WHY VACCINATE YOUR POTBELLIED PIG? by: D. Bruce Lawhorn, DVM, MS

The subject of annual vaccinations in dogs and cats is currently being debated. Such a debate is not really pertinent to potbellied pigs (PBPs). For example, Texas State law requires an annual rabies vaccination in dogs and cats even though many rabies vaccines in these species are labeled for 3 years protection. In my particular area of Texas, the Texas Department of Health area veterinarian recently reported that we have 3 times more confirmed cases of rabies in wildlife (bats, skunks, raccoons) than the same time last year (and we had a lot last year!). The Texas Department of Health is currently holding a series of public meetings on 3 year versus 1 year rabies vaccinations. Many veterinarians express concern about the compliance by pet owners with 3 year rabies vaccinations versus one year, especially in very transient population areas where client compliance with routine vaccination is already low. A high percentage (at least 70 percent) of the cat and dog population in an area need to be properly vaccinated to effectively minimize the spillover of rabies from wild animals to pets and then to humans. Note that rabies is almost always fatal in people. This is the main issue.

The need for yearly vaccinations for distemper, parvovirus, etc. in dogs and feline distemper, rhinotracheitis, etc. in cats is also being debated within the veterinary profession (these are mainly vaccines against viral diseases). Vaccine-induced sarcomas in cats have actually been the catalyst to drive these debates. Logical alternatives to routine annual vaccinations against viral diseases are less frequent vaccination with vaccines known to last longer than a year (there are very few of these – mainly rabies vaccines) and/or blood testing to indicate if the pet still might have a presumed protective antibody titer from previous vaccinations (the presumed protective titer for distemper, parvovirus, etc. in dogs and distemper, rhinotracheitis, etc. in cats in published research is based on a minimum number of studies with very small sample sizes). The cost of blood testing for an antibody titer may actually be more expensive than routine vaccination which has been done for decades.

This debate does not really apply to PBPs because none of the routine vaccinations (mainly bacterial vaccines) such as erysipelas, leptospirosis (6 types) lasts for more than 6 months. There is no approved rabies vaccine for any type of swine and no company will go through the expensive vaccine approval process when there are no more than 0-3 reported confirmed cases in the U.S. every year (would be a very small market for an approved swine rabies vaccine!). Nevertheless, at the discretion of the attending veterinarian and with the owners consent, PBPs have been vaccinated with killed rabies vaccine. For example, in situations of a wildlife rabies epidemic within a state, veterinarians might be allowed by state veterinary authorities to vaccinate PBPs after the owners understand and sign a release that explains that there is no scientifically-proven evidence for efficacy and duration of protection from the use of this particular killed rabies vaccine in pigs. Also, the PBP owner must agree that if their rabies vaccinated PBP is truly exposed to a rabid animal (e.g. through a bite wound), for the protection of human health, the PBP would be immediately euthanatized and the brain submitted for rabies testing.

PBP owners and sanctuary operators need to understand the rationale for routine vaccination. PBPs, like other pigs, get disease-causing organisms from their dam (called sow-to-pig transmission), littermates or exposure from any other type of pig such as in sanctuary situations, flea markets or county shows. Organisms such as Erysipelothrix rhusiopathiae, Actinobacillus pleuropneumoniae (APP), Strep species, Mycoplasma species, Haemophilus species various viruses, E. coli species (in gut) and a multitude of others reside in the lymphatic system in areas such as the tonsils, lymph nodes and gastrointestinal tract. Staph and Strep species and many other bacteria populate the skin. External parasites such as sarcoptic mange mites reside in the skin. These organisms can cause disease right away (if there are enough of them) or just quietly wait it out until the PBP is stressed by some event (transportation, extremes of heat or cold, pregnancy, lactation, malnutrition, cancer or re-occurring infectious disease). So this is the scientific explanation for sickness from an infectious disease in a PBP that has not been around another pig in months or years!

Sarcoptic mange is an example of sow-to-pig transmission that is easy to understand. A young pig that is exposed to sarcoptic mange from his dam and/or littermates is populated on the skin with only a few mites. The PBP is then taken to a home at a young age and 3-4 months later is itching and scratching and has crusts above the hooves, around the head and ears and on other parts of the body (all the time the mites have been breeding, multiplying and spreading within tunnels in the skin until this condition is obvious). In about 50 percent of cases, the owner has itchy red spots on the arms and abdomen which are also sarcoptic mange lesions. The owner takes the itchy PBP to a veterinarian and a skin scraping taken from multiple sites reveals sarcoptic mange mites and mite eggs! Normal PBPs do not have sarcoptic mange mites on skin scrapings. So the diagnosis is made and an Ivomec (ivermectin give SC) or Dectomax (doramectin give IM) injection is given and repeated in 14 days (ivermectin) or 21 days (Dectomax). If this PBP is never again exposed to sarcoptic mange mites and the correct dose for the weight of the pig is given (presumed to be the same dose for PBPs and domestic swine – directions on the label), the pig should look much better in 2 weeks and be cured with no further treatments. Although people to pig transmission of mites has never been proven, the owners should get treated to avoid any possibility of giving mange mites back to their pigs (Of course, owners also need treatment to get relief from their itching!).

Likewise, in a PBP, the bacteria and viruses that originated from their dam or other pigs can be unapparently carried, and disease can then occur after stress (sometimes the stress event is not easy to pinpoint!), even in the total absence of any other pigs!

These are reasons for vaccination of the PBP, even if it is the only pig in the household.

Other reasons to vaccinate PBPs relate to human health and legal issues. When PBPs were first presented as possible licensed pets in cities, lawyers from municipalities wanted to know which vaccinations should be required. Since there are no approved rabies vaccines for any type of pig, these could not be legally required for registration. So, erysipelas, a very common disease of pigs that could be transmitted to people, (called a zoonotic disease) was selected as one disease to vaccinate against as an annual requirement for PBP licensing. (30-50 percent of domestic swine carry erysipelas organisms and show no disease.)

Also, leptospirosis (lepto) is a common disease (usually subclinical – not apparent) of domestic swine. Domestic swine get lepto from urine of other infected swine, other livestock and rodents. Lepto is also a zoonotic disease and was chosen as another required vaccination for PBPs for municipal pet licensing (should vaccinate against 6 types of lepto to include all common pig types!). Note that leptospirosis in people is usually a flu-like disease. It used to be called “swine herder’s disease” since it was very common in pig herdsman. So the idea behind vaccination of PBPs for lepto-6 is to prevent lepto infection, or to decrease the PBP urine shedding of lepto in the case of subclinical or “silent infection” in the pet. In either case, the human risk of catching lepto from the vaccinated PBP would be minimized.

So these are the reasons for initial and at least yearly vaccination of the PBP. Usually, APP (3 types – fatal pneumonia disease in pigs) are included with the erysipelas – a combination vaccine (one shot) and lepto-6 is another vaccination (one shot). Give both injections once then repeat in 3-4 weeks followed by at least annual boosters. Vaccinations are more imperative when large numbers of PBPs are congregated in one area, but it has been explained how even an isolated, household PBP can have a clinical disease such as erysipelas.

Note that vaccine reactions can occur in any species of animals. These occur more commonly on the second vaccination of initial series or on boosters. Veterinarians use an epinephrine injection IM as an initial therapy for a vaccine reaction. Additional therapy may be necessary. Those PBPs showing adverse reaction to a vaccine should not be revaccinated with the offending vaccine.

Another topic that has not been discussed much is tetanus. It definitely can occur in PBPs! Soil contamination of wounds, typically after castration when the incision site is left open, is how it typically starts. PBPs that stay outside in a lot are at the most risk. For prevention, initially administer tetanus toxoid once (0.5 cc IM, Tetanus Toxoid, Ft. Dodge) then 4 weeks later followed by an annual booster (it is not known how long immunity lasts in pigs but may be longer than 1 year). So tetanus toxoid vaccine can be given at the exact same time erysipelas-APP combination vaccine (Pneu-Pac-ER, 2cc IM, Schering) and lepto vaccine (2cc IM, Brativac-6, Pfizer) are given. Alternatively, these vaccinations can be staggered and given on separate days.

Remember that any wound on a pig that could be contaminated with dirt could be a way that a pig gets tetanus (prompt initial cleaning and daily cleaning of wounds prevents infection!). Tetanus antitoxin (500-1000 units IM depending on size) should be administered by veterinarians (or dispensed by veterinarians to trained personnel to be administered to PBPs) to any PBP undergoing a routine foot trim, tusk trimming, etc. If a PBP has received adequate vaccinations (two initial doses) with tetanus toxoid 2 weeks or more before the foot trim, tusk cutting or other procedure that creates a wound, tetanus antitoxin administration is then unnecessary.

Based on the above information, it is important that PBPs not be exposed unnecessarily to commercial swine due to possible transmission of infectious disease organisms that have not been diagnosed in PBPs (eg. exposure at local, county, state fairs and exhibitions). Significant sickness and mortality in PBPs could occur as a result of such exposure.

In summary, the scientifically-based, valid reasons for routine vaccinations in PBPs have been discussed.

Bruce Lawhorn, DVM, MS
Professor/Extension Swine Veterinarian
Texas Cooperative Extension Service/Dept Large
Animal Medicine & Surgery
College of Veterinary Medicine
The Texas A&M University System
College Station, Texas 77843-2487
979-845-4353 (p)
979-862-3795 (fax)
E-mail: BLawhorn@cvm.tamu.edu