Common Human Disease

Human Health and Diseases of Class 12

Common Human Disease


Caused by pathogens like virus, bacteria, protozoans, fungi, helminthes and arthropod parasites.

Transmitted either by close contact or through vector or carrier.

Viral Diseases

Viruses are small particles, between living and non-living, become living only in the host cells as obligatory parasites. Possess either DNA or

RNA. Utilize hosts replication machinery for the synthesis of their components.

Viruses infecting animal are mostly retroviruses; most being air-borne but some may be transmitted through food and water, blood contact and

also through other secretions.

 Measles (Rubeola)

Acute infectious viral disease of children below the age of 5 but adults may also contract the infection if they are not immunized against it.

Pathogen : RNA-virus Rubella or Polynosa marbillorum.

Incubation period : 10 days. Disease is divisible into 2 stages, pre-eruptive (last 3-4 days) and eruptive (last for 2-3 days).

Transmission : by droplet infection and fomite method or articles soiled by the patient. Portal of entry is either respiratory tract or conjunctiva of eye.

Symptoms : Kollip’s spot inside cheeks a day before the appearance of skin rashes.

Eruption of rashes on backside of ears, later spreading towards the trunk and limb regions.

Inflammation of nasal mucous membrane.

Fever with red watery eyes, sensitive to light.


Isolation of infected child, and articles being used by the patient.

Immunization of all children with Swartz vaccine (or MMR)

Administration of sulphonamide drugs and vitamin A prevents secondary infection.


Acute disease of children of age 5-15 yrs.

Pathogen : Paramyxovirus – spherical, RNA-virus with a lipid coat.

Portal of entry : Generally oral.

Transmission : Through droplet or direct infection.

Incubation period : 12 - 26 days.

Symptoms :Painful swelling of parotid glands with high fever.

Difficulty in swallowing and opening of mouth.

High fever with headache, chills and anorexia.

In adults cause inflammation of testis (orchitis), fallopian tube and ovary (salpingo-oophoritis), mammary glands (mastitis) etc.


Worldwide known as infantile paralysis.

Virus attacks motor neurons of anterior or dorsal horns of brain stem and spinal cord resulting in non supply of nerve impulses to certain

muscles and hence their atrophy.

Pathogen : Smallest single-stranded RNA virus called Polio virus of 3 types – I (causing 80%), II, III.

Portal of entry : Contaminated food or water.

Transmission : Through nasal secretions, urine and faeces.

Incubation period : 5 - 17 days. Virus multiplies mostly in alimentary canal and then through lymph vessels and blood vessels reach CNS.

Symptoms :

Preparalytic stage lasts for 1 - 14 days; with fever, headache, sore throat, nausea, vomiting and diarrhoea, stiffness of neck and back,  drowsiness, twitching and convulsions.

During paralytic stage, necrosis of dorsal horn cells of spinal cord and brain stem followed by muscle atrophy.

Sometimes respiratory centres of the brain are affected and breathing stops, patient needs iron lung for artificial breathing.


Medicines ineffective.

Patients isolated; proper sanitation.

Oral vaccine developed by Jonas Salk and Albert Sabin 1940 is given to babies.

Public Pulse Polio Immunization Programme is organized in India for eradicating polio.

Chicken pox

Highly infectious among children below 10 years, also occurs in adults, mostly during winter and spring.

Single attack gives durable immunity.

Pathogen : Varicella zoster belongs to herpes group of viruses.

Transmission : Spreads directly or through contaminated articles of patients.

Incubation period : 14 - 16 days.

Symptoms :Slight fever, shivering and pain in back.

Transitory rashes followed by raised pinkish spots, first appearing on trunk, then on forehead and face, rashes change into scab in 5-6 days

which later fall without leaving any scar.


Attenuated virus vaccine is helpful. Passive immunity as zoaster immunoglobulins are used.

Proper sanitation and isolation of patients.

Use of boric acid, calamine and benzyl benzoate reduces the severity of itching.

Common cold

Pathogen : Rhinovirus belongs to picornavirus group and is single-stranded RNA.

Transmission : Through droplet infection; pharyngeal and nasal secretions.

Symptoms : Mild persistent fever, headache, sneezing, watery eyes, excessive nasal secretions and cough.

Treatment : No specific medicine, preventive measures widely recommended.

 Influenza (Flu )

Highly infectious respiratory disease.

Commonest site of infection is epithelial (or mucous) lining of nose, throat and upper respiratory tract.

Pathogen : Orthomyxovirus, a single-stranded RNA-virus with a lipid covering.

Incubation period : 24-72 hrs.

Symptoms : Mucous and watery discharge from nose; sneezing, headache and fever.

Muscle ache, inflammation of respiratory mucosa.

Extreme conditions are pneumonia, bronchitis and ear infection.

Treatment : No medicines available but vaccination reduces the incidence.

 Dengue or backbone fever

Tropical viral disease spread by female Aedes aegypti and other related species. Once infected mosquito remains infective for life.

Pathogen : Flavi virus or Toga virus with single stranded RNA.

Incubation period : 3 - 8 days.

Transmission : By the bite of Aedes aegypti.


(i) In classical dengue

High fever, headache, severe pain in joints, nausea, vomiting and rashes on chest and upper limbs.

(ii) In haemorrhagic dengue

All symptoms of classical dengue and bleeding through skin, gums, gastro-intestinal tract.


Prevention by elimination of mosquito.

Can be detected by tourniquext test.

 Rabies (Hydrophobia)

Caused by virus.

Common reservoir host - dog, foxes, wolves, jackals mongoose, bats and cats.

Transmitted by saliva which enters the wound; induces bitting behaviour in victims.

In man rabies results in fear of water.

July 6 is celebrated as World Rabies day.

Yellow fever

Haemorrhagic disease transmitted by the infected Aedes aegypti.

Pathogen : Arbovirus, with single-stranded RNA.

Symptoms :

High fever with severe headache and vomiting.

Rupture of veins in kidney, spleen and liver.

Extreme cases show yellow skin due to severe jaundice.

Max Theiler in 1951 got Nobel Prize for the developing vaccine against it.

 Viral hepatitis (Epidemic jaundice)

Characterized by inflammation of liver; blockage of biliary excretion, hyperbilirubinemia resulting in jaundice.

Hepatitis is of two types : viral and toxic. Viral hepatitis is of five types – A, B, C, D and E.

Hepatitis A or infectious epidemic hepatitis or epidemic jaundice

Pathogen : Hepatitis A virus (HAV); small, naked, virus with single-stranded RNA.

Incubation period : 25 - 30 days.

Transmission : Through faecal - oral route.

In India, common in children due to improper sanitation/hygiene, immunity develops after infection.

Carrier stage absent. Recovery takes 8 - 12 weeks.

Patient starts to pass HAV even before symptom appears.

Virus multiplies in intestinal epithelium and then reaches liver through blood.

Symptoms :

Fever, nausea, vomiting, anorexia and liver tenderness, enlargement of spleen.

Pain in right upper abdominal quadrant leading to jaundice.


Diet control and bed rest required.

Vaccines available; antibiotics given to prevent secondary infections. Short term protection obtained through immunoglobulin injections.

Hepatitis B or serum hepatitis or transfusion hepatitis.

Pathogen : Hepatitis B virus (HBV); also called Dane particle, spherical with circular ds-DNA.

Occurs in blood and body fluids (saliva, mother’s milk, semen, vaginal secretions).

Transmission : Through kissing, sharing of safety razor, needlestick injury, use of contaminated needles and syringes, ear piercing, tatooing, sexual contact.

Incubation period : 90 days.


Fatigue, weakness, myalgia (pain in muscles), anorexia, vomiting, pain in right upper abdominal quadrant, brownish urine and jaundice.

Fatality less than 1%, complete recovery occurs in 90–95% cases, some patients become carrier after recovery.

Infection tested by presence of antigens : HBsAg (surface Ag), HBcAg (core Ag) and HBeAg (‘e’ Ag).


Bed rest and fat free diet.

Antibiotics should be taken.

Vaccine available : A drug from Phyllanthus amlarus provides relief.

Hepatitis C

Pathogen : HCV, with single-stranded RNA.

Transmission : Through needlestick injury, cuts, contaminated needles and syringes, sexual contact, contaminated blood.

Incubation period : 6 - 8 weeks but may take several months.


Mostly subclinical with milder symptoms showing little or no jaundice so disease remains unattended.

It may become chronic leading to liver damage, cirrhosis and hepatocellular carcinoma.

Hepatitis D or Delta Hepatitis

Pathogen : Delta virus (HDV), spherical with single-stranded small circular RNA with simultaneous infection of HBV.

HDV genome can encode for its nucleoprotein but not the capsid which requires genome of HBV. The support provided by HBV in forming HD virion is called piggybacking.

Symptoms :

Similar to that of hepatitis B but are more severe causing large scale damage.

Mortality : 20%.

Hepatitis E

Non A, non B hepatitis (HNANB), naked and spherical virus with single-stranded RNA. Capsid show surface depressions.

Transmission : Faecal contaminated water and food.

Incubation period : 5 - 6 weeks.


Similar to hepatitis A.

Jaundice deeper and prolonged.

Fatality 0.5 - 0.3% but 10 - 20% in pregnant women.

Carrier stage absent.


Personal cleanliness, use of boiled water, well cooked, warm and clean food.

Elimination of flies.

Vaccine available.

Toxic Hepatitis

Caused by toxic chemicals called hepatotoxins which damage or destroy liver cells e.g. Amanita toxin, carbon tetrachloride, yellow

phosphorus, alcohol and some drugs. May enter from any route.


Chronic inflammatory disease of eyes, worldwide in distribution.

Pathogen : Chlamydia trachomatis; an intermediate group between virus and rickettisiae (bacteria) with cell-wall, DNA and RNA and multiplies by binary fission.

Portal of entry : Direct contact with articles used by infected persons.

Incubation period : 5 - 12 days

Symptoms : Inflammation, discomfort and discharge from eyes.

Treatment : Application of antibiotics.

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