Means of Transmission

Microorganisms are transmitted in animal health care settings by four main routescontact, droplet, air-borne and vector-borne transmission. The same microorganism may be transmitted by more than one route.


1. Contact Transmission
    • This is the most important and frequent mode of transmission of Healthcare-Associated Infections (HAIs). It can be divided into direct and indirect contact transmission.
    • Direct contact transmission involves direct body surface-to-body surface contact resulting in the physical transfer of microorganisms from an infected or colonized animal. For example:
      • Two dogs in an outdoor pen that come into direct contact when they sniff each other may transmit pathogens present in their noses or perineal areas.
      • Staff member’s hands that touch a wound on an animal may result in transmission of opportunistic pathogens from the normal microorganisms of the person’s hands.
      • Infectious organisms present in the animal’s wound can be transmitted to staff.

dog to human transmission

Two examples of Direct Contact Transmission

Indirect contact transmission (fomite transmission) results from the physical transfer of micro-organisms from the original animal (or human) source to a new host, without direct contact between the two. This typically involves contact with:

    • An inanimate object
    • Environmental surface
    • Skin/coat of another animal or person that has been contaminated by the original source

For example, handling one animal and then petting another animal without washing one’s hands results in indirect contact between the two animals.

animal to animal transmission

Indirect Contact through environmental surfaces and contents, fomites such as hands, or another animal


2. Droplet Transmission
    • For example, a cat with an upper respiratory tract infection can transmit viruses or bacteria to another cat by sneezing directly on it. Droplets can also contaminate the surrounding environment and lead to indirect contact transmission.

droplet transmission from cat


3. Airborne Transmission
    • This transmission occurs by the spread of droplets or dust particles containing the infectious agent. Microorganisms carried in this manner remain suspended in the air for long periods of time and can be dispersed widely by air currents. They may be inhaled by another host anywhere within the facility.

airborne transmission from dog


4. Vector-Borne Transmission
    • This transmission occurs when vectors such as mosquitoes, flies, ticks, fleas, rats, and other vermin transmit microorganisms. Some act as simple mechanical vectors, whereas others spread microorganisms by biting. In animal centres, it is important to have control measures in place to reduce or eliminate the presence of such vectors.

vector transmission animals


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