Three years ago, on January 30th, 2020, the leader of the World Health Organization declared a major event: the spread of a new coronavirus, originally found in China, had reached a level of concern for it to be declared a "Public Health Emergency of International Concern." The virus, now known as SARS-CoV-2 causing COVID-19, continues to spread. For infectious disease experts, discussing future pandemics is crucial.
The World Health Organization maintains a list of viruses and bacteria that have the potential to cause pandemics. Jill Weatherhead from Baylor College of Medicine explains that prioritizing diseases is based on two criteria: the ability to spread and the human ability to treat them.
The list helps direct investment in research, funding, and efforts toward the pathogens with the highest potential to harm humans. The WHO creates "blueprints" with research priorities and strategic goals for each disease on the list. A revised list is expected shortly, as the WHO brought together over 300 scientists to review and update the list in late 2022.
Nipah Virus
Animal hosts:
Fruit bats, including flying foxes, and domestic animals such as pigs, horses, cats, and dogs.
Transmission:
Humans can get the Nipah virus from infected animals or contaminated food, which can also spread from person to person.
Impact:
The fatality rate of 40% to 75%. It can cause brain swelling (encephalitis).
Treatment:
No vaccine for humans or animals. Monoclonal antibody therapies under development.
Pandemic potential:
Outbreaks occur annually in Asia, but there are preventive measures, such as avoiding contact with bats and sick animals, thoroughly washing fruits that bats may have touched and not consuming raw juices from bat-fed fruits, and peeling fruits before eating to reduce the risk of international transmission.
Crimean-Congo Hemorrhagic Fever
Animal hosts:
Ticks, livestock
Transmission:
Humans usually contract the virus from ticks or infected livestock. Close contact with an infected person's blood or bodily fluids is required for person-to-person transmission.
Impact:
The fatality rate of 10% to 40%. Endemic in Africa, the Balkans, the Middle East, and Asia. Causes severe viral hemorrhagic fever, organ and cardiovascular system damage, and severe bleeding.
Treatment:
A vaccine is used in Bulgaria, but its efficacy is unknown and not licensed elsewhere. Other vaccines in development and the antiviral drug ribavirin may help treat infections.
Pandemic potential:
It's hard to identify infected animals, and the ticks carrying the virus are widespread. The threat can be reduced by avoiding tick bites and wearing protective clothing around livestock.
Lassa Fever
Animal host:
Rodents, including rats
Transmission:
Endemic in West Africa spreads through contact with rodents' urine and feces, direct contact with infected persons' secretions (blood, urine, feces), sexual contact, or contaminated medical equipment.
Impact:
1% fatality rate, up to 15% in severe cases. Deadly for people and fetuses in the 3rd trimester of pregnancy, with common complications of permanent deafness.
Treatment:
No vaccine, but the antiviral drug ribavirin may help treat infections
Pandemic potential:
Limited spread due to primary transmission from exposure to specific types of rats found only in certain countries.
Ebola Virus
Animal Host:
Bats
Transmission:
The Ebola virus is spread through contact with the bodily fluids of infected humans or animals. This can include blood, semen, breast milk, urine, saliva, and feces. It can also be spread through needles and other medical equipment that have been contaminated.
Impact:
The Ebola virus is often deadly, with fatality rates ranging from 25% to 90%, depending on the strain. It can cause severe illness, death, and long-term health problems such as eye and joint problems.
Treatment:
No licensed vaccine is available, but several experimental vaccines are in development.
Pandemic potential:
The Ebola virus is known to occur in Africa but has not yet become a global pandemic. Outbreaks can be controlled with effective public health measures, such as contact tracing and isolation of infected individuals.
Middle East Respiratory Syndrome (MERS)
Animal Host:
Camels
Transmission:
After the virus first spreads from camels to humans, it can then spread between people through close contact with an infected person.
Impact:
According to the World Health Organization (WHO), the fatality rate of MERS is 35%.
Treatment:
While several vaccines for MERS are in the process of being developed, none have been approved yet. Since 2012, 27 countries have reported cases of MERS.
Pandemic potential:
Unlike SARS-CoV-2, which causes COVID-19, MERS primarily resides deep within the respiratory tract, making it less easily spread through coughing and sneezing.
Zika Virus
Animal Host:
Mosquitoes
Transmission:
It can be spread through mosquito bites, from a pregnant person to a fetus, through sexual contact, and possibly through blood transfusions.
Impact:
Although not usually fatal, Zika can lead to serious brain defects in fetuses, such as microcephaly, as well as miscarriages and other congenital disabilities.
Treatment:
Currently, no vaccine or treatment exists.
Pandemic potential:
Currently, the spread of Zika is mainly contained in areas where mosquitoes carrying the virus are found.
SARS (Severe Acute Respiratory Syndrome)
Animal Host:
Palm civets were largely blamed for the 2003 outbreak, but bats and other wildlife also may carry it.
Transmission:
After a spillover from animals to humans, SARS can be transmitted from person to person through close contact with an infected person. It spreads through droplets from coughs and sneezes and sometimes through contaminated surfaces.
Impact:
Has a fatality rate of less than 1%.
Treatment:
No approved treatment or vaccine.
Pandemic potential:
The virus is usually only spread by people with symptoms, making it easier to contain through quarantine and public health measures. In 2003, it caused 8,000 cases and 700 deaths in 29 countries but was eventually contained.
According to the WHO, an unknown disease can cause a significant pandemic, but they do not list diseases in order of threat. The study of bat viruses by Raina Plowright of Cornell University shows that a small percentage of bat species carry thousands of viruses, and it's uncertain which of these viruses present a risk to humans as current technology doesn't allow for a definite determination of infectivity and transmission potential.
NPR Org. mentioned that the variants also pose a threat, as even the smallest genetic change can lead to significant consequences, including the hypothetical scenario of a pathogen with a 50% fatality rate that efficiently spreads from person to person.
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