Table 1.

Different routes of ASFV transmission and their characteristics and transmission efficiency.

Transmission Route	Characteristics	Transmission Efficiency
Oral transmission	Ingesting virus-contaminated feed, drinking contaminated water, or swallowing virus particles.	The most important route of ASFV transmission; transmission efficiency via drinking water is much higher than that via feed.
Aerosol transmission	The titer of ASFV in the air is positively correlated with the amount of virus excreted from feces.	ASFV can be spread in a pig house over a short distance by aerosols.
Insect-borne transmission	ASFV is the only known insect-borne DNA virus; the Ornithodoros ticks are the most common vector, though other insects (stable flies, leeches, kissing bugs, and swine lice) may also spread ASFV.	Ornithodoros soft ticks are an ideal virus reservoir to maintain the sylvatic cycle of ASFV among desert warthogs and Ornithodoros tick species.
Iatrogenic transmission	Virus-carrying pigs and susceptible pigs are immunized or injected with a therapeutic drug with the same needle.	The infection efficiency of iatrogenic transmission and its importance in the epidemiology of ASFV are yet to be fully appreciated.
Semen transmission	ASFV can be isolated from semen of infected boars, but no direct evidence shows that ASFV can be transmitted through semen; the Terrestrial Animal Health Code stipulates that boar semen should not carry ASFV.	Lacking convincing data.
Vertical transmission	Knowledge and data on ASFV vertical transmission are still lacking, except for one study reporting molecular evidence of vertical transmission of the virus.	It is difficult to draw conclusions currently.