Allergy

ALLERGIC REACTIONS

Some people are highly sensitive to one or more substances. These substances are called ALLERGENS and they are generally weak antigens. Antibodies to allergens combine with receptors on the body’s mast cells. Every person is not allergic to all allergens nor does the first exposure to an allergen causes Allergy. It only helps to form antibodies. However, on second exposure the allergens combine with anti body - bound mast cells.

This complexing causes the cells to burst and release histamines which are responsible for inflammatory responses. Allergic reactions are usually very rapid. The most common manifestations are  limitation of the mucous membrane, frequent sneezing, skin rashes, watering of eyes and inability to breathe.

When large amount of histamine is suddenly released by the mast cells, a severe allergic reaction occurs, that is known as Anaphylactic shock. For example some persons die even to a single dose of penicillin.

previous topic :Hepatitis

Hepatitis-Symptoms Types Treatment

HEPATITIS

Hepatitis may be defined as infection of liver caused by viruses like hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus, and hepatitis E virus (HEV). Hepatitis caused by other than HAV & HBV is called non - A non - B hepatitis. 

Hepatitis is also caused by cytomegalo virus, Epstein - Barr virus, yellow fever virus and Rubella virus. Viruses of herpes simplex, varicella and adenovirus can also cause severe hepatitis in immune compromised patients.

Approximately 4 million people in India suffer every year from one or the other form of acute viral hepatitis.

Hepatitis - A

It is formerly known as infectious” hepatitis or epidemic jaundice caused by hepatitis A virus. Risk of transmitting HAV is greatest from 2 weeks before and 1 week after the onset of jaundice. Incubation period of HAV is 15 to 45 days.

1.Hepatitis – A - Modes of transmission

a. Fecal-oral route- is the major route of transmission. It may occur by direct (person to person) contact (or) indirect by way of contaminated water, food or milk.
b. It rarely transmits through parental route and through sex (Homosexuals)

2. Hepatitis – A -Clinical features
The clinical symptoms of Hepatitis A occur in 3 phases

i. There is an initial prodromal phase lasting for 2 - 5 days characterised by anorexia (loss of appetite), nausea, malaise and mild fever. Severe vomiting may also occur.

ii. This is followed by Icteric phase with onset of jaundice, dark coloured urine and pale stools.

iii. Recovery phase is characterized by gradual resolution of symptoms.
3. Control and treatment  Pre exposure prophylaxis can be given to the  people who migrate to endemic area.
ii. Post exposure prophylaxis is with Immune serum globulin (0.02 mI/kg) given intramuscularly with in 2 weeks of exposure.
iii. There is no specific vaccine for HAV.

Hepatitis B

It is formerly known as “serum” hepatitis. U is caused by Hepatitis ‘B’ virus and transmitted usually by parenteral route. Hepatitis ‘B’ is a major public health problem in India.

HB virus is present in blood saliva, vaginal secretions and semen of infected persons. The disease may be transmitted to others either during the incubation period or acute phase of the disease. The Incubation period of HB virus is 45 to 180 days.

1. Hepatitis B-Mode of transmission

i. It is transmitted by transfusion of infected blood and blood products, dialysis, contaminated syringe needle pricks to skin and through surgical & dental procedures.
It may be transmitted from HBV carrier mothers to their babies.

ii. 2.Hepatitis B- Clinical features
The clinical symptoms of hepatitis B are similar to other types of viral hepatitis.
But it is complicated by carrier state and by chronic liver disease which nay follow the infection. Chronic liver disease may lead to primary liver cancer.

iii. 3.Hepatitis B- Prevention and treatment
There is no specific treatment for Hepatitis B. However, the following preventive measures can be taken in the form of vaccines.

i. Hepatitis Plasma derived vaccine
This vaccine is given in 3 does at 0, 1st and 6th months. Each dose contains 1 ml of vaccine. It should be given intramuscularly. Children under 10 years of age should be given half of the above close at same time intervals. Booster doses may be given a ter 3 - 8 years.

ii. Hepatitis B-Recombinant DNA - Yeast derived vaccine
This vaccine is given in a dose of 10-20 ig initially and again at 1st and 6th month.
If a person shows the symptoms immediately after receiving Hepatitis B positive blood, Hepatitis ‘B’ immunoglobin I (HBIG) injection may be given for protection. Two doses

cn HBIG should be given (0.05 to 0.07 mI/kg of body weight) at an interval of 30 days.

Hepatitis C

Hepatitis C virus is the commonest cause of post transfusion hepatitis. The virus is mainly transmitted through transfusion of contaminated blood products. 50% of cases are related to intravenous drug user’s needles.

The incubation period from 6 - 7 weeks. There is 50% incidence of chronic hepatitis, which may lead to cirrhosis of liver or liver cancer. Interferon is the only drug that has been found effective in the treatment of HCV infection.

Hepatitis D
Hepatitis D virus alone cannot cause hepatitis. Hepatitis 0 or Delta infection occurs either as a concomitant infection of HDV with hepatitis B or as a super infection. It occurs among drug addicts and hemophiliacs.
Delta hepatitis can be an acute or a chronic hepatitis with the latter frequently leading to hepatic cirrhosis. Treatment, prevention and mode of transmission are same as that of Hepatitis D.

Hepatitis E
The infection caused by the hepatitis E virus is essentially a water borne disease. After an incubation period of 2 - 9 weeks, a self limiting acute viral hepatitis appears, lasting for a period of several weeks, followed by recovery. Clinical features are similar to Hepatitis ‘A’ infection.

previous topic AIDS-HIV and AIDS-HIV symptoms and controlling measures

AIDS-Clinical Manifestations

Clinical Manifestations of AIDS

The clinical manifestation of AIDS Acquired immune deficiency syndrome occurs in 4 stages namely:

i. Initial infection of the virus and antibody production:
Most HIV - infected people have no symptoms for the first five years or so. Few patients may show mild illness like fever, sore throat and rash. HIV antibodies usually appear within 2 to 12 weeks in the blood stream. The period between HIV infection and antibody production is called “Window Period.

II. Asymptomatic carrier state:
Infected people have antibodies, but no overt signs of disease except persistent generalised lymphadenopathy. (enlargement of lymph nodes).

iii. Aids - Related complex (ARC):
ARC is due to damage to the immune system but without opportunistic infections and cancers.
ARC exhibits clinical features like Diarrhoea lasting longer than a month, fatigue, loss of more than 10% of body weight, fever, night sweats & generalised lymphadenopathy.

iv. Aids:
Aids is the last stage of HIV infection. A number of opportunistic infections and cancers occur at this stage. Death is due to uncontrolled or untreatable infection.
Opportunistic infections & cancers are Tuberculosis, kaposi sarcoma (cancer) oropharyngeal candidiasis, penumocysuis carinii pneumonia, recurrent skin infections.

3.   AIDS-Diagnosis
Aids is diagnosed by two methods namely
a. Clinical diagnosis and b. Laboratory diagnosis. a. Clinical diagnosis: An adult or adolescent (>12 years of age) is considered to have AIDS if at least 2 of the following major signs are present in combination with at least 1 of the minor signs listed below.

AIDS-Major signs-syptoms:

i. Weight loss> 10% body weight.
ii. Chronic diarrhoea for more than 1 month
iii. Prolonged fever for more than 1 month.

AIDS-Minor signs-syptoms:
I. Persistant cough for more than 1 month.
ii. Generalised pruritic dermatitis. 
iii. Oropharyngeal candidiasis
iv. Generalised lymphadenopathy.
v. History of Herpes zoster (a viral disease).

iii. AIDS-Laboratory diagnosis:
The AIDS can be diagnosed in a patient by using the following tests.
i. Elisa - Test and

 

ii. Tridot - Test which are Screening Tests and
iii. Western - Blot Test which is Confirmatory Test.
These tests are used to detect HIV antibodies. A person whose blood contains HIV antibodies is said to be HIV positive

AIDS- CONTROL
Aids is controlled by the following methods 

i. Educating the people to make life saving choices (avoiding indiscriminate sex, using condoms etc.).
ii. Intra venous drug users should be informed that the sharing of needles and syringes involves special risk.
iii. Womens suffering from Aids should avoid becoming pregnant because infection can be transmitted to her children.
iv. Blood should be screened for HIV1 and HIV2 before transfusion transfusion. Pre sterilised disposable needles, syringes should be used as far as possible.

5. AIDS- Treatment
At present there is no vaccine or cure for treatment of HIV infection. The drugs like zidovudine, didanosine, zalcitabine and stavudine are proved to be useful in prolonging the life of Aids patients.

AIDS-Acquired Immuno deficiency Syndrome

Acquired Immuno Deficiency Syndrome(AIDS)

The acquired Immuno-deficiency syndrome (AIDS) is fatal illness caused by a retrovirus called Human immuno-deficiency virus (HIV). The HI virus breaks down the body’s immune system, leaving the victim vulnerable to a host of life threatening opportunistic infections viz., neurological disorders or unusual malignancies. The term AIDS refers only to the last stage of the HIV infection. There are five groups of adults at risk for developing AIDS. They are

1. Homosexual or Bisexual males (60%)
2. Intravenous drug abusers (23%)
3. Recipients of blood and blood products (2%)
4. Heterosexual contacts (6%)
5. Haemophiliacs (1%)
1
The HIV is 10000th. of a millimetre in diameter. It is a protein capsule containing two short strands of genetic material (RNA) and enzymes. The virus replicates in actively dividing T4 lymphocytes and can remain in lymphoid cells. The virus has the unique ability to destroy human T4 helper cells or T -4 cells. (a type of human T - lymphocytes). There are two types of HIV. The most common virus HIV - 1 and a more recently discovered virus HIV -2. Once a person is infected, the virus remains in the body lifelong. The virus also infects other cells of immune system such as B-cells, macrophages, and nerve cells.

The incubation period of HI virus varies from few months to 6 years or more. When the virus reproduces, the infected T-helper cells are destroyed that leads to profound lymphopenia with a total lymphocyte count often below 500/mm3 of blood.

  HIV (AIDS)-TRANSMISSION
Human Immuno - deficiency virus is not transmitted by contamination that is insects or food or drinking water.

Human Immuno-deficiency virus is transmitted from person to person in the following ways.
i. Sexual transmission ii. Blood contact iii. Maternal - foetal transmission.

i. Sexual transmission:

AIDS is the first and foremost sexually transmitted disease. Veginal, anal or oral sex can spread AIDS from person to person. Adolescent girls and women above 45 years of age are more prone to get HIV infection.

ii. Blood Contact:

AIDS is transmitted by transfusion of contaminated blood. Needle sharing by drug users is also another method of transmission.

iii. Mother to child transmission:
HIV may pass from an infected mother to her foetus through
placenta orto her infant during delivery or by breast feeding.

HIV or AIDS  is not transmitted through following ways

also visit basics of immunity  and Hepatitis-symptoms-Types-Treatment

Immune System-Cells

Cells of the Immune System

The major cells of the immune system are lymphocytes. Lymphocytes that are critical for immune reactions are of two types namely B -cells and

T- cells. Both cells develop from stem cells located in the liver of the foetus and in bone marrow cells of adults. 

The lymphocytes which are differentiated in the bone marrow are B - Cells. The lymphocytes that migrate to thymus and differentiate under its influence are called T - cells. The young lymphocytes migrate to lymphoid tissues such as spleen, lymph nodes and tonsils where they undergo final maturation. Matured lymphocytes circulate in the body fluids. T-cells are responsible for cellular immunity and B- cells produce antibodies about 20 trillion per day. Both components require antigens to trigger them into action but they respond differently.

 

Antigens

An antigen is a substance when introduce into an individual, stimulates the production of an antibody with which it reacts. Antigens are large molecules of proteins or polysaccharides. Some of the antigens are the parts of microorganisms others include pollen, egg white, certain fruits, vegetables, chicken, feathers etc.

 

Antibodies

Antibodies are protein molecules called immunoglobulin (Ig). They are produced by lymphocytes. The antibodies inactivate antigens. An antibody  consists of four amino acid chains bounded together by disulphide bonds. Of the four chains two are long, heavy chains and two are short, light chains. All of them are arranged in the shape of the letter ‘Y’. The tail portion of antibody having two heavy chains is called constant fragment (Fc). On the tip of each short arm, an antigen- binding fragment (Fab) is present which specifically hold antigen.

Based upon the five types of heavy chains, the immunoglobulin's are classified into five major types. Light chains are similar in all

 

types of Immunoglobulin's.

lgG is the most important long acting antibody representing about 80% of the antibodies. The second important antibody is 1gM. IgA is called secretory antibody, found in tears, saliva and colostrum, (the first milk secreted by mother). IgD serves as a receptor site at the surface of B cells to secrete other antibodies. IgE plays an important role in allergic reactions by sensitizing cells to certain antigens.

previous topic is immunity basics

Immunity-Basics

IMMUNITY

The ability of the organisms to resist almost all types of toxins that damage the tissues and organs is called Immunity. The study of resistance towards disease is called Immunology. Protection against infectious disease is immune response which is concerned with the reaction of the body against foreign antigen.

I

MMUNITY TYPES:

Immunity against infectious diseases is of two important types viz.

1. Innate Immunity and 2. Acquired Immunity.

 

1. Innate immunity

Innate or native immunity is the resistance to infections which an individual possesses by virtue of his genetic and constitutional make up. It is not affected by prior contact with microorganisms or immunisation. The various organs in human body like epithelial surface, blood and tissues are naturally adapted for exhibiting immunity. Natural defence in the body is also mediated by

i. Microphages - Polymorpho - nuclear leucocytes and

ii. Macrophages - Histiocytes, reticulo endothelial cells and monocytes.

2. Acquired Immunity

The immunity that is acquired by an individual is known as Acquired immunity. Acquired immunity is of two types, namely

a. Active immunity b. passive immunity 

a. Active immunity:

If the resistance is developed as a result of an antigenic stimulus, it is called Active Immunity. For example a person who has recovered from an attack of measles develops Natural immunity.

b. Passive immunity:

If the resistance is transmitted to a recipient in a readymade form, it is known as passive immunity.

The acquired immunity is also of two types namely

i. Humoral immunity or B cell immunity ii. Cell mediated immunity or T cell immunity.

i. Humoral Immunity:

The term humor refers to plasma and lymph. The humoral immune system defends mostly against bacteria and viruses that enter the body fluids. The humoral immunity is antibody mediated.

ii.Cell mediated Immunity:

The cell mediated immune system is carried out by highly specialsed cells, which work against pathogens, including fungi and protista that have invaded host cells. The system also reacts against transplants. It is thought to be important in protecting the body from its own cells if they become cancerous.

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