Sickle cell anaemia is a blood disorder inherited from parents in which the Red blood cells become rigid and sickle-shaped which may lead to different health issues such as anaemia, swelling in the hands and feet, bacterial infections and stroke.

It is an autosomal disorder linked to the recessive alleles.

It has not been eliminated from the African population because it provides immunity against malaria.

Falciparum malaria is the most prevalent malaria in the African continent which is responsible for deaths in this region.

People with sickle cell anaemia are less vulnerable to falciparum malaria.

So, the correct answer is 'It provides immunity against malaria'

Yellow fever is caused by a RNA virus of genus Flavivirus. This virus is transmitted by mosquito, Aedesaegypti in human beings.

Hey fever or Allergic rhinitis is inflammation of nasal airways. It occurs when an allergen is inhaled by an individual with sensitive immune system.

Common cold and AIDS are viral disease caused by rhinovirus and HIV virus respectively.

Streptococcus pneumoniaea and Haemophilus influenza bacteria causes pneumonia in humans which infects the alveoli of the lungs and cause severe problem in respiration.

Ranikhet disease is the disease of poultry in which chickens dies very quickly. This disease is caused by a virus that spread very quickly.

The primary and secondary immune response are carried out with the help of two special types of lymphocytes present in our blood called B-lymphocytes and T-lymphocytes.

Suspension of attenuated pathogen that are not able to cause disease, that stimulates antibody formation is called vaccine. It is prepared by killing the pathogen.

Inflammation at the spot of insect bit is result of chemical released by the body such as histamine and kinins in response to chemical released by insect in the body.

The treatment of snake bite by anit-venom is an example of artificial acquired passive immunity. Anti-venom neutralize the effect of venom in the body.

If a person has received a cut and is bleeding needs to be given anti-tetanus treatment. Anti-tetanus injection contains preformed antibodies to initiate quick response.

ELISA stands for enzyme linked immuno sorbent assay. ELISA is diagnostic test for AIDS.

Utilization of clothes used by AIDS patient do not cause HIV infection in healthy person. It is transmitted by utilization of syringe used by AIDS patient, foetus of AIDS infected mother and by breast feeding to children by AIDS patient.

Development of vaccine is difficult for AIDS because HIV gene undergoes mutation at rapid. Virus cannot be killed by antibiotics produced by vaccine.

Hepatitis D virus cannot survive independently and requires another hepatitis virus for its multiplication.

Cancerous cells are killed by radiation therapy to treat certain types of cancer. As cancer cells divide rapidly and can be easily killed by radiation.

AZT in full azidothymidine drug used to delay development of AIDS in patients although; this drug does not control the AIDS completely.

The cells of malignant tumors divide rapidly. The malignant tumors of organs that originate from mesoderm that causes angiosarcoma.

Thyroid cancer is treated by an isotope of Iodine called I-131. Iodine is essential for production of thyroxin hormone.

AID is caused due to HIV virus. Carrier of HIV virus person appears healthy. If a body ache last over 4 weeks and loss of body weight by 10% without any reason may be a symptom of AIDS.

Hepatitis B virus (HBV), hepatitis C virus (HCV), and HIV are the body fluid borne viruses that can spread from an infected person to a healthy person when body fluid with the virus enters the body. These viruses are spread through sexual contact, exposures to blood in health care settings, and behaviors associated with injection drug use. Because of these shared modes of transmission, persons living with or at risk for HIV are also at substantial risk of HBV and HCV infection.  The incubation period of HIV is not shorter; it can stay in the body of the infected individual for as long as many years without showing any symptom.

Benign tumors normally remain confined to their original location and do not spread to other parts. The malignant tumors are mass of proliferating cells that grow very rapidly. The mass of proliferating cells called neoplastic or tumors cells.

Addiction is a psychological attachment to certain effects such as euphoria and temporary feeling of well-being is associated with drugs and alcohols. These drive people to take them even these are not needed.

Dependence is the tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome is regular dose of drug or alcohol is suddenly discontinued.

Dope test is done to estimate the level of blood alcohol by analyzing the blood and urine sample. A drunken person is not able to take correct decision due to improper co-ordination of nervous system and feels free from all worries.