Biology Today — May 2017

COMMUNICABLE DISEASES

• These are classified into nine types according to the nature of
pathogen, i.e., the disease causing agent.

Viral Diseases

Viral hepatitis

• Viral hepatitis is commonly called jaundice.

• In early stage, the liver is enlarged and congested. In later
stage, the liver becomes smaller, yellowish or greenish.

• The symptoms in early phase include – fever, anorexia, nausea, vomiting,
epigastric discomfort, pain in muscles and joints.

• The urine is dark in colour. Leukopenia (reduction in the number of WBCs) is followed by lymphocytosis (increase in the number
of lymphocytes). Splenic enlargement is sometimes present.
Table: Other viral diseases
Disease Pathogen Mode of
transmission/
Incubation
period

Symptoms Prevention

1. Dengue fever Flavi-ribo virus By bite of
   Aedes aegypti
   mosquito/3-8
   days

Fever, headache, muscles and joint

pains, rashes, nausea, vomiting,

excessive thirst, bleeding from nose,

mouth, gums

Eliminating mosquito breeding

places and applying mosquito

repellents

2. Common cold Rhino virus Droplet contact/
   3-7 days

Nasal congestion, running nose,

sneezing, sore throat, cough, fever,

headache

Washing hands frequently and

using face masks

3. Mumps Paramyxo
   virus

Droplet contact/

7-18 days

Fever, painful swelling of parotid

glands

Avoiding contact with the sick;

MMR vaccine is available

4. Measles Rubeola virus Droplet contact/
   8-15 days

Fever, rash, itching, inflammation of

respiratory passage

Same as that of mumps

5. Chicken pox Varicella
   zoster virus

Direct contact and

droplet contact/

14-21 days

Fever, rash which changes into

vesicles, pustules and then brown

scab which falls off

Scabs should be collected and

burnt, soiled articles should be

washed and boiled. Vaccine is

available

6. Smallpox
   (Eradicated
   from earth)

Variola virus Direct contact

and droplet

contact/    12   days

High fever, chill, headache, vomiting,

rash that turn into scabs that fall

off

Same as that of chickenpox

7. Poliomyelitis Polio virus Contaminated
   food and water/
   7-14 days

Stiffness of neck, paralysis of skeletal

muscles, fever, headache, pain

Avoiding contaminated food

and water. Salk vaccine and OPV

vaccine available

8. Swine flu Swine
   influenza
   (H 1 N 1 ) viruses

Droplet contact Fever, cough, bodyaches, headache,

chills

Avoiding close contact with the

sick. Vaccine is available

9. SARS (Severe
   Acute
   Respiratory
   Syndrome)

Corona virus Droplet contact/

2-7 days

Fever, chills, muscleache, cough,

dizziness, running nose, vomiting,

diarrhoea

Avoiding contact with the sick