Clinical Refresher: The Five Routes of Disease Transmission

With the direct contact method, a susceptible animal becomes exposed through physical contact when the agent from an infected animal or the environment enters open wounds, mucous membranes, or the skin through blood, saliva, nose-to-nose, rubbing, or biting another animal. ( )

The situation surrounding COVID-19 changes on a daily, and even hourly, basis is the U.S. While there’s currently no evidence that this particular strain of coronavirus will affect cattle, biological risk management is still important for the people working on farms and ranches and for preventing the spread of illness between them. Best practices include frequent hand washing, avoiding close contact between people and staying home if you feel sick, the CDC says.

“It is important to clarify that COVID-19 and the bovine coronavirus are very different viruses,” says Dr. A.J. Tarpoff, assistant professor and extension specialist at Kansas State University. “The corona virus family is a huge family of viruses. Each of the viruses typically only affect individual species. So it would not be expected at all for the COVID-19 to circulate or have any health effect on our cattle herds.”

There are five main routes of disease transmission: aerosol, direct contact, fomite, oral and vector. Diseases can be spread to humans (zoonotic) by those same five routes. By implementing prevention practices for each route of disease transmission, veterinarians and producers can reduce their risk of common, everyday diseases entering their clinics and farms, as well as foreign animal or emerging diseases. Another advantage of this approach is that control measures for one route of transmission can minimize the risk and impact of a number of diseases.

Route Definitions:

Aerosol: Pathogenic agents contained in aerosol droplets are passed from one animal to another, or between animals and humans. Most pathogenic agents do not survive for extended periods of time within the aerosol droplets and close proximity of infected and susceptible animals is required for transmission

Direct contact: A susceptible animal becomes exposed through physical contact when the agent from an infected animal or the environment enters open wounds, mucous membranes, or the skin through blood, saliva, nose-to-nose, rubbing, or biting another animal. Some disease agents can spread between animals of different species, as well as to humans.

Subtype: Reproductive Diseases spread through venereal contact (from animal-to-animal through coitus) and in-utero (from dam to offspring during gestation).

Oral: Consumption of pathogenic agents in contaminated feed, water or licking/chewing on contaminated environmental objects. Feed and water contaminated with feces or urine are frequently the cause of oral transmission of disease agents. Contaminated environmental objects could include equipment, feed bunks, water troughs, fencing, salt and mineral blocks, and other items an animal may lick or chew.

Fomite: A contaminated inanimate object transmits a disease agent from one susceptible animal to another. It involves a secondary route of transmission (direct contact or oral) for the pathogen to enter the host. Examples include contaminated shovels, clothing, bowls/buckets, brushes, tack, and clippers.

Subtype: Traffic Vehicle, trailer, or human causes the spread of a pathogenic agent through contaminated tires, wheel wells, undercarriage, clothing, or shoes/boots by spreading organic material to another location.

Vector-borne: An insect acquires a pathogen from one animal and transmits it to another either mechanically or biologically. Mechanical transmission: disease agent does not replicate or develop in/on the vector; it is simply transported by the vector from one animal to another (e.g., flies). Biological transmission: vector takes up the agent, usually through a blood meal from an infected animal, replicates and/or develops it, and then regurgitates the pathogen onto or injects it into a susceptible animal. Fleas, ticks, and mosquitoes are common biological vectors of disease.

Zoonotic: Diseases transmitted between animals and humans. Human exposure occurs through one of the previously listed five main routes of transmission (aerosol, direct contact, fomite, oral, and vector-borne). It is a separate route of transmission due to its importance.

For more information on the novel coronavirus, visit the resource center on AgWeb. For more about the virus and livstock, Dr. Tarpoff recommends this article by South Dakota State University extension specialist Dr. Russ Daly.

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