In this file:
· Can pigs become infected with ASF by eating flies?
· As candidates flock to Iowa State Fair, officials watch for African swine fever
Can pigs become infected with ASF by eating flies?
At present the only blood-feeding insect demonstrated to be a vector of African swine fever is the stable fly, which can maintain high levels of virus for 2-3 days.
Ann Hess, National Hog Farmer
Aug 09, 2019
A 2018 study entitled, “Infection of pigs with African swine fever virus via ingestion of stable flies” is making the rounds again as several industry experts try to make sense of the unexpected spread of African swine fever to farms in Eastern Europe with relatively decent biosecurity.
To investigate this possibility further, Danish researchers allowed pigs to ingest flies that had fed on ASFV‐spiked blood, which had a realistic titer for an infected pig. Some of the pigs became infected with the virus.
While it’s unlikely that ingestion of ASF-infected flies is a common route for transmission, the scientists say the results indicate that Stomoxys flies could be one possible route of transmission over short distances (e.g., within farms), while larger flies, such as the Tabanidae, might explain some longer distance examples of ASFV transmission (e.g., into and between farms). The researchers concluded that blood‐feeding flies could be a route for the observed, but unexplained, introduction of ASFV into farms with high biosecurity.
We know that ASF can be transmitted to pigs through feeding of food waste containing contaminated pork products as well as direct contact with infected pigs, their waste, blood, contaminated clothing, feed, equipment and vehicles, and in some cases, ticks. But we really haven’t talked about flies yet.
According to Peter Fernandez, a former Animal and Plant Health Inspection Service veterinarian, at present the only blood-feeding insect demonstrated to be a vector of ASF is the stable fly (Stomoxys calcitrans), which can maintain high levels of virus for 2-3 days and inject or transmit the virus to pigs up to 24 hours after virus ingestion.
“In experiments with purposefully infected stable flies, pigs that ate flies could also become infected,” Fernandez says. “Both of these are examples of mechanical transmission.”
The infectious disease epidemiologist says a number of experiments have attempted to investigate the possibility of other insects as competent vectors for ASF such as: hard ticks, blow fly larvae, lice, mosquitoes and mites. However, all provided little or no evidence of effective transmission.
“ASF virus is known to be transmitted by soft ticks of the genus Ornithodoros both in a natural sylvatic cycle among African warthogs and Ornithodoros moubata and also in domestic swine and Ornithodoros erraticus in the Iberian Peninsula,” Fernandez says. “This is the only known biological vector of ASF, which means the virus actually replicates in pigs and also in soft ticks. All other transmission mentioned is mechanical transmission which means there is no replication in the insect vector and the insect acts as a small ‘flying syringe.’”
While the mechanical transmission by flies seems pretty low on the totem pole in terms of transmission, future studies on the role of blood-feeding flies may be warranted...
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As candidates flock to Iowa State Fair, officials watch for African swine fever
By Jessie Higgins, UPI
Aug. 9, 2019
Aug. 9 (UPI) -- As presidential hopefuls flock to the Iowa State Fair this weekend, officials there will be on the lookout for an unseen intruder: African swine fever.
The state has increased its health inspection requirements for pigs brought to the fair, which began Thursday. The extra precautions are meant to guard against the deadly virus, which has decimated China's hog population and is currently sweeping across Asia and parts of Eastern Europe.
"It's not in the U.S. right now. It's not in the Western Hemisphere right now," said Dr. Dave Pyburn, the vice president of science and technology at the National Pork Board. "But if it were to get here, we don't want it to spread."
The disease was reported in China a year ago. It has since infected the entire country, wiping out 30 to 40 percent of its herd, analysts estimate. It is now spreading across Asia and into Europe.
Industry experts say the arrival of African swine fever in the United States could devastate the nation's pork industry. There is no treatment or vaccine for the disease -- which is nearly always deadly to hogs, but does not infect humans. That leaves only culling and biosecurity measures to contain an outbreak.
The U.S. Department of Agriculture is taking several steps to stop the disease from crossing the border by training dogs to sniff out pork smuggled in through luggage at airports and encouraging farms to institute more biosecurity measures.
That is exactly what Iowa State Fair officials are doing, Pyburn said...