Hand, Foot, and Mouth Disease (HFMD) is a common, highly contagious viral illness that typically affects infants and children, though adults can contract it as well. The disease is characterized by a distinctive rash on the hands and feet and painful sores in the mouth. A person can get HFMD back to back, sometimes shortly after recovery, because the body’s immune response is specific only to the exact strain of the virus that caused the initial illness. Understanding the biology of the virus explains why a second bout can occur so quickly.
The Role of Viral Strains in Repeat Infections
HFMD is caused by various types of viruses belonging to the Enterovirus family, not a single organism. These causative agents are categorized into different serotypes, which have distinct surface structures recognized by the immune system. The most common serotypes responsible for HFMD worldwide include Coxsackievirus A16 (CVA16), Enterovirus 71 (EV-A71), and Coxsackievirus A6 (CVA6).
When a person recovers from the disease, their body develops serotype-specific immunity to the exact strain that caused that particular infection. This provides robust protection against that one strain but offers little to no defense against the others circulating at the same time. If a child is infected with CVA16 and then exposed to EV-A71, they can contract the disease again because the immune system does not recognize the new serotype.
The lack of cross-protection between the different serotypes is the biological reason why a person may experience multiple infections in the same season, or even within a few weeks. The continuous circulation and emergence of various strains ensures that the risk of repeat infection remains present until the body has built immunity to all prevalent serotypes.
Typical Symptoms and Course of Illness
The initial phase of HFMD often begins subtly with general symptoms like a low-grade fever, reduced appetite, and a feeling of being unwell. This is followed by a sore throat, which precedes the appearance of the signature lesions. The incubation period, the time between exposure and symptom onset, typically ranges from three to six days.
The characteristic rash and mouth sores usually appear a day or two after the fever begins. The mouth lesions, known as enanthem, start as small, painful blisters inside the mouth and on the tongue that quickly turn into ulcers. The rash, or exanthem, consists of flat red spots or small blisters on the palms of the hands and soles of the feet, and sometimes on the buttocks or genitals.
The acute illness usually lasts for about seven to ten days, with most patients recovering completely without complications. However, the severity of the illness can vary significantly depending on the specific viral serotype involved. Infections caused by Enterovirus 71 (EV-A71) are associated with a higher risk of severe complications, including neurological problems like aseptic meningitis, compared to those caused by Coxsackievirus A16 (CVA16).
Reducing the Risk of Recurrence and Transmission
HFMD is spread through respiratory droplets, close personal contact, and contact with contaminated surfaces. Meticulous hygiene is the most effective defense against transmission and recurrence. Frequent handwashing with soap and water for at least 20 seconds is necessary, particularly after using the toilet, changing diapers, and before preparing food. Alcohol-based hand sanitizers are less effective than soap and water, especially when hands are visibly soiled with fecal matter, which is a major route of viral shedding.
Environmental cleaning is important because the virus can survive on surfaces for several hours. High-touch surfaces, such as doorknobs, countertops, and shared toys, must be disinfected regularly. Effective disinfectants for enteroviruses often include a solution containing bleach or cleaning products that specifically list active ingredients.
To limit the spread in group settings, children diagnosed with HFMD should be kept home until they are no longer contagious. Isolation is recommended until the child has been fever-free for 24 hours without medication and until all blisters have dried up or scabbed over. Avoiding close contact, such as hugging, kissing, and sharing eating utensils or cups, also helps prevent the virus from passing to others.