Myocarditis, Lyme; Cardiac, Vascular Tumors

The HHV 8 antibody test would be most helpful in confirming the diagnosis of the gross and microscopic lesion shown in images 1A & 1B. HHV 8, also known as human herpesvirus 8 or Kaposi's sarcoma-associated herpesvirus (KSHV), is strongly associated with Kaposi's sarcoma, a cancer that can present with the type of lesions shown in the images. Therefore, testing for HHV 8 antibodies can help confirm the diagnosis of Kaposi's sarcoma in this case.

The most likely causative agent for the tricuspid vegetation in this case is Staphylococcus aureus. This is because the patient is a young "street kid" who uses intravenous drugs, which puts him at high risk for developing infective endocarditis. Staphylococcus aureus is a common cause of infective endocarditis in this population, and the presence of a heart murmur suggests an infection of the heart valves. Imaging revealing a tricuspid vegetation further supports the diagnosis of infective endocarditis caused by Staphylococcus aureus.

The obligate intracellular pathogens of the genera Rickettsia, Ehrlichia, and Anaplasma are transmitted by vectors, with Anaplasma being mainly transmitted by Ixodes ticks. These ticks can also be co-infected with Babesia or the agent of Lyme disease.

The presentation of severe headache, fever, malaise, macular rash, and tick exposure suggests a possible tick-borne illness. The presence of edema, petechial rash, and the spreading nature of the rash indicate endothelial cell invasion and cellular destruction. Tick-borne illnesses such as Rocky Mountain spotted fever or Lyme disease can cause damage to endothelial cells, leading to symptoms like rash, edema, and petechiae. Prompt treatment with doxycycline is necessary to prevent further complications.

The most likely microbial etiology for this patient's myocarditis is Coxsackievirus. Coxsackievirus is a common cause of viral myocarditis, which is inflammation of the heart muscle. The patient's symptoms of fever, myalgias, shortness of breath, and palpitations are consistent with myocarditis. The irregular pulse and enlarged heart on x-ray further support this diagnosis. Lyme disease, diphtheria, and Streptococcus pyogenes evoking acute rheumatic fever are not typically associated with myocarditis.

The correct answer is "Transmission by infected feces of reduvid bug after its bite." This is the preceding event in the disease because it suggests that the patient has contracted Chagas disease, which is caused by the parasite Trypanosoma cruzi. The symptoms described, such as palpitations, chest pain, dyspnea on exertion, and swollen ankles, are consistent with the cardiac manifestations of Chagas disease. The presence of cardiomegaly on the x-ray and ST-wave abnormalities on the EKG further support this diagnosis.

Ehrlichia differs from other Rickettsia in that it invades mononuclear leukocytes, while other Rickettsia typically invade polymorphonuclear leukocytes.

Rickettsia:
Immune Response:

Antibodies form but are not protective
Antibodies can be used for diagnosis; cross-reacting antibodies to Proteus vulgaris was basis for older Weil-Felix reaction
CD8+ T cells important in clearance of organisms by destroying infected endothelial cells
Interferon-γ and TNF-α activate infected endothelial cells to kill organisms

Biology of Rickettsia and Orientia

Obligate intracellular bacteria
Small : 0.3-1µm
Gram-negative - contain lipopolysaccharide and peptidoglycan
Serotyping by surface proteins called OmpA and OmpB
Invade vascular endothelial cells by phagocytosis
Escape from phagosome to cytoplasm where they obtain ATP, amino acids, and phosphorylated sugars

The patient's symptoms and physical examination findings suggest that he may have infective endocarditis, which is an infection of the heart valves. The presence of aortic diastolic murmur and sore red nodules on the tips of his fingers (known as Osler's nodes) are consistent with this diagnosis. In cases of infective endocarditis, the most common causative organism is Streptococcus viridans, which is catalase-negative, alpha hemolytic, and optochin resistant. Therefore, the correct answer is Catalase-negative, alpha hemolytic, optochin resistant.

Although a myxoma is not cancer, complications are common. Untreated, a myxoma can lead to an embolism (tumor cells breaking off and traveling with the bloodstream), which can block blood flow. Myxoma fragments can move to the brain, eye, or limbs.

If the tumor grows inside the heart, it can block blood flow through the mitral valve and cause symptoms of mitral stenosis. This may require emergency surgery to prevent sudden death.

Myxomas are the most common type of primary heart tumor.

The tumor is derived from multipotential mesenchymal cells and may cause a ball valve-type obstruction.

About 75% of myxomas occur in the left atrium of the heart, usually beginning in the wall that divides the two upper chambers of the heart. The rest are in the right atrium. Right atrial myxomas are sometimes associated with tricuspid stenosis and atrial fibrillation.

Myxomas are more common in women. About 10% of myxomas are passed down through families (inherited). Such tumors are called familial myxomas. They tend to occur in more than one part of the heart at a time, and often cause symptoms at a younger age than other myxomas

Bartonella (formerly known as Rochalimaea) is a genus of Gram-negative bacteria. Facultative intracellular parasites, Bartonella species can infect healthy people but are considered especially important as opportunistic pathogens. Bartonella are transmitted by insect vectors such as ticks, fleas, sand flies, and mosquitoes. At least eight Bartonella species or subspecies are known to infect humans.

Bartonella henselae is the organism responsible for cat scratch disease, a self-limited disease except in immunocompromised hosts.

The correct answer is flea. Murine typhus is caused by Rickettsia typhi, which is transmitted to humans through the bite of infected fleas. Fleas become infected when they feed on small mammals, such as rats, that carry the bacteria. When an infected flea bites a human, it can transmit the bacteria, leading to the development of murine typhus. This explains why an outbreak of murine typhus occurred and why affected patients experienced symptoms such as fever, headache, chills, and rash.

The patient's symptoms and physical examination findings are consistent with infective endocarditis. The presence of tender red nodules on his fingertips, splinter hemorrhages in fingernail beds, a Roth spot in the fundus, and a diastolic decrescendo murmur over the aortic and pulmonic areas suggest embolic phenomena. The blood cultures growing Streptococcus mutans indicate a bacterial infection. The likely order of events in his illness is that nonbacterial thrombi formed on his aortic valve, bacteria in the blood attached to the nonbacterial thrombi, and emboli caused infarcts in his fingers and eye.