Biological transmission;
■ Three types of biological transmission ocur;
1. Developmental transmission: with an essential phase of
development occurring in the vector (e.g., Dirofilaria immitis in mosquitoes);
2. Propagative transmission: when the agent multiplies in the vector (e.g., louping ill virus in ixodid ticks);
3. Cyclopropagative transmission: a combination of 1 and 2 (e.g.,
Babesia spp. in ticks).
LONG-DISTANCE TRANSMISSION OF INFECTION
■ Infectious diseases can be transmitted by the methods just described over long distances as a result of the;
– Mobility of infected animals, – Microorganisms,
– Parasites, – Vectors, – Fomites,
– Airbone transmission
■ Droplet nuclei: The evaporation of water from droplets (which can occur when droplets are airborne or on the ground) produces
desiccated it, ranging in diameter from 2 to 10 nm.
■ Lee wave: A complex meteorological hypothesis has been presented suggesting that the secondary outbreaks were caused by virus
particles being pulled downwards in a current of air, which was forced
into vertical oscillation as it flowed over a hill. This phenomenon is
called a lee wave
TYPES OF INFECTION
According to the Location in the Body ■ General Infection (systemic infection): Infections that can spread
to the whole body after entering the body and can be determined in more than one system
– E.g.: equine plague, cattle plague
■ Local Infection: Infections which are seen only in a specific tissue, organ or system of the body
– E.g.: Infertile staphylococcal and streptococcal infections
■ Focal Infection: Infections which are seen in the mucous membranes of the animals such as pharynx, larynx, tonsil, sinus and tooth nests
– E.g.: Streptococcus, Corneal bacteria
TYPES OF INFECTION
According to the Location in the Body ■ Latent Infection: Some microorganisms may remain in the body
without causing symptoms. It is called latent infection.
■ However, the term latent indicates that when the host resistance is broken, the agent may cause clinical disease.
– E.g.: Parainfluenza virus infection
■ Opportunistic Infection: Some microorganisms, which do not cause disease in normal and experimental conditions and are found in the normal flora of the host, can cause disease when the host resistance is broken or the immune system is suppressed.
– E.g.: Candida infections
TYPES OF INFECTION
According to the Location in the Body
■ Hidden Infection: Some microorganisms are not likely to cause any disease in their host. They are either random or flora in the host. However, they spread the agent to the environment and cause infection in susceptible animals.
– E.g.: C. jejuni infection in March
■ Common (Co) Infection: In some infections, multiple agents must be together to cause the disease.
– E.g.: P. multocida, Mycoplasma and Parainfluenza-3 virus
■ Secondery Infection: If a microorganism is involved in the disease as a second agent and the disease is exacerbated, this process is called a secondary infection.
– E.g.: In AIDS
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.
