Cardiovascular System Infection - Myocarditis

DefinitionMyocarditis is inflammation of the heart muscle

(myocardium)

It resembles a heart attack but coronary arteries are not blocked

Myocarditis is most often due to the infection by1- Common viruses, such as Parvovirus B192- Non-viral pathogens (less commonly)

Borrelia burgdorferi (Lyme disease) Trypanosoma cruzi (Chagas disease)

Myocarditis could be caused by hypersensitivity response to drugs

The definition of myocarditis varies, but the central feature is an infection of the heart, with an inflammatory infiltrate, and damage to the heart muscle, without  the blockage of coronary arteries that define a heart attack (myocardial infarction) or other common non-infectious causes. 

Myocarditis may or may not include death (necrosis) of heart tissue

It may include Dilated cardiomyopathyDilated cardiomyopathy or DCM is a condition

in which the heart becomes weakened and enlarged, and cannot pump blood efficiently

The decreased heart function can affect the lungs, liver, and other body systems

Dilated cardiomyopathy or DCM Gross pathology of idiopathic cardiomyopathy

Opened left ventricle of heart shows a thickened, dilated left ventricle withsubendocardial fibrosis manifested as increased whiteness of endocardium autopsy

Cellular infiltration and cardiac necrosis

Histopathological image of myocarditis at autopsy in a patient with acute onset of congestive heart failure due to viral infection.

Myocarditis is associated with an autoimmune reaction

Streptococcal M protein and Coxsackie B virus have regions (epitopes) that are similar to cardiac protein myosin

M protein is a virulence factor that can be produced by certain species of Streptococcus

M protein is strongly anti-phagocytic protein and is a major virulence factor

 Cross-reactivity of anti-M protein antibodies with heart

muscle is the basis for Rheumatic fever

After the virus is gone, the immune system may attack cardiac myosin

Causes of MyocarditisIn Europe and North America, viruses are common

cause of myocarditis

Worldwide, however, the most common cause is Chagas disease, an illness endemic to Central and South America that is due to infection by the protozoan Trypanosoma cruzi

Transmission of trypanosomiasis occurs when the Winged bug  of the genus Triatoma deposits feces on the skin surface and subsequently bites; the human host then contaminating the bite area, with infected feces

Photomicrograph of Giemsa-stained Trypanosoma cruzi (CDC)

Triatoma infestans

Trypansoma cruzi parasite in a thin blood smear (CDC Photo)

Rhodnius prolixus nymphs and adult

Rhodnius prolixus

Triatoma infestans Panstrongylus geniculatus

Pathogenesis of Trypanosoma cruziHuman American trypanosomiasis, or Chagas disease, is a fatal

disease of humans

The disease has two forms, a trypomastigote found in human blood, and an amastigote found in tissues

The acute form usually goes unnoticed and may present as a localized swelling at the site of entry

In the chronic stage, 10 to 20 years after infection, the parasite invades the myofibrils of the heart causing myocarditis

The gradual autoimmune destruction of heart myocardium lead to cardiac enlargement and arrhythmias, and heart failure

Signs and symptomsThe acute phase lasts for the first few weeks or months of

infection. Mild symptoms can include fever, fatigue , headache, rash, loss of appetite, diarrhea, and vomiting

The signs on physical examination can include mild enlargement of the liver or spleen, swollen glands, and local swelling (a chagoma) where the parasite entered the body 

The symptomatic chronic stage affects the nervous system, digestive system, and heart

About two thirds of people with chronic symptoms have cardiac damage, including dilated cardiomyopathy, which causes heart rhythm abnormalities and may result in sudden death

Cardiac muscle pathology; Chagas disease

Heart radiology Chagas diseaseHeart pathology Chagas disease

Romaña's sign, the swelling of the child's eyelid, is a marker of acute Chagas disease. The swelling is due to bug feces being accidentally rubbed into the eye, or because the bite wound was on the same side of the child's face as the swelling. Photo courtesy of WHO/TDR.

Toxoplasma gondii infectionToxoplasma gondii is a species of parasitic

protozoa in the genus Toxoplasma

The definitive host of T. gondii is the cat, but the parasite can be carried by many warm-blooded animals (birds or  mammals, including humans)

Toxoplasmosis, the disease of which T. gondii is the causative agent, is usually minor and self-limiting but can have serious or fatal effects on a fetus whose mother first contracts the disease during pregnancy or on an immunocompromised human

Toxoplasma gondii Life cycle

Life cycle of T. gondii