Resources Lesson 2: Communicable Diseases
Communicable diseases are infectious diseases caused by bacteria, viruses, fungi or parasites that can be transmitted from infected individuals to susceptible individuals. These pathogens may be transmitted through food, water, air, direct and indirect contact, as well as vectors such as insects.
To start, look at this video and see how disease patterns have changed over time, with Non-communicable diseases taking over from Communicable diseases - but look to the end to see how communicable diseases are making a comeback!
Communicable diseases are important causes of illness and death in low-to middle-income countries. Here are some data from Our World In Data presented as an interactive picture Childhood deaths from the five most lethal infectious diseases worldwide:
From Our World in Data. Licensed under CC BY 4.0.
The Disease Control Priorities DCP3 has an excellent section on Major Infectious Diseases and the accompanying file includes the following:
"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 percent, 35 percent, and 36 percent, respectively" Nevertheless "infectious diseases will remain a major threat to humankind, especially in LMICs, requiring vigilance, surveillance, and new interventions of all types."..."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 delivery of such interventions will be critical to driving down the burden of infection. An ultimate goal for selected infections is eradication. 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. 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. 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. Despite the development of new drugs to combat infectious diseases, antimicrobial resistance is threatening to remove many of the tools in our current armamentarium."
Also in the DCP3 file is the comment: "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 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." This was published in 2018 - nicely predicting the possibility of the emergence of the COVID-19 pandemic.
Here is a nice review: The global challenges of infectious diseases. Written from an Australian perspective, it also considers the global situation and concludes: "In the field of infectious diseases, every year is replete with surprises...global strategies to reduce AMR (antimicrobial resistance), coupled with the extraordinary advances in molecular diagnostics, are essential for outbreak preparedness and to advance control of endemic pathogens. However, to attempt to see beyond the present to the next 10 years in infectious diseases would be audacious. As Niels Bohr is believed to have said, “prediction is very difficult, especially about the future”. The paper was written in 2015, before COVID-19 emerged!
The paper Infectious Disease Threats in the Twenty-First Century: Strengthening the Global Response also warns us of the need to strengthen the global response (to the list of outbreaks we must now include COVID-19) "Humanity's relative good fortune with respect to infectious disease can be attributed, in part, to the elaborate global health system the world has gradually developed as a bulwark against infectious disease threats, both known and unknown. This system consists of various formal and informal networks of organizations that serve different stakeholders; have varying goals, modalities, resources, and accountability; operate at different territorial levels (i.e., local, national, regional, or global); and cut across the public, private-for-profit, and private-not-for-profit sectors.
Despite its track record, whether the global health system as currently constituted can provide effective protection against an expanding and evolving array of infectious disease threats has been called into question by recent outbreaks of Ebola, Zika, dengue, Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), and influenza, as well as the looming specter of rising antimicrobial resistance (AMR). Taken together, these diseases—along with a slew of other known and unknown pathogens—jeopardize not only human health, but also various forms of social and economic well-being. Of particular concern is the lack of a single entity that has a sufficiently high-level and comprehensive view of the full range of potential threats—whether naturally occurring, accidental, or due to intentional biological attack—and of the network of organizations tasked with their surveillance, prevention, and mitigation."
A provocative paper, WHO and the future of disease control programmes by Dye et al summarises: "Huge increases in funding for international health over the past two decades have led to a proliferation of donors, partnerships, and health organisations. Over the same period, the global burden of non communicable diseases has increased absolutely and relative to communicable diseases. In this changing landscape, national programmes for the control of HIV/AIDS, tuberculosis, malaria, and neglected tropical diseases must be reinforced and adapted for three reasons: the global burden of these communicable diseases remains enormous, disease control programmes have an integral and supporting role in developing health systems, and the health benefits of these control programmes go beyond the containment of specific infections. WHO's traditional role in promoting communicable disease control programmes must also adapt to new circumstances. Among a multiplicity of actors, WHO's task is to enhance its normative role as convenor, coordinator, monitor, and standard-setter, fostering greater coherence in global health." Note: You can access the abstract and full paper free of charge through this link, but have to register to see the full paper.
We have focused on Immunisation in this section, as it is one of the most cost-effective public health interventions available and is a proven tool for control and prevention, including the elimination and eradication of communicable diseases. The Global Alliance for Vaccines and Immunisation (GAVI) is a global public-private partnership that is committed to the mission of saving children's lives and protecting population health by enhancing access to immunization in developing countries. There are proven strategies and outreach activities to reach even the hard to reach and vulnerable populations - find out about these by following the links below:
1. Overview of the ten facts about immunisation, put together by WHO.
2. The WHO page Immunization coverage reports data to 2018 and summarises:
- Global measles mortality has declined by 73%
- Most children today receive lifesaving vaccines
- Uptake of new and underused vaccines is increasing.
- Immunization currently prevents 2-3 million deaths every year
- An estimated 19.4 million children under the age of one year did not receive basic vaccines
3. Read the WHO fact sheet on measles as an example of a vaccine-preventable disease of major public health significance.
We can't end this section on communicable diseases without at least a brief mention of investigating outbreaks. As we have seen with the COVID-19 pandemic, this is a key plank for control of communicable disease. Here are the steps identified by the US CDC Steps of an Outbreak Investigation: (you can click on any of the steps to see more detail - you will have to adapt some of the steps to fit your particular setting)
- Prepare for field work
- Establish the existence of an outbreak
- Verify the diagnosis
- Construct a working case definition
- Find cases systematically and record information
- Perform descriptive epidemiology
- Develop hypotheses
- Evaluate hypotheses epidemiologically
- As necessary, reconsider, refine, and re-evaluate hypotheses
- Compare and reconcile with laboratory and/or environmental studies
- Implement control and prevention measures
- Initiate or maintain surveillance
- Communicate findings