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Tularemia
is caused by Francisella tularensis. Fifty percent of the cases have been reported in Missouri, Arkansas, and Oklahoma. Infection can be transmitted by tick bites (Dermacentor) or by handling animal carcasses such as rabbits, squirrels, beaver, muskrats, and deer. The diagnosis is suggested by the history of exposure, clinical progression, and generalized lymphadenopathy. The ulceroglandular form of tularemia is the most common clinical presentation and can present as more of a glandular form that lacks evidence of cutaneous lesions either because it healed before presentation or was minimal or atypical. Francisella is a facultative intracellular pathogen, so cell-mediated immunity involving TH1 cells and macrophages is most important for protection.

Francisella spp. are small, pale-staining, slow-growing, aerobic, gram-negative coccobacilli that optimally grow at 35° C. Francisella spp. also requires the presence of cysteine for growth as do Brucella, Legionella and Pasteurella. This can be remembered with the mnemonic "The 4 sisters "Ella" worship in the "Cysteine" chapel." Cysteine or cystine is required in the bacterial medium for growth. Granuloma formation would be the most common pathologic response, and granulomas are simply a manifestation of the type IV hypersensitivity response. The table below provides several examples of different Type IV hypersensitivities.
Ecthyma gangrenosum
the hallmark lesion of Pseudomonas aeruginosa infection. It is a common nosocomial infection in patients with cystic fibrosis, neutropenia, chronic granulomatous disease, or severe burns. P. aeruginosa is a gram-negative rod that is oxidase-positive, aerobic (and a facultative nonfermenter), and catalase-positive. It is a prodigious producer of a capsule (slime layer) and is also distinguished by its production of a blue-green pigment and a grapelike odor
Correct answer is D. This patient has toxoplasmosis, an infection caused by Toxoplasma gondii in immunocompromised hosts. Toxoplasma is a protozoan that infects humans who ingest the oocysts from cat feces or incompletely cooked lamb or pork.

Toxoplasmosis:

An opportunistic infection found in low CD4 HIV-AIDS patients (CD4<100) and fetuses.
MRI appearance of multiple ring-enhancing lesions with surrounding edema, characteristic of a brain abscess. A ring-enhancing lesion is a mass that contains a rim of contrast enhancement (bright signal on MRI) surrounding a dark core that corresponds to central necrosis.
In AIDS, the most frequent causes of a ring-enhancing lesion are primary brain lymphoma and toxoplasmosis.
In the fetus, toxoplasmosis causes extensive damage to brain parenchyma and retina.
Pyrimethamine and sulfadiazine is the treatment and prophylaxis of choice for Toxoplasmosis gondii infection in HIV-infected adults.
Anopheles mosquitoes (choice A) transmit malaria parasites. Cerebral malaria is caused by Plasmodium falciparum, which causes sludging of infected red blood cells in the small cerebral capillaries. Vascular occlusion ensues, resulting in numerous small infarcts. The pathology does not manifest itself as ring-enhancing lesion on MRI.

Bird droppings (choice B) represent the vehicle of infection for two of the most common opportunistic fungal infections affecting immunocompromised patients: cryptococcosis and histoplasmosis. Cryptococcus neoformans causes meningoencephalitis and can also cause "soap bubble" lesions (containing numerous Cryptococcus fungi) scattered through the brain. Affected patients would present with general malaise, meningeal signs, and altered mental status rather than focal neurologic signs. Histoplasma capsulatum rarely affects the brain. These fungi can be visualized in tissue sections by silver stains.

Cooling systems (choice C) may harbor Legionella pneumophila, spreading the bacteria in aerosolized form. L. pneumophila is a gram-negative bacterium that causes Legionnaire disease, a fatal form of pneumonia that first appeared in participants at a meeting of the American Legion. It has been reported in immunocompromised patients as well.

Rodent droppings (choice E) are the vehicle for hantavirus, which causes a fatal respiratory illness and is endemic to the desert Southwestern part of the United States.

Toxoplasma gondii is an intracellular, parasitic protozoan.
Cats are the definitive host; however, the most common source in the United States is poorly cooked pork.
Toxoplasmosis often affects people who are immunocompromised.
Treatment is with sulfadiazine and pyrimethamine.

MedEssentials (4th Ed.): pp. 127

First Aid (2018): pp. 177.1, 155.1-158.1

First Aid (2017): pp. 173.1, 151.1-154.1

First Aid (2016): pp. 160.1, 139.1-142.1
correct answer is C. This patient's history of alcohol abuse, nodular cirrhosis on examination, and elevated bilirubin all suggest that liver pathology may exist. Elevated erythropoietin (EPO) levels are indicative of hepatocellular carcinoma.

Ectopic overproduction of EPO stimulates red blood cell production and causes polycythemia (paraneoplastic erythrocytosis; inappropriate absolute polycythemia). Other EPO-secreting tumors include renal cell carcinoma, hemangioblastoma, and pheochromocytoma.

Types of polycythemia:

Types of Polycythemia
Chronic carbon monoxide exposure (choice B) causes a reactive polycythemia. Consider:

Occupational exposures: work in underground parking garages, taxi drivers with prolonged exposure to car pollution, and industrial workers.
Carboxyhemoglobin can give a falsely high oxygen saturation on pulse oximetry.
Increased carboxyhemoglobin and erythropoietin levels.
Polycythemia vera (choice D) causes primary polycythemia. It is a bone marrow disorder with proliferation of hematopoietic cells, characteristically associated with erythropoiesis, increased viscosity, and low levels of erythropoietin.

Reactive polycythemia (choice E) is a response to hypoxemia that results in an absolute increase in red cell mass. Decreased oxygen saturation on pulse oximetry and elevated erythropoietin level are present. It is commonly seen in:

Congenital cardiac malformations (choice A)
Chronic smokers
Chronic lung conditions (COPD, pulmonary fibrosis)
High altitudes

Polycythemia can be an important finding to suggest an underlying malignancy (paraneoplastic syndrome).
Hepatocellular carcinoma is associated with increased erythropoietin production (paraneoplastic syndrome).
Secondary polycythemia (e.g., tumors) is related to elevated erythropoietin levels and is distinguished from primary polycythemia vera, which diagnostically has low serum erythropoietin levels.

MedEssentials (4th Ed.): pp. 162

First Aid (2018): pp. 386.1, 421.2

First Aid (2017): pp. 375.1, 411.2

First Aid (2016): pp. 368.1, 404.2

Pathoma (2018): pp. 58.3, 123.3

Pathoma (2014-2017): pp. 58.3, 123.3
Polycythemia
A disorder characterized by an abnormal increase in the number of red blood cells in the blood