Veterinary Epidemiology and Zoonosis

LANDSCAPE EPIDEMIOLOGY

• The study of diseases in relation to the ecosystems in which they are found, is landscape epidemiology.
• Medical ecology, horizontal epidemiology and medical geography also convey the same meaning.
• Investigations are frequently qualitative, involving the study of the ecological factors that affect the occurrence, maintenance and in the case of infectious agents, transmission of disease.
• This contrasts with the quantitative associations between specific diseases and the hypothesized factors - sometimes termed 'Vertical epidemiology'.
• Landscape epidemiology was developed by Russian Pavlovsky (1964), and later expanded by Audy (1962) and Galuzo (1975).

Nidality

• Russian steppe biome was the home of the great plagues such as Rinderpest.
• Many arthropod-transmitted infections present in the steppes were also limited to distinct geographical areas. These foci were natural homes of these diseases and were called nidi (Latin; nidus - nest).
• The presence of a nidus depends on its limitation to particular ecosystems.

Objectives of landscape epidemiology

• Landscape epidemiology is founded on the concept that if the nidality of diseases is based on ecological factors then a study of ecosystems enables predictions to be made about the occurrence of disease and facilitates the development of appropriate control strategies.
  • Example: Kyasanur forest disease. It is caused by an arbovirus. It is apparently restricted to an area 600 miles square in Mysore. The virus endemically and inapparently infects some small mammals, including rats in the local rain forest. The virus is transmitted by several species of ticks of which only Haemaphysalis spinigera infest man. When man creates ecological mosaics by cultivating areas for rice, his cattle roam into the surrounding rain forest and may become infested with virus-infected ticks. Dense population of ­ticks therefore build up around villages and when infected, these ticks can transmit the infection to man.