Special Topics On Swine Disease-Toxoplasmosis

Special Topics On Swine Disease-Toxoplasmosis

Overview: The causative agent of toxoplasmosis is Toxoplasma gondii, a protozoan parasite belonging to the genus Toxoplasma, commonly referred to as Toxoplasma. This parasite is a type of coccidian and is named for its crescent (bow) shape. Toxoplasma has five distinct stages in its life cycle: tachyzoites, tissue cysts, schizonts, gametocytes, and oocysts. It can infect humans and a wide range of animals, including mammals, birds, and some cold-blooded reptiles, with over 200 host species documented, making it a zoonotic parasitic disease.

Toxoplasma does not have specialized locomotion structures but is capable of movement. Tachyzoites are sensitive to temperature and common disinfectants such as 1% Lysol or 3% phenol, which can kill them within one minute of contact. Tissue cysts are more resistant, while oocysts are highly resistant to acids, alkalis, and most common disinfectants. Even 1% sulfuric acid or 2.5% potassium dichromate cannot inactivate oocysts. However, oocysts are susceptible to heat, desiccation, and ammonia.

Transmission Routes:

1. Congenital Infection: Transmission occurs when the fetus is infected in utero from the mother.
2. Acquired Infection: The parasite mainly invades the host through mucous membranes or broken skin. Oral ingestion leads to infection via the intestinal mucosa. Common routes include:
   • Digestive tract infection
   • Direct contact infection
   • Aerosol transmission
   • Other routes, such as blood transfusion, organ transplantation, or accidental inoculation during occupational exposure

The disease tends to occur more frequently in the warmer months from May to October and is particularly severe in piglets aged 3 to 5 months.

Clinical Symptoms: The morbidity rate can exceed 60%, with mortality rates as high as 64%, particularly severe in piglets weighing 10-50 kg. The disease usually progresses acutely. Infected pigs show sudden anorexia and fever exceeding 41°C, which can last for 7-10 days. Symptoms include labored breathing (abdominal or sitting-dog posture), serous or purulent nasal and eye discharge, and often constipation with pellet-like feces covered in mucus. In later stages, diarrhea and orange-colored urine may occur. Vomiting is seen in some cases. Sick pigs exhibit depression and marked weakness.

Neurological symptoms such as hindlimb paralysis may develop within days. As the disease progresses, purple-red spots or petechial hemorrhages appear on the ears, snout, limbs, inner thighs, and lower abdomen. Scabs may form on the ears, and necrosis at the ear tips can occur. Death typically results from respiratory distress and a sharp drop in body temperature. Pregnant sows often experience abortions or stillbirths. Some pigs develop chorioretinitis or even blindness. If pigs survive the acute phase, they may enter a chronic stage with only mild signs such as poor appetite and dullness, eventually becoming stunted pigs.

Treatment: Sulfonamides are commonly used for treatment:

●Sulfadiazine (SD) 70 mg/kg combined with pyrimethamine 6 mg/kg, administered orally twice daily (initial dose doubled) for 3-5 days.
●Sulfamethoxypyridazine (SMM) 60 mg/kg, intramuscular injection once daily for 3-5 days.
●Potentiated sulfonamide (containing 2% trimethoprim) 0.2 mL, intramuscular injection once daily for 3-5 days.
●Sulfamonomethoxine (SMZ) 100 mg/kg, administered orally once daily for 2-3 days.

Prevent cats from entering pig pens, and farm workers should avoid contact with cats. Do not feed pigs raw meat scraps.

Prevention: Since toxoplasmosis is mainly caused by ingesting oocysts from cat feces, it is critical to strictly prohibit cats from entering pig houses and prevent contamination of feed and water with cat feces, either directly or indirectly. Rodent control is also important. Most disinfectants are ineffective against oocysts, but steam or heat treatment can kill them. Only livestock that tests serologically negative for toxoplasmosis should be used for breeding. Animals play a crucial role in the spread of toxoplasmosis, and this should be given sufficient attention.

4o