Dealing with Diphtheria in Calves By Heather Smith Thomas Nevada Rancher
Upper respiratory problems in cattle include diphtheria—which is infection and/or inflammation of the vocal folds of the larynx (voice box) at the back of the throat. Infection (necrotic laryngitis) and swelling from inflammation can be serious if it restricts the airways and makes breathing difficult. Dr. Steve Hendrick, Coaldale Veterinary Clinic, Coaldale, Alberta (a feedlot, dairy and cow-calf practice in southern Alberta) sees quite a few cases of diphtheria, in cow-calf operations and in feedlots. “It’s not something we deal with every day, but it happens fairly frequently, and today there are some better ways to treat severe cases.” Swelling in this area can restrict breathing, since air must travel through the larynx to get into the windpipe and on down to the lungs. “It can be very difficult for the animal to breathe, depending on how much swelling or trauma is involved in that area,” he says.
CAUSES – “We generally think that the trauma (opening the way for infection and inflammation) is caused by eating abrasive feeds like kochia or woody plants, or young calves trying to eat coarse straw. Trauma could also be caused by use of a tube feeder on baby calves. If the surface of that tube is rough instead of smooth (such as if it got chewed on when you were putting it into the calf’s mouth), or if it is forced down abruptly into the throat, it may scrape or
irritate the tissues of the larynx. This can result in infection and inflammation.” The infection is generally caused by pathogens that are present in the environment and commonly inhabit the upper respiratory tract. They simply need an opportunity to invade those tissues. “The main ‘bug’ that causes diphtheria is Fusobacterium necrophorum which is the same one that causes foot rot, liver abscesses and is often found in the gut and upper respiratory tract,” says Hendrick. “We also suspect that viruses such as IBR can play a role because they can damage the outer mucosa (lining of the respiratory tract) and open the way for the bacterial infection. In feedlots we also commonly see diphtheria in conjunction with histophilosis,” he says. Histophilus somni is a bacterium that lives in the nasal passages of cattle and sometimes causes an acute, often fatal, septicemic disease that can involve the respiratory, cardiovascular, musculoskeletal, or nervous system, especially if it becomes complicated with other infectious agents (viruses or bacteria). “When doing a necropsy after a calf has died from this type of septicemia, when I cut open the larynx, it’s quite common to find a secondary laryngitis. Many of the respiratory bacteria including Histophilus, Manheimia, Mycoplasma, etc. can also cause infections in the larynx as well, but Fusobacterium is the one we blame the most for diphtheria, especially in baby calves. In the feedlot, however, you can get variety of ‘bugs’ that may be involved,” he says.
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SYMPTOMS – The calf will usually show some difficulty breathing. Due to the swelling in the larynx (which narrows the opening), the calf must make more effort for every breath. “Air has to pass those swollen folds, so they are also constantly getting more irritated with each breath, rubbing against each other,” says Hendrick. If you are near the calf you can hear wheezing noises as he breathes. At first glance you may think he has pneumonia because he is struggling for breath, but if you observe the respiratory effort you can tell the difference. A calf with pneumonia has trouble pushing the air out (of damaged lungs) whereas a calf with diphtheria is making more effort to draw the air in. Also, a calf with diphtheria will often be drooling and slobbering frothy saliva because he has trouble swallowing; saliva drips from his mouth. “If the calf is so busy trying to breathe, he can’t take time to swallow, and it drools from the mouth. Extra salivation can also be due to irritation from sores in the mouth as well as the throat,” Hendrick says. Sometimes the infection is mainly in the mouth and not in the throat, and that’s not as much problem for the calf because he can still breathe. The larynx area serves as a valve, sending food down the esophagus and air down the windpipe. “Most of the time you are just breathing, and the valve only closes off the airway when you swallow. When the calf has trouble breathing he doesn’t take time to swallow,” says Hendrick. If swelling in the throat closes off the airway too much, the calf may suffocate. If he is wheezing and struggling for breath and staggering from lack of oxygen, it becomes an emergency. You may need to slice through the windpipe below the larynx (carefully cutting between the ribs of cartilage surrounding the windpipe—with a very clean, sharp knife), for the calf to breathe through. Diphtheria is seen most commonly in calves, but older animals are not completely immune and sometimes they can also be affected. A mature animal has a larger throat and windpipe, however, and may not have as much trouble breathing if this area becomes swollen. “The infection may still affect the larynx and in some cases cause enough scar tissue in the vocal folds to affect the animal’s voice,” says Hendrick. Some of these cows seem to lose their voice and can’t bawl as loud anymore.