Cryptococcosis

An infection acquired by inhalation of soil contaminated with the encapsulated yeast Cryptococcus neoformans, which may cause a self-limited pulmonary infection or disseminate, especially to the meninges, but sometimes to the skin, bones, viscera, or other sites.

Cryptococcosis is a defining opportunistic infection for AIDS, although patients with Hodgkin's or other lymphomas or sarcoidosis or those receiving long-term corticosteroid therapy are also at increased risk.

AIDS-associated cryptococcal infection may present with severe, progressive pneumonia with acute dyspnea and an x-ray pattern suggestive of Pneumocystis infection.

Primary lesions in the lungs are usually asymptomatic and self-limited

Pneumonia usually causes cough and other nonspecific respiratory symptoms. Rarely, pyelonephritis occurs with renal papillary necrosis development.

Most symptoms of cryptococcal meningitis are attributable to brain swelling and are usually nonspecific, including headache, blurred vision, confusion, depression, agitation, or other behavioral changes. Except for ocular or facial palsies, focal signs are rare until relatively late in the course of infections. Blindness may develop due to brain swelling or direct involvement of the optic tracts. Fever is usually low-grade and frequently absent.

Pernicious anaemia 

The special features are:

• Due to intrinsic factor deficiency
• Gastric atrophy with histamine fast achlorhydria
• Genetic basis (racial distribution and blood group A).
• Seen with auto immune disorders.
• Antibodies to parietal cells and to intrinsic factors are seen

Parathyroid hormone 

Parathyroid hormone (PTH) is a polypeptide (84 amino acid residues) secreted by the chief cells of the parathyroid glands (four glands: two in each of the superior and inferior lobes of the thyroid; total weight 120 mg).

The main action of PTH is to increase serum calcium and decrease serum phosphate.

Its actions are mediated by the bones and kidneys -
In bone, PTH stimulates osteoclastic bone resorption and inhibits osteoblastic bone deposition. The net effect is the release of calcium from bone.
In the kidney, PTH has the following effects:
- Increases calcium reabsorption.
- Decreases phosphate reabsorption.
- Increases 1-hydroxylation of 25-hydroxyvitamin D (i.e. activates vitamin D).

PTH also increases gastrointestinal calcium absorption. 

Rocky Mountain Spotted Fever (Spotted Fever; Tick Fever; Tick Typhus)

An acute febrile disease caused by Rickettsia rickettsii and transmitted by ixodid ticks, producing high fever, cough, and rash.

Symptoms and Signs

The incubation period averages 7 days but varies from 3 to 12 days; the shorter the incubation period, the more severe the infection. Onset is abrupt, with severe headache, chills, prostration, and muscular pains. Fever reaches 39.5 or 40° C (103 or 104° F) within several days and remains high (for 15 to 20 days in severe cases),

Between the 1st and 6th day of fever, most patients develop a rash on the wrists, ankles, palms, soles, and forearms that rapidly extends to the neck, face, axilla, buttocks, and trunk. Often, a warm water or alcohol compress brings out the rash. Initially macular and pink, it becomes maculopapular and darker. In about 4 days, the lesions become petechial and may coalesce to form large hemorrhagic areas that later ulcerate

Neurologic symptoms include headache, restlessness, insomnia, delirium, and coma, all indicative of encephalitis. Hypotension develops in severe cases. Hepatomegaly may be present, but jaundice is infrequent. Localized pneumonitis may occur. Untreated patients may develop pneumonia, tissue necrosis, and circulatory failure, with such sequelae as brain and heart damage. Cardiac arrest with sudden death occasionally occurs in fulminant cases.

TUBERCULOSIS

A chronic, recurrent infection, most commonly in the lungs

Etiology, Epidemiology, and Incidence

TB refers only to disease caused by Mycobacterium tuberculosis, M. bovis, or M. africanum. Other mycobacteria cause diseases similar to TB

Pathogenesis

The stages of TB are primary or initial infection, latent or dormant infection, and recrudescent or adult-type TB.

Primary TB may become active at any age, producing clinical TB in any organ, most often the apical area of the lung but also the kidney, long bones, vertebrae, lymph nodes, and other sites. Often, activation occurs within 1 to 2 yr of initial infection, but may be delayed years or decades and activate after onset of diabetes mellitus, during periods of stress, after treatment with corticosteroids or other immunosuppressants, in adolescence, or in later life (> 70 yr of age), but especially after HIV infection. The initial infection leaves nodular scars in the apices of one or both lungs, called Simon foci, which are the most common seeds for later active TB. The frequency of activation seems unaffected by calcified scars of primary infection (Ghon foci) or by residual calcified hilar lymph nodes. Subtotal gastrectomy and silicosis also predispose to development of active TB.

Pulmonary Tuberculosis

recrudescent disease occurs in nodular scars in the apex of one or both lungs (Simon foci) and may spread through the bronchi to other portions

Recrudescence may occur while a primary focus of TB is still healing but is more often delayed until some other disease facilitates reactivation of the infection.

In an immunocompetent person whose tuberculin test is positive (>= 10 mm), exposure to TB rarely results in a new infection, because T-lymphocyte immunity controls small, exogenous inocula promptly and completely.

Symptoms and Signs:

Cough is the most common symptom,

At first, it is minimally productive of yellow or green mucus, usually on rising in the morning, but becomes more productive as the disease progresses

Dyspnea may result from rupture of the lung or from a pleural effusion caused by a vigorous inflammatory reaction

Hilar lymphadenopathy is the most common finding in children. due to lymphatic drainage from a small lesion, usually located in the best ventilated portions of the lung (lower and middle lobes), where most of the inhaled organisms are carried.

swelling of the nodes is common

Untreated infection may progress to miliary TB or tuberculous meningitis and, if long neglected, rarely may lead to pulmonary cavitation.

TB in the elderly presents special problems. Long-dormant infection may reactivate, most commonly in the lung but sometimes in the brain or a kidney, long bone, vertebra, lymph node, or anywhere that bacilli were seeded during the primary infection earlier in life

TB may develop when infection in an old calcific lymph node reactivates and leaks caseous material into a lobar or segmental bronchus, causing a pneumonia that persists despite broad-spectrum antibiotic therapy.

With HIV infection, progression to clinical TB is much more common and rapid.

HIV also reduces both inflammatory reaction and cavitation of pulmonary lesions. As a result, a patient's chest x-ray may be normal, even though AFB are present in sufficient numbers to show on a sputum smear. Recrudescent TB is almost always indicated when such an infection develops while the CD4⁺ T-lymphocyte count is >= 200/µL. By contrast, the diagnosis is usually infection by M. avium-intracellulare if the CD4+ count is < 50. The latter is noninfectious for others.

Pleural TB develops when a small subpleural pulmonary lesion ruptures, extruding caseous material into the pleural space. The most common type, serous exudate, results from rupture of a pimple-sized lesion of primary TB and contains very few organisms.

Tuberculous empyema with or without bronchopleural fistula is caused by a more massive contamination of the pleural space resulting from rupture of a large tuberculous lesion. Such a rupture allows air to escape and collapse the lung. Either type requires prompt drainage of pus and initiation of multiple drug therapy

Extrapulmonary Tuberculosis

Remote tuberculous lesions can be considered as metastases from the primary site in the lung, comparable to metastases from a primary neoplasm. TB of the tonsils, lymph nodes, abdominal organs, bones, and joints were once commonly caused by ingestion of milk infected with M. bovis.

GENITOURINARY TUBERCULOSIS

The kidney is one of the most common sites for extrapulmonary (metastatic) TB. Often after decades of dormancy, a small cortical focus may enlarge and destroy a large part of the renal parenchyma.

Salpingo-oophoritis can be a complication of primary TB after onset of menarche, when the fallopian tubes become vascular.

TUBERCULOUS MENINGITIS

Spread of TB to the subarachnoid space may occur as part of generalized dissemination through the bloodstream or from a superficial tubercle in the brain

Symptoms are fever (temperature rising to 38.3° C [101° F]), unremitting headache, nausea, and drowsiness, which may progress to stupor and coma. Stiff neck (Brudzinski's sign) and straight leg raising are inconstant but are helpful signs, if present. Stages of tuberculous meningitis are (1) clear sensorium with abnormal CSF, (2) drowsiness or stupor with focal neurologic signs, and (3) coma. Likelihood that CNS defects will become permanent increases with the stage. Symptoms may progress suddenly if the lesion causes thrombosis of a major cerebral vessel.

Diagnosis is made by examining CSF. The most helpful CSF findings include a glucose level < 1/2 that in the serum and an elevated protein level along with a pleocytosis, largely of lymphocytes. Examination of CSF by PCR is most helpful, rapid, and highly specific.

MILIARY TUBERCULOSIS

When a tuberculous lesion leaks into a blood vessel, massive dissemination of organisms may occur, causing millions of 1- to 3-mm metastatic lesions. Such spread, named miliary because the lesions resemble millet seeds, is most common in children < 4 yr and in the elderly.

TUBERCULOUS LYMPHADENITIS

In primary infection with M. tuberculosis, the infection spreads from the infected site in the lung to the hilar nodes. If the inoculum is not too large, other nodes generally are not involved. However, if the infection is not controlled, other nodes in the superior mediastinum may become involved. If organisms reach the thoracic duct, general dissemination may occur. From the supraclavicular area, nodes in the anterior cervical chain may be inoculated, thus sowing the seeds for tuberculous lymphadenitis at a later time. Most infected nodes heal, but the organisms may lie dormant and viable for years or decades and can again multiply and produce active disease.

Strep viridans

Mixed species, all causing α-hemolysis.  All are protective normal flora which block adherence of other pathogens.  Low virulence, but can cause some diseases:

Sub-acute endocarditis can damage heart valves.

Abscesses can form which are necrotizing.  This is the primary cause of liver abscesses.

Dental caries are caused by Str. mutans.  High virulence due to lactic acid production from glucose fermentation.  This is why eating sugar rots teeth.  Also have surface enzymes which deposit plaque.