INFECTIONS

 Bacterial infection is extracellular ,  viral & protozoal are intracellular , hence antibiotics don’t act   on viruses , but   the  body makes up by interferon.

In Diabetes , the high Bld sugar predisposes to bacterial infections , but not viral.       

 Infected-cell synthesis of RNA and proteins is inhibited globally. Interferon probably results in the death   of the infected cell.

Though the virus genes may aquire resistance to interferon or other host defence  factors like T cell , in immuno competent individuals , viral infections are generally well managed.   

MALARIA

Residents of endemic areas have immunity - natural as well as acquired.

IgM  antibodies are generally effective as well as T - cell immunity play a role. Pigmented Phagocytic cells arefound  in the liver, spleen, bone marrow etc.

Presence of abnormal Hb, Sickle trait , G6PD deficiency, Thalassaemia and Pyruvatekinase deficiency offer resistance.

Splenomegaly shows immunity and even though there is parasitaemia, there  is little fever.

 In the endemic areas fully mature parasites , i.e. gametocytes appear after 2 weeks and are harmless.

In Falciparum Malaria, hepatosplenomegaly is actually a sign of underlying defence mechanism, the spleen causing destruction of infected RBC's and liver presents the malaria antigen to cytotoxic T - cells.

      The natural history of malaria in immune individuals is primary fever followed by a latent period and relapses followed by acquired immunity or anaemia due to destruction of RBC's .

 TYPHOID

1.       Effective  Chemotherapy does not prevent complications.

              e.g. Haemorrhage and perforation.

2.       Immunity is humoral with somatic  and flagellar agglutinins produced to the S. typhi.

3.       Antibiotic Therapy increases the risk for Typhoid.

GANGRENE

          Gangrene can be

a)       only a subcutaneous cellulitis localized or spreading

b)       can be myonecrotic invading the muscle but

myonecrosis is relatively  uncommon as deep muscle has to be involved without an opening to outside for             anaerobic conditions to exist.

   Despite the fact that more than 30% of deep wounds are infected by Clostidia,the      incidence of myonecrosis is very low.

PARASITES

e.g, Tapeworms:

Taenia  solium causes  cysts formation throughout the body. It is harmless

Taenia  saginate (cysticercosis) also forms cysts .The larvae take 5 to20 yrs to die.Only the dead larvae can cause inflammation. Hence Treatment is harmful.

Taenia Echinococcus causes hydatid cyst, 70% of them cause solitary cyst in the right  lobe of liver, where it grows harmlessly many a  time.