Str. agalactiae

β-hemolytic, with its capsule being the major virulence factor.  Capsule inhibits phagocytosis and complement activation.  The CAMP factor (a hemolysin) is another virulence factor.

Group B strep are normally found in GI tracts and vaginas. 

Major disease is neonatal sepsis/meningitis after passage through infected birth canal.  May lead to meningitis, and CNS damage is high.  Mothers colonized with Group B strep should be treated pre-delivery.

Adrenocortical Hyperfunction (Hyperadrenalism)

Hypercortisolism (Cushing Syndrome) is caused by any condition that produces an elevation in glucocorticoid levels. The causes of this syndrome are 
A. Exogenous through administration of exogenous glucocorticoids; the most common causeB. Endogenous 
1. Hypothalamic-pituitary diseases causing hypersecretion of ACTH (Cushing disease)
2. Adrenocortical hyperplasia or neoplasia 
3. Ectopic ACTH secretion by nonendocrine neoplasms (paraneoplastic)

Pathological features 

- The main lesions of Cushing syndrome are found in the pituitary and adrenal glands. 
- The most common change in the pituitary, results from high levels of endogenous or exogenous  glucocorticoids, is termed Crooke hyaline change. In this condition, the normal granular, basophilic cytoplasm of the ACTH-producing cells in the anterior pituitary is replaced by homogeneous, lightly basophilic material. This is due to accumulation of intermediate keratin filaments in the cytoplasm. 
- There is one of four changes in the adrenal glands, which depends on the cause.
1. Cortical atrophy 
2. Diffuse hyperplasia
3. Nodular hyperplasia 
4. Adenoma, rarely a carcinoma 

1. In patients in whom the syndrome results from exogenous glucocorticoids, suppression of endogenous ACTH results in bilateral cortical atrophy, due to a lack of stimulation of the cortex by ACTH. In cases of endogenous hypercortisolism, in contrast, the adrenals either are hyperplastic or contain a cortical neoplasm. 
2. In Diffuse hyperplasia the adrenal cortex is diffusely thickened and yellow, as a result of an increase in the size and number of lipid-rich cells in the zonae fasciculata and reticularis. 
3. Nodular hyperplasia, which takes the form of bilateral, up to 2.0-cm, yellow nodules scattered throughout the cortex. 

4. Primary adrenocortical neoplasms causing Cushing syndrome may be benign or malignant. The  adrenocortical adenomas are yellow tumors surrounded by capsules, and most weigh < 30 gm .

Osteogenesis Imperfecta (OI) (Brittle bone diseases) 

It is a group of hereditary disorders caused by gene mutations that eventuate in defective synthesis of and thus premature degradation of type I collagen. The fundamental abnormality in all forms of OI is too little bone, resulting in extreme susceptibility to fractures. The bones show marked cortical thinning and attenuation of trabeculae. 

Extraskeletal manifestations also occur because type I collagen is a major component of extracellular matrix in other parts of the body. The classic finding of blue sclerae  is attributable to decreased scleral collagen content; this causes a relative transparency that allows the underlying choroid to be seen. Hearing loss can be related to conduction defects in the middle and inner ear bones, and small misshapen teeth are a result of dentin deficiency 

Aneurysm

An aneurysm is a localized abnormal dilation of a blood vessel or the heart

Types:
1. True aneurysm - it involves all three layers of the arterial wall (intima, media, and adventitia) or the attenuated wall of the heart.
 e.g. Atherosclerotic, syphilitic, and congenital aneurysms, and ventricular aneurysms that follow transmural myocardial infarctions. 

2 False aneurysm 
(also called pseudo-aneurysm) is a breach in the vascular wall leading to an extravascular hematoma that freely communicates with the intravascular space ("pulsating hematoma"). 
E.g. ventricular ruptures after MI that are contained by a pericardial adhesion
E.g. a leak at the junction of a vascular graft with a natural artery.

Aneurysms are classified by macroscopic shape and size 
Saccular aneurysms 

spherical outpouchings (involving only a portion of the vessel wall, and often contain thrombi. 

Fusiform aneurysms

diffuse, circumferential dilation of a long vascular segment; 

they vary in diameter and length and can involve extensive portions of the aortic arch, abdominal aorta, or even the iliacs.

Aortic Aneurysm 

The two most important causes are: 

1- atherosclerosis : the most common cause 
It causes thinning and weakening of the media. The intimal plaques compress the underlying media and also compromise nutrient and waste diffusion from the vascular lumen into the arterial wall. The media consequently undergoes degeneration and necrosis, thus allowing the dilation of the vessel 

2- cystic medial degeneration of the arterial media. E.g. Marfan syndrome.

3- Other causes include: trauma, congenital defects (e.g., berry aneurysms), infections (mycotic aneurysms), systemic diseases, such as vasculitis.

Mycotic  Aneurysm :  
Infection of a major artery that weakens its wall is called a mycotic aneurysm

possible complications: thrombosis and rupture. 

It can originate from: 
(1) embolization of a septic thrombus, usually as a complication of infective endocarditis 
(2) extension of an adjacent suppurative process; 
(3) circulating organisms directly infecting the arterial wall 

Mycotic AAAs are atherosclerotic lesions infected by lodging of circulating microorganisms in the wall 

- e.g.  bacteremia from a primary Salmonella gastroenteritis. 

Abdominal Aortic  Aneurysm

Atherosclerotic aneurysms occur most frequently in the abdominal aorta ,the common iliac arteries, the arch, and descending parts of the thoracic aorta can also be involved 

Pathogenesis 

AAA occurs more frequently in men and rarely develops before age 50. 

Atherosclerosis is a major cause of AAA 

 hereditary defects in structural components of the aorta (e.g., defective fibrillin production in Marfan disease affects elastic tissue synthesis) 
 
 Morphology :
  Usually positioned below the renal arteries and above the bifurcation of the aorta 
  
  AAA can be saccular or fusiform 
  
  as large as 15 cm in diameter, and as long as 25 cm. 
  
  Microscopically: atherosclerosis with destruction and thinning of the underlying aortic media 
  
  the aneurysm frequently contains a laminated mural thrombus
  
  Syphilitic Aneurysm 
  
  Caused by The spirochetes T. pallidum 
  
  Tertiary stage of syphilis can cause obliterative endarteritis of the involve small vessels in any part of the body, including the vasa vasorum of the aorta 
  
  This results in ischemic medial injury, leading to aneurysmal dilation of the aorta and aortic annulus, and eventually valvular insufficiency. 
  
  valvular insufficiency and massive volume overload lead to hypertrophy of the left ventricle. The greatly enlarged hearts are sometimes called "cor bovinum" (cow's heart).
  
  CLINICAL CONSEQUENCES
  
  1.  Rupture → massive potentially fatal hemorrhage 
  2. Obstruction of downstream vessel → tissue ischemic injury
  3. Embolism → from atheroma or mural thrombus 
  4. Impingement and compression on an adjacent structure 
  5. Presentation as an abdominal mass 

Hepatitis D virus—can only infect cells previously infected with hepatitis B. 
 Delta hepatitis (HDV) is associated with a 35-nm RNA virus composed of a delta antigen-bearing core surrounded by HBV's Ag coat;

HDV requires HBV for replication.

Delta hepatitis can cause quiescent HBV states to suddenly worsened . Its transmission is the same as that of HBV.
 
 Hepatitis E virus—a high mortality rate in infected pregnant women.

Hepatitis E (HEV) is caused by a single-stranded RNA virus. The disease is typically self-limited and does not evolve into chronic hepatitis; it may, however, be cholestatic.

Pregnant women may develop fulminant disease.

Transmission is by the fecal oral route.

HEV occurs mainly in India, Nepal, Pakistan, and Southeast Asia.
 

Parvoviruses
 - smallest DNA virus
 - erythema infectiosum (fifth disease) is characterized by a confluent rash usually beginning on the cheeks ("slapped face") which extends centripetally to involve the trunk; fever, malaise and respiratory problems; and arthralgias and joint swelling (50%).
 
 other associations:
 - aplastic anemia in patients with chronic hemolytic anemias (e.g., sickle cell disease, spherocytosis).
 - repeated abortions associated with hydrops fetalis.
 - pure RBC aplasia by involving the RBC precursors (no reticulocytes peripherally).
 -chronic arthritis