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  Case study of viral diseases, Biology tutorial

Acquired Immunodeficiency Syndrome (AIDS):

History:

The first cases of AIDS were identified in U.S.A in 1981 while virus which causes it was recognized in 1983 at institute Pasteur in Paris and later rediscovered in U.S.A. at National Cancer Institute in Bethesda. Ever since AIDS pandemic was identified.

Virology:

Virus causes AIDS is named as Human Immuno-deficiency virus (HIV) is the member of family Retroviridae and of sub-family Lentrivirinae. There are 2 variants of HIV (that is HIV - 1 and HIV - 2). The structure of two variants is similar, like all retroviruses. HIV has RNA in its core as genome. Genome is a single stranded RNA, Positive sense, of approx 9-10kb. Virion is approx 100 - l40nm in diameter with the cylindrical core. The genome has at least 5 extra replication genes. Virus is enveloped with different glycoproteins. Virus is enveloped with different glycoproteins.

Clinical Presentation:

After infection, a person may remain symptom-tree for years. The unknown proportion of infected people does experience fever, malaise and possible skin rashes between 21 weeks and 3 months after infection. From that point on an average of 5 - 9 years may pass before AIDS, once it has developed is extremely high and may reach 100% maybe the provocative finding in AIDS is that huge majority of people infected with HIV, have no symptoms at all but may be spreading disease. AIDS victim may be separated in three categories, The Dead, Dying and doomed. AIDS is classified by severe cellular dysfunction, otherwise unexplained severe opportunistic infections (like pneumorytist Carinii Pneumonia, PCP), and neurological disorders or selected malignancies comprising Kaposi sarcoma.

Major Signs:

  • 10% weight loss of body weight
  • Chronic diarrhoea for 1 month
  • Prolong fever for 1 month (intermittent of constant)

Minor Signs:

  • Persistent cough for 1 month
  • Generalized dermatitis
  • Chronic Progressive and disseminated herpes simplex infection.
  • Oropharygeal candidiasis
  • Generalized lymphadenipathy.

Pediatric AIDS is suspected in the infant or child presenting with at least two major signs related with at least 2 minor in absence of known causes of immunosuppression.

Diagnosis:

AIDS could be diagnosed in laboratory as follows

1. Cellular test to estimate ratio of helper (T4) and suppressor (T8) lymphocyte subtypes.

2. Antibody tests to identify HIV-antibodies.

3. ELISA, of which most laboratory implored. Type of ELISA for HIV antibody testing is known as competitive elisa.

Treatment:

No reliable anti-HIV therapy has been developed. Secondary opportunistic infections can be treated with drugs, surgery, and irradiation. AZT (antiviral drug) developed against HIV which looks capable has been found to have side effects of neurological disorders same applies to Ribavirin, that also is another antiviral drug. Alpha-Interferon has been tried but no consistent result was attained.

Vaccines:

No anti-HIV vaccine is obtainable till date. Different approaches toward development a vaccine are being investigated. Vaccine development against HIV is tricky as it mutates quickly, goes through latency, and resists immune responses which generally control viral infections. HIV also illustrated a marked variation, particularly in envelope antigens, yet parts of envelope proteins and most core protein are served.

Rabies:

Disease is as old as man existence. The virus rabies belongs to family Rhandoviridae and genus_Lyssavirus. The genome of virus is a single stranded RNA, Linear, non-segmented, and negative sense with molecular k weight of 4 million. Virion is enveloped. Infection is zoonostic, and is transmitted to man via bite of infected animal like Dogs. It causes the lethal form of encephalitis.

Epidemiology:

It is a natural infection of dogs, cats, bats and wild animal such as: wolf, fox, skunk etc. it could also be found in rodents and cattle. Infection by bite of vampire bats in central and South America is also the problem rabies spread. Animal which remains healthy after 10 days of bite can be considered as being free of virus. Viruses are present in saliva of infected animal generally 4 days before onset of symptoms of disease. Generally 15% of bitten individuals by the rabid animal developed disease. Rabies is more common after bites on head or neck rather than bites/wounds on limb. Rabies infection because of corneal transplantation had been reported. Spread of rabies virus is by bite if infected vampire hats in West Indies and Central and South America.

Pathogenesis and Pathology:

Following an animal bite, virus multiplies in peripheral tissue to the wound and spread to CNS via the nerves. Disease is virtually always fatal, frequently leading to death some cases of recovery had been reported but rare.

Death follows convulsion. There is little or no lesions of virus in CNS with little evidence of destructive effects on cells but the major changes are typical intra-cytoplasmic inclusions within the neurones known as negri bodies. They are particularly found in perivascular mononuclear infiltration and are stained by sellers stain.

Clinical Features/Symptoms:

Rabies infection start with non-specific constitutional pro- dronatal comprising fever, fatigue, musculo-skeletal pains, occular pains, nervousness, hypersensitivity to stimulus by generally excitement with tremor muscular contractions and convulsions: usually Spasm of muscles of swallowing therefore old name of disease- hydrophobia. There is presence of virus in saliva, skin, eyes and the brain. At this phase, there is hyper salivation, excessive sweating, hyperpyrexia,' hypotension and tarchychadia that are all autonomic disturbance of the infected animal/individuals.

This phase is followed by dumb condition of animal. Here, all the conditions in furious stage are aggravated and animal now becomes dumb-like and paralyzed. There is no hydrophobia in dumb stage.

Incubation Period:

The incubation period is generally long, taking approx 4-12 weeks when wound is on limb but at time take much more time. Incubation is though shorter if wound is on the head or neck (approx 10 days).

Isolation/Diagnosis:

Rabies virus could be isolated from specimens of tissue, brain, CSE saliva and urine. Specimens are inoculated in healthy vulnerable lab- mice intracerebrally. Observe for paralysis and convulsion. Proper diagnosis of Rabies is as follows:

1. Direct demonstration of virus in smear or brain tissues by electron microscopy or immunoflourescence demonstration of Rabies virus antigen.

2. Examination of brain smear by Selle's Stain to show inclusion bodies (negri bodies) that are stained RED.

Treatment and Controls:

Passive immunization is performed by injection of human anti- rabies immunoglobulin whereas active immunization must be started after passive immunization. Long incubation of rabies is the appropriate disease for prophylactic immunization after exposure.

The Control of rabies:

1) Government introduction of quarantine on influx of dog and other domestic animals in country.

2) Campaign on vaccination of domestic animals as done in some countries such as Latin America.

3) Pre-exposure vaccination is desirable for all persons who are at high risk of contact with rabid animals inside the country and approx travel 1mg to other countries.

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