#18,012
A little over two weeks after their first FAQ (Frequently Asked Questions) on HPAI H5N1 in dairy cattle we have new update, dated April 16th. I've selected some excerpts to highlight, but you'll want to follow the link to read the full 5-page document.
I'll have a brief comment after there break.
What is the appropriate nomenclature for this virus, now that it has appeared in dairy cows?
From USDA’s perspective, highly pathogenic avian influenza or H5N1 are the most scientifically accurate terms to describe this virus. This is also consistent with what the scientific community has continued to call the virus after it has affected other mammals. As a reminder, genomic sequencing of viruses isolated from cattle indicates there is no change to this virus that would make it more transmissible to or between humans, and the CDC considers risk to the public to be low at this time. However, people with more exposure to infected animals do have a greater risk of infection. Since the virus is not highly pathogenic in mammals, H5N1 is the most fitting of the two scientifically correct options. It is important to note that “highly pathogenic” refers to severe impact in birds, not necessarily in humans or cattle.
How did these cattle contract H5N1?
Wild migratory birds are believed to be the original source of the virus. However, the investigation to date also includes some cases where the virus spread was associated with cattle movements between herds. Additionally, we have similar evidence that the virus also spread from dairy cattle premises back into nearby poultry premises through an unknown route.
As a reminder, analysis sequences of viruses found in cattle thus far have not found changes to the virus that would make it more transmissible to humans and between people. While cases among humans in direct contact with infected animals are possible, CDC believes that the current risk to the public remains low.
Is this the same virus that has been in circulation among wild and commercial flocks in recent months, or is this a different virus?
Tests so far indicate that the virus detected in dairy cows is H5N1, Eurasian lineage goose/Guangdong clade 2.3.4.4b. This is the same clade that has been affecting wild birds and commercial poultry flocks and has caused sporadic infections in several species of wild mammals, and neonatal goats in one herd in the United States. A full list can be found here.
How is a case of H5N1 in cattle confirmed by USDA?
USDA encourages producers to work with their veterinarians to report cases of sick cattle to State Animal Health Officials and their APHIS Veterinary Services Area Veterinarian in Charge. Veterinarians should submit samples to a National Animal Health Laboratory Network (NAHLN) laboratory for initial testing. Samples with non-negative test results are then submitted to the National Veterinary Service Laboratories in Ames, Iowa for confirmatory testing. USDA considers a positive test result from testing performed by the NVSL as confirmation, and NVSL carries out viral genome sequencing.
Combined with the recent detections of H5N1 in baby goats in Minnesota, is there reason to be concerned H5N1 may spread to mammals more commonly than previously believed?
H5N1 has been found in wild birds, poultry flocks, several species of wild mammals, farm cats, and neonatal goats in one herd in the United States. A full list can be found here. Many species are susceptible to influenza viruses, including wildlife that often come into direct contact with wild birds. Many of these animals were likely infected after consuming or coming into contact with birds that were infected with H5N1. In the case of the neonatal goats in Minnesota, they were exposed to domestic birds (ducks and chickens) infected with H5N1 through shared pasture and a sole water source. However, recent testing indicates the virus has also been spread by cattle movements between herds.
Has USDA confirmed at this point that cow-to-cow transmission is a factor?Yes, although it is unclear exactly how virus is being moved around. We know that the virus is shed in milk at high concentrations; therefore, anything that comes in contact with unpasteurized milk, spilled milk, etc. may spread the virus. Biosecurity is always extremely important, including movement of humans, other animals, vehicles, and other objects (like milking equipment) or materials that may physically carry virus. USDA APHIS is continuing to examine herds that have diagnosed cows to better understand the mode of transmission. To date, we have not found significant concentration of virus in respiratory related samples, which indicates to us that respiratory transmission is not a primary means of transmission.
Why is APHIS taking a voluntary, rather than mandatory, approach to testing dairy herds?
It is important to keep in mind that while H5N1 is highly pathogenic in birds, that is not the case in cattle. At this time, APHIS does not think it would be practical, feasible or necessarily informative to require mandatory testing, for several reasons ranging from laboratory capacity to testing turnaround times. We are working actively to learn more about the emergence of H5N1 in cattle, but right now we are seeing that a small portion of the affected herds are becoming ill, and that the number of herds exhibiting symptoms is relatively small. For context, there are more than 26,000 dairy herds nationwide. We are strongly recommending testing before herds are moved between states, which should both give us more testing information, and should mitigate further state-to-state spread between herds.
If this is truly the best we can do, then we need to greatly improve our capacity for laboratory testing and investigating outbreaks before the next `unprecedented' event occurs.
The beef/dairy industry and government agencies are understandably keen to reassure the public of the safety of the food supply, and the very low risk to human health from infected cattle.
But bland reassurances, repeated without accompanying evidence, soon loses its powers of persuasion.
