Organisms such as clostridia, erysipelas, salmonella and E. coli may contaminate the environment, soil or concrete surfaces (for example in the farrowing houses) and if attempts are not made to reduce or eliminate them they may overwhelm incoming pigs.

Most respiratory infections die out of the environment fairly quickly but faecal pathogens tend to be more persistent.

Diseases and organisms spread by pig faeces

• Actinomyces (Corynebacterium) pyogenes.
• Bacteroides.
• Campylobacters.
• Classical swine fever virus.
• Clostridia.
• Actinobaculum (Corynebacterium, Eubacterium) suis.
• E. coli.
• Enteroviruses.
• Porcine epidemic diarrhoea viruses.
• Erysipelothrix which cause erysipelas.
• Fusebacterium necrophorus.
• Klebsiella.
• Lawsonia intracellularis which causes porcine enteropathy (PE) and Ileitis.
• Parasitic diseases (internal ones).
• Porcine parvovirus.
• Porcine reproductive respiratory syndrome (PRRS) virus.
• Rotavirus.
• Salmonellosis.
• The spirochetes which cause swine dysentery.
• Streptococci.
• Transmissible gastro-enteritis (TGE) virus.
• Yersinia.
• Foot-and-mouth disease.
• Swine vesicular disease virus.

Contamination by food and water

Water can become a major source of contamination in both outdoor and indoor pig producing systems. Outdoors the fouling of wallows by faeces and urine from sows provides a potential medium for the survival of some organisms. Leptospira from rats and other wildlife may contaminate streams and be drunk by pigs. Feed may be contaminated by salmonella from vermin and birds or its ingredients may have been contaminated at source. Diseases that can be spread by food and water include; E. coli, erysipelas, clostridia, salmonellosis and leptospirosis.

External parasites
Mange, lice and ticks can be carriers of some infectious agents and act as mechanical vectors or indirect hosts in diseases such as African swine fever, Japanese B. encephalitis and eperythrozoonosis. House flies may spread infections such as Streptococcus suis.

Inoculation
There are many diseases on the farm that result from contaminated skin damage. These include tail biting, ear nibbling, greasy pig disease, trauma to the gums following teeth removal, necrosis of knees in piglets, joint infections, eperythrozoonosis (needle contamination) and of course fighting.

Opportunist invaders
Opportunist invaders are those organisms that normally on their own would not cause disease but given the opportunity by additional factors will assume a pathogenic role. Typical examples include skin damage resulting in greasy pig disease, vulval discharges and endometritis.