Epidemics and Pandemics
Outbreak Overview
Microbes may be small, but they have been a constant influence on human evolution. Whilst many microbes are beneficial, just occasionally a microbe has the potential to cause disease on a grand scale and where transmission rates are high, it can rapidly spread through the population. In the middle ages, historians can track the spread of the Black Death, caused by Yersinia pestis, slowly spreading throughout Europe and the Middle East. The advent of improved transportation has massively increased the potential for a pandemic that rapidly reaches all continents, as was seen in the 2020 COVID outbreak.
Once an outbreak is identified, there is a multifaceted approach required to contain and limit the scale of infections. Tests need to be developed to confirm diagnosis of infection, transmission routes need to be identified and countered, suitable therapeutics need to be developed to treat infected patients, vaccines may be developed, and tools for surveillance and monitoring to identify new strains or mutations that could affect the efficacy of current tools and treatments are essential.
Transmission and control
Transmission between people relies on providing an environment where microbes can transfer between hosts. Some microbes can be relatively fragile, they dry out easily or are rendered inactive on exposure to UV light. Human Immunodeficiency Virus (HIV) is one such virus, and it requires transfer of bodily fluids with the virus to transfer between hosts. Other microbes use a host, such as arthropods, as in the case of Malaria and Dengue to aid transmission.
Other microbes can be much more durable, Bacillus anthracis (anthrax) is very resistant to drying, with the bacteria forming spores that can survive decades, or perhaps even centuries lying dormant in soil before coming into contact with a suitable host.
Some of the most transmissible microbes are those that can survive in the air or on surfaces for a time, Norovirus can live on hard surfaces for around 2 weeks if not disinfected – whilst this is much longer than the 2-3 days COVID could survive, the arial transmission capabilities coupled with triggering particle spreading coughs and sneezes certainly helped the spread of COVID.
- The transmission rate is logged as the ‘R0’ value for a disease
- The R0 value represents the average number of people that a single infected person will transmit the disease to in a completely susceptible population. [1]
\(R_{0}\) (Reproduction Number) | Transmission Type | |
Measles | 12 to 18 | Airborne |
Whooping Cough (Bordetella pertussis) | 12 to 18 | Airborne Droplet |
Chickenpox (Varicella) | 9 to 12 | Airborne / Contact |
Polio | 5 to 7 | Fecal-Oral |
Smallpox | 3.5 to 6 | Airborne / Contact |
SARS-CoV-2 | 3 | Airborne / Contact |
Influenza | 1 to 2 | Airborne Droplet |
Mitigation of transmission depends on the route of spread, but generally relies on good hygiene, disinfecting hands and surfaces to kill microbes before a new host comes along, and single use devices, such as syringes etc, or using barriers to prevent microbes reaching a new host. Increasing the distance and airflow between people can reduce the likelihood of transmission of airborne pathogens. Control of vectors in the environment by using pesticides or biological agents such as Wolbachia to reduce numbers of transmitting hosts. Personal protective equipment, such as facemasks and laboratory gloves were essential in the COVID pandemic, and mosquito netting can help prevent bites in the night. To study some of the most dangerous pathogens in a laboratory, such as Ebola, this can extend to full positive pressure body suits with laboratories completely isolated from outside environments.
Tools for detection
A number of tests can be developed to detect and infection, and each has their own advantages and disadvantages.
A spread is required to monitor active infections , discover past infections and assess immunity as well as genomic surveillance. Cheap test such as LAMP and Lateral flow tests are needed to quickly identify new cases.
- Lateral Flow Tests (LFTs) – rapid screening.
- PCR (RT-PCR) – diagnostic gold standard.
- ELISA (serology) – population immunity and seroprevalence.
- Next-Generation Sequencing (NGS) – genomic epidemiology.
- LAMP – low-cost molecular testing for resource-limited settings.
- Wastewater surveillance – community-level early warning.
- Digital PCR (optional) – high-sensitivity quantification for specialised surveillance.
Future Pandemic Prevention
Governments are aware of emerging infectious diseases that may post a threat to public health. Pathogens are assessed on their potential to cause an epidemic or pandemic and lists published to help guide researchers and prioritise diagnostics and therapeutics to increase preparedness.
Countermeasures
The development of therapeutics and vaccines are essential to protect public health. Many bacterial pathogens are currently susceptible to antibiotics, but with increasing use , antibiotic resistance is growing, and alternatives need to be sought. For viruses anti-viral drugs can be used, but as viruses hijack the host cell processes, druggable targets can be limited without causing further harm to the patient.
Vaccination can help prevent infection, or ameliorate the severity of the disease. New strains of pathogens can limit the efficacy of vaccines, but because the human immune system is adaptive, there can be some protection.
As vaccines need to be administered before contact to prime the immune system, the challenge is to produce a safe and effective vaccine as quickly as possible in the event of a new outbreak. The study of emergent pathogens with the potential to cause a pandemic is therefore vital to aid swift efficacious vaccine production.
