Hepatitis A virus.
- Hepatitis A (HAV) is a self-limited hepatitis caused by an RNA virus 

- Symptoms last 2 to 4 weeks.
- There is no risk of developing chronic hepatitis in the future.
- Incubation period is short, lasting 2 to 6 weeks.
- Infection is identified by HAV-specific antibodies (IgM if acute, IgG if past disease).
- The usual route of infection is fecal-oral transmission by contaminated food. There is no carrier state and no chronic disease
- Laboratory diagnosis: ELISA test for IgM antibody.
- Vaccine: killed virus.
- Prevention: serum immunoglobulins are available.

Respiratory Pathology

A. Pulmonary infections

1. Bacterial pneumonia

a. Is an inflammatory process of infectious origin affecting the pulmonary parenchyma.

2. Bacterial infections include:

a. Streptococcus pneumoniae (most common).

b. Staphylococcus aureus.

c. Haemophilus influenzae.

d. Klebsiella pneumoniae.

e. Anaerobic bacteria from the mouth

(aspiration of oral secretions).

3. Viral infections include:

a. Influenza.

b. Parainfluenza.

c. Adenoviruses.

d. Respiratory syncytial virus.

Note: viruses can also cause pneumonia. Infection of the interstitial tissues, or interstitial pneumonia, is commonly associated with these types of infections.

Common symptoms include fever, dyspnea, and a productive cough

Two types:

(1) Lobar pneumonia

(a) Infection may spread through entire lobe(s) of lung. Intraalveolar exudates result in dense consolidations.

(b) Typical of S. pneumoniae infections.

(2) Bronchopneumonia

(a) Infection and inflammation spread through distal airways, extending from the bronchioles and alveoli. A patch distribution involving one or more lobes is observed.

(b) Typical of S. aureus, H. influenzae,and K.pneumoniae infection

Diseases that Produce a Productive Cough

Pneumonia

Lung abscess

Tuberculosis

Chronic bronchitis

Bronchiectasis

Bronchogenic carcinoma

Classification

Diseases of the respiratory system can be classified into four general areas:

• Obstructive Diseases (e.g., Emphysema, Bronchitis, Asthma)
• Restrictive Diseases (e.g., Fibrosis, Sarcoidosis, Alveolar Damage, Pleural Effusion)
• Vascular Diseases (e.g., Pulmonary Edema, Pulmonary Embolism, Pulmonary Hypertension)
• Infectious, Environmental and Other Diseases (e.g., Pneumonia, Tuberculosis, Asbestosis, Particulate Pollutants)

Aplasticanaemia and pancytopenia.

Aplastic anaemia is a reduction in all the formed elements of blood due to marrow hypoplasia.

Causes

- Primary or Idiopathic.
- Secondary to :

1    Drugs :

Antimetabolites and antimitotic agents.
Antiepileptics.
Phenylbutazone.
Chloramphenicol.

2    Industrial chemicals.

Benzene.
DDT and other insecticides.
TNT (used in explosives).

3    Ionising radiation

- Familial aplasia

Pancytopenia (or reduction in the formed elements of blood) can be caused  by other conditions also like:
-Subleukaemic acute leukaemia.
-Megaloblastic anaemia
-S.L.E.
-hypersplenism.
-Marrow infiltration by lymphomas  metastatic deposits, tuberculosis, myeloma etc

Features:
- Anaemia.
- Leucopenia upper respiratory infections.
- Thrombocytopenis :- petechiae and bruising.

Blood picture:

- Normocytic normochromic  anaemia with minimal anisopoikilocytosis in aplastic anaemia. Other causes of pancytopenia may show varying degrees of anisopoikilocytosis
- Neutropenia with hypergranulation and high alkaline phosphatase.
- Low platelet counts

Bone marrow:
- Hypoplastic (may have patches  of norm cellular or hyper cellular marrow) which may -> dry tap. .
- Increase in fat cells , fibroblasts , reticulum cells, lymphocytes and plasma cells
- Decrease in precursors of all three-Series.
- Underlying cause if any, of pancytopenia may be seen
 

Myocardial infarction (MI)—heart attack

A. Ischemia versus MI: Ischemia is a reversible mismatch between the supply and demand of oxygen. Infarction
is an irreversible mismatch that results in cell death caused by the lack of blood flow (oxygenation). For instance, chest pain caused by ischemia can be relieved by administering nitroglycerin (a vasodilator) to the patient. If the patient has an MI, the pain will not be relieved with nitroglycerin.

1. MIs most commonly occur when a coronary artery is occluded by a thrombus generated in an atherosclerotic artery.

2. Symptoms include:
a. Chest pain, shortness of breath.
b. Diaphoresis (sweating), clammy hands.
c. Nausea, vomiting.

3. Consequences:
a. Death (one third of patients).
b. Arrhythmias (most common immediate cause of death).
c. Congestive heart failure.
d. Myocardial rupture, which may result in death from cardiac tamponade.
e. Thrombus formation on infarcted tissue; may result in systemic embolism.
 

Chronic hepatitis

Chronic hepatitis occurs in 5%-10% of HBV infections and in well over 50% of HCV; it does not occur in HAV. Most chronic disease is due to chronic persistent hepatitis. The chronic form  is more likely to occur in the very old or very young, in males, in immunocompromised hosts, in Down's syndrome, and in dialysis patients.

a. Chronic persistent hepatitis is a benign, self-limited disease with a prolonged recovery. Patients are asymptomatic except for elevated transaminases. 

b. Chronic active hepatitis features chronic inflammation with hepatocyte destruction, resulting in cirrhosis and liver failure. 
(1) Etiology. HBV, HCV, HDV, drug toxicity, Wilson's disease, alcohol, a,-antitrypsin deficiency, and autoimmune  hepatitis are common etiologies.
(2) Clinical features may include fatigue, fever, malaise, anorexia, and elevated liver function tests. 
(3) Diagnosis is made by liver biopsy.

8. Carrier state for HBV and HCV may be either asymptomatic or with liver disease; in the latter case, the patient has elevate transaminases.
a. Incidence is most common in immunodeficient, drug addicted, Down's syndrome, and dialysis patients. 
b. Pathology of asymptomatic carriers shows "ground-glass"" hepatocytes with finely granular eosinophilic cytoplasm.

Keloids
1. Characterized by a progressively enlarging scar.
2. Caused by an abnormal accumulation of collagen at the site of injury.
3. More common in African-Americans.