Veterinary Epidemiology and Zoonosis

MAPPING

• Mapping out the distribution of a disease or variable is a fascinating task. Maps can very well display the spatial distribution of a disease and the associated factors. It is also known as cartography.
• Besides knowing the areas where the disease is present it also helps in understanding the mode and direction of transmission of an infectious disease.
• Maps can also suggest the possible causes of diseases of unknown etiology.
• The maps can be qualitative or quantitative.
• In the former type, the location of present/absence of disease is indicated. However, no information can be obtained regarding the amount of disease.
• In the later type, the amount of a disease in a particular area is displayed.
• Maps can either be constructed according to shape of a district, state or country (called as geographic base maps) or according to size of population concerned (called as demographic / isodemographic base maps).
• In demographic type, the morbidity and mortality values are presented in relation to the size of population.
• Therefore, accurate information on morbidity, mortality and population are required for these maps.
• These are not commonly used in Veterinary practice.
• Generally, geographic base maps are used and most of the atlases consist of these maps.
• There are several types of geographic base maps:

Point (dot or location) map

• Show the location of a disease in a political map.
• Locate by dot or circle, area can also be named.

Distribution map

• Shows the area in which the disease occurs.
• Example: Area endemic to disease, area sporadic to disease and area free from the disease are shown under different markings or shade.

Choloroplethic map

• Display of quantitative information.
• Example: Areas with <25% prevalence, 26%-50% prevalence, 51%-75% prevalence and >75% prevalence of helminthes in a particular district (political map) are shown in different shades / markings.
• Mapping according to administrative region is not a true boundary for incidence.

Isoplethic map

• True boundary of disease is depicted in a geographic map, not region-wise as in a political map.

Demographic map

• Presenting mortality and morbidity information in relation to population size.
• Ratios or rates are presented in these types of maps.
• Less useful in veterinary practice since it is difficult to get accurate information.