y Kent Andersen
There’s no doubt that the cases of avian influenza in US dairy cattle herds have come as unwelcome surprise. While animal to animal transmission is a factor in its spread among dairy cattle, the significance of human movements as a disease vector must not be forgotten.
The first case of avian influenza infection in dairy cattle was in Texas, and as of last week a total of seven states including Kansas, Ohio, Michigan, Idaho and New Mexico and now North Carolina have reported outbreaks of highly pathogenic avian influenza (HPAI) in dairy herds.
While animal to animal transmission is a factor in avian influenza spread among dairy cattle, the significance of human movements as a disease vector must not be forgotten.
Biosecurity recommendations for dairy farmers include monitoring cattle health, managing movement and transport, quarantining new animals, cleaning and disinfecting trucks or trailers, and limiting non-essential visitors.1
Additionally, some dairy farmers are reportedly chopping down trees to discourage wild birds, keeping water tanks clean and free from wild bird droppings, limiting visitors and disinfecting vehicle tires.2
The first cases of avian influenza in dairy cattle appear to have been due to introduction by wild birds, with subsequent cases possibly spreading cattle to cattle. As a result, the USDA is recommending minimizing the movement of cattle.
For any disease, animal movement creates a risk of spreading it through animal-to-animal contact. Agricultural officials say that Michigan and Ohio dairy herds with outbreaks of avian influenza received cattle from Texas.
In addition to animal-to-animal spread, the human factor must be considered as dairy producers ramp up biosecurity to protect their herds. Human movement, including vehicle movement, between premises, is potentially equally or even more important as has been seen in swine networks.
Using a full year’s worth of movement data from three large swine networks, Dr. Tara Prezioso DVM MPH at University of Illinois Department of Pathobiology confirms that the role of human and vehicle movements is more important that we think. Anonymized data was provided by Farm Health Guardian for her research. The data represents movements in and out of 455 properties over a 12-month period and includes over 500,000 visits. The properties include finishing sites, sow barns, feed mills and truck washes. The visit types include people, livestock and deadstock trucks, feed trucks and service vehicles.
Dr. Prezioso created and compared four groups of data, or subnetworks:
- Full network (all movements included)
- Human network (employees, visitors, maintenance, etc.)
- Animal network (only livestock and deadstock truck movements)
- Truck network (only truck visits for which there is no human contact e.g. feed delivery)
She aimed to see whether including the human movements into the network significantly changed the statistics and therefore how disease would spread. She theorized that a swine farm network including human movement will identify risk structures not present in animal movement networks alone.
The movement networks in the dairy sector are somewhat different from the swine industry, but the principle holds true. In addition to limiting animal movements, the role of people and vehicle movements needs to be factored in to protect dairy herds.
