PROTECTING YOURSELF FROM PIG DISEASES

W.E. Morgan Morrow
Department of Animal Science
North Carolina State University
Raleigh, NC 27695-7621

Ricky Langley
N.C. Dept. Environment and Natural Resources
Raleigh, NC 27699-1912

Introduction

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.

Transmission

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

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 TransmissionPrevention 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. NONot 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 illnessIngestion 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 rarelyInoculation when contact pig's urine but can be inhaled or ingested. wear protective clothing Yes, fetus may die.
Staphylococcosis, Staphyloccus aureus VariesEndocarditis is potentially fatal Ingest, inoculateWash hands, general personal hygiene. NOrare interspecies transfer
Streptococcosis, Streptococcus suis FeverPermanent hearing loss, death Inhale, ingestWash hands, face mask. NOinterspecies spread is rare
Tetanus,Clostridium tetani Muscle spasmsDeath. Case fatality is 30-90%. InoculationVaccination 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. NOfewer than 100 human cases of M. avium confirmed
YersiniaY. enterocolitica Fever, diarrhea, joint pain Ingestion Wash hands, general personal hygiene. NOThe pig is the usual reservoir.

Vaccines are generally not available for bacterial diseases listedabove.

Viruses

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 fruit bats.

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 in swine.

Encephalomyocarditis: (EMC) It is an RNA virus. It is rare in humans and not fatal.

Internal Parasites

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.

Fungi

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.

Mites

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 scabies mite.

Infection

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.

Take-Home Message

Suggested reading

Safety and Health in Agriculture, Forestry, and Fisheries. Ricky Langley, Robert McLymore, William Meggs, and Gary Roberson. Government Institutes.

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.