Hepatitis C virus.

 It is most often mild and anicteric but occasionally severe with fulminant hepatic failure. It is caused an RNA virus, which may be transmitted parenterally (a cause of post-transfusion hepatitis); the route of transmission undetermined in 40%-50% of cases
a. 90% of blood transfusion-related hepatitis is caused by hepatitis C.
b. 50% progress to chronic disease.
c. Increased risk for hepatocellular carcinoma.

d. Incubation period: ranges from 2 to 26 weeks, but averages 8 weeks.
-  Antibody is detected by enzyme-linked immunosorbent,assay (ELISA). The incubation period is between 2 and weeks with peak onset of illness 6-8 weeks after infection 
- Most patients progress to chronic liver disease, specifically chronic persistent hepatitis or chronic active hepatitis 
- Cirrhosis is common in patients with chronic active hepatitis and occurs in 20%-25% of infected patients. HCV is also associated with hepatocellular carcinoma.

e. Treatment and prevention: α-interferon is used to treat chronic hepatitis C. There is currently no vaccine available.

IMMUNITY AND RESISTANCE TO INFECTION

Body's resistance to infection depends upon:

I. Defence mechanisms at surfaces and portals of entry.

II. Nonspecific or innate immunity

Ill. Specific immune response.

Smallpox (variola)
 - vesicles are well synchronized (same stage of development) and cover the skin and mucous membranes.
 - vesicles rupture and leave pock marks with permanent scarring.

Psoriasis
1. Characterized by skin lesions that appear as scaly, white plaques.
2. Caused by rapid proliferation of the epidermis.
3. Autoimmune pathogenesis; exact mechanism is unclear.

Vitiligo is an autoimmune destruction of melanocytes resulting in areas of depigmentation.
 - commonly associated with other autoimmune diseases such as pernicious anemia, Addison's disease, and thyroid disease.
 - common in the Black population

Alcoholic (nutritional, Laennec’s) cirrhosis

Pathology
 
Liver is at first enlarged (fatty change), then return to normal size and lastly, it becomes slightly reduced in size (1.2 kg or more).
- Cirrhosis is micronodular then macronodular then mixed.   

M/E  
Hepatocytes:-  show fatty change that decreases progressively. Few hepatocytes show increased intracytoplasmic haemochromatosis. 
b. Fibrous septa:-  Regular margins between it and regenerating nodules.
 -Moderate lymphocytic infiltrate.      
 – Slight bile ductular proliferation.
 
Prognosis:-   It Progresses slowly over few years.