Question

Read the following statements (i - iv) related to diseases and identify the correct statements.

(i) Droplet infection and animal bite are direct modes of transmission of diseases.
(ii) Tobacco smoke causes lung cancer.
(iii) Vectors like mosquitoes carry pathogens and infect people with waterborne diseases.
(iv) Proto oncogenes when activated can turn normal cells into cancerous cells.

Answer 1

Any harmful deviation from the normal structural or functional state of an organism, associated with certain signs and symptoms is called disease.

Transmission is the process by which disease causing microorganisms (pathogens) spread from one individual to another individual. Diseases or infections can be transmitted in many ways, it can be directly transmitted from one person to another, or with the help of a carrier.

There are two common modes of transmission of diseases:

1. Direct Transmission - The pathogen is transmitted directly from an infected person to a healthy person. For example, if a wounded person comes in contact with the blood of a hepatitis B infected patient, the wounded person might contract the disease.

Direct disease transmission include :

• Person to person transmission - Smallpox
• Droplet transmission - Tuberculosis (Mycobacterium tuberculosis)
• By skin contact - Ringworm infections (Trichophyton)
• Transmission through body fluids - AIDS (Human Immuno deficiency Virus)

Indirect Transmission - The pathogens are not transmitted directly from the infected person to a healthy person but through vectors such as flies, mosquitoes, dogs, etc.

Indirect disease transmission include :

• Airborne transmission - Common cold (Rhinovirus)
• Through contaminated objects - Chickenpox
• Through insects - Malaria (Plasmodium vivax)
• Contaminated food and water (faecal-oral route) - Typhoid (Salmonella typhi)
• Transmission through animals - Rabies

Transmission through animals is coming under indirect transmission of diseases, so statement i is incorrect.

Some disease causing microorganisms are transmitted by insects that feed on hosts such as birds, animals, and humans and carry infectious agents from them. For example malaria is a vector-borne disease, transmitted by female Anopheles mosquito. Waterborne disease are transmitted through contaminated food and water. This can be transmitted by vectors lik house flies not by mosquitoes. Hence statement iii is incorrect.

Figure : Vector-borne disease transmission

Proto oncogenes are a group of genes that cause normal cells to become cancerous when they are mutated. The mutant, cancer promoting forms of genes are referred to as oncogenes. The proto oncogene acts as a positive growth regulators in normal cells and is involved in promoting the differentiation and proliferation of cells.

Mutations can cause hyperactivity in proto oncogenes and can lead to the formation of tumors. Hence statement iv is correct.

Figure : Activation of proto oncogene

Tobacco products increase the risk for lung cancer by damaging the cells that line the lungs. Tobacco contains cancer causing agents (acetaldehyde, isoprene etc.) or carcinogens that change the tissues line the respiratory tract results in cancer of the mouth, throat, oesophagus, stomach, voice box (larynx), trachea, bronchus etc. Hence statement ii is correct.

Figure : Mouth cancer caused by smoking