Generally speaking, workers on pig farms are more at risk from
mechanical/electrical injury (e.g., tractors, fans, and augers)
than microorganisms. However, recent political activity, in the
USA in particular, has sensationalized those diseases transmissible
from pigs to people (zoonotic diseases). Potential pathogens
are numerous and include bacteria, viruses, parasites, and fungi
but most infections are mild and easily prevented with simple
procedures such as wearing protective gear and hand washing.
This is not to trivialize the fact that some people are particularly
susceptible to, and severely incapacitated by, some diseases that
are carried by some hogs. For example, an immuno-compromised
person may suffer extraordinarily from a Salmonella infection
contracted on a pig farm but that is the exception, not the rule.
A recent study (Fowler 1998) demonstrated that despite a four
fold increase in hog population in North Carolina there has been
no increase in the number of cases of Salmonellosis reported.
For diseases to be transmitted from hogs to people the causative
organism (pathogen) must be either ingested, inoculated, or inhaled.
Knowing this presents a clear opportunity to prevent infection.
For example, if people washed their hands before handling food
or touching their mouths, the likelihood of accidentally ingesting
any pathogen, e.g., Salmonella, Toxoplasma, or Campylobacter,
would drop dramatically. Factors that will increase the susceptibility
of individual workers include stress, fatigue, poor general health,
pregnancy, immunosuppression, and age.
Ingestion: Many, if not most, of the zoonotic diseases
for pig farmers are acquired by eating the infectious organism.
Breaking the fecal-oral cycle depends on simple personal hygiene.
At work, you should always wash your hands before eating, smoking,
or touching your mouth.
Inoculation: Tetanus is the most serious disease for pig
farmers that is transmitted by inoculation. Every farm worker
should be vaccinated for tetanus.
Inhalation: Although the inhalation of dust and other
matter can be a health hazard it is not the usual mode of transmission
for zoonotic pathogens. The major exception is the transmission
of Streptococcus suis. Because children can be severely
affected by Streptococcus suis they should wear face masks
when working with pigs. Fortunately, cases are rare.
Bacteria are single-celled organisms with cell walls. They are
characterized by shape as cocci, bacilli and spirilla and differentiated
based on gram stain and other biochemical tests. They are usually
considered to be either gram positive or gram negative.
|Disease and Agent||Usual Symptoms||Worst outcome||Transmission||Prevention||Increased Risk for fetus or females||Notes|
|Anthrax, Bacillus anthracis||Skin form: itchy, then vesicles, then necrosis. Lung form: fever, weakness, difficulty breathing, death. Intestinal form: weakness, fever, vomiting, diarrhea, wasting.||Death if patient is not treated.||Ingestion or inhalation of spores.||Wash hands, general personal hygiene.||NO||Not usually associated with pigs or pig workers|
|Brucellosis,B. suis||Flu-like symptoms||Death rarely||Eradicated in NC and most of USA|
|Campylobacter, C. jejuni||Diarrhea, abdominal pain, malaise, fever, nausia, and vomiting||Prolonged illness||Ingestion||Wash hands, general personal hygiene.||NO|
|Erysipeloid.E. rhusiopathiae||Red, dark, swollen lesions often on hands.||Death if patient is not treated.||Handling pigs/pork, skin wounds||Wash hands, general personal hygiene.||NO|
|Leptospirosis,Leptospira interrogans||Flu-like symptoms||Death rarely||Inoculation when contact pig's urine but can be inhaled or ingested.||wear protective clothing||Yes, fetus may die.|
|Staphylococcosis, Staphyloccus aureus||Varies||Endocarditis is potentially fatal||Ingest, inoculate||Wash hands, general personal hygiene.||NO||rare interspecies transfer|
|Streptococcosis, Streptococcus suis||Fever||Permanent hearing loss, death||Inhale, ingest||Wash hands, face mask.||NO||interspecies spread is rare|
|Tetanus,Clostridium tetani||Muscle spasms||Death. Case fatality is 30-90%.||Inoculation||Vaccination and clean all wounds.||NO|
|Tuberculosis,M. avium||Cough blood, sweating at night, cough, fever,||Death if patient is not treated.||Wash hands, general personal hygiene.
||NO||fewer than 100 human cases of M. avium confirmed
|YersiniaY. enterocolitica||Fever, diarrhea, joint pain||Ingestion||Wash hands, general personal hygiene.||NO||The pig is the usual reservoir.|
Vaccines are generally not available for bacterial diseases listedabove.
Viruses are classified depending on how they look under a microscope,
their outer shell, and the type of genetic material (RNA or DNA).
Viruses cannot multiply outside the host cell. Outside the host
they can live for only a few hours to a few weeks.
Nipah: This newly identified virus has killed about 103
people in Malaysia. The epidemic started in 1997 with an outbreak
of encephalitis among pig-farm workers in the state of Perak in
Malaysia. The virus, which is transmitted
from pigs to humans, swept through more than half of Malaysia's
thirteen states. By May 1999, the Malaysian Ministry of
Health, in association with the Centers for Disease Control and
Prevention (CDC), Atlanta, reported 258 cases of encephalitis
in adults, with a case-fatality rate of almost 40%. Initially,
the causative agent was thought to be Japanese encephalitis virus
because that was common in the area. The abnormal (for JEV) clinical
signs led researchers to search for another agent. They eventually
identified another virus that they named Nipah after the Malaysian
village where it claimed its first victim. To prevent its spread,
the Malaysian government ordered the destruction of about 1 million
pigs. The virus has been isolated from humans, pigs, dogs, cats,
horses, goats and bats and it has basically ruined the pig-farming
industry in most of Malaysia. Nipah virus has not been identified
in the USA.
Menangle: This is a very rare virus and only one outbreak
in New South Wales, Australia has been identified.
It caused flu-like symptoms in people. It is also carried by
Influenza: The first thing to realize is that swine
flu and human influenza (Spanish Flu which killed 20 million to
40 million people in 1918 and 1919) were not caused by the same
virus--they had a common ancestor. However, the epithelial cells
of pigs seem to have receptors for both human and avian influenza
and that supports the idea that pigs may be the mixing vessel
wherein human pathogens my develop. To keep on top of the situation
public health officials should monitor human clinical flu outbreaks
and determine which type is involved.
Hepatitis-E: HEV was experimentally reproduced in swine
in Russia in 1990. Subsequently, studies by US and Nepalese investigators
in the Kathmandu Valley found that 33% of pigs had evidence of
past or current infection. About 9% of pig workers had antibodies
to the virus. Work in the USA seems to indicate that swine HEV
is genetically very distinct from the HEV strains previously compared.
It is very closely related to HEV US-1 and US-2. Indications
are that swine HEV and the US human HEV strains together form
a distinct branch. Experimentally, cross-species infection has
been demonstrated for this new branch of HEV strains. Therefore,
it is possible that swine-to-human HEV infection is occurring.
HEV has the potential to infect people working with pigs. Results
of recent sero-survey of large-animal veterinarians in the mid-west
revealed that about 10% had antibodies to HE-these infections
were probably entirely subclinical. The risk that HEV represents
to people on hog farms, or the risk that it may be transmitted
to their families or to other members of the community, is unknown.
There are no data suggesting economic losses due to HEV infections
Encephalomyocarditis: (EMC) It is an RNA virus. It is
rare in humans and not fatal.
Ascariasis: Caused by the worm Ascaris suum. Ingestion
of the ova sets up a transient infection in humans. It is easily
prevented by hand washing and general personal hygiene.
Balantidiasis: Caused by Balantidium coli. Humans
are very resistant but swine are major source for humans. An infection
is acquired by ingestion of the parasite. It is easily prevented
by hand washing and general personal hygiene
Toxoplasmosis: Caused by Toxoplasma gondii. Workers
can acquire an infection by eating pork containing cysts or ingesting
the oocysts excreted by cats that live around the hog operation.
It is easily prevented by hand washing and general personal hygiene
and not eating undercooked pork.
Cryptosporidiosis: Caused by a coccidian protozoa,
Cryptosporidium parvum, that causes diarrhea, vomiting, wasting,
and abdominal pain. Some people may have no symptoms. In the
worst cases it can cause severe prolonged diarrhea with wasting
and death. It is transmitted through contaminated water and the
directly through the fecal-oral route. It is easily prevented
by hand washing and general personal hygiene.
Ringworm: Caused by a variety of fungi. The commonest
cause in swine is Microsporum nanum. In humans they cause
scaly lesions with itching and hair loss. It is easily prevented
by hand washing and general personal hygiene.
Scabies: In swine the organism is Sarcoptes scabiei
var. suis which can live on people but not reproduce
on them. In other words, humans are a dead-end host for the pig
Human's susceptibility to any disease depends on many factors
starting at the most basic level of innate resistance. For example,
humans are innately resistant to PRV and TGE because our cells
do not have the particular characteristics of pig cells that enable
PRV and TGE virus to infect the cells and cause disease. Many
pig diseases fit into this category, however, for some we do not
have this innate resistance and we are susceptible. Fortunately,
just because the hazard exists does not mean that any time the
organism is present in the environment that we are going to be
infected and to get sick. Out general health status and (specifically
our immune status) provides further protection. In addition,
we must be infected with an adequate dose of the organism or it
will fail to establish an infection.
Safety and Health in Agriculture, Forestry, and Fisheries. Ricky
Langley, Robert McLymore, William Meggs, and Gary Roberson. Government
Fowler GF, Xanthakos S, and Corey GR. Of Hogs and Men. Does
North Carolina's hog industry raise the risks of infectious diseases?
North Carolina Medical Journal, Vol 59, 1998, pages 12-15.
Abram Benenson, Control of Communicable Diseases Manual 1995 (16th
Ed). American Public Health Association.
Zoonosis Updates, from the Journal of the American Veterinary
Medical Association, second edition, published by the American
Veterinary Medical Association, Schaumburg, Illinois, 1995.