Worldwide, the top cause of heart muscle inflammation is a parasite, not a virus
In Europe and North America, myocarditis usually follows a viral infection. Across the whole planet, though, the leading cause is Chagas disease, spread by a single-celled parasite endemic to Central and South America. About 1.5 million acute cases occurred in 2013, most of them mild and most in young people.
Myocarditis means inflammation of the heart muscle itself. People may feel breathless, get chest pain, tire quickly during exercise or notice an irregular heartbeat, and the trouble can last hours or months. Because a virus is often behind it, many also report fever, aching joints, vomiting or diarrhoea, and it frequently arrives together with inflammation of the sac around the heart. In children the breathing difficulty of later stages is often mistaken for asthma. When inflammation persists and reshapes the ventricles, it can become a chronic cardiomyopathy and lead to heart failure.
Doctors divide it by tempo. Fulminant myocarditis erupts over hours to days, producing heart failure even at rest and needing drugs or machines to support circulation. The acute, non-fulminant form creeps in over days to months and does not require mechanical support. In rich countries the usual culprits are RNA viruses such as Coxsackie B3 and B5; the long list also includes influenza, parvovirus B19 and SARS-CoV-2. Toxoplasma, bacteria, autoimmune diseases like lupus, some chemotherapy drugs and stimulants such as cocaine can inflame the heart too.
Vaccines occasionally play a part. Smallpox vaccine can cause it, and regulators in the United States and Europe estimate about one case per 100,000 people after mRNA Covid-19 vaccination, with risk highest in males aged 16 to 29 after the second dose. During the SARS outbreak of 2002 to 2004, viral genetic material turned up in heart tissue from 35% of patients who died in the Toronto area, consistent with coronaviruses entering heart cells through ACE2 receptors.
Diagnosis combines an ECG, raised troponin, cardiac MRI and sometimes a biopsy, with ultrasound to exclude valve disease. Treatment may involve ACE inhibitors, beta blockers and diuretics plus a pause from exercise; severe cases can need a defibrillator or a new heart. Cardiomyopathy, including myocarditis, caused 354,000 deaths in 2015, up from 294,000 in 1990.
Source: Myocarditis
