Diphtheria: Antitoxin & Vaccine

Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Diphtheria is no longer a major concern in many places. Read on to learn about the medicine and vaccine that have helped decrease the prevalence and severity of diphtheria.

What is Diphtheria?

You might have heard of diphtheria before. You know that it used to be a problem, but it's not common anymore. But what is diphtheria?

Diphtheria is caused by Corynebacterium diphtheriae, a type of bacteria. It is normally a respiratory infection. C. diphtheriae normally infects mucous membranes, particularly the throat. It grows thick, easily distinguished patches.

A patient with diphtheria, showing the characteristic gray patch in his throat.

The most dangerous aspects of diphtheria infection come from a toxin produced by the bacteria, creatively named diphtheria toxin. Even antibiotic treatments, which kill the bacteria, are not sufficient to cure a person from diphtheria, because the toxin is not removed by the antibiotic.

Diphtheria toxin is an incredibly potent toxin--just a small amount can be lethal to a human. Diphtheria toxin can stop host cells from producing their own proteins. Since proteins are essential for keeping a cell alive, the cell dies. The toxin attacks organs throughout the body, including the heart and liver.

Prior to the development of an antitoxin and vaccine, diphtheria was responsible for about 15,000 deaths per year in the United States. Now, there have only been two diphtheria cases reported in the United States between 2004 and 2015, according to the CDC.

Diphtheria Antitoxin

Since the toxin was found to be the most dangerous part of diphtheria infection, it makes sense that stopping the toxin would be a quick and easy way to save the lives of infected patients, right? You're not alone in thinking this way.

Diphtheria antitoxin (DAT) is made by inoculating horses with higher and higher doses of diphtheria bacteria. The horses would make antibodies against the toxin, which are separated out of the rest of the horse's blood.

The patient would then be injected with the DAT. The antibodies, produced in the horse, would attack the diphtheria toxin to help cure the patient of the diphtheria.

Unfortunately, this method of producing antitoxin is imperfect, meaning there are many opportunities for the serum to get contaminated. There have been several instances of patients getting other bacterial infections, such as tetanus, from DAT.

An old bottle of diphtheria antitoxin used to help treat diphtheria.

Due to the success of the diphtheria vaccine, DAT is no longer commonly given. DAT is only given to patients with confirmed diphtheria infection.

Diphtheria Vaccine

Preventing diphtheria infection is an even better idea than treating it. Prevention means no one has to worry about getting to the doctor to get treated on time. It also prevents the need of DAT, which can itself be dangerous. So, in many countries, a vaccine containing inactivated diphtheria toxin is on the normal childhood schedule.

Again, since diphtheria toxin is the dangerous part of infection, it is the target of vaccination. The diphtheria vaccine was made by inactivating the diphtheria toxin with formaldehyde. This left a structurally sound, but non-functioning version of the toxin. The toxin is used to train the immune system on what to recognize and destroy.

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