Bird flu: treatment and prevention of spread

Avian influenza is an acute viral disease of birds caused by influenza A viruses with the H5 or H7 surface antigen. In recent years, the highly pathogenic H5N1 variant of clade 2.3.4.4b has become the most significant for humans and agriculture. It has caused a prolonged epizootic in wild birds and domestic poultry flocks and has for the first time widely affected cattle, increasing the likelihood of human contact with the virus. However, the risk to the general population is assessed as low, and there is no evidence of sustained human-to-human transmission. [1]

In 2025, regulators and public health centers recorded sporadic cases of infection in humans in Asian countries, as well as isolated cases in North America among workers exposed to infected animals. Most infections were associated with close, unprotected contact with birds, mammals, or contaminated environments. Some patients developed severe respiratory damage, while others experienced mild symptoms, including conjunctivitis. [2]

In parallel, numerous outbreaks persist among poultry and certain mammal species, requiring a combination of biosecurity measures on farms, surveillance, vaccination of poultry where this has proven effective, and targeted prevention in people at risk. [3]

At the pandemic preparedness level, stockpiles of antigens and adjuvants are maintained for rapid delivery of human vaccines, and candidate vaccine viruses are updated to account for antigenic shifts in circulating strains. For workers at occupational risk, several countries have entered into contracts for the supply of pre-epidemic vaccines. [4]

What is known today about threats and transmission routes?

The main routes of human infection are contact with the mucous membranes of the eyes, nose, and mouth, or inhalation of aerosols when handling sick or dead birds, cattle, untreated milk, manure, bedding, and other materials. The risk increases in the absence of adequate protective equipment. [5]

In 2024, widespread H5N1 circulation was confirmed for the first time in dairy cattle in several US states, changing the risk profile: viral RNA was detected in raw milk, and laboratory experiments showed its relative persistence in unprocessed milk and on surfaces. This required stricter milk handling regulations on farms and emphasized the inadmissibility of raw milk consumption. [6]

Pasteurized dairy products remain safe: regulators have not detected infectious viruses in finished products, and heat treatment reliably inactivates the influenza virus. It is recommended to avoid consuming raw milk and products made from it. [7]

Congestion of people and animals at live poultry markets, as well as high poultry farm densities, increases the risk of interspecies transmission and requires temporary restrictions and deep sanitization when the virus is detected.[8]

Clinical picture in humans

The incubation period is typically several days. Symptoms range from mild to severe. Some patients experience conjunctivitis, fever, myalgia, and respiratory symptoms. In severe cases, pneumonia and respiratory failure develop, and complications involving other organs are possible. The mortality rate in historically confirmed cases of H5N1 is generally high, due to statistical selection of severe cases and delays in seeking medical attention. [9]

Poultry and dairy farm workers are more likely to experience mild forms of the disease, especially with timely initiation of antiviral therapy. However, the low proportion of severe cases in these cohorts does not negate the need for strict prophylaxis and contact monitoring. [10]

To date, sustained human-to-human transmission has not been identified. However, given the evolutionary potential of influenza viruses, epidemiological surveillance of symptomatic contacts is essential. [11]

In hospital settings, early isolation, infection control measures and immediate initiation of antiviral therapy if suspected are required, without waiting for final laboratory test confirmation.[12]

Diagnostics

Diagnosis is based on the detection of viral RNA using reverse transcriptase PCR from respiratory samples and, in the case of conjunctivitis, from conjunctival scrapings. Samples are collected as early as possible. In cases of hospitalization with influenza-like syndrome and epidemiological links, prompt typing for H5 is recommended. [13]

Some healthcare systems have strengthened testing algorithms, expanding the indications for testing hospitalized patients to quickly identify possible cases of infection. This allows for faster implementation of staff protection measures and epidemiological investigations. [14]

Serology can be used for retrospective assessment in outbreaks, but PCR remains key for clinical decision-making. Laboratory biosafety and transportation protocols are in place when handling samples. [15]

In addition to human testing, veterinary surveillance and genomic typing of circulating strains in poultry and mammals with updating of candidate vaccine viruses is needed to prepare for large-scale human vaccination in an unfavorable scenario. [16]

Treatment: Antiviral therapy and support

The standard treatment for suspected H5N1 is immediate administration of oseltamivir at the standard dose twice daily for 5 days. Treatment should be initiated as soon as possible and not delayed beyond 48 hours from the onset of symptoms, especially in severe cases or hospitalization. [17]

Alternatively, intravenous peramivir or inhaled zanamivir, as well as baloxavir, may be used. For severe cases and those with a slow clinical and virological response, prolongation of the course or dose increase is considered, while monitoring for toxicity and side effects. Adamantane-type drugs are not recommended due to widespread resistance. [18]

Combinations of neuraminidase inhibitors and polymerase inhibitors are being studied as a way to reduce the risk of resistance and improve outcomes, but high-quality randomized clinical data for H5N1 in humans are still lacking. Treatment is always complemented by respiratory support, management of complications, and prevention of hospital-acquired infections. [19]

Post-exposure prophylaxis with oseltamivir for high-risk contacts is administered at the therapeutic dose twice daily, usually for 5 days if contact has ended, or longer if exposure continues. The decision is made based on the nature of the contact and the availability of protective equipment by the exposed individual. [20]

Table 1. Antiviral drugs for H5N1 in humans

Preparation	Class	Standard for adults	Key Notes
Oseltamivir	Neuraminidase inhibitor	75 mg twice daily for 5 days	Start as early as possible. Prolongation and dose adjustment are possible in severe cases. [21]
Peramivir	Neuraminidase inhibitor	Intravenously, once or according to the regimen, as indicated	Consider if oral administration is not possible. [22]
Zanamivir	Neuraminidase inhibitor	Inhalations according to instructions	Do not use in case of severe broncho-obstruction. [23]
Baloxavir	Polymerase inhibitor	Once by body weight	Data on H5N1 are limited, but activity has been confirmed in models.[24]

Table 2. Post-exposure prophylaxis in humans

Situation	Who is it indicated for?	Scheme	Duration
Close unprotected contact with confirmed or probable H5N1	Farm workers, veterinarians, household contacts	Oseltamivir at a therapeutic dose twice a day	Usually 5 days after last contact, longer with continued exposure.[25]
Asymptomatic person with PCR confirmed H5	Any exposed without protection	Oseltamivir at a therapeutic dose twice a day	5 days and observe symptoms. [26]

Prevention in humans: protective equipment, nutrition and everyday life

Personal protection when working with poultry, cattle, raw materials, and contaminated environments includes protection for the head, eyes, respiratory tract, hands, body, and footwear. Goggles, headgear, a respirator of at least N95 rating, water-resistant coveralls with an apron if necessary, gloves, and shoe covers are recommended. Proper donning and doffing procedures, training, and supervision are essential. [27]

Employers are required to assess risks, provide occupational health and safety plans, biosecurity training, access to protective equipment and its disposal, and monitor personnel health after incidents. Persons who have been in contact with sick animals or materials are advised to seek medical observation and testing if symptoms develop. [28]

Raw milk and milk products, as well as undercooked meat and eggs, should be avoided in the diet and at home. Pasteurized dairy products are safe, as heat treatment inactivates the virus. Farms are tightening controls on the collection, storage, and disposal of milk from sick animals. [29]

In some regions, temporary restrictions on live poultry markets and animal movements, with mandatory cleaning and disinfection, are introduced during outbreaks. This reduces the risk of contact and breaks transmission chains between flocks and people. [30]

Table 3. Personal protective equipment and application scenarios

Scenario	Minimum set	Additionally
Slaughter, disposal, litter removal	N95 respirator, goggles, gloves, overalls, headgear, shoe covers	Apron, double gloves, splash shield. [31]
Milking and handling milk on farms during an outbreak	N95 respirator, goggles, gloves, waterproof gown or coveralls	Strengthened control over milk and waste disposal. [32]
Examination and treatment of animals	Respirator, goggles, gloves, gown	Training on how to remove protection, monitoring staff for symptoms. [33]

Prevention in poultry and livestock farming

The basis for control remains strict biosecurity, rapid isolation and elimination of outbreaks, zoning and movement of animals with permission, cleaning and disinfection, and surveillance of wild birds. Vaccination of birds may be recommended as part of a comprehensive strategy, but does not replace other measures. [34]

Field data from France showed that mass vaccination of ducks was accompanied by a sharp reduction in epizootic activity and the number of outbreaks. This supported the EU regulatory approach, which permitted and standardized poultry vaccination, subject to monitoring and trade requirements. [35]

Regulators and scientific networks support the collection of standardized surveillance data, allowing for rapid updating of measures and the identification of new patterns of cross-species transmission. In the United States, expanded use of vaccination in poultry production and enhanced testing and monitoring are being discussed. [36]

Veterinary vaccines and schedules vary by poultry species. In practice, farm technological limitations are taken into account, as many available vaccines require individual injections, making coverage difficult in some housing systems. [37]

Table 4. Poultry vaccination and regulatory approaches

Region	Policy	Key result
France	Mandatory vaccination of ducks from October 2023	A reduction in the number of outbreaks by tens of percent, according to observational and model estimates. [38]
European Union	Permission and rules for the use of vaccinations from 2023, standardization of reporting	Consistency between surveillance and trade data. [39]
USA	Strengthening monitoring, preparing vaccination plans, pilots	Assessing logistics and trade impact. [40]

Human Vaccines: Readiness and Targeted Use

Pre-epidemic vaccines are being purchased for human use in a number of countries, intended for rapid use in high-risk occupational groups. Contracts provide for the supply of doses and scaling options. Protection against specific circulating strains depends on antigen matching, which is updated through a network of candidate vaccine viruses. [41]

The European Union has signed agreements to supply doses to poultry workers and veterinarians, with the possibility of extending the purchases over several years. The United States maintains a national stockpile of pre-epidemic vaccines and the capacity to quickly fill finished products. [42]

Some candidates utilize cell-based technologies and adjuvants, which accelerate scaling and enhance immunogenicity. At the same time, the development of broad-spectrum and universal platforms targeting cross-protection against multiple influenza strains continues. [43]

It should be remembered that human vaccines are used specifically for at-risk groups and as a preparedness tool. Mass prevention of the population is not being carried out, as the current risk assessment for the general population remains low. [44]

Table 5. Vaccines for humans: where and for whom

Parameter	State
Target groups	Poultry and veterinary workers, personnel involved in the elimination of outbreaks
Supplies and contracts	Long-term framework agreements with options for increasing supply volumes
Antigenic matching	Updated as strains evolve and recommendations for candidate viruses are made
Mass application	Not indicated at current low risk to the general population
Sources	Regulatory publications and contracts for pre-epidemic supplies [45]

Nutrition and food safety

Pasteurized milk and milk products are safe because pasteurization inactivates the influenza virus. Regulators have not detected infectious viruses in pasteurized products during market inspections. Raw milk and milk products should not be consumed due to an established biological risk. [46]

When cooking poultry and eggs, maintaining adequate internal temperatures and proper kitchen hygiene effectively reduces risk. During outbreaks on farms, attention is paid to the safe collection and disposal of milk from sick animals and to personnel's exposure to waste. [47]

Regional authorities, where necessary, implement surveillance programs for dairy products and raw materials, which helps promptly identify and localize risks. Consumer information and labeling facilitate the selection of pasteurized products. [48]

Table 6. Food safety during H5N1 outbreaks

Product	Risk without treatment	Risk reduction measures
Raw milk	Confirmed biological risk	Avoid use, follow disposal rules. [49]
Pasteurized milk	Safely	Standard pasteurization and quality control. [50]
Bird and eggs	Risk of insufficient heat treatment	Sufficient heat treatment, kitchen hygiene. [51]

Frequently Asked Questions

Do all contacts require prophylactic medication
? No. The decision is individual and depends on the type of contact, the availability of protective equipment, and the exposure status. For close unprotected contact, oseltamivir is prescribed at a therapeutic dose, typically for 5 days after the last contact. [52]

Is there human-to-human transmission?
No consistent human-to-human transmission has been identified. The risk to the general population is assessed as low, but monitoring of contacts is essential. [53]

When to start treatment:
Immediately upon suspicion, without waiting for test results, especially in severe cases or hospitalization. The earlier oseltamivir is started, the higher the likelihood of a favorable outcome. [54]

Are there vaccines for humans?
Yes, a number of countries stockpile pre-epidemic vaccines for target risk groups and update candidate vaccine viruses. The population is not vaccinated on a mass scale. [55]