Aetiologies – Other

Other aetiological agents implicated as causes of myocarditis are:

Bacteria

• Lyme disease
• Mycobacteria
• Mycoplasma
• Legionella
• Streptococcus species
• Chlamydia pneumonia

The image depicts a number of Gram-negative mycoplasma hominis and T-strain mycoplasma isolates which had been grown on agar medium.

Fungi

• Aspergillus
• Cryptococcus
• Candida

The image is a photomicrograph depicting the appearance of a conidiophore of the fungus Aspergillus flavus.

Parasites

The commonest cause of myocarditis and subsequent dilated cardiomyopathy worldwide is Chagas disease caused by the protozoan Trypanosoma cruzi [5]. This disease is endemic in Central and South America and most patients remain asymptomatic for many years after infection following which about 20% develop chronic heart failure.

The image depicts HeLa cell monolayer culture infected with Trypanosoma cruzi.

Immunocompromised individuals have a higher incidence of myocarditis and are more likely to be affected by toxoplasmosis.

• Trypanosoma cruzi Chagas disease
• Toxoplasmosis
• Schistosomiasis
• Trichinosis

Medicines and toxins

Many drugs and toxins have been implicated in the development of myocarditis. This may be via a direct toxic effect of the drug on the heart or an immunologically mediated mechanism. In addition, an allergic phenomenon with eosinophilic infiltration of the myocardium in response to a hypersensitivity reaction to drugs has been described.

Immunological diseases

• Diabetes mellitus
• Thyrotoxicosis
• Inflammatory bowel disease
• Systemic lupus erythematosus
• Giant cell myocarditis

Idiopathic

although up to half of cases of myocarditis are labelled idiopathic, a viral aetiology is often suspected but unproven. Studies on patients with idiopathic dilated cardiomyopathy found evidence of viral particles in endomyocardial biopsy specimens in up to two thirds of patients (reference Kuhl U, Pauschinger M, Noutsias M, et al. High prevalence of viral genomes and multiple viral infections in the myocardium of adults with idiopathic left ventricular dysfunction. Circulation 2005 Feb 22. 111(7):887-93)