The good news about parasitic diseases

Monday, October 3, 2011

Many once-common parasitic diseases have largely been eliminated. In the first of two articles, a swine specialist discusses parasite groups that no longer afflict our herds

by S. ERNEST SANFORD

I realize that I often write about the latest new scourge to descend on our pigs or something equally disturbing even if not so new.  So, this time, I've decided to write about something that the swine industry has to celebrate, the elimination of a vast array of parasitic diseases that were very common in our pigs for most of the last century and are now history or very rare occurrences.

The following is a list of common parasitic diseases that you'll find described in text books on pig diseases:
External Parasites
Lice (Pediculosis)
Mange (Sarcoptic Mange)
Internal Parasites
Roundworms (Ascariasis)
Nodular Worms (Oesophagostomiasis)
Lung Worms (Metastrongylosis)
Threadworms (Strongyloidosis)
Whipworms (Trichuriasis)
Trichinosis (Trichimella spirilis)
Coccidiosis (Isospora suis)
Cryptosporidiosis (Cryptosporidium spp.)
Eperythrozoonosis (Mycoplasma
[formerly Eperythrozoon] suis)

I've left out parasites that we would not expect to see in Canada and, even so, I'm sure most readers will hardly even recognize the names of many of the above parasitic diseases, let alone have had first-hand experiences of them in their herds. Why?  Most of these parasitic diseases, quite common in the 1900s, had been eliminated or severely reduced in importance by the end of the last century. 
In this article, I will deal with external parasites.

Louse infestation
Haematopinus suis is the pig louse and the source of louse infestation. I'm sure there must be an occasional herd somewhere in Ontario that still has lice, but I haven't seen one in 25 to 30 years. Producers and veterinarians got rid of lice decades ago with the use of parasiticides (parasite killers), attention to detail and improvement in management fostered by the movement of pigs into total indoor, confinement rearing.

The pig louse is a blood sucker, which means its bite actually penetrates the skin and draws blood meals from the pig. This resulted in lice being the main means of transmission of certain pig diseases, the principal one being swine pox.

The eradication of lice also meant that swine pox has become a rarity and another in the list of diseases I haven't seen in decades. (There is a congenital swine pox that is still occasionally seen in newborn pigs at birth and has nothing to do with lice.)

Mange (Sarcoptic Mange)
Sarcoptic mange in pigs, caused by the mange mite, Sarcoptes scabeii var suis, is by far the most important external parasitic disease of pigs, worldwide. Sarcoptic mange affects many other species, including humans, but this particular mite is host-specific and seldom infects humans. Mange is rarely seen today in herds in Ontario.

Though it has not been completely eliminated, the use of avermectins by veterinarians and producers in mange eradication programs in the 1980s and 1990s has pushed this parasitic disease almost into the historical interest category. I have dealt with only a handful of mange cases in pigs over the last 15-20 years, and even before that mange cases had already become few and far between.

Epidemiology. The mange mite goes through several developmental stages (egg, larvae, nymphs, adults) all of these stages occurring in the epidermis, the superficial layer of the skin. Spread is by contact with infested pigs especially in crowded conditions. They burrow through the epidermis, forming tunnels, and are very irritating, causing the pig to scratch.

A hypersensitivity reaction is often created, causing even more scratching and trauma to the skin. Colonization usually occurs first in the inner surface of the ear before spreading over the body, tail and legs.

Clinical signs. Frequent rubbing and scratching are telltale signs of mange infestation. Decreased growth rate, reduced feed efficiency and low sow productivity follow. Morbidity within a herd is high, mortality is unusual.

Acute mange lesions are seen in younger pigs that have developed hypersensitivity and consist of reddened raised areas (macules and papules), especially over the rump, flanks and abdomen. In older animals, lesions are chronic, consisting of crusts in the inner ear, and could be present over much of the body. Scratching is less common in chronic cases.

Diagnosis. Clinical signs and lesions are suggestive of mange. Confirmation is by identification of the mites under a microscope from skin scrapings of lesions.

Control. The use of acaricides (mite killers) as topical treatments has largely been replaced by the use of avermectins in whole herd eradication programs. These programs have been so successful that, today, mange is a disease almost of historical significance and is rarely seen in modern production systems.

I'll deal with internal parasites (roundworms, lung worms, coccidiosis, etc.) in a subsequent article. BP

S. Ernest Sanford, DVM, Dip. Path., Diplomate ACVP, is a swine specialist with Boehringer Ingelheim Vetmedica (Canada) in Burlington. Email: ernest.sanford@boehringer-ingelheim.com