micro sheet # 7 - Noor 7addaden

Micro 7th lec.
Date : 22/2/2011
Done By : Noor Haddadin
Virology

• Viral systemic infections
As we talked before, viruses in order to produce infection the must be attached to the cells as in the mucosal cells of respiratory tract and the it should enter through specific type of cells in order to replicate and produce infection. And once the virus is replicated it produces damage(lysis) in infected cells or it might only increase in number without damage. The virus is released from the infected cells by budding the transmitted to the blood stream and causes viraemia : (increase the particles of the virus in the blood stream). Also can transmit the virus into other organs (liver,spleen,CNS) can cause cirrhosis or meningitis and so on.
The first primary viraemia is not associated with clinical infection. The virus is present but without clinical features or symptoms.The cause for not having any symptoms in this vireamia stage maybe due the presence of humoral antibodies. If the virus overcomes these antibodies, secondary viraemia appears which is associated with more clinical symptoms of the disease, so these clincal features may take time to appear.

• Growth of viruses
Isolation of viruses is not always easy, if there is need to isloate, then we use one of the following:
- Cell and tissue culture : is used in research labs , here we obtain small biopsy (cell lines) directly from the organ, obtain the cells on the culture media , allow these cells to grow. If viruses appear in the culture they will produce cytopathic effect (CPE)
CPE : is a change in the appearance of the virus-infected cells.
- Primary cell lines: obtained directly from an animal and can keep the differentiated state for a short period days to weeks (limited life span).

- Continuous cell lines (permanent culture): have unlimited proliferation capacity and which origionated from embryos,tumors or transformed cells. These cells have abnormal chromosomal count, which can be used to study the CPE of the virus.


• Lab Diagnosis of viral infections:

1. Detection using cell culture : by cell culture the virus titer can be detected by counting plagues produced in cell monolayers. We count the holes produced by the virus and by that we know the infectivity of this virus.
The changes in the cells include: elongation ,lysis, swelling, multinucleated giant cells usually from viruses cauing malignancy. For example : cytomegalovirus and herps produce elongation or multinucleated giant cells. Influenza virus causes roundation and lysis in the cells.


2. Other methods to study cells is by using different mycroscopes or certain staining like (H&E) to detect the CPE of the virus.

3. Serological methods : if we have patient infected with any type of viruses, within 2 - 5 days, we can detect the antibodies that are formed against the virus’ antigens by preparing a blood sample.In the next week we take a second sample from the patient if the titer (level) if the antibodies increase 4 folds at least the patient is considered to be infected.

Also a definitive identification of the virus grown in cell culture or by cerological methods is made by using known antibody in one of several tests like : enzyme – linked immunosorbent assay (ELISA), agglutination,immunoflorecent technique , radioimmuno essay.

4. Molecular technology : accurate can recognise the subtype of the virus, can be done within 2 houres. We look for specific primer of the nucleic acid or glycoprotein of the virus’ envelope.It helps to study the genotype of the virus.

5. Cell culture : is used for the preperation of the vaccines.






• Viral respiratory tract infection

Viral and bacterial respiratory infection is common specially viruses, mainly sore throat the major symptom of viral or bacterial infection, associated with the mucosa of tonsils (tonsilitis).
Bacterial infection in the throat is associated with more inflamatory reaction, accumulation of pus, edema , redness and more easily to be recognised, where as the viral infection is usually mild.
Colds is reffered to runny nose, sore throat infection and tonsilitis can be easily spread to the miidle ear and to sinusis.
More in children due to less pathological barriers than adults so infection can easily spread. They have less antibodies on the mucosa of their RT.
Infection can spread from upper RT to lower.
Pneumonia is a mixed infection starts as viral and continues in bacterial.
Up to 90% of colds in URT infection is caused by viruses, only 10% or less is caused by bacteria, and 1% or less might be due to the 2 organisms. So it is not recommended to use antimicrobial agents, they may increase the severity of the disease in certain cases.
When sombody sneezes around 1000 – 10000 particles of viruses spread per 1 m . They can spread easily such saliva , contact or by working in the oral cavity.


• Upper respiratory diseases

1. Colds : watery to mucoid , purulent nasal discharge often proceeded by sore throat and bacterial infection
2. Pharyngitis (sore throat): inflamation of tonsils and pharynx and formation of pus occur in bacterial infection but in viral ones itching and redness are more common to appear.
3. Tonsilitis: alone is due to bacterial rarely to viral.
4. Sinusitis and otitis media : often is a mixed infection in children.
5. Influenza and influenza like viruses : starts in the URT in form of sore throat associated with fever (it reaches 39 C ) with short incubation period.

• Lower respiratory tract infection

Starts with cough due to multiplication of the virus in the superficial layers of the bronchi and bronchioles .
The following is caused by bacteria or viruses.
1. Acute bronchitis : inflamation of the bronchi , there are certain viruses that affect these bronchi more than others.
2. Acute bronchiolitis : more sever affects terminal bronchioles causes rapid breathing and continuous cough like wooping cough.
3. Pneumonia and bronchopneumonia : as we said starts with viral infection then is followed by severe inflamatory bacterial reaction.

• Viral respiratory pathogens

Orthomyxovirus : influenza virus
(Ortho from orthodox which means straight forward) so from its name once they are attached to the mucosa of RT will result in features of influenza.

In the past during the large outbreak of RT diseases in 1918 , millions of Europeans died from Influenza , and at that time they couldn’t imagine that the causitive agent of Influenza is a small partical cold virus , they thought it was bacteria. In 1933 they studied the general morphology of influenza virus, but the details like the spikes or nucleic acid later in the 1950’s.


Good Luck 