, Vaccines, Diagnostics, Behavioral Interventions, and Delivery Methods—to Prevent and Treat These Diseases
Approaches to infectious disease control
Vaccines and curative treatments for some of the major infectious diseases have existed for decades. Many of them are relatively inexpensive and highly cost-effective, yet many are underused because of cost and lack of access attributed to poorly functioning health care systems. New drugs and vaccines will continue to be the mainstays in preventing and treating infections, but the delivery of such interventions will be critical to driving down the burden of infection.
According to the National Center for Biotechnology Information (NCBI) report, to date, only two diseases—smallpox in humans and rinderpest in cattle and other ruminant animals— have been eradicated. Elimination of polio, yaws, and Guinea worm infections is being pursued. This is a more distant but still possible goal for malaria (Shretta and others 2017). A handful of other infections—such as measles, mumps, rubella, lymphatic filariasis, and cysticercosis— are candidates for elimination because of disease characteristics or the available means to control them (CDC 1993). Those infectious diseases that persist require continued effort to develop new drugs and vaccines for treatment and prevention as well as strategies that allow such treatments to be used most effectively across the globe.
Interestingly, the re-emergence of old diseases like dengue, tuberculosis (TB), malaria, etc. killed more people in the Asia Pacific. Among an estimated 2.5 billion people at risk for dengue, 70 per cent of them are in the Asia-Pacific region. The 2019 Lancet Countdown on Health and Climate Change found that spurred on by global heating, the ability of dengue fever to be transmitted by mosquitoes in 2017 was at the second-highest level recorded since 1950, while 9 of the 10 most suitable years for transmission had happened since 2000.
The number of dengue cases reported to WHO increased over 8-fold over the last two decades, from 505,430 cases in 2000 to over 2.4 million in 2010, and 4.2 million in 2019. The largest number of dengue cases ever reported globally was in 2019. In 2019, the Philippines declared an epidemic, with 622 deaths, and dengue affecting a staggering 146,000 people. In Thailand, the numbers doubled from last year to 20,000 cases, with children suffering the most. From January to August 2019, 200,000 people in Sri Lanka contracted dengue, and more than 100 died, according to the United Nations Development Program. Cases were also reported in Bangladesh (101,000), Malaysia (131,000), the Philippines (420,000), and Vietnam (320,000) in Asia.
Some reports indicate that lockdown imposed because of coronavirus may be fueling dengue outbreaks across Southeast Asia. Singapore has reported 18,900 as of July 20, 2020, and the total number of cases this year is expected to exceed the 22,170 cases reported in 2013.
Dengue fever is typically a self-limited disease with a mortality rate of less than 1 per cent when detected early and with access to proper medical care. When treated, severe dengue has a mortality rate of 2-5 per cent, but, when left untreated, the mortality rate is as high as 20 per cent.
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