Photo by Ichtor, Dreamstime.com.
From a very young age, I was raised to fear tetanus, and I bet you were, too. It was my first introduction to the cold, cruel fact that teeny, tiny living things were out there and had the potential to hurt me (kill me!) if we didn't take care of that boo-boo pronto. However, what exactly IS tetanus? The disease has been around for thousands of years, but it wasn't until 1884 that Clostridium tetani, the rod-shaped bacterium at the heart of the disease, was first identified.
Over time, research has shown that the bacterium produces spores; that those spores are commonly found in aquatic sediments, soil and intestinal tracts; and that they can remain inactive but infectious for over 40 years. And although humans and livestock are exposed to these spores on a daily basis, they require an open wound to germinate. Deep wounds are particularly vulnerable to infection, because they are more likely to be contaminated with dirt and manure and less likely to be completely cleaned and exposed to air. This bacterium thrives in anaerobic environments (i.e., where oxygen is scarce or absent) and where tissue cells have died (necrosis) due to trauma. From the standpoint of livestock, small wounds created during birthing, disbudding, castrating, tail docking and shearing can serve as points of entry. The same goes for dog bites and other puncture wounds.
The bacterium's spores quickly multiply in necrotic tissue and produce an extracellular toxin, tetanospasmin, that infiltrates motor nerves along the wound. These nerves then pass the toxin along to the nerve tract and, ultimately, the spinal cord. Communication between the spinal cord and muscles is then blocked, and to make a long story short, rigorous muscle spasms result. These spasms can be so rigorous that they fracture bone and/or tear muscle. If enough toxin is produced at the wound site, the lymph system picks it up, delivers it to the bloodstream, and ultimately the entire central nervous system falls under attack.
This incubation period averages 10 to 14 days, and clinical signs can appear within seven to 21 days of infection. Early signs include muscle stiffness in the neck, hind legs and in the wound region, and initial muscle spasms usually occur in the jaw, hence the disease's nickname, lockjaw. Consequently, the animal will not be able to eat or drink. More general muscle stiffness will follow within a day and the animal may start to resemble a sawhorse in its stance. It may lack coordination and walk in an odd way. It may exhibit extreme reflexes in response to being handled or to sudden noises (it is common for infected sheep, goats and pigs to fall to the ground when startled). The animal's tail may be elevated. A protruding third eyelid may be evident. It could have a fixed stare. Bloating may occur. It might be sweating, breathing heavily and experience a rapid heart rate. Cardiac arrhythmias, tachycardia and hypertension can occur, and ultimately respiratory failure will transpire due to rigorous spasms of the larynx, diaphragm and intercostal muscles along the ribs. Death can occur within 10 days from when the first symptoms appear. Infected livestock have a 10 to 45 percent chance of surviving, depending on the animal and severity of the infection.
Treatment of an infected animal involves a thorough wound cleaning, significant doses of antitoxin and broad-spectrum antibiotics, and placing it in a quiet, dark and safe space. That said, response to treatment is usually poor. When it comes to tetanus, preventing it from getting a foothold is the best way to go. Prevention includes maintaining a clean operation by removing sharp metal debris in the pasture, barnyard or stall. However, accidents occur on even the cleanest farms, so vaccines are your best bet.
Active immunization means vaccinating with tetanus toxoid, an inactivated tetanus toxin, and following it up with a second injection in two to four weeks. The animal's body will begin to recognize the inactivated toxin and white blood cells will form antibodies in response. One to two weeks after the second injection, it will be fully prepared to produce those antibodies should it come into contact with the bacteria. The animal will remain protected for about a year. Booster injections should be given annually thereafter to maintain immunity. The caveat with active immunization is it does not provide immediate protection.
Passive immunization involves administering antitoxin to an animal that has been exposed to the disease and is either not vaccinated for tetanus or its vaccination history is unknown. Antitoxin contains antibodies to the tetanus toxin. It is derived from the blood of horses that have been actively vaccinated with tetanus solutions and processed in such a way as to contain high levels of antibodies. Antitoxin provides immediate but short-term (seven to 14 days) protection. Allergic reactions have occurred with a small number of animals, because it is derived from horse blood.
Tetanus is something we all want to avoid, not only for the sake of our livestock, but also for the sake of ourselves. Working around the farm, be it with fencing, around machinery, in dusty barns or while handling animals, can lead to the occasional puncture wound, laceration or splinter. Humans should receive a tetanus booster every 10 years. When was the last time YOU were vaccinated?
The author, a regular contributor to Farming, is a biologist who lives and farms in Vermont's Northeast Kingdom.