Subacute bacterial endocarditis (also called endocarditis lenta) is a type of endocarditis

Endocarditis

Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves . Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices...

 (more specifically, infective

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 endocarditis).

It can be confused with essential mixed cryoglobulinemia.

It can be considered a form of Type III hypersensitivity

Type III hypersensitivity

Type III hypersensitivity occurs when antigens and antibodies are present in roughly equal amounts, causing extensive cross-linking.-Presentation:...

.

Causes

It is usually caused by a form of streptococci viridans

Streptococcus

Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...

 bacteria that normally live in the mouth and throat (Streptococcus mutans

Streptococcus mutans

Streptococcus mutans is a facultatively aerobic, Gram-positive coccus-shaped bacterium commonly found in the human oral cavity and is a significant contributor to tooth decay.The microbe was first described by J Kilian Clarke in 1924.-Introduction:...

, mitis, sanguis or milleri). Other strains of streptococci (bovis

Streptococcus bovis

Streptococcus bovis is a catalase- and oxidase-negative, non-motile, non-sporulating, Gram-positive lactic acid bacterium that grows as pairs or chains of cocci. It is a member of the Lancefield group D streptococci. Most strains are non- or gamma-hemolytic, but some also display alpha-hemolytic...

and equines) can also cause subacute

Course (medicine)

In medicine, a course of medication is a period of continuous treatment with a drug, sometimes with variable dosage. Treatment with some drugs should not end abruptly...

 endocarditis, usually in patients who have a form of gastrointestinal cancer

Gastrointestinal cancer

Gastrointestinal cancer refers to malignant conditions of the gastrointestinal tract, including the esophagus, stomach, biliary system, pancreas, bowels, and anus. The symptoms relate to the organ affected, and can include obstruction , abnormal bleeding, or other associated problems...

.

Prognosis

Underlying structural valve

Heart valve

A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...

 disease is usually present in patients before developing subacute endocarditis. It is less likely to lead to septic

Sepsis

Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...

 emboli

Embolism

In medicine, an embolism is the event of lodging of an embolus into a narrow capillary vessel of an arterial bed which causes a blockage in a distant part of the body.Embolization is...

 than is acute endocarditis, but subacute endocarditis has a relatively slow process of infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 and, if left untreated, can worsen for up to one year before it is fatal.

Summary
In cases of subacute bacterial endocarditis, the causative organism(streptococcus viridans) needs a previous heart valve disease to colonize and cause such disease.

On the other hand, in cases of acute bacterial endocarditis, the organism can colonize on the healthy heart valve, causing the disease.

Treatment

The standard treatment is with a minimum of four weeks of high-dose intravenous penicillin

Penicillin

Penicillin is a group of antibiotics derived from Penicillium fungi. They include penicillin G, procaine penicillin, benzathine penicillin, and penicillin V....

 with an aminoglycoside

Aminoglycoside

An aminoglycoside is a molecule or a portion of a molecule composed of amino-modifiedsugars.Several aminoglycosides function as antibiotics that are effective against certain types of bacteria...

 such as gentamicin

Gentamicin

Gentamicin is an aminoglycoside antibiotic, used to treat many types of bacterial infections, particularly those caused by Gram-negative organisms. However, gentamicin is not used for Neisseria gonorrhoeae, Neisseria meningitidis or Legionella pneumophila...

.

The use of high-dose antibiotics is largely based upon animal models.