MSC in Microbiology


Viruses usually infect one particular type of cell.

For example, common cold viruses infect only cells of the upper respiratory tract .

What are viral diseases?
Viral diseases are extremely widespread infections caused by viruses, a type of microorganism.

o Initiating an viral Infection require three points must be met to ensure successful infection in an individual host:
1. Sufficient virus must be available to initiate infection
2.
The cells at the site of infection must be susceptible for the virus.
3.
The local host antiviral defense systems must be absent or at least initially ineffective


There are four main effects of virus infection on the cell:
(1) Death
(2) Fusion of cells to form multinucleated cells
(3) Malignant transformation
(4) No apparent morphologic or functional change .


Compared with the number of drugs available to treat bacterial infections, the number of antiviral drugs is very small

The major reason for this difference is the difficulty in obtaining selective toxicity against viruses ; their replication is intimately involved with the normal synthetic processes of the cell.


Amantadine : This drug specifically inhibits influenza A virus

Maraviroc : blocks the binding of HIV to CCR-5
—an important co-receptor for those strains of HIV that use
CCR-5 for entry into the cell

Interferon : is effective in the treatment of some patients with chronic hepatitis B and chronic hepatitis C infections


Because few drugs are useful against viral infections, prevention of infection obtained by the using of vaccines is very important.

Prevention of viral diseases can be achieved by the use of vaccines that induce active immunity or by the administration of preformed antibody that provides passive immunity


The first human vaccines against viruses were based using weaker or attenuated viruses to generate immunity

British physician, Edward Jenner in 1796 he used matter from cowpox pustules to inoculate patients successfully against smallpox , which is caused by a related virus

By 1900, there were two human virus vaccines, against smallpox and rabies , and three bacterial vaccines against
Typhoid fever, Cholera and Plaque


There are two types of vaccines that induce active immunity: o Vaccine contain live virus whose pathogenicity has been attenuated o Vaccine contain killed virus.

Some vaccines, such as the hepatitis B vaccine, contain purified viral proteins and are often called subunit vaccines
Note: In general, live vaccines are preferred to vaccines containing killed virus because their protection is greater and longer-lasting.

Live, attenuated o Measles mumps, rubella (MMR combined vaccine) o Varicella (chickenpox) o Influenza (nasal spray) o Rotavirus o Yellow fever

Inactivated/Killed o Polio (IPV) o Hepatitis A o Rabies

There are many types of viruses that cause a wide variety of viral diseases.

HIV disease and AIDS

Hepatitis virus (HAV, HBV, HCV)

Mumps

Measles and Rubella

Dengue haemorrhagic fever

Herpes viruses infections

Rabies

Poliomyelitis
 Burkitt’s lymphoma


Influenza viruses are common pathogens of the upper respiratory tract

Influenza virus subtypes are designated by a nomenclature that is based on their surface glycoproteins
—namely,
Hemagglutinin (H) and Neuraminidase (N).

The first human influenza viruses to be isolated in the
1930s were designated H1N1 based on serological reactions.


In 1958, an antigenic shift resulted in the emergence of human H2N2 viruses, and in 1968, a shift to H3N2 viruses occurred; the latter strains have remained the most prevalent in recent years.

Emergence of new influenza strains in the human population occurs via transmission from other animal species, especially poultry.

Typically , human and avian influenza viruses are different and are not infectious for both species. However, pigs can become infected with both types of viruses, and act as a
“mixing vessel” to produce recombinant viruses capable of transmission to humans .


Occasionally, direct avian–human transmission can occur, often with enhanced pathogenicity, as demonstrated by the emergence of the recent H5N1 avian influenza in many countries throughout Southeast Asia; human-tohuman spread of H5N1 avian influenza has not been conclusively documented.


Corona viruses are a large family of viruses that can cause a range of illnesses in humans, from the common cold to s evere a cute r espiratory s yndrome (SARS).

The new strain of Coronavirus is MERS-CoV (formerly called
“novel coronavirus”) was first identified in
September 2012 among individuals with severe acute respiratory illness in Kingdom of Saudi Arabia

Like SARS, MERS spreads from close contact with an infected person.


Symptoms include: o High temperatures o Body aches o Sore throat o Running nose and cough.
o Shortness of breath o In most circumstances, these symptoms last for days and then disappear.

Mode of transmission:
•
The original source(s), route(s) of transmission to humans, and the mode(s) of human-to-human transmission have not been determined ; however there is clear evidence of person-to-person transmission.

Incubation Period:
•
Exactly not approved , but it is about from 7 to 10 days


The HIV infection is caused by the human immunodeficiency virus

HIV is an enveloped RNA virus

After HIV is in the body, it starts to destroy CD4+ cells , which are white blood cells that help the body fight infection and disease

AIDS is the most advanced stage of HIV infection( A cquired I mmune D eficiency S yndrome).


HIV is spread through contact with certain body fluids from a person infected with HIV. These body fluids include:

Blood

Vaginal & Semen fluids

Rectal fluids

Breast milk


Soon after infection with HIV, some people have flu-like symptoms, such as fever, headache, or rash.

The symptoms may come and go for a month .

After this earliest stage of HIV infection, HIV continues to multiply but at very low levels.

More severe symptoms of HIV infection, such as chronic diarrhea , rapid weight loss , and other signs of opportunistic infections , generally don’t appear for many years.

Opportunistic infections are occur more frequently or are more severe in people with weakened immune systems


The following criteria are used to determine if a person infected with HIV has AIDS:
 The person’s immune system is severely damaged as indicated by a CD4 count of less than 200 cells/mm 3 in a sample of blood. The CD4 count of a healthy person ranges from 500 to 1,600 cells/mm 3 .

The person has one or more opportunistic infections.


The use of HIV medicines to treat HIV infection is called antiretroviral therapy (ART).

ART involves taking a combination of HIV medicines
(called an HIV regimen) every day.

ART can’t cure HIV infection
, but it can help people infected with HIV live longer, healthier lives.

HIV medicines can also reduce the risk of transmission of
HIV.


Notes on Medical Virology , Author: Eman K. Aldigs,
Published by OMICS Group eBooks 731 Gull Ave, Foster
City. CA 94404, USA

Microbiology, Lippincott’s Illustrated Reviews . Cynthia
Nau Cornelissen, Bruce D. Fisher, Richard A. Harvey.
Third edition