Diagnosis and Prevention of Porcine Toxoplasma gondii

Toxoplasmosis is a zoonotic parasitic protozoonosis caused by Toxoplasma gondii infection in animals and humans. The disease is distributed all over the world, with high morbidity and mortality, which not only seriously harms the healthy development of pig industry, but also has a direct impact on human health.

Toxoplasma gondii can invade pigs through mouth, eyes, nose, respiratory tract, intestines and skin. after infected with toxoplasmosis, pigs are mainly characterized by persistent fever, dyspnea, wheezing and skin redness. accompanied by nervous system symptoms and reproductive disorders in sows (its main features are similar to classical swine fever, swine lung disease, porcine eperythrozoonosis and so on, and are easy to be misdiagnosed. It can only be diagnosed by veterinary laboratory diagnosis.

Porcine toxoplasmosis can be seen clinically as acute, subacute and chronic toxoplasmosis, and it is often accompanied by symptoms of concurrent infection or secondary infection in clinical cases. and lead to the use of common antibiotics and antiviral drugs treatment is ineffective or even ineffective, mild will affect the growth and development of suckling piglets And further affect the weight gain and the uniformity of growth and development of weaned piglets, which can easily lead to the formation of stiff pigs in some diseased piglets. If it is serious, it will cause a large number of sick piglets to die. The disease is a stubborn disease in pig farms. If pig toxoplasmosis occurs in pig farms, the morbidity and mortality of the whole pig farm can reach more than 60%. If it is not controlled in time and effectively, it will cause huge economic losses to pig farms and seriously threaten human health. In view of the harm of porcine toxoplasmosis, this paper makes a brief analysis on the diagnosis and prevention of porcine toxoplasmosis, in order to provide reference for the effective prevention and treatment of porcine toxoplasmosis.

I. Epidemiological characteristics

The final hosts of Toxoplasma gondii are cats and cats, and the intermediate hosts are all kinds of mammals and birds. Pigs are also one of the intermediate hosts of Toxoplasma gondii. The stage of sexual reproduction of Toxoplasma gondii is completed in the intestinal epithelial cells of cats and cats, and excretes the oocysts, and the intermediate host will be infected if the oocysts and trophozoites are swallowed. Toxoplasma gondii mainly invades nucleated cells, especially reticular endothelial cells, and divides and propagates, and trophozoites are released after cell rupture, which leads to acute infection in pigs. If the cell is not ruptured, it will form a cyst and lead to chronic infection or recessive infection in pigs. There is no difference in the susceptibility of pigs to Toxoplasma gondii in breeds, age and sex. generally, the morbidity and mortality of piglets aged from 2 months to 4 months are higher, and large pigs and adult pigs show recessive infection because of their strong resistance. if infection occurs in pregnant sows in the later stage of pregnancy, it will often show abortion, stillbirth and lower survival rate of piglets.

Porcine toxoplasmosis mostly occurs in summer and autumn, especially in warm, humid climate and rampant blood-sucking insects. Human and cats, pigs, chickens and other animals can be infected by direct contact with food and drinking water containing oocysts through digestive tract and respiratory tract, and can also be infected through skin and mucosa during acute attack, and fetus can be infected through placenta.

Second, clinical symptoms

The incubation period of pigs infected with Toxoplasma gondii (invasive oocyst) is generally 3 ~ 7 days. At the beginning of the disease, the pigs showed anorexia or lack of food, low energy, conjunctival congestion and flushing; after 3 ~ 4 days, the diseased pigs showed high fever, the body temperature rose to 40.5 ℃ ~ 42.0 ℃, showing missed fever, loss of appetite and even abandonment, like to lie down, like to drill straw piles or puddles, conjunctival puddles pale, yellow-stained eyes In the later stage of development, the diseased pigs were mainly characterized by dyspnea, abdominal breathing, wheezing, coughing and runny nose, and the stools were dry first and then thin or dry alternately, and the feces were gray-green or coal tar. With the development of the course of the disease, hemorrhagic purple spots appeared on the ear tip, vulva, prepuce tip and abdominal skin of diseased pigs, and there were blood stasis spots on the lower part of the body and ears of some diseased pigs. Palpation can feel enlarged body surface lymph nodes, especially inguinal lymph node enlargement.

Infection in suckling pigs is often accompanied by neurological symptoms, such as circle rotation, ataxia and other symptoms, while some diseased pigs show difficulty in lying down, gait instability during artificial driving, and joint enlargement in some diseased pigs. and inguinal lymph node enlargement is obvious. It takes about 2 weeks for sick pigs to recover, but they often leave neurological symptoms such as cough, dyspnea, hindquarters paralysis, torticollis, epileptic spasm and so on. If acute toxoplasmosis infection occurs in pregnant sows, high fever occurs at first, then loss of appetite, sick sows are sleepy, and a few days later, miscarriages or stillbirths occur in sows, and weak babies die within a few days. Sows often heal themselves after abortion and generally do not leave sequelae.

3. Pathological changes of autopsy

The ears, extremities and nasal kisses of dead pigs are blue-purple, and white foamy fluid is common around the nostrils and nasal cavities; most dead pigs have enlarged inguinal lymph nodes and rope-shaped mesenteric lymph nodes with a light red appearance, and the section is turned out in the shape of marinade spots; there are scattered central sunken ulcers of millet or sorghum rice in the cecum and colon, with grayish-yellow pseudomembrane on the surface. In the heart, the right heart is dilated, there are blood clots in the heart cavity, and the myocardium is turbid and fragile; the volume of the lung is slightly enlarged, the pulmonary lobular interstitium widens, and foamy fluid flows out of the section; the liver is enlarged and degenerated, and scattered or densely scattered bleeding spots and gray-white or grayish-yellow lesions with needle tips large to millet size can be seen on the surface; splenomegaly, section structure blurred, hemorrhagic infarction can be seen on the capsule in a few cases. Renal degeneration, scattered bleeding spots can be seen on the capsule in some cases; needle tip bleeding spots can be seen on the bladder mucosa; gastric fundus gland congestion or bleeding and superficial ulcers; intestinal congestion or catarrhal inflammation.

IV. Diagnosis

A preliminary diagnosis can be made according to the epidemiological characteristics, clinical symptoms and pathological changes of porcine toxoplasmosis. The diagnosis must be confirmed by veterinary laboratory examination to detect pathogens or specific antibodies. In general, veterinary laboratories can take blood, cerebrospinal fluid, lymph nodes, liver, feces and other materials of dead pigs to make tablets and smears, Giemsa staining microscopic examination, looking for Toxoplasma gondii eggs under the microscope. The commonly used methods of immunological diagnosis include methylene blue staining, biotin-avidin enzyme-linked immunosorbent assay, immune cell adhesion test, fluorescent antibody technique and so on.

Porcine toxoplasmosis is easy to be confused with classical swine fever, porcine lung disease and porcine eperythrozoonosis in terms of symptoms and pathological changes. Therefore, attention should be paid to differential diagnosis to prevent misdiagnosis.

First, the differential diagnosis of swine toxoplasmosis and classical swine fever: both have clinical symptoms such as depression, elevated body temperature, red skin, cyanosis and so on, but although systemic skin cyanosis can be seen in pigs with swine fever, cough, dyspnea and other symptoms can not be seen in pigs. Autopsy examination of dead pigs with classical swine fever shows a little bleeding in kidney and bladder, and hemorrhagic infarction in spleen. In the case of chronic classical swine fever, there were button-like ulcers in the ileocecal valve, no gray-white necrosis in the liver, no interstitial enlargement in the lungs, and no gel-like substance.

The second is the differential diagnosis of porcine toxoplasmosis and porcine lung disease: both have clinical symptoms such as mental depression, elevated body temperature, red skin, cyanosis and dyspnea, but after the onset of porcine lung disease, rales and friction sounds can be heard in chest auscultation. Percussion rib pain, and cough aggravated; autopsy showed rough lung capsule, cellulose film, dark red and yellowish lung section such as marble pattern.

The third is the differential diagnosis of porcine toxoplasmosis and porcine eperythrozoonosis: both have clinical symptoms such as depression, elevated body temperature, redness of skin, dyspnea and so on, but after the onset of porcine eperythrozoonosis, the main manifestations are cough and wheezing. and the diseased pig's voice is hoarse; the diseased pig's mucous membrane is congested first and then pale, with mild yellow staining and thin blood. During the autopsy of dead pigs, the blood coagulation was poor, and there were yellow striped necrotic areas on the surface of the liver.

V. Prevention and control measures

1. Preventive measures

First, pig farmers should pay attention to the prevention of porcine toxoplasmosis at ordinary times. The environmental hygiene around pig farms and pig houses should be cleaned regularly, and rodent disinfection should be done regularly. Pig farms should prohibit the use of slaughterhouse wastes, kitchen garbage and raw meat soup to feed pigs, and breeding cats and dogs should be prohibited in pig farms. Domestic and wild cats should be strictly prevented from coming into contact with pig houses and pig herds, and the pollution of feline excreta to pig houses, feed and drinking water should be strictly blocked. At the same time, it is necessary to kill beetles, mosquitoes, flies and earthworms in and around the field as far as possible, so as to prevent the mechanical transmission of porcine toxoplasmosis.

Second, it is necessary to do a good job in epidemic prevention and supervision of pigs in peacetime. Other animals with toxoplasmosis and their excretions, aborted fetuses and feces of sows should be strictly treated innocuously, and the site should be strictly disinfected to prevent them from polluting the surrounding environment.

Third, in the high incidence season of porcine toxoplasmosis, in order to effectively control the epidemic of porcine toxoplasmosis in pig farms, preventive drugs should be applied to pigs. 500 grams of sulfadiazine and 25 grams of pyrimethamine can be added to each ton of feed for 7 days to effectively prevent the occurrence of porcine toxoplasmosis.

2. Treatment measures

First, once suspected swine toxoplasmosis occurs in pig farms, sick pigs should be isolated in time, decisive elimination measures should be taken for seriously diseased pigs, and harmless treatment measures such as deep burial should be taken for sick and dead pigs. 3% quicklime solution is used every day to disinfect the internal and external environment of the pig house.

Second, the diseased pigs diagnosed with porcine toxoplasmosis should be treated in time. For the diseased pigs with acute toxoplasmosis (generally, the therapeutic effect is obvious within 3 days after the onset of the disease, but after 5 days, the cure effect is poor, even after the treatment measures are taken, after the symptoms of the diseased pigs disappear, Toxoplasma gondii will also enter the tissue to form cysts, and will cause the diseased pigs to become carriers) According to the body weight of diseased pigs, 0.3 ml of compound sulfadiazine sodium injection (1 g of sulfadiazine sodium and 0.2 g of trimethoprim per 10 ml) can be injected intramuscularly, the first injection dose can be doubled, 3 times a day for 3 consecutive days, and the same amount of sodium bicarbonate injection should be injected intramuscularly. For seriously ill pigs, symptomatic treatment measures should be taken, such as antipyretic, infusion, and antibiotics to prevent secondary infection. If the condition of the diseased pig is controlled, the treatment should be continued for another 1 ~ 2 days. For suspected diseased pigs that have not yet shown clinical symptoms, sulfamethoxine can be mixed into the feed of all pigs according to 0.1% preventive dose, or sodium sulfamethoxine or Fugongkang + TMP can be mixed and fed to the pigs for 7 days.