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Internal Parasites

Swine performance is influenced by internal parasites, most dramatically in the young, growing pig. Parasites reside in the stomach and intestinal tract of the pig, causing irritation, impaction, indigestion and lack of appetite. Parasites cause loss of nutrients from feed consumed by competing with the host, and by causing poor digestion, gut ulceration and even blood loss. Even small numbers of the large roundworm, Ascaris suum, can depress feed intake and daily gain. Some worm parasites may be found in the lungs, where they interfere with respiration, sometimes resulting in pneumonia.

Even though internal parasites are commonly associated with pasture and dry lot husbandry, some parasites such asIsospora may be present in total confinement. Ascarid infections frequently are found in finishing barns with concrete floors. The reason for continuing parasitism in these units is that transmission is by infective eggs and oocysts, which are difficult to keep out of any environment. Therefore, appropriate deworming schedules and sanitation are mandatory for parasite prevention programs.

Large Roundworm
Most hogs have Ascaris infections during their lifetimes. These roundworms are usually found in greatest numbers in pigs up to two to three months of age with far fewer in older pigs. Sows usually are not clinically affected, but serve as carriers. Roundworms are long (6 to 12 inches), stout, pinkish worms, sometimes with curved tails. The adults live in the small intestine, grazing on the gut lining and ingesting particulate and liquid materials from digesting food.

Each female lays thousands of microscopic eggs per day. Eggs become infective after about one month. When another pig swallows them, they hatch in the stomach or small intestine. The tiny larva that emerges penetrates the gut wall and is carried to the liver through the bloodstream. In the liver, larvae migrate for one-half to one week and then are swept through the bloodstream to the lungs. From there the larvae are coughed up, swallowed and returned to the small intestine, where they grow and mature within two months. Thus pigs may be 1-1/2 to 2 months of age before eggs can be detected in fecal samples, but immature adult worms may be passed earlier. The significance of this is that clinical signs may occur before eggs are detectable in feces.

Several clinical events may occur in the infected pig including inflammation of the liver, spots on the liver, thickened lung tissue leading to inefficient respiration, and colic or gut pain. Often most obvious to the producer is competition of the pig and its roundworm burden for nutrients, so that wormy pigs are set back and appear unthrifty. Otherwise healthy pigs with a low worm burden may appear normal, but performance as judged by feed conversion may be depressed.

Whipworm
The whipworm, Trichuris suis, is slender, 2 to 2-1/2 inches long, and found in the cecum and upper large intestine. The slender head end of this small worm penetrates the gut lining, causing irritation and some blood loss. Female worms sporadically produce microscopic eggs in pigs three months of age and older. Eggs are infective and capable of surviving long periods in soil or on dirt- and feces-covered slatted and concrete floors. When pigs ingest eggs, infections remain in the intestinal tract of the pig and larvae do not migrate. There is a period of three months from the time of infection to passing eggs; bloody scouring may occur during this period as well as during egg production.

Nodular Worm
The name "nodular worm" stems from the nodules produced by a larval stage of Oesophagostomum.These nodules are formed as a fibrotic host response in the walls of the cecum and colon in an attempt to wall off the larvae. Larvae that escape nodule formation emerge in the gut and mature into adults less than one inch in length. The microscopic eggs are passed in the feces and hatch outside the pig. Pigs usually become infected with these larvae while feeding. The worms are confined to the gut. Condemnation of the large intestine or colon at slaughter is an economic loss when these are used for sausage casings. In the live pig, scouring may result from infection.

Threadworm
This tiny intestinal worm, Strongyloides, occurs commonly in baby pigs. The adults (females only) are practically microscopic and live in the wall of the small intestine. Microscopic eggs are passed in the feces of pigs as young as four days of age. Farrowing pens, dirt lots and pastures become contaminated; larvae that are hatched may be ingested in water and feed or may penetrate skin. Most importantly, these infective larvae may be passed in sow colostrum so that infection takes place at first nursing. Prenatal infections can also occur. Heavy infections may cause intensive scouring in neonatal pigs, resulting in acute dehydration. Protective immunity develops rapidly in pigs not overwhelmed by this early infection.

Kidney Worm
The kidney worm, Stephanurus, is a short (one inch), stout, black and white worm found in the fat around the kidney and sometimes in the kidney. Mature infections are found primarily in sows, since it takes nine months to one year after infection before eggs are produced by adult kidney worms. Because infection occurs in and around the kidneys, eggs are passed in the urine.

Wooded lots and shaded farrowing pens often become contaminated areas where larvae hatch from eggs and enter the soil. Pigs may become exposed to infective larvae by ingestion, skin penetration, and ingestion of infected earthworms. Larvae then move from the small intestine and eventually into the liver, where they remain for two to four months.

Other organs such as the lungs and spleen may also be infected. From the liver, larvae migrate to areas around and in the kidneys and even into back muscle. Most of the damage is found in the liver, which becomes heavily scarred, and in nearby muscle tissue.

Lungworm
Lungworms, Metastrongylus, are short (one to two inches), slender and white and occur in clusters deep in the respiratory tract (bronchioles). Eggs are coughed up, swallowed, and passed in the feces. Lungworm eggs are ingested by earthworms, allowing easy exposure to hogs that root in the soil and eat infected earthworms. Larvae are circulated by the lymphatic system from the small intestine, through the heart, and then into the lungs. Thumping or coughing with pneumonia is common in infected pigs. Pigs may pass eggs one month after infection.

Prevention
Parasite control should include good sanitation. Good nutrition is critical to the pig's ability to mount an immune response and maintain performance in the presence of parasites. Since roundworms and whipworms have transmissible eggs, indoor facilities need to be well-cleaned and traffic minimized. Gilts should be kept out of contaminated areas, and weaned pigs kept away from older breeding stock. Unfortunately, roundworm and whipworm eggs persist for long periods, kidneyworm and lungworm larvae are found in earthworms, and Strongyloides may be passed in colostrum. Management can be improved by working with a veterinarian.

Treatment
Those dewormers that are currently approved for use are effective and usually safe when given according to label directions. These include ivermectin, fenbendazole, pyrantel, dichlorvos and piperazine.

The deworming schedule should include pre-breeding for all breeding stock and pre-farrowing for gilts and sows, prevention of Strongyloides and roundworms in baby pigs, and one or more dewormings in weanling and growing pigs. Specific strategic schedules can be arranged with our veterinarians.

Formulations for group administration are provided as well as for individual treatment. Remember to use only label-approved drugs and label-approved routes of administration. Use approved formulations and appropriate drugs for the target parasite species and stages.

Coccidia
Neonatal (baby pig) coccidiosis caused by Isospora suis is often found when pigs are raised in confinement. Clinical signs of yellowish or gray pasty to liquid diarrhea appear at one to two weeks of age with dehydration evident even though nursing continues. Infection occurs in cells lining the small intestine. Oocysts (microscopic egg-like forms) are passed five days after infection. Oocysts mature in 12 hours in the farrowing crate, and disease and mortality are directly proportional to the number of infective oocysts ingested. There has been no good evidence that sows are carriers and pass oocysts to their piglets. The source for this coccidian is still not known.

The other coccidia, Eimeria, which are found in weanling and older pigs, apparently cause little or no damage. Differentiation of Isospora from Eimeria can be made microscopically by fecal examination but coccidiosis in baby pigs is apparently Isospora only. Unfortunately, none of the anti-coccidial drugs are effective against Isospora, but sanitation of farrowing crates by thorough cleaning can be successful in controlling it. Control is best achieved by:

  • Thorough cleaning and sanitation between each farrowing
  • Monitoring of movement of personnel and supplies
  • Control of pests and rodents to reduce mechanical transmission of the oocysts

External Parasites

Flies, lice and mites are the most problematic external parasites of swine. Some can transmit diseases. For example, the pig louse may carry swine flu viruses or swine pox. Flies can mechanically transmit bacteria and viruses from one pig to another, directly in the case of biting flies or indirectly by contaminating feed. Flies can also transmit infections from one pig farm to another.

Mites and lice are important because of their effect on growth, feed efficiency, and spread of disease.

Flies
Flies make contact with feces, skin and discharges from all surfaces of the pig. It follows, therefore, that if the number of flies in the environment reaches a high enough level, they can become major transmitters of disease organisms, not only within a building, but also between buildings and sometimes between pig herds. Such infections include pathogenic strains of E. coli, swine dysentery, salmonellosis, streptococcus infections, rotavirus and TGE. Bacillus bacteria, molds, staphylococci, yeasts, streptococci and coliforms have all been isolated from flies in farrowing houses. This illustrates the potential for the dissemination of organisms. Major outbreaks of greasy pig and coccidiosis can be maintained by very high fly populations. When sows are sick with mastitis, flies are attracted to the udder and skin surfaces in great numbers and they can be responsible for enhancing severe outbreaks.

They have also been shown experimentally to transmit Streptococcus suis type 2 which causes meningitis and because adult flies can live for up to four weeks and travel up to 1.5 miles, transmission between farms becomes a possibility. They can be responsible for piglet diarrhea persisting in farrowing houses.

If fly populations are allowed to build up, particularly in farrowing houses, they cause annoyance to herdsmen and distress to sows and piglets. Fly dirt causes heavy contamination of surfaces, particularly around warm areas, lamp surfaces, and lights. Large fly populations on a pig farm can also be a nuisance to nearby communities.

Lice
Lice are relatively uncommon in herds today, particularly if mange treatment is carried out, because this will also destroy the pig louse.

The adult female lays two-four eggs per day over a period of 20-30 days. The eggs are attached to the hair by a cement-like substance and they hatch out as nymphs 10-21 days afterwards. The cycle from adult to adult is approximately 30 days. They are blood sucking and cause a certain amount of irritation but their economic effects are probably relatively low. They are aesthetically, however, not acceptable and severe infestations can cause anemia. They are easily visible on the skin. Lice are the easiest parasites to keep out of the herd as they will only enter on a pig.

Mange
Mange is a parasitic disease of the skin caused by one of two mites, either Sarcoptes scabiei or Demodex phylloides. Sarcoptic mange (sometimes called scabies) is by far the most common and important because it is irritating and uncomfortable for the pig, causing it to rub and damage the skin which becomes unsightly. It significantly depresses growth rate and feed efficiency.

The mite spreads directly from pig to pig, either by close skin contact or contact with recently contaminated surfaces. If pigs are housed in groups, there is increased opportunity for spread. The mite dies out quickly away from the pig, under most farm conditions, in less than five days. This is an important factor in control. If a herd is free from mange, it is one of the easiest of diseases to keep out because it can only be introduced by carrier pigs. However, once it is introduced it tends to become permanently endemic unless control measures are taken.

The common signs are ear shaking and severe rubbing of the skin against the sides of the pen. Approximately three to eight weeks after initial infection, the skin becomes sensitized to the mite protein and a severe allergy may develop with very tiny red pimples covering the whole of the skin. These cause intense irritation and rubbing to the point where bleeding may occur. Head shaking is a common symptom and hairs are often rubbed away leaving bare patches. The incubation period to the appearance of clinical signs is approximately three weeks although it may be several months before signs are noticed in large pig populations, particularly in feeder pigs housed in pens with solid partitions.

After the acute phase, thick lesions develop on the ear, along the sides of the neck, the elbows, the front parts of the hocks, and along the top of the neck. Persistent skin irritation with small red spots on the skin developing into thickened areas suggests the presence of disease. The skin of pigs can also be examined at slaughter for evidence of the small red pimples. Herds with active disease always show a high level of grade 2 or grade 3 lesions. Diagnosis is confirmed by demonstrating the presence of the mite. To do this scrapings are taken from suspicious lesions on the skin and particularly inside the ears. Mange mites, which are rounded in shape and only 0.5mm in length, may be just visible to the naked eye. However to positively identify the mite, the scrapings should be examined microscopically.  Injectable ivermectin products are a readily available, highly effective treatment for mange.

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