Diphtheria

Overview of diphtheria

Microbial infections are common in the tropics and the subtropics. These regions have climatic and environmental conditions that are optimum for microbial growth. In due course of time, these diseases turn into epidemics and result in millions of fatalities. Diphtheria is one such disease caused by the bacterial species Corynebacterium diphtheriae. It is mainly observed in people who lack immunity due to nutritional deficits or for not being immunized in childhood.  In the year 2013, nearly 4700 cases of diphtheria were reported, with 3300 cases leading to death. Although the mortality rates have been brought down by a significant percentage, the current global burden is still quite high and needs to be addressed seriously.

What is diphtheria?

Diphtheria is a type of contagious disease triggered by the bacterium Corynebacterium diphtheria. It derives its name from the Greek term “diphthera” which means “leather hide”. The onset of the disease is marked by a sore throat and fever. In the more advanced stages, greyish or whitish patches appear in the throat. This partially blocks the air passage and produces a hoarse cough. It is preventable by means of adequate vaccinations.

How does the disease occur?

The pathogenesis of diphtheria is complex. The immunosuppressed people acquire the diphtheria bacilli in the nasopharynx. This pathogen then produces a particular toxin that impedes cellular protein synthesis. This is then followed by the destruction of the local tissues and the formation of pseudomembrane. The toxin generated at the site of this membrane is henceforth absorbed into the bloodstream and is circulated to the important tissues of the body. This toxin leads to certain serious complications such as- low platelet count (thrombocytopenia) and presence of protein in the urine (proteinuria). Another non-toxic variant of this pathogen can lead to mild pharyngitis, but do not give rise to the formation of pseudomembrane.

How does the disease spread?

Diphtheria is a highly communicable disease and spreads via human to human transmission. The disease mainly spreads via respiratory droplets discharged when the infected person coughs or sneezes. These droplets when inhaled by a healthy person cause infection. A direct contact with the skin lesions can also transmit the infection. Indirect infections may also take place if the patient uses any object which is later used by a healthy person. Sharing of common items of use such as towels, bed-sheets and utensils with the patient can also cause infection. Zoonotic transmission (animal to human transmission) is also possible, but rare.

What are the main signs and symptoms of the disease?

The symptoms of Diphtheria begin around 2-7 days (incubation period) after the infection. The disease mainly manifests through the following signs and symptoms-

• Low-grade fever (100.4^oF)
• Occasional chills
• Fatigue and general malaise
• Bluish discoloration of the skin (cyanosis)
• A sore throat
• Formation of a thick coating at the back of the throat
• Unusual hoarseness of the voice
• Barking cough
• A constant headache
• Problems in swallowing
• Difficulty breathing
• Smelly nasal discharge with blood
• Lymphadenopathy
• Increased heart rate
• Myocarditis
• Cranial and peripheral nerve palsies

What are the different types of diphtheria?

Based on the pathophysiology and the site affected, the following classification of the disease is done-

• Anterior nasal diphtheria: The onset of this type mimics common cold and flu. The patients tend to have a mucopurulent nasal discharge which may even contain blood. Clinical examination reveals the formation of a white membrane on the nasal septum. The comparatively low absorption of the toxins makes the symptoms mild.
• Pharyngeal and tonsillar diphtheria: The pharynx and the tonsils are the commonly affected sites in diphtheria. The systemic absorption of toxin is quite high in this case. The early symptoms of the disease include but are not limited to- mild fever, soreness of throat, general malaise and eating disorders (anorexia). Within 2-3 days, a bluish-white membrane develops on the tonsil and extends to cover a part of the soft palate. As the disease progresses, this membrane turns greenish, greyish or blackish along with bleeding. Mild to moderate mucosal erythema occurs in the vicinity of the membrane. Obstruction of the respiratory passage may occur at a later stage due to excessive pseudomembrane formation.
• Laryngeal diphtheria: It involves the larynx and often occurs as a progression of the pharyngeal type. The patients have fever, hoarseness of voice and a barking cough. Here also a membrane forms on the tonsil and the palate, which may lead to respiratory blockage. In the end stage, these patients may suffer from coma and death. In laryngeal diphtheria, the patients are often found to have swollen neck and throat, also known as “bull neck”. It is accompanied by a characteristic barking cough and hoarseness of voice. All these symptoms are collectively known as diphtheritic croup.
• Cutaneous diphtheria: It is also known as skin diphtheria. It mainly affects the inhabitants of the tropical zone. Rashes and ulcers form on the skin. These eruptions are usually very scaly with prominent borders and membrane. Microbes other than the Corynebacterium diphtheria may also be present at the site of infection. Some of the commonly affected sites in this type are the vulvovaginal area, the mucous membranes of the conjunctiva and the external auditory canal.

What are the main diagnostic criteria?

CDC has devised the following diagnostic criteria for the disease-

• Laboratory criteria: Includes throat culture and histopathologic diagnosis
• Clinical criteria: Upper respiratory tract illness, sore throat, low-grade fever, a sticky, dense grey pseudomembrane.

How can you treat and prevent the disease?

CDC recommends the following medications for diphtheria-

• Metronidazole
• Erythromycin: Given orally or injected
• Procaine Penicillin G: Intramuscular injection

The best prevention against this disease is to get vaccinated. The available vaccines are DTaP, Tdap, DT, and Td. These provide immunity from diphtheria and tetanus. DTap and DT are administered to children younger than 7 years of age. Diphtheria is a life-threatening disease that can lead to a number of serious complications and even death. Studies have shown that the overall case-fatality rate for diphtheria is as high as 20% in people less than 5 years or greater than 40 years of age. Timely immunizations along with booster doses can help minimize this burden to a considerable extent.

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