TYPES OF INFECTION
According to the Course of Infection in the Body
■ Peracute infection: Infections with a short duration of incubation and usually show little or no clinical symptoms are called peracute infections.
– E.g.: NewCastle Disease, Neonatal Septicemia
– Peracute infections are formed by highly virulent and invasive microorganisms in highly sensitive hosts.
– Since the duration of peracute infections is very short in the host and spreading to the environment, an intensive population of
animals is required to spread such infections.
■ Acute infection: Infections with a short duration of incubation and clinical symptoms in short duration are called acute infection. E.g.:
Chichem typhus, Anthrax
TYPES OF INFECTION
According to the Course of Infection in the Body
■ Chronic infection: Infections with long duration of incubation and infection are called chronic infection.
– E..g: Paratuberculosis, leukosis, brucellosis
– Chronic infections can last many days, weeks or even years.
– In this type of infections, the factor that determines the nature of the infection is not the host but the agent itself.
DISEASE IN POPULATION The structure of animal populations
■ The organization of animal populations can usually be described as either contiguous or separated.
■ Contiguous populations: A contiguous population is one in which there is much contact between individuals in the population and members of other populations.
– Therefore predispose to transfer and persistence of infectious diseases over large areas because of the inherent mixing and movement of animals.
– Most human populations are contiguous because there is mixing of individuals by travel. Populations of small domestic animals also are usually contiguous.
■ Assessing the size of contiguous populations: It is often difficult to assess the size of contiguous animal Populations. Only limited routine demographic data about small domestic animals are available.
DISEASE IN POPULATION The structure of animal populations
■ Separated populations: occur as discrete units such as herds and flocks.
– They are particularly common in countries that practice intensive animal production, with many animals on one farm.
– Nevertheless, contact may still occur between separated populations, both directly and indirectly.
– A separated population can be closed, with no movement of animals into or out of the unit.
– A separated population also can be open, with limited movement of individuals in and out.
– Separated populations, especially of the closed type, are less likely to be infected with agents from other areas than contiguous populations.
DISEASE IN POPULATION The structure of animal populations
■ Assessing the size of separated populations: It is often easier to obtain information on the size of a separated than a contiguous
population.
■ The large numbers of animals kept under conditions of intensive husbandry in a single separated unit usually have only one owner.
Reference: Veterinary Epidemiology, 4ed. Michael Thrusfield with Robert Christley, Brown H, Diggle PJ, French N, Howe K, Kelly L, O’Connor A, Sargeant J, Wood H.
