5. Epidemic Diseases

Epidemic means “upon or above” and occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience. Epidemics of infectious disease are generally caused by a change in the ecology of the host population (e.g. increased stress or increase in the density of the vector species), a genetic change in the parasite population or the introduction of a new parasite to a host population (by movement of parasites or hosts). An epidemic may be restricted to one location; however, if it spreads to other countries or continents and affects a substantial number of people, it may be termed a pandemic. The epidemic diseases are whooping-cough, measles, influenza, and recent epidemics like Dengue, Swine flu and Chikungunya.

DENGUE: Dengue fever is an infectious disease carried by mosquitoes and can be caused by any one of four types of dengue virus: DEN-1, DEN-2, DEN-3, and DEN-4.This disease used to be called “break -bone” fever because it sometimes causes severe joint and muscle pain that

feels like bones arc breaking.

Dengue fever symptoms of typical uncomplicated (classic) dengue usually start with fever within 4 to 7 days after you have been bitten by an infected mosquito. These symptoms include: high fever, up to 105°F, severe headache, retro-orbital (behind the eye) pain, severe joint and muscle pain, nausea and vomiting, and rash. The rash may appear over most of the body 3 to 4 days after the fever begins, and then subsides after 1 to 2 days. There may be a second rash a few days later.

SWINE FLU : Swine flu has been creating a terror effect all around the globe and has been declared an epidemic in most parts of the world. In India, day by day, the graph of infected persons has been claimed to go up so, it is important to take into consideration this disease, as it may prove to be a deadly one. Swine influenza, also called pig influenza, swine flu, hog flu, and pig flu, is an infection caused by any one of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) is any strain of the influenza family of viruses that is endemic in pigs. As of 2009, the known SIV strains include influenza C and the subtypes of influenza A known as H1N1,H1N2, H2N1, H3N1, H3N2, and H2N3.

The main route of transmission is through direct contact between infected and uninfected animals. These close contacts are particularly common during animal transport. The direct transfer of the virus probably occurs either by pigs touching noses, or through dried mucus. Air- borne transmission through the aerosols produced by pigs, coughing or sneezing is also an important means of infection.

CHIKUNGUNYA : Chikungunya occurrence was first detected in human blood samples in 1952-53 from Tanzania, Africa. This disease was reported in India for the first time in Calcutta in 1963. Chikungunya virus is transmitted by two mosquitoes, Aedes albopictus and Aedes egypti from the infected to a normal person. The disease is also locally named as Joint Pain disorder. This mosquito is an oracious day time feeder and bites people only during day time and the mosquito Aedes albopictus is also termed as a tiger mosquito for it shows the characteristic presence of white stripes on the body and its large size than a normal mosquito.

Symptoms are expressed after an incubation period of 1-12 days after a mosquito bite, which include fever, headache, joint pain (or Arthralgia), Arthritis affecting multiple joints, swelling of joints, Rash (rare symptom), conjunctival infection, photophobia, chills, nausea, vomiting, and bleeding or hemorrhage (rare symptom).


Attribution: "Science and Technology" by Dr. B. R. Ambedkar Open University.
Unit: 05, Page No: 55 - 71