Avian Flu Outbreaks: Understanding the Impact and Taking Precautions

Introduction

Avian influenza, commonly known as bird flu, has been a recurring threat to both avian and human health worldwide. The virus is spread globally through the migration of infected wild birds that transmit it to domesticated animals, including chickens. The 2024 outbreaks have brought renewed attention to this dangerous virus, with highly pathogenic avian influenza subtype H5N1 leading the charge [1]. For the first time, H5N1 avian flu has infected dairy cows, with infections identified across at least thirteen states [2]. The infection is concentrated in cow udders, and milk from infected cows has been found in supermarkets. Viruses or viral fragments have been identified in many samples of milk on store shelves. Two studies have shown that some standard pasteurization protocols reduce the concentration of active virus but may not eliminate it entirely [3,4]. A new mutation of the virus that is more efficient at attacking mammals has been detected in a Texas man [5]. A more recent case has also been reported in Michigan, where the dairy worker reported coughing in addition to ocular discharge, elevating concerns about the potential for human-to-human airborne transmission [6]. H5N1 remains widespread among wild birds globally and has caused outbreaks in poultry and an increasing set of mammals, including cats, mice, goats, foxes, raccoons, skunks, harbor seals, and bears. It has caused significant and even deadly brain infections in multiple mammals. There have been isolated human cases, notably three recent infections in U.S. dairy workers. In the last 20 years, more than 700 human cases of H5N1 have been reported across over 60 countries [7]. The risk for humans would become much greater if the virus adapts to transmit directly from human to human. Until now, there is no evidence of such transmission. 

In the meantime, outbreaks of avian flu have involved millions of birds, with outbreaks in poultry occurring at least 11 times, and 4 of these outbreaks have involved millions of birds. Since the current outbreak began in 2022, nearly 100 million chickens and turkeys in the US have died either directly from infection or have been suspected of being exposed and were subsequently killed (culled) to prevent further transmission [8].

We provide a concise overview of the 2024 avian flu outbreaks, focusing on the health impacts, epidemiological risks, and precautions necessary to control the outbreak and reduce the risk of human-to-human transmission. We draw from recent research and historical data to offer a systematic perspective on understanding this persistent threat.

Health Impacts

On Avian Species

The 2024 avian flu outbreaks have had a devastating impact on poultry and wild birds alike. High mortality rates were observed, severely affecting the poultry industry economically. 100 million birds have been killed or culled [8]. The rapid spread of the virus among bird populations underscores the highly pathogenic nature of the H5N1 strain. Previous studies, such as those conducted in France during the 2020-2022 outbreaks, highlighted similar patterns of widespread infection and significant economic losses [9].

On Mammals

As increasing numbers of mammalian species have been infected, the evidence of the harm that they can cause also increases. Deaths of cats, goats, and harbor seals have been identified, and brain infections have been identified in multiple animals [10].

On Humans

For years, individual cases of avian influenza in people have been identified due to close contact with poultry around the world. The main concern for wider outbreaks has been the potential for human-to-human transmission due to changes in the virus. The potential severity of an avian influenza outbreak has been illustrated by the H1N1 influenza pandemic of 1918. While there has not been observed human-to-human transmission of H5N1, the potential for transmission remains a serious concern as mutations take place that make it more transmissible to and among mammals. The current transmission between cows elevates the risk both because of the direct transmission between cows (as opposed to transmission from wild birds directly to cattle) and because of the direct contact of cows with people being infected. Previous incidents have shown that when the virus does achieve human-to-human transmission, it can be very deadly and achieve pandemic status. The ongoing risk of a pandemic stemming from such zoonotic transmission necessitates actions to reduce the risk, vigilant public health strategies, and preparedness for actions in case of interhuman transmission.

Epidemiological Risks and Prevention

The spread of avian flu is influenced by several factors, including migratory bird patterns, human interaction with infected birds, infected mammals including domesticated farm animals (chickens and cows) and pets (cats and dogs), and human interaction with domesticated farm animals and pets. The 2024 outbreaks were exacerbated by such factors, with significant spread observed across continents. 

The key to prevention of a wider outbreak among people is to prevent transmission from infected domesticated animals to people, control the outbreak in domesticated animals, and even to engage in efforts to reduce the infections in wild birds. 

Identifying where infections are currently present (surveillance testing), and what transmission mechanisms are possible are key to prevention. Currently, the most important mechanisms of transmission to the public are the consumption of contaminated dairy products, eggs, and meat. It is known that consumption can cause infections in cats from contaminated cat food. 

There is concern that transmission to pigs could lead more rapidly to transmission to and between people because the pigs could then be infected by both avian and human flu, increasing the risk of a hybrid virus strain that combines their properties, allowing for human-to-human transmission of strains with avian virus properties. 

Studies from the 2022 European avian flu events illustrate how the virus’s persistence in wild bird populations poses a continuous threat [11].

Transmission Mechanisms

• The mechanism of transmission in cattle has not been definitively established, but both contact and airborne transmission are expected in high-density chicken and cattle farming conditions. For example, milking equipment is not generally disinfected between cows, and the high concentration of virus in milk suggests direct contact may lead to transmission. Specific studies have also pointed to airborne transmission. 
• Role of Airborne Transmission in Outbreak Spread:

A study on the 2015 avian influenza outbreaks in the U.S. indicated that airborne transmission via fine particulate matter might have played a significant role [12]. The research results provide insights into the risk of airborne transmission via fine dust particles and the importance of preventative and containment strategies such as air filtration, containment, or swift depopulation of infected flocks, which are crucial in controlling the spread.

• Airborne Transmission Between Mammals:

A study demonstrated that avian flu (H5N1) can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host [13]. The authors concluded that avian A/H5N1 influenza viruses can acquire the capacity for airborne transmission between mammals without recombination in an intermediate host and, therefore, constitute a risk of becoming a human pandemic influenza. This finding underlines the significant risk associated with H5N1, emphasizing the necessity for vigilant monitoring and preparation for such transmission scenarios.

Prevention by Consumers

To avoid being infected, consumers should not consume raw farm products, including unpasteurized milk, undercooked (runny) eggs, or undercooked meat – including both beef and chicken. Pasteurized milk and cheese products are often considered safe.  Recent studies indicate that standard pasteurization significantly reduces the concentration of active virus in milk but does not eliminate it completely, leaving open the possibility that some risk exists in consuming dairy products that are pasteurized. Additional precautions may be taken, including the consumption of ultra-pasteurized dairy products, which generally have fewer active microbes and are therefore considered safer. Consumers should avoid eating raw eggs and homemade mayonnaise or potato salad. Undercooked meat has been shown to have infectious viral particles [14].

Historically, the main safety precautions from milk and meat are to prevent products from infected cattle from entering the food chain and the pasteurization of milk. However, the detection of viral particles or fragments in multiple samples of store-bought milk has shown that the first is not currently reliable because tests for cattle infection are not adequate [15].  The second method, pasteurization, provides some protection, but recent studies have indicated that it is also not reliable. Transparency is essential, and the public has a right to know how safe their dairy products are to consume. Authorities, notably the USDA, should publish studies, including their data, on pasteurization that either confirm the safety of dairy products or identify modifications for implementation, such as extended time or higher temperatures, to ensure food safety. A recent study by USDA personnel has been shared and is undergoing peer review [16]. It is imperative that aggressive measures are taken to prevent milk from infected cows from entering the dairy supply, as well as properly pasteurizing the milk. 

For the public, the other principal source of danger is transmission from wild birds. This risk of transmission from birds includes  avoiding, when possible, direct contact with the carcasses of wild birds or their droppings. Where disposal is needed, contact with the carcass or droppings should be avoided by using gloves or directly covering with a plastic bag. 

Prevention on Farms

Controlling outbreaks in farms of both poultry and cattle requires high levels of vigilance and preventive measures. 

Workers on farms that have been identified as having infected animals are at high risk for infection from poultry and cattle, including both airborne and physical contact with the animals, dairy and meat products, animal waste, and equipment.  Workers should wear appropriate and recommended personal protective equipment (PPE) when exposed to an infected or potentially infected animal(s). Airborne and contact protection includes coveralls or aprons, masks, goggles, rubber boots, head covering, and gloves.  Moreover, washing or discarding the PPE between handling different groups of birds should also be encouraged, in order to avoid cross-contamination between birds due to contaminated PPE. 

Prevention of the spreading of infection across poultry farms that are proximate to each other requires aggressive culling of birds. Outbreaks have led to the culling of millions of birds from this avian flu outbreak in the US alone. Protocols for establishing an area of culling and an area of monitoring for infection spreading have been established to protect the regional farming industry from widespread outbreaks and damage.  

The new transmission of avian flu to cattle has resulted in uncertainty about how to address the outbreaks among cattle as protocols have not been established. It is known that avian flu rapidly spreads in herds, and can be transmitted through unsterilized milking equipment. While cattle have not been culled at the same level as poultry, deaths of cattle from infection have occurred, and many cattle have reduced milk production or do not recover from infection and are therefore culled by farmers. 

The use of poultry waste as feed for cattle should be stopped as the high levels of virus that may be present have been identified as leading to a high risk of transmission.

Cats and mice have been found to be infected in farms and may become vectors of wider transmission. 

Barns should be protected from the entry of wild birds using nets.

Frequent surveillance testing of animals and rapid response, if infections are detected, can reduce the scale and impact of outbreaks. 

The prevention of transmission among farms requires reducing the mobility of animals and equipment among farms, and the testing of any animals that are being transferred between farms. 

Mitigation Strategies in Poultry Processing can also be used and adopted for cattle. Research suggests that modifications in the processing of infected chickens can significantly reduce the generation of infectious airborne particles. Simple changes like containing birds in specific containers during the killing and bleeding processes can mitigate airborne transmission risks [17].

Precautionary Measures and Control Strategies

Biosecurity Measures

Effective biosecurity measures are crucial in preventing the spread of the virus within poultry operations. This includes controlling the movement of poultry, sanitizing facilities, and restricting access to farms, which have proven effective. Lessons from recent outbreaks have shown that rapid implementation of such measures can curb the spread of the virus significantly. Similarly, restricting the transport of cattle or testing them before transportation to other farms can reduce farm-to-farm transmission opportunities.

Public Health Strategies

Public health responses to avian flu outbreaks include heightened surveillance, rapid testing of suspected cases, restrictions of transport, and public awareness campaigns about the risks of contact with wild birds and undercooked poultry or the risk of transmission (including airborne). The development of vaccines and antiviral drugs also plays a vital role in controlling the spread among human populations.

The CDC emphasizes several key prevention strategies for those at risk of exposure to H5N1, including avoiding unprotected contact with infected or potentially infected live or dead animals or surfaces contaminated by these animals. For individuals working with poultry and other animals in infected areas, the use of personal protective equipment (PPE) is crucial to minimize risk. Additionally, while H5N1 bird flu does not usually infect humans, the CDC advises maintaining good personal hygiene and handling food safely, ensuring that poultry and eggs are cooked properly to eliminate potential virus transmission [18].

The CDC also advises that getting a seasonal flu vaccine can help reduce the risk of simultaneous infection with seasonal and avian influenza viruses, which can complicate diagnosis and treatment outcomes. This is an essential preventive measure for healthcare workers, vulnerable populations, and others who might be exposed to flu viruses in outbreak areas.

Conclusion

The avian flu outbreaks of 2024 have yet again brought to the forefront this virus’ global reach and dangerous nature. The virus is highly pathogenic and can cause severe respiratory illness in birds and mammals, including humans. The impact on both avian and human health underscores the need for a comprehensive and coordinated approach to disease management and prevention strategies.

The emergence of a disease can cause justified concern and even fear. It is important to note that these worries are not optimally tackled by public health communications urging people to calm down but by performing actions that establish control over the threat [19]. 

Some of the necessary actions include monitoring and implementing active measures to prevent the transmission of the disease. This includes culling of chickens, but the question remains about what to do with cattle. Preventing the transportation of sick animals to prevent the spread of the disease remains crucial. Additionally, the use of poultry waste as feed for cattle has been pointed to as a very high risk due to the high levels of virus that may be present. Stopping this practice is crucial to reduce the risk of the disease spreading and gaining additional transmission routes among cattle and workers. To prevent exposure to the disease, pets should be kept away from bird droppings and carcasses. Finally, the USDA and other researchers should clearly identify what pasteurization methods are safe for dairy products. Extending the duration of pasteurization by the necessary amount or raising the temperature can ensure the safety of dairy products. By taking these actions, we can reduce the risk of the disease spreading and keep ourselves and our communities safe.

The avian flu virus is already a substantial agricultural disaster and has the potential to cause a global human pandemic. It is crucial to take prompt and proactive measures to mitigate its spread. Preventing current transmission in agriculture and farm workers is also the way to prevent the evolution of human-to-human transmission. To achieve this, it is essential to learn from past outbreaks and invest in ongoing prevention, and implement actions to mitigate the risk of transmission. Research on transmission mechanisms and prevention measures should help identify effective means to control transmission both on farms and to the public. A coordinated approach to disease management, including early detection, rapid response, and effective control measures, is necessary to minimize the effects of future epidemics.

Surveillance systems are needed to monitor the spread of the virus, identify potential hotspots, and ensure the safety of the food supply system. This surveillance system should be able to track the virus’ molecular evolution and provide information on the emergence of new strains. Furthermore, it is essential to prioritize preventive measures and the development of effective vaccines and antiviral drugs to prevent the virus’s spread and treat infections that do arise.

In conclusion, the avian flu virus remains a significant threat to human and animal health, and concerted efforts are required to manage and prevent its spread. This time, we have a chance to avoid a pandemic by acting quickly and proactively. By investing in research, developing effective prevention strategies, and implementing robust surveillance systems, we can hope to prevent imminent and future epidemics or pandemics.