1. Cardiovascular System Infection - Myocarditis

2. Definition
Myocarditis 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 by
1- Common viruses, such as Parvovirus B19
2- Non-viral pathogens (less commonly)
Borrelia burgdorferi (Lyme disease)
Trypanosoma cruzi (Chagas disease)

3. 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. 

4. Myocarditis may or may not include death (necrosis) of heart tissue
It may include Dilated cardiomyopathy
Dilated 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

5. Dilated cardiomyopathy or DCM
Gross pathology of idiopathic cardiomyopathy
Opened left ventricle of heart shows a thickened, dilated left ventricle with subendocardial fibrosis manifested as increased whiteness of endocardium autopsy

6. 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.

7. 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

8. Causes of Myocarditis
In 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

9. Photomicrograph of Giemsa-stained Trypanosoma cruzi (CDC)
Triatoma infestans
Photomicrograph of Giemsa-stained Trypanosoma cruzi (CDC)
Trypansoma cruzi parasite in a thin blood smear (CDC Photo)

10. Rhodnius prolixus
Triatoma infestans
Panstrongylus geniculatus
Rhodnius prolixus nymphs and adult

11. Pathogenesis of Trypanosoma cruzi
Human 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

13. Signs and symptoms
The 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

14. Cardiac muscle 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.
Heart pathology Chagas disease
Heart radiology Chagas disease

15. Toxoplasma gondii infection
Toxoplasma 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

16. Toxoplasma gondii Life cycle

17. Life cycle of T. gondii