Introduction
In recent years, the world has witnessed a resurgence of certain infectious diseases that pose significant threats to global health. Diseases such as bird flu, mPox (formerly known as monkeypox), Marburg virus, Nipah virus, Dengue virus, and vaccine-derived poliomyelitis are emerging as global concerns due to factors like globalization, environmental changes, and increased human-animal interactions. This article explores the epidemiology, transmission, sources, treatment, and prevention of these infectious diseases, highlighting the risks they pose to humanity.
Bird Flu (Avian Influenza)
Epidemiology
Bird flu refers to influenza viruses that primarily infect birds but can also infect humans. The most concerning strain is the highly pathogenic avian influenza (HPAI) H5N1 virus. Since its emergence in the late 1990s, H5N1 has caused sporadic human infections with a high mortality rate of around 60%. Recent years have seen a global resurgence of H5N1 outbreaks in both poultry and wild birds.
In 2024, the United States reported its first potential human-to-human transmission case in Missouri, where at least eight individuals are under investigation after exposure to a confirmed case with no known animal contact. This development is alarming as it could represent the first confirmed human-to-human spread of H5N1 in the U.S. Globally, over 18.75 million birds have been culled due to outbreaks, raising concerns about the virus’s pandemic potential.
Transmission and Sources
Bird flu viruses are transmitted to humans through direct contact with infected birds, their droppings, or contaminated environments. Poultry markets and farms are common sources of infection. The virus can survive in bird droppings and secretions, facilitating its spread. While human-to-human transmission has been limited, recent cases suggest it can occur under close and prolonged contact. The virus has also been detected in dairy herds across multiple U.S. states.
Treatment
Antiviral medications like oseltamivir (Tamiflu) and zanamivir (Relenza) can be effective if administered early. However, resistance to antivirals is a growing concern. Supportive care in a hospital setting is often necessary due to severe respiratory complications. Vaccines specific to certain avian influenza strains have been developed but are not widely available to the public.
Prevention
Preventing bird flu involves controlling the disease in poultry populations through culling infected birds, vaccination, and biosecurity measures. For humans, avoiding contact with infected birds, practicing good hygiene, and thoroughly cooking poultry products are key preventive steps. The Centers for Disease Control and Prevention (CDC) has issued new recommendations for personal protective equipment (PPE) for workers in high-risk environments. Surveillance and rapid response to outbreaks are critical to prevent the spread.
mPox (Monkeypox)
Epidemiology
mPox is a viral zoonotic disease first identified in humans in 1970 in the Democratic Republic of Congo. Historically confined to Central and West Africa, mPox saw a significant global increase in cases starting in 2022. By the end of 2023, over 87,000 confirmed cases and 140 deaths were reported in non-endemic countries. While new cases have subsided in 2024, mPox remains a concern, especially in communities with lower vaccination rates.
Transmission and Sources
The virus is transmitted to humans through close contact with an infected person or animal, or with material contaminated with the virus. Human-to-human transmission occurs through respiratory droplets, skin lesions, and bodily fluids. The 2022–2023 outbreak highlighted transmission primarily within social and sexual networks, particularly among men who have sex with men, though anyone can contract mPox through close contact.
Treatment
There is no specific antiviral treatment approved for mPox, though the antiviral agent tecovirimat (TPOXX) has been used under compassionate protocols for severe cases. The disease is generally self-limiting, but severe cases can occur, especially in children and immunocompromised individuals. Supportive care to manage symptoms is essential.
Prevention
Vaccination with smallpox vaccines, such as JYNNEOS (MVA-BN), offers protection against mPox due to the genetic similarity of the viruses. Vaccination efforts have been ramped up globally, focusing on at-risk populations. Preventive measures include isolating infected individuals, practicing good hygiene, and using PPE when caring for patients. Continued surveillance is critical to prevent future outbreaks.
Marburg Virus Disease
Epidemiology
Marburg virus disease is a severe and often fatal hemorrhagic fever first identified in 1967 during outbreaks in Germany and Serbia linked to laboratory work with African green monkeys. Sporadic outbreaks have occurred in Africa, with mortality rates ranging from 24% to 88%.
In September 2024, Rwanda confirmed its first-ever outbreak of Marburg virus disease. As of late September, 26 cases have been reported, with six deaths. The outbreak has primarily affected healthcare workers in Kigali, the capital city, raising concerns due to its population density and international travel connections. The World Health Organization (WHO) has mobilized emergency response efforts, including medical supplies and infection prevention support.
Transmission and Sources
The natural reservoir of the Marburg virus is the African fruit bat (Rousettus aegyptiacus). Human infection occurs through prolonged exposure to mines or caves inhabited by bat colonies. Human-to-human transmission happens via direct contact with blood, secretions, organs, or other bodily fluids of infected individuals, and with surfaces contaminated with these fluids. The majority of cases in Rwanda are healthcare workers, emphasizing the importance of strict infection control.
Treatment
There is no proven antiviral treatment for Marburg virus disease. Supportive hospital therapy is essential, including rehydration and symptomatic treatment to improve survival rates. Experimental treatments, such as monoclonal antibodies and antivirals like remdesivir, are under investigation but have yet to be widely implemented.
Prevention
Preventing Marburg virus involves avoiding exposure to fruit bats and ensuring proper infection control practices in healthcare settings. Protective clothing and equipment are essential for healthcare workers. Community engagement and education about the risks of bat exposure and safe burial practices are crucial in controlling outbreaks. Cross-border containment efforts are underway to prevent spread into neighboring countries.
Nipah Virus Infection
Epidemiology
Nipah virus was first identified in 1998 during an outbreak among pig farmers in Malaysia. The virus causes severe respiratory illness and encephalitis, with a mortality rate between 40% and 75%. Outbreaks have primarily occurred in South and Southeast Asia, with Bangladesh and India reporting cases in recent years.
In September 2023, the Indian state of Kerala experienced an outbreak resulting in several deaths2. Although the outbreak is now under control, the WHO and Indian health authorities remain vigilant due to the virus’s high mortality rate and potential for human-to-human transmission.
Transmission and Sources
The natural hosts of Nipah virus are fruit bats of the Pteropus genus. Transmission to humans occurs through consumption of food contaminated with bat saliva or urine, such as raw date palm sap. Human-to-human transmission can occur through close contact with infected individuals, particularly in healthcare settings2.
Treatment
There is no specific antiviral treatment for Nipah virus infection. Intensive supportive care is the mainstay of treatment, focusing on managing respiratory and neurological symptoms. Ribavirin has been used experimentally but without definitive evidence of efficacy.
Prevention
Preventive measures include avoiding consumption of raw date palm sap, implementing protective barriers to prevent bats from accessing sap collection sites, and practicing good hygiene. In healthcare settings, strict infection control practices are necessary to prevent nosocomial transmission. Public health campaigns focus on raising awareness about zoonotic transmission.
Vaccine-Derived Poliomyelitis
Epidemiology
Despite significant progress in eradicating polio, vaccine-derived poliovirus (VDPV) has emerged as a new threat. Oral polio vaccines (OPV), which contain weakened live virus, have been instrumental in reducing wild poliovirus cases. However, in rare instances, the weakened virus can mutate and spread in under-immunized populations, leading to outbreaks of vaccine-derived poliomyelitis.
As of mid-2024, the WHO has reported over 1,000 cases of circulating vaccine-derived poliovirus (cVDPV) in more than 25 countries, including Afghanistan, Pakistan, Nigeria, Yemen, and parts of sub-Saharan Africa. These outbreaks threaten to reverse decades of progress toward polio eradication.
Transmission and Sources
VDPV emerges when the weakened strain from the OPV mutates in communities with low immunization coverage. The mutated virus can then spread from person to person through the fecal-oral route, primarily in areas with poor sanitation and hygiene.
Treatment
There is no cure for polio once it infects the nervous system. Treatment focuses on supportive care to manage symptoms and prevent complications, such as respiratory failure or paralysis. Rehabilitation and physical therapy can help patients recover some mobility after infection.
Prevention
Prevention of vaccine-derived poliomyelitis relies on maintaining high immunization coverage with the inactivated polio vaccine (IPV) and improving sanitation and hygiene practices. The switch from OPV to IPV in many countries has been part of global eradication efforts. Surveillance and immunization campaigns are essential to stop outbreaks of cVDPV.
Dengue Fever
Overview and Cause
Dengue fever is a mosquito-borne viral infection caused by the Dengue virus (DENV), which has four distinct serotypes: DENV-1, DENV-2, DENV-3, and DENV-4. Infection with one serotype provides lifelong immunity to that serotype but not to the others. Subsequent infections by different serotypes increase the risk of severe forms of the disease, such as dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS).
Transmission
Dengue is transmitted primarily through the bite of infected Aedes mosquitoes, particularly Aedes aegypti and Aedes albopictus. These mosquitoes become infected when they bite a person already infected with the virus. Dengue cannot spread directly from person to person.
Epidemiology
Dengue is prevalent in tropical and subtropical regions worldwide, with the highest burden in Southeast Asia, the Pacific islands, Latin America, and the Caribbean. According to the WHO, approximately 390 million people are infected annually, with about 96 million showing clinical symptoms. In 2024, countries like Brazil, India, and Bangladesh reported alarming surges in dengue cases, exacerbated by factors such as climate change and urbanization.
Clinical Symptoms
Symptoms typically begin 4–10 days after a mosquito bite and can include:
- High fever
- Severe headache
- Pain behind the eyes
- Joint and muscle pain
- Rash
- Nausea and vomiting
- Mild bleeding (e.g., gums or nose)
Severe cases may progress to DHF or DSS, involving:
- Severe abdominal pain
- Persistent vomiting
- Bleeding under the skin
- Blood in vomit or stool
- Organ failure
Without proper medical care, severe dengue can be fatal, particularly in children.
Treatment
There is no specific antiviral treatment for dengue. Management focuses on supportive care to control symptoms:
- Hydration to prevent shock
- Pain relievers like acetaminophen (avoiding NSAIDs due to bleeding risk)
- Hospitalization for close monitoring in severe cases
For DHF and DSS, urgent medical attention is critical, including intravenous fluids, blood transfusions, and monitoring of platelet levels and organ functions.
Prevention
Preventing dengue focuses on mosquito control and limiting exposure to mosquito bites:
- Eliminating mosquito breeding sites (e.g., stagnant water)
- Using insect repellents and wearing protective clothing
- Installing screens and using mosquito nets
- Aerial spraying of insecticides in outbreak areas
A vaccine called Dengvaxia has been approved but is recommended only for individuals who have had a previous dengue infection and live in endemic areas due to concerns about increased risk of severe dengue in those never exposed to the virus.
Global Challenges and Outlook
Dengue’s rapid global spread is accelerated by climate change, increasing mosquito habitats, and urbanization. The lack of specific antiviral treatments and the limited scope of current vaccines remain significant public health challenges. Efforts are focused on:
- Innovative vector control strategies, such as releasing Wolbachia-infected mosquitoes to reduce populations
- Developing new vaccines that are safe and effective for broader populations
- Improving surveillance and public health campaigns for early detection and prevention
Global Risks and Challenges
The resurgence and spread of these infectious diseases highlight several global health challenges:
- Environmental Changes: Deforestation, urbanization, and climate change facilitate the movement of viruses from animals to humans and expand the habitats of disease vectors like mosquitoes.
- Globalization: Increased international travel and trade contribute to the rapid spread of infectious diseases across borders.
- Healthcare Infrastructure: Under-resourced healthcare systems struggle to manage outbreaks, leading to higher mortality rates and wider spread.
- Vaccine Hesitancy and Under-Immunization: Gaps in vaccination coverage contribute to the resurgence of diseases like polio and hinder efforts to control outbreaks.
Strategies for Control and Prevention
Effective management of these diseases requires a multifaceted approach:
- Surveillance and Early Detection: Robust systems enable prompt response to contain outbreaks.
- Research and Development: Investment in vaccines, antiviral drugs, and diagnostic tools is critical.
- Public Health Education: Educating communities about transmission risks and preventive measures empowers individuals.
- Strengthening Healthcare Systems: Enhancing capacity, training personnel, and ensuring availability of protective equipment are essential.
- One Health Approach: Recognizing the interconnectedness of human, animal, and environmental health leads to more effective prevention strategies.
- Policy and International Cooperation: Governments and organizations must collaborate on policies addressing cross-border health threats.
Conclusion
The increasing reports of human-to-human and animal-to-human transmission of bird flu, mPox, Marburg virus, Nipah virus, Dengue virus, and vaccine-derived poliomyelitis are alarming reminders of the persistent threats posed by infectious diseases. These pathogens exploit weaknesses in public health systems, environmental management, and global cooperation. By understanding their epidemiology, transmission mechanisms, and the risks they pose, we can better prepare and respond to these challenges. Collective efforts in surveillance, research, education, and policy-making are imperative to mitigate the impact of these diseases and protect global health.
