Epizootic Hemorrhagic Disease or Blue Tongue
October 3, 2012
Today was a great day, slight north wind and seventy degrees. Enough to make a little fat boy thankful the heat is over. As if this drought wasn't enough, now we have a new problem in our cow herds. If you have a cow drooling and walking tender footed (lame) you probably have Epizootic Hemorrhagic Disease or possibly Blue Tongue.
About three to four weeks ago we started getting calls and examining animals which drooled, lost weight and had problems walking in the pastures. We thought about Blue Tongue and even considered some more severe vesicular diseases. Then we began to see and hear about dramatic deer losses in the area. Some producers found spots with seven to 10 deer carcasses in one spot while others found them floating in their dugouts. After reports of problems in Nebraska, Epizootic Hemorrhagic Disease (EHD) was suspected.
In deer EHD is a viral disease causing high fever, anorexia (off feed), respiratory distress and swelling of the tongue and conjunctivae (eye lids). The deer develop internal hemorrhages and usually die. In some cases the disease becomes chronic and they may recover in several weeks if the swelling of the tongue allows them to eat and drink.
The virus is carried by biting midges (sand gnats or no-see-ums) and transmitted to ruminants (domestic and wild) when bitten. The hot dry summer must have been the perfect formula for the late summer populations of the midges. EHD virus is a close relative to Blue Tongue virus. There are several strains of each type of virus so differentiation is difficult because clinical signs are very similar.
In our cattle herds we usually saw an indicator cow standing alone. She was reluctant to move and may be breathing hard with a lot of foam around her mouth. When rounded up and placed in a chute to examine, we usually found a temperature of 104–105 degrees Fahrenheit. Close examination of the muzzle and tongue revealed lesions with areas of the tongue surface and muzzle sloughing or falling away. These painful lesions prevent the animal from eating and drinking. We would generally see cracks and lameness (sore feet) making these animals unable to move about the pasture. These animals usually recover within a week to 10 days.
After the initial cow was diagnosed in about five to seven days we see more cows with similar signs. We've sent in blood samples for blue tongue and received a few positives. When the Animal Industry Board (state vet) became involved, they requested EHD testing also. The gold standard is an elisa test for the EHD virus. The EHD virus has been conclusively diagnosed in deer losses in southeastern South Dakota.
We have had reports of deer dying throughout our region. We receive calls and examine cows every day. I believe many producers with problems are not even bothering to call with problems. Dairy animals are not immune and we have seen several dairies with individual cases. Last week we tested a ewe which was down with a high fever. It seems to have become an epidemic in our area.
Of the hundred plus herds we have seen, most involve one to three cows. Several herds near large deer populations had as high as 20 percent of the cows in pasture infected. Even in these pastures we rarely saw calves with the disease. In one herd they may have spread the disease in their calves by working the calves with vaccines about 10 days before we saw temperature spikes in the calves. We have only seen a 1-2 percent death loss in pasture cattle. Usually it's cows which are weak and don't have the body reserves to survive the recovery period. Some other areas report losses in some herds of 20 percent, but we have not seen losses this high.
It is believed that high numbers of the herd have an in-apparent infection with the virus, spike a temperature and recover with no clinical signs. We cannot prove any affect on fertility in these cows, but generally high fevers in early to mid-gestation result in some type of embryonic death. Time will tell as we pregnancy examine these herds.
Good nutrition and mineral seems to be important in minimizing the problems resulting from infection. Lick tubs are being uses to substitute protein sources. We also recommend fly control. Pour-Ons have been effective, but sprays and misters work also. Herds using monthly fly control have seen few cases.
The area of heaviest infection is east of the Missouri River and south of Interstate 90. The good news is, the whole problem should end with the first frost and the midge dies. If you have questions, contact your veterinarian.