Highly Pathogenic Avian Influenza

Highly pathogenic avian influenza (H5N1) is a viral zoonotic disease of wild and domestic bird species that can infect humans and other mammals. Human infections have been very rare and generally isolated to farm workers. There have not been any recorded cases of transmission from humans to other humans (World Health Organization).  The H5N1 variant of the virus was first detected in cattle in March 2024 when a dairy cow in Texas tested positive for the virus. It is suspected that the virus crossover to cattle occurred in late 2023.    

Fast Facts (as of Jan. 24, 2025)
1 dairy herd tested positive in Churchill County, Nevada, in January 2025
1 dairy herd tested positive in Nye County, Nevada, in December 2024
937 dairy cow cases in 16 states in the U.S. 
67 human cases in the U.S. in 2024, most of them in California
1 human death from H5N1 avian influenza in the U.S. 
3 detected cases of H5N1 in poultry in Nevada since the first detection in Carson City in July 2022 

Species That Can Contract H5N1:

• Birds
• Humans
• Cats
• Dogs
• Juvenile goats
• Cattle
• Wild mammals consuming infected birds: Seals, bears, foxes, mink, zoo animals (tigers and leopards) 

Clinical Signs in Cattle:

• Decreased milk production
• Abnormal milk (yellow discoloration, thickening, clots, flakes, etc.)
• Decreased feed consumption
• Fever
• Dehydration
• Increased respiratory rate
• Nasal discharge

H5N1 Transmission Between Dairy Herds:

While contact tracing hasn’t yet provided definitive sources of transmission of H5N1 between dairy herds/farms, there are several transmission risks that could be allowing the spread of H5N1 between dairy farms. The information below is from the Aug. 23, 2024, National Epidemiologic Brief of Highly Pathogenic Avian Influenza H5N1 Genotype B3.13 in Dairy Cattle, and reflects the responses from farms with confirmed H5N1 infections.

• Other species: Over 75% of all dairy farms surveyed had cats, and of those with cats, up to 33% of the farms infected with H5N1 had sick or dead cats on the farm.  Cats, poultry and wild birds are all potential fomites (objects that can carry infectious material, also known as passive vectors).
• Shared transportation vehicles: 34% of farms used trucks and trailers shared with other farms within 30 days prior to onset of clinical signs. Over 50% of the farms that shared vehicles did not clean them between each use.
• Contaminated equipment: 21% of farms use the same equipment to handle manure and animal feed, and nearly 50% of those farms do not clean the equipment between each use.
• Shared personnel and housing: Over 17% of dairy employees visited a different dairy within 30 days of onset of clinical signs of H5N1. Over 25% of dairy workers own their own livestock at their personal residence. 14% of dairy employees have household members who work at other livestock farms.
• Support services: Veterinarians, nutritionists, breeding techs, feed delivery personnel, milk haulers, contract drivers, renderers and hoof trimmers are all potential sources of between-farm virus transmission.
• Bedding: Most farms reported fresh bedding is accessible to wild and domestic animals prior to use, creating a potential for contamination.
• Feed and feed storage: All farms reported birds, wild animals, and rodents all have access to cattle feed and feed ingredients.  It is almost impossible to keep birds, rodents and wildlife from accessing feed, but minimizing contact is desired.
• Waste milk disposal: Some farms fed raw waste milk to calves, dogs, cats and swine. Pasteurization can prevent the spread of H5N1 to other animals on the farm.

Recommendations for Protecting Farm Workers:

Farms with a confirmed/potentially infected animal:

• Put engineering controls into place to provide proper ventilation to reduce exposure to pathogens.
• Implement administrative controls to reduce exposures to pathogens, such as: surveillance for sick animals, testing for H5N1, monitoring animal feed and production levels, monitoring employees for illness, training workers on Personal Protective Equipment (PPE) and biosecurity practices, providing handwashing stations and showers, keeping food and beverages in a safe storage location, and preventing workers from eating and drinking while working with animals.
• Ensure workers wear PPE according to Centers for Disease Control (CDC) recommendations for high-exposure situations, using items such as: approved respirators, safety goggles, disposable gloves and optional outer work gloves, boots/boot covers, head/hair covers, fluid-resistant coveralls or fluid-resistant sleeved apron, optional face shields over safety goggles and respirator, and optional waterproof apron over coveralls.

Farms within a region with confirmed/ potentially infected farms:

• Implement administrative controls to reduce exposures to pathogens, such as: surveillance for sick animals, testing for H5N1, monitoring animal feed and production levels, monitoring employees for illness, training workers on PPE and biosecurity practices, providing handwashing stations and showers, keeping food and beverages in a safe storage location, and preventing workers from eating and drinking while working with animals.
• Implement use of PPE including, but not limited to, items such as: approved respirators, safety goggles, disposable gloves and optional outer work gloves.

Farms with healthy animals and not in a region with confirmed infections:

Implement administrative controls to reduce exposures to pathogens, such as: surveillance for sick animals, testing for H5N1, monitoring animal feed and production levels, monitoring employees for illness, training workers on PPE and biosecurity practices, providing handwashing stations and showers, keeping food and beverages in a safe storage location, and preventing workers from eating and drinking while working with animals.

Personal Protective Equipment (PPE) for farm workers is available through the Nevada Department of Agriculture and can be requested by calling 775-353-3709.

Financial Assistance:

The USDA is providing financial assistance to livestock producers for the development of enhanced biosecurity plans and H1N5 testing costs. For producers with infected animals, additional financial assistance is available for purchasing PPE and heat treatments for disposing of milk. The USDA-Farm Services Agency is also accepting applications for emergency assistance for milk losses due to H5N1 infection. 

Resources:

1. Detection of Highly Pathogenic Avian Influenza (H5N1) in Dairy Herds: Frequently Asked Questions
2. Protecting Poultry Workers From Avian Influenza
3. Secure Milk Supply Plan: Enhanced Biosecurity Resources for Producers
4. EXCITE Extension Fact Sheet: Keeping Our Farms Safe - Protecting against H5N1 

References:

1. American Veterinary Medical Association News: Nation enters third year of historic HPAI epizootic
2. CDC: Avian Influenza (Bird Flu) 
3. CDC: H5 Bird Flu: Current Situation
4. CDC: Interim guidance for employers to reduce exposure to Novel Influenza A (such as H5N1 Bird Flu) for people working with or exposed to animals
5. CDC: What causes bird flu in pets and other animals
6. County of Los Angeles Public Health: Public Health Alerts Residents of Expanded Recall of Raw Milk and Cream Products Following Multiple Detections of H5 Bird Flu
7. Global Center for Health Security: Is there a vaccine for H5N1 Influenza?
8. Nevada Department of Wildlife: Highly pathogenic avian influenza confirmed in wild bird populations
9. University of Minnesota-CIDRAP: Study suggests earlier US-licensed H5N1 vaccines prompt antibodies to current strain
10. USDA-Animal and Plant Health Inspection Service: H5N1 and Safety of the US Meat Supply 
11. USDA-Animal and Plant Health Inspection Service: HPAI in Livestock - Financial Assistance
12. USDA-Animal and Plant Health Inspection Service: Highly pathogenic Avian Influenza H5N1 B3.13 in Dairy Cattle: National Epidemiologic Brief
13. World Health Organization: Avian Influenza Weekly Update Number 970