STgen™ is committing its transparency, education and proactive protocols with the industry’s ongoing highly pathogenic avian influenza (HPAI) condition within the lactating dairy cow population in the U.S.
On March 25, 2024, the United States Department of Agriculture (USDA), the Food and Drug Administration (FDA), and the Centers for Disease Control and Prevention (CDC) jointly announced the identification of highly pathogenic avian influenza (HPAI), specifically avian influenza virus type A (H5N1), in lactating dairy cows. Since then, infections with A (H5N1) have been confirmed in lactating dairy cows from over 50 herds in nine different states.
So far, tests conducted indicate that the virus detected in lactating dairy cows is H5N1 derived from the Eurasian lineage goose/Guangdong clade 2.3.4.4b. This is the same virus that has been affecting wild and domestic birds and has caused sporadic infections in various species of wild mammals, both in North and South America.
Signs of the infection
Common clinical signs in affected lactating cows include loss of appetite, reduced milk production, and abnormal appearance of milk (thick, discolored). Affected herds have experienced an abrupt decline in milk production. Although avian influenza virus type A (H5N1) is associated with high morbidity and mortality in birds ("highly pathogenic"), this has not been the case for lactating dairy cows. Affected animals recover with supportive treatment in 7-10 days with little or no mortality. High viral loads in the milk are observed during the course of the disease, but virus shedding stops after 7-10 days. Cases of asymptomatic cows with virus in their milk have been reported. The virus has also been detected in nasal swabs, urine, and blood, although in much lower quantities and proportions than in milk.
The spread of the H5N1 virus among lactating cows within the same herd and between herds due to the movement of lactating cows has been demonstrated by the USDA. Due to the high viral load in the milk and mammary glands, it is suspected that the virus is spreading among animals during the milking process, either through contact with infected equipment or through virus aerosolized during cleaning procedures.
It is not clear how the avian virus was passed to cattle. Genetic analysis of the viral sequence indicates that the virus may have been circulating in cattle since late 2023 (November-December). Clinical presentation of the disease was observed in early 2024, but the cause was unknown until its confirmation in March of the same year.
Who is infected?
All reported infections to date are in lactating dairy animals. No infections have been reported in beef cattle, non-lactating dairy females or males. Current restrictions on animal movement within the United States, either at the state or federal level, are focused only on lactating dairy cows.
On April 23, 2024, the FDA reported the detection of H5N1 inactive particles in milk from retail stores. Tests suggest that these particles are remnants of the inactivated virus, likely killed during the pasteurization process. Further tests have not detected any live virus in commercial milk samples, and U.S. health officials believe that people cannot get sick from drinking pasteurized milk. From this we can currently conclude that pasteurized milk is safe for human consumption. A USDA study also reaffirmed that the meat supply is safe, after testing 30 samples of retail ground beef from states where dairy herds tested positive for H5N1. The samples were all negative to the RT-qPCR test.
How do we test?
The original detection of the virus, as well as subsequent cases, is based on Reverse Transcription quantitative Polymerase Chain Reaction (RT-qPCR) testing, which detects the presence of viral genetic material. A positive result confirms the presence of the virus, although it does not necessarily indicate a risk of infection, as in the case of supermarket milk, dead virus particles also test positive. On the other hand, a negative result indicates the absence of the virus and confirms safety of the product.
Among the advantages of the RT-qPCR test are high sensitivity, high specificity, rapid result time, scalability, cost, and its inherently quantitative nature.
Most RT-qPCR tests for the detection of influenza type A target the matrix (M) genes, as they have a relatively conserved sequence among different flu virus variants. The RT-qPCR test for the M gene is capable of detecting many types of influenza A. Confirmation of the H5N1 variety is subsequently performed through specific tests for the H and N genes.
Other tests used for epidemiological control include antibody tests, useful for determining past infections, but they do not represent a direct measure of the risk of contagion. An animal positive for the presence of antibodies does not necessarily represent current virus presence, and the absence of antibodies does not guarantee that the animal is not releasing viral particles, given the delay between initial infection and antibody production.
Clinically affected lactating cows test positive for avian influenza antibody tests. So far, non-lactating animals present in the same establishment as affected lactating cows have not shown an immune response to the virus, suggesting that they were not infected despite the presence of the virus in the herd.
What about bulls?
The risk of transmission of avian influenza H5N1 through bovine semen has not been investigated. So far, there have been no reports of A (H5N1) virus infecting bulls, but this does not eliminate the possibility of symptomatic or asymptomatic infections in males.
Given the limited information available, assessing the risk of infection in AI centers is not yet possible. Consequently, biosecurity measures aimed at keeping the virus out of the semen supply are generic and cannot warrant absence of H5N1 in semen. In this context, testing each individual batch of semen is the best approach at ensuring lack of disease transmission via artificial insemination. This analysis is possible using the RT-qPCR test.
The strategy of testing each batch of semen by RT-qPCR is widely used in the commercialization of porcine semen to avoid the risk of PRRS virus transmission. Similar strategies have also been used for the international market of bovine semen when the country of origin poses a risk of infection with Schmallenberg virus or Bluetongue virus.
What is STgen™ doing?
We are committed to transparency and education when it comes to avian influenza affecting cattle. Going forward STgen™ is reinforcing its biosecurity measures, avoiding any unnecessary movement of animals and continuing our quarantining processes. Additionally, our Bovine Genetic Business unit, STgenetics®, will be testing all new batches of STgenetics® frozen bull semen to provide assurances in the quality of semen leaving our facilities. Only batches that test negative will be released for commercial distribution. As we continue to learn more about highly pathogenic avian influenza (HPAI) we promise to keep our customers up to date on our findings and will continue our transparent communication to move our industry forward.
General Summary:
- Avian influenza virus H5N1 infects lactating dairy cows and is transmitted between them.
- The first cases were detected in January 2024, and viral sequence analysis suggests that the virus adapted to cattle by late 2023.
- Mortality due to infection in cattle is low or nil.
- The disease mainly affects milk production, but animals recover quickly.
- Milk from infected animals has high levels of viral particles, but pasteurization inactives the virus.- The virus has not been detected in non-lactating animals, nor have antibodies been detected in these animals despite exposure to sick lactating cows.
- There is no information on the possibility of infection in bulls.
- The possibility of H5N1 transmission through semen is unknown.
- The RT-qPCR test is highly sensitive and allows identification of viral particle presence.
Risk of transmission through semen:
- It is possible that bulls do not get infected (based on observations that only lactating animals become infected).
- The high level of biosecurity maintained by semen collection facilities greatly limits the chances of contagion.
- Semen frozen before the H5N1 outbreak in cattle should be considered free of risk.
- To ensure the safety of frozen semen, the RT-qPCR test can be used for each new batch of semen produced.
More Resources:
From the FDA
• Updates on Highly Pathogenic Avian Influenza (HPAI)
From the USDA
• HPAI Detections in Livestock Webpage
• APHIS Recommendations for HPAI in Livestock – Producers, Veterinarians and State Animal Health Officials
• APHIS Recommendations for HPAI Virus in Livestock – Workers
• Testing Recommendations for HPAI in Cattle
• Improving Biosecurity with Wildlife Management Practices: Preventing Access to Barns and Other Facilities
From the CDC
• Recommendations for Worker Protection and Use of PPE to Reduce Exposure to Novel Influenza A Viruses Associated with Severe Disease in Humans (English and Spanish)
• Protect Yourself from H5N1 When Working with Farm Animals
Scientific reports:
https://virological.org/t/preliminary-report-on-genomic-epidemiology-of-the-2024-h5n1-influenza-a-virus-outbreak-in-u-s-
cattle-part-1-of-2/970/2
https://wwwnc.cdc.gov/eid/article/30/7/24-0508_article
https://www.biorxiv.org/content/10.1101/2024.05.01.591751v1
https://www.biorxiv.org/content/10.1101/2024.04.16.588916v1
https://www.biorxiv.org/content/10.1101/2024.05.03.592326v1
Scientific commentaries:
https://www.science.org/content/article/scientists-call-new-measures-control-bird-flu-cows-drop-bucket
https://www.science.org/content/article/us-dairy-farm-worker-infected-as-bird-flu-spreads-to-cows-in-five-states
https://www.nature.com/articles/d41586-024-01256-
5#:~:text=US%20federal%20officials%20announced%20on,states%20as%20of%2030%20April.