Epidemiology of communicable diseases

1. Chickenpox (Varicella or water pox)

Agent factors :

  • Agent – Vericella zoster virus or Human herpes virus
  • Infective materials – Respiratory secretions, cutaneous lesions and the vesicular fluid.

Host factors :

  • Age – It is common in young children below 10 years of age.
  • Immunity – One attack gives life long immunity, second attack is rare.
  • Pregnancy – Infection during the first trimester may cause “congenital varicella syndrome” to foetus characterised by low birth weight, micro-opthalmia, cataract, skin lesions etc.

Environmental factors :
In India it is common in Jan-June and overcrowding favours its transmission.

Mode of transmission :
By droplets, transplacental transmission (mother to foetus) in 3% cases.

Incubation Period :
“The period between exposure to an infection and the appearance of the first symptoms.”
Usually 15 days, may vary from 1-3 weeks.

Clinical features :
There are two stages.

  1. Pre eruptive or prodromal stage – Mild fever, back pain, malaise from few hours to one day in children.
  2. Eruptive stage – Appearance of rashes. New lesions appear daily.

Complications :
Pneumonia, encephalitis, haemorrhages, congenital varicella syndrome and Rey’s syndrome.

Laboratory diagnosis :
Presence of round particles in electronic microscopy of vehicle fluid.

Control and Management :
There is no specific treatment. Patients are managed symptomatically with antipyretics, analgesics and soothing creams.

Prevention :
Use of varicella vaccine given between 1-12 years of age.

2. Measles (Rubeola)

Agent Factors :

  • Agent – RNA paramyxovirus.
  • Infective material – Secretions of the nose, throat and respiratory tract.

Host factors :

  • Age – Affects mainly children between 6 months and 3 years of age.
  • Immunity – Infant are protected by maternal antibodies up to 6 months of age. In some infants, maternal antibodies persist beyond 9 months.
  • Nutrition – Measles tend to be very severe in the malnourished child.

Environmental factors :
Measles is a winter disease.

Transmission :
Directly from person to person by droplet infection.

Incubation Period :
“The period between exposure to an infection and the appearance of the first symptoms.”
It is 10 days from exposure to onset of fever, and 14 days to appearance of rashes.

Clinical features :
There are three stages of disease.

  1. Prodromal stage – It begins 10 days after infection, and lasts until 14 days. The symptoms are fever, coryza with sneezing and nasal discharge, cough, redness of the eyes, lacrimal ion and photophobia. One or two days before the appearance of the rash, Koplik’s spots appear on the buccal mucosa opposite the first and second upper molars.
  2. Eruptive Stage – There are dusky-red rashes which begins behind the ears and spread rapidly in a few hours over the face and neck and extend down the body taking 2-3 days to progress to the lower extremities.
  3. Post measles stage – The immunity deteriorates so chances of infection are increased i.e., pyogenic infection (infections in which pus is produced), candidiasis (a fungal infection on skin or mucous membrane), reactivation of Pulmonary TB etc.

Complications :

  • Diarrhoea
  • Pneumonia
  • Respiratory infections
  • Febrile convulsions (convulsions that caused by fever)

Prevention of measles :

Measles vaccination – 0.5 ml single subcutaneous injection at 9 months of age. This age can be lowered to 6 months of there is measles outbreak in the community.

Leave a Comment

Your email address will not be published. Required fields are marked *