Disease Causative Agents

• Measles, mumps, rubella, and varicella (commonly known as chickenpox), influenza are the chronic diseases of a virus. 
• These can be prevented from spreading by using vaccines. This vaccine works by prior exposure of a small dose of the virus or a protein from the virus, which activates the immune response.

Some infectious diseases can be passed from person to person. Some are transmitted by bites from insects or animals. And others are acquired by ingesting contaminated food or water or being exposed to organisms in the environment. Therefore, (d) is the correct answer.

Pathogen is the term used to describe an infectious agent that causes disease in the host. Therefore, (a) is the correct answer.

Air, water and soil are carriers of infectious organisms. Soil can cause contamination of plants and infect them and hence, the human. Air is the most common carriers of pathogens around us. Therefore, (d) is the correct answer.

There are numerous ways through which infections can be transmitted. Coughing by the infected person can cause transfer as the organisms coming out are inhaled by the healthy person. No use of proper sanitization can also cause transmission of diseases. Therefore, (b) is the correct answer.

Explanation: It is an actual infectious disease of cattle, buffalo, sheep and goat. It distances transportation. In India, the disease is enzootic in nature. Etiology environmental conditions, malnutrition and long distance transportation. In India, the disease is enzootic in nature.

Biological agents which cause disease are known as pathogens that are the micro-organisms which when successfully infect the human body, multiply and produce toxins in incubation period which interfere with the normal functioning of the body and cause disease. A virus is a small, infectious, biological agent that replicates only inside the living cells of other organisms.

Pneumonia is an inflammatory condition of the lung affecting primarily the small air sacs known as alveoli. Symptoms include some combination of a productive or a dry cough, chest pain, fever, and trouble breathing. Pneumonia may spread via airborne droplets from a cough or sneeze. Pneumonia is usually caused by infection with viruses or bacteria and less commonly by other microorganisms, certain medications and conditions such as autoimmune diseases.

• Measles is a highly contagious infectious disease caused by the measles virus. Symptoms include fever, often greater than 40 °C, cough, runny nose, and inflamed eyes. Measles is an airborne disease which spreads easily through the coughs and sneezes of infected people.
  
• Diphtheria is an infection caused by the bacterium Corynebacterium diphtheriae. Symptoms include a sore throat and fever. In severe cases, a grey or white patch develops in the throat. Diphtheria is usually spread between people by direct contact or through the air (droplet).
  
• Pertussis, commonly known as a Whooping cough is a highly contagious bacterial disease. Symptoms include a runny nose, fever, and cough. Pertussis is caused by the bacterium Bordetella pertussis. It is an airborne disease which spreads easily through the coughs and sneezes of an infected person.
• Gonorrhoea is a sexually transmitted infection caused by the bacterium Neisseria gonorrhoeae. Symptoms include burning with urination, discharge from the penis, or testicular pain. Women may have burning with urination, vaginal discharge, vaginal bleeding between periods, or pelvic pain. Hence, it is not transmitted by droplets.

• Droplet infection is an infection transmitted from one individual to another by droplets of moisture expelled from the upper respiratory tract through sneezing or coughing.
• Pneumonia is an inflammation of the parenchyma of the lungs. It is caused by the bacterium Streptococcus pneumoniae.
• Symptoms include a cough with phlegm or pus, fever, chills and difficulty breathing.
• The bacteria that are commonly found in the nose or throat, can infect the lungs if they are inhaled. They may also spread via airborne droplets from a cough or sneeze.
• So, the correct answer is '.Pneumonia ,Streptococcus pnemoniae,Droplet infection'.

Vectors are the organisms, which carries the infectious agents from sick person to another healthy person. For example, mosquito carries malarial parasite from infected person to healthy person. Therefore, option A is correct.

• Meningitis is the Inflammation of the brain and spinal cord membranes, typically caused by an infection.
• If the meningitis is caused by bacterium Neisseria meningitidis, it is called as Meningococcal meningitis.
• Symptoms include pain in sudden high fever, severe persistent headache, neck stiffness, nausea or vomiting, joint pains, drowsiness, confusion, etc.
• People spread meningococcal bacteria to other people by sharing respiratory and throat secretions (saliva or spit) when they cough or sneezes.
  
• Hence Meningococcal meningitis infection is transmitted chiefly from person to person.
• So, the correct answer is 'Meningococcal meningitis.

Disease causing microbes can spread through the air. This occurs through the little droplets thrown out by an infected person who sheezes or coughs. Another person standing close by can breathe in these droplets and the microbes infect him also. Diseases which spread like this are common cold, pneumonia and tuberculosis.