Diphtheria is an upper respiratory problem in cattle characterized by an infection or inflammation of the vocal folds. It can be serious if swelling restricts the airway and makes breathing difficult.
Dr. Steve Hendrick of Coaldale Veterinary Clinic at Coaldale, Alta., 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 to the lungs. In severe, acute cases the calf may die of suffocation.
Hendrick says that they think eating abrasive feeds such as kochia or woody plants causes trauma, which opens the way for infection and inflammation. Coarse straw is also a suspect with young calves. Using a tube feeder on young calves can also damage tissue. If the tube’s surface is rough instead of smooth or if it is forced abruptly into the throat, it may scrape or irritate larynx tissue. This can result in infection and inflammation, says Hendrick.
Pathogens that are present in the environment and commonly inhabit the upper respiratory tract generally cause the infection. 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.
Viruses such as infectious bovine rhinotracheitis (IBR) can also play a role because they can damage the outer lining of the respiratory tract and open the way for bacterial infection, he adds. In feedlots, diphtheria is also commonly found with Histophilus somni, a bacterium that lives in nasal passages of cattle. Histophilus sometimes causes an acute, often fatal, septicemic disease that can involve the respiratory, cardiovascular, musculoskeletal, or nervous system. It’s especially deadly if it becomes complicated with other 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,” says Hendrick. Many of the respiratory bacteria including Histophilus, Mannheimia and Mycoplasma, can cause infections in the larynx, but Fusobacterium takes most of the blame for diphtheria, especially in baby calves, he adds.
“In the feedlot, however, you can get a variety of ‘bugs’ that may be involved,” he says.
The calf will usually have some difficulty breathing. Due to swelling in the larynx, which narrows the opening, each breath requires more effort from the calf.
“Air has to pass those swollen folds, so they are also constantly getting more irritated with each breath, rubbing against each other,” says Hendrick.
The calf may make wheezing noises as he breathes. At first glance it may look like pneumonia, but observing respiratory effort reveals the difference. A calf with pneumonia has trouble pushing air out of damaged lungs. A calf with diphtheria is making more effort to draw air in through the narrowed airway.
“Extra salivation can also be due to irritation from sores in the mouth as well as the throat,” Hendrick says. Sometimes infection is mainly in the mouth and not in the throat. In those cases, it’s not as much of a 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 in humans as well as animals, Hendrick adds.
“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. That often leads to continual drooling and frothy saliva.
If swelling in the throat closes 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. A producer may need to slice through the windpipe below the larynx, creating an opening for the calf to breathe. That means carefully cutting between the ribs of cartilage surrounding the windpipe with a very clean, sharp knife.
Diphtheria is seen most commonly in calves, but older animals are not completely immune. However, a mature animal has a larger throat and windpipe and may not have as much trouble breathing if this area swells.
“The infection may still affect the larynx and in some cases may 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 loudly anymore.
“Infection in the larynx is generally very responsive to oxytetracycline because this antibiotic has a good distribution throughout the body. We also have good luck with penicillin.”
Some people prefer to use the newer, longer-lasting drugs because then they don’t need to treat as often, says Hendrick. A person’s choice might come down to ability to catch the calf, he adds.
It may take a long time to overcome the infection. Every breath can damage the already swollen voice box which is why it takes a long time to heal. Blood supply to this area of the body is also limited which makes getting enough antibiotics to the infection more difficult. This is why treatment may have to be continued for several weeks.
“Producers need to talk to their own veterinarian regarding treatment and what might be recommended. Usually if treatment can be started early, if we can treat these animals for about a week or two, we can clear it up,” says Hendrick.
Hendrick says diphtheria is one disease that a person should keep treating until the infection has completely cleared up. If treatment stops too soon, the calf will relapse. It becomes a lot harder to clear the infection, and the calf may succumb to the disease.
Sometimes it may take as much as a month of treatment to overcome the disease, but there is a new way to help those persistent and serious cases.
“What we do now is use a tracheostomy insert, to bypass the swollen, irritated larynx and allow the calf to breathe through a hole in his windpipe. This insert comes in two pieces, and your veterinarian can place it into the calf’s windpipe below the larynx. We have great success with this in baby calves and in feedlot calves,” he says.
Hendrick says they’ve used inserts on calves that were close to suffocating. The insert gives the calf instant relief and helps the larynx heal.
“Usually the infection is already gone after a couple weeks’ treatment and this breathing bypass just takes away the irritation so the larynx can heal,” he explains.
One of Hendrick’s clients has a wife who is a vet-tech. She fits inserts into their calves herself when they have diphtheria on their ranch. Ranchers can learn how to fit inserts from their vets. But most will only have sporadic cases and would probably just have their veterinarian do it for them if they had a problem calf, says Hendrick.
“This can be an effective way to help a calf heal if it doesn’t respond enough to the initial week or two of antibiotics and is still having trouble breathing or isn’t improving adequately. It takes a bit of care when the calf has the insert, because it may plug up now and then with mucus,” he says.
Producers will need to check the insert regularly for mucus, he says. If it starts to plug up, a person can usually hear the calf making a wheezing sound as he breathes.
“If that happens you need to take the insert out and clean it. But once it’s clean the calf can breathe just fine again,” he explains.
Just as important as a good antibiotic is anti-inflammatory medication to reduce swelling and irritation in the throat. This can ease the calf’s breathing and also help irritated tissues start to heal.
“Talk to your veterinarian about what you should use. Often in the feedlot and on ranches we recommend using dexamethasone as a single dose, right at the beginning, to help reduce that swelling. We don’t want to repeat it because prolonged use of steroids tends to hinder the immune system, but the dexamethasone can certainly make a difference for the calf,” says Hendrick.
“There are also a number of non-steroidal anti-inflammatory drugs that can be used, but they are not as potent as some of the other options. Discuss this with your veterinarian and treat the calf as soon as you realize he has a problem. We also have to make sure we treat these calves long enough, with antibiotics,” he says.
By identifying diphtheria-stricken calves early, treating them for long enough and, if needed, easing their breathing, producers and vets can save these calves.
Heather Smith Thomas raises beef cattle with her husband on their ranch in Idaho. She writes articles for ag publications as well as books on horse care and cattle management.