Study of Viruses and how they pertain to certain individuals, Lecture notes of Pharmaceutical Microbiology

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04.04.

Virology

MICROBIOLOGY III

General Properties of Viruses

✤ Viruses are the smallest obligate intracellular infective agents containing only one type of nucleic acid as their genome (DNA or RNA) ✤ They have no metabollic activity, they lack enzymes necessary for protein and nucleic acid synthesis. Thus they require a host for the mentioned processes to take place. ✤ Their sizes ranges from 30 - 200 nm the small pox / pox virus being the largest and the parvo virus being the smallest. ✤ The infective extracellular virus particle is called the virion.

CULTIVATION OF VIRUSES

✤ ANIMAL INOCULATION : Used for primary isolation of certain viruses, to study pathogenesis of viral diseases and viral oncogenesis. ✤ Infant or suckling mice are used in isolation of arboviruses and coxsackie viruses. ✤ Animals may be inoculated by several routes - intracerebral, sub- cutaneous, intraperitoneal or intranasal. ✤ Besides mice, animals like guinea pigs, rabbits and ferrets are also used.

✤ EMBRYONATED EGG INOCULATION: 7-12 days old ✤ Chorioallantoic membrane (CAM) : inoculated mainly for growing pox viruses where it produces visible lesions like pcks where each pock is derived from a single virion. ✤ Allantoic cavity : for growing influenze virus for vaccine production. ✤ Amniotic sac : primary isolation of influenza viruses ✤ Yolk sac Inoculation : cultivation of some viruses and certain bacteria (chlamydia and rickettsiea.

Herpes Viruses

✤ Viruses are the smallest obligate intracellular infective agents containing only one type of nucleic acid as their genome (DNA or RNA) ✤ They have no metabollic activity, they lack enzymes necessary for protein and nucleic acid synthesis. Thus they require a host for the mentioned processes to take place. ✤ Their sizes ranges from 30 - 200 nm the small pox / pox virus being the largest and the parvo virus being the smallest. ✤ The infective extracellular virus particle is called the virion.

HEPATITIS VIRUSES

✤ Viral hepatitis is a systemic disease with primary inflammation in the liver. There are 6 : Hepatitis A, B, C, D, E and G. Hep. B is a DNA virus while other A, C, D , E, G contain RNA genome.

Modes of Transmission

✤ (^) SEXUAL CONTACT : the most important mode of transmission among both homo and hetero. ✤ (^) Parenteral transmission : occur through blood after receiving infected blood transfusions, blood products, sharing contaminated syringes and needles as in drug abusers or accidental inoculation. ✤ (^) PERINATAL : From an infected motherto her child either transplacentallt or perinatally during labour.

E.L.I.S.A

✤ (^) Short for Enzyme-linked Immunosorbent assay test which is the most widely used screening test for HIV infection. ✤ (^) ELISA has sensitivity over 99.5% with test kits contaning both HIV 1 and HIV 2 antigens. An acceptabe alternative to serum is saliva for antibody testing by ELISA. ✤ (^) The antigen obtained is coated on the microtiter wells or other suitable solid surfaces. The test serum is asses and if antibodies are present it binds to the antigen. ✤ (^) After washing away the unbound serum, antihuman immunoglobulin linked to suitable enzyme is added followed by colour forming substrate. ✤ (^) If the test serum contains anti HIV antibodies, a visible detectable colour is formed. ✤ (^) Its positive when there is no colour and negative when there is. I think?

Lab Diagnosis

✤ SCREENING TESTS :

✤ ELISA

✤ (^) Rapid tests : Dot blot assay, particle agglutination and HIV spot and comb tests ✤ (^) Simple tests are based on ELISA particle. ✤ (^) SUPPLEMENTAL TESTS ✤ (^) Western Blot : HIV proteins are separated by polyacrylamide gel electrophoresis and the separated proteins are blotted on to strips of nitrocellulose paper. These strips are reacted with test sera. Antibodies to HIV proteins, if present in test serum, combine with different fragments of HIV. The position of the colour band on the strip indicates teh fragment of antigen with which antibodies have reacted. ✤ (^) Indirect Immunofluorescence: HIV infected cells are fixed onto glass slides n reacted with serum followed by fluorescein conjugated antihuman gamma globulin. Positive: apple green fluorescence. ✤ (^) Radio Immuno Precipitation assay.