This year, the novel coronavirus (COVID-19) has been relatively quiet, but another viral epidemic has spread across the globe. Cases of high-pathogenic avian influenza (H5N1) virus, which has spread among birds and cattle, being transmitted to humans have been reported, creating fear of a pandemic. The dengue fever transmitted by mosquitoes and the emergence of MPOX (formerly known as monkeypox), which came from animals, have surged dramatically, and the poliovirus has impacted the war-torn Gaza Strip. These are viruses threatening 2024.
◇Avian influenza virus threatening humans
Avian influenza has spread among cattle on farms in the United States, subsequently being transmitted to humans. The H5N1 avian influenza virus originally infected only birds such as migratory birds and poultry, but recently it has spread to mammals.
Livestock such as cattle and pigs, as well as wild animals like foxes, cats, weasels, seals, dolphins, and raccoons, have also been infected. Since the beginning of this year, farm workers who came into contact with infected cattle have been infected. As of the 17th, the U.S. Centers for Disease Control and Prevention (CDC) reported that 58 farm workers in the United States have tested positive for the H5N1 virus.
Fortunately, there have been no confirmed cases of the H5N1 virus spreading between humans. However, global health authorities and researchers are closely monitoring the possibility of mutations that could allow human-to-human transmission, as the mortality rate is high when humans contract avian influenza.
According to the Korea Disease Control and Prevention Agency, the mortality rate for human infections from avian influenza is approximately 35% to 40%, while the mortality rate for high-pathogenic H5N1 human infections is reported to be as high as 60%. Based on this, it was predicted that if H5N1 human infections were to become a pandemic, 41.8% of the population could be infected within 300 days, resulting in approximately 290,000 severe cases.
◇Dengue fever cases surge due to rising temperatures
Dengue fever cases transmitted by mosquitoes have also surged. Dengue fever, which had been rampant in South America, including Brazil and Paraguay, has spread to North America, resulting in a surge in infections. By early December, approximately 12.7 million cases of dengue fever had been reported in North America. This figure exceeds the global record of 5.3 million cases reported by the World Health Organization (WHO) last year.
Dengue fever is caused by being bitten by the Aedes aegypti mosquito, which carries the dengue virus, and the Aedes albopictus mosquito. Symptoms such as high fever, headache, and chills appear 5 to 7 days after being bitten. Among those infected, 5% progress to severe cases such as dengue hemorrhagic fever, which can lead to death.
This year, confirmed cases of the Oropouche virus (OROV), which is in the same virus family as dengue fever, have also increased. This virus is known to be transmitted from hosts like sloths and monkeys to humans by small flies or mosquitoes. Symptoms such as fever, chills, headache, muscle pain, nausea, and vomiting are similar to those of dengue fever.
Scientists have pointed to climate change and urbanization, which have led to rising temperatures, as the main causes of the surge in dengue fever cases. Researchers from Beijing Normal University published a study last May in Science stating that "with the rapid rise in sea temperatures in the Indian Ocean, global dengue cases have increased." U.S. scientists have also analyzed that dengue occurrences in the Americas and Asia increased by about 18% compared to periods without warming.
◇MPOX spreads beyond Africa to 20 countries
MPOX (formerly known as monkeypox) spread this year to countries neighboring the Democratic Republic of the Congo in Africa. Later, cases of infection were reported in the U.S., Sweden, Pakistan, and the Philippines as well. On the 10th, the international journal Nature announced the 10 individuals who illuminated the scientific and technical fields this year, one of whom was Dr. Placide Mbala, an epidemiologist at the National Institute of Biomedical Research in the Democratic Republic of the Congo. He warned that MPOX would spread beyond Congo, allowing for prompt global response.
MPOX is endemic in Central and West Africa and causes symptoms such as vesicular rashes, acute fever, and muscle pain accompanied by headaches. The MPOX that has spread this year is of a different subtype known as MPOX lineage 1b. Its transmission speed and patient mortality rate were relatively high, and the types of patients were also different from before. In 2022, MPOX mainly spread among gay men in the U.S. and Europe, but an analysis conducted by the WHO in October found that 75% of this year's confirmed cases were among children and adolescents under 17 years old, with genders being nearly equal.
Danish pharmaceutical company Bavarian Nordic has expanded production of the MPOX vaccine, JYNNEOS (MVA-BN), and has applied for approval to use it not only for adults but also for adolescents. JYNNEOS was initially developed as a smallpox vaccine, and later received approval as an MPOX vaccine with additional indications. The United Nations approved the first MPOX vaccine for children last November.
In the Gaza Strip, where the health system has collapsed due to the Israel-Hamas war, cases of poliovirus have emerged. The poliovirus, which causes permanent muscle weakness and paralysis, spreads through contaminated water and is highly contagious.
The WHO discovered a type 2 variant poliovirus in wastewater samples collected from the Gaza Strip last July and warned of the risk of the spread of infectious diseases. According to U.N. data, there have been no cases of poliovirus in the Gaza Strip for the past 25 years. Poliovirus has been eradicated in most countries due to global vaccination efforts, but cases have also emerged in Pakistan and Afghanistan, where combat is frequent and vaccinations are limited. The same situation applies to Gaza.
Reference material
CDC (2024), https://www.cdc.gov/bird-flu/situation-summary/index.html
medRxiv (2024), DOI: https://doi.org/10.1101/2024.01.08.24301015
Science (2024), DOI: https://doi.org/10.1126/science.adj4427