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April 16, 2017

By: Lisa Shimeld

Vertical versus Horizontal Transmission of Infectious Diseases


1. Vertical transmission (AKA mother-to-child transmission or perinatal transmission)

Transmission of an infection from the parental generation to their offspring. This can occur in utero or immediately after birth (ingestion of breast milk or direct contact during or after birth).


Syphilis –Bacterial disease (STI) that can be transmitted across the placental barrier to the fetus during primary or secondary stages of the disease.

BVDV – Viral disease of significant economic importance seen in grazing animals such as cattle and alpacas. Transmitted across the placental barrier to the fetus.

Chlamydia – Another STI that can be transmitted vertically to a child as it passes thru the birth canal of an infected woman.

2. Horizontal transmission

Transmission of an infectious disease agent (bacterium, virus, fungus, etc.), usually between members of the same species that are not parent and child. Horizontal transmission usually occurs through contact with bodily excretions or fluids such as sputum or blood, that contains the infectious agent.

Examples include:

• STIs (sexually transmitted infections)
• Colds, flu, diphtheria , etc.
• Carriers (other species) may also be involved:
o Anterior transmission – by the bite of an infected organism (vector), such as a mosquito
transmitting malaria to humans
o Posterior transmission – transmission by contact with infected feces as in Chagas disease

3. Zoonosis (plural zoonses)

Infectious disease transmitted between species (sometimes by a vector) from animals other than humans to humans, or from humans to other animals (reverse zoonosis).

This includes:

• Lyme disease – Borrelia burgdorferi transmitted from deer to humans by the bite of infected ticks.

• Rabies – Viral disease transmitted from infected animals to humans (or to other animals) by means
of infected saliva thru a bite.

All rights reserved by Lisa Shimeld, April, 2017.