2. Epidemiology

• Rabies virus (RNA enveloped) under rhabdovirus family.
  • Susceptibility of the virus to physical and chemical agents:
    • Destroyed rapidly by soap, detergents, alcohol, oxidizing agents, ammonium compounds, proteolytic enzymes, ultraviolet rays and X-rays
    • Highly resistant to cold and dryness
      • Survive 35 seconds at 60°C, 4 hours at 40°C, 1-2 weeks in brain tissue at room temperature, several days at 0 to-4°C

Global:

The number of human deaths globally due to dog-mediated rabies is estimated to be 59 000 annually, with an associated loss of 3.7 million DALYs.² The majority of deaths are estimated to have occurred in Asia (59.6%) and Africa (36.4%) and most DALYs were due to premature death (>99%) and a few to adverse events after administration of nerve tissue vaccines (0.8%). The overall economic cost of dog-mediated rabies was estimated in a probability decision-tree model to be US$ 8.6 billion (95% confidence interval, 2.9–21.5 billion).2 An enhanced verbal autopsy survey within the Million Deaths Study suggested that 12 700 deaths (95% confidence interval, 10,000–15,500 were due to furious rabies in India in 2005. The survey did not include cases of paralytic rabies.³ 

In Bangladesh:

A recent study showed that there are a high number of rabies deaths in males when compared to females. Almost half the deceased was under the age of 15 (47%) and 82% rabies victims from rural areas and 88 % of the case died in home.⁴ Annually, there are 2-3 lacs animal bite cases reported and Bangladesh has current figure an estimated dog population 1.7 million of which 83% are a stray dog.⁵  

Fig. 2: District wise Rabies case density in Bangladesh of consecutive 3 years (2019- 2021)

Rabid canine animals include mostly Dog; in very few cases other animals are Cat, Fox, Jackal, Mongoose, Monkey and other Wild-animals.

• Commonly by contaminated saliva of rabid animal and gains entry into the human body by the animal bite or scratch or through an open wound.
• More than 95% of human cases are acquired from a rabid dogs.
• In rare cases: contamination of mucus membranes with saliva or brain tissue, aerosol transmission, and corneal/organ transplantation.
• Casual contact with a rabid case (e.g., by touching a case with rabies) or contact with non-infectious fluids or tissue (e.g., urine or feces) does not alone constitute an exposure.
• Viruses are not present in the blood (no viremia). Therefore, contact with blood or blood products is not responsible for virus transmission.

The incubation period varies from 5 days to several years (usually 2–3 months; rarely more than 1 year), depending on the amount of virus in the inoculum, the density of motor endplates at the wound site and the proximity of virus entry to the central nervous system.^6-7

The incubation period depends on factors inclusive of:

1. Location and severity of bite wound
2. The amount of virus inoculated within the wound
3. Degree of innervations at the site of the bite wound