The human parechoviruses are members of the genus Parechovirus, of the Picornaviridae family. They are genetically similar to the enteroviruses. Infection may cause an undifferentiated febrile illness, and many cases have been reported in infants. They present with fever, irritability, and poor feeding. The illness may be associated with a rash (reported as macular, maculopapular, or erythematous). Infection may be severe and lead to shock. Neurologic manifestations may include meningitis, encephalitis, and acute flaccid paralysis. Gastrointestinal (GI) manifestations include the hemorrhage-hepatitis syndrome (hepatitis, thrombocytopenia, coagulopathy) in infants, necrotizing enterocolitis, and gastroenteritis. Human parechovirus infection (HPeV) has also been associated with myocarditis. There are 4 species of Parechovirus, of which only PeV-A causes disease in humans, with PeV-A3 most often associated with the most severe disease.

In July of 2022, the US Centers for Disease Control and Prevention (CDC) announced a health advisory relating to multiple reports of HPeV circulating in multiple US states. Reported cases present with fever, sepsis-like syndrome, or neurologic illness (eg, seizures, meningitis) in neonates and young infants. All specimens tested by the CDC for these recent cases have been type PeV-A3.

Symptoms of upper respiratory tract infection, fever, and rash are common in those aged between 6 months and 5 years. Both mild and acute GI illness with fever, diarrhea, and/or vomiting, has also been reported in children. However, in infants younger than 3 months, severe illness can occur, including a sepsis-like presentation, seizures, meningitis, and/or meningoencephalitis. Fulminant hepatitis has also been described. Intriguingly, the spinal fluid in infants with HPeV is often pauci-cellular (few to no white blood cells).

HPeV infection is less commonly reported in adults, perhaps due to immunity from previous exposure in childhood. In adults, it may present with a broad spectrum of clinical syndromes, including myalgia, muscular weakness, fever, sore throat, testicular pain, flaccid paralysis, and diarrhea, as well as increased creatine phosphokinase. There are also reports of adult myocarditis and adult pericarditis associated with HPeV infection.

Transmission can occur from both symptomatic and asymptomatic infected individuals via fecal-oral and respiratory routes. Shedding can occur for 1-3 weeks to 6 months from the GI tract following infection. The incubation period is unknown.

PeV-A3 demonstrates a cyclical pattern of infection with peaks occurring biennially.

Diagnosis is generally made by isolating viral RNA by nucleic acid testing, although few laboratories can also culture the virus. Commercial laboratory assays, multiplex platforms for meningitis and encephalitis, and testing through state public health laboratories are available to test cerebrospinal fluid (CSF) for PeV. CDC laboratory support is also available.

No specific antiviral therapy is available.