Diagnosis Methods and Prevention and Control Measures of Swine Toxoplasmosis Explained
Toxoplasmosis is a zoonotic parasitic protozoal disease caused by Toxoplasma infection in animals and humans. The disease is distributed worldwide and has a relatively high morbidity and mortality rate. It not only seriously harms the healthy development of the pig industry, but can also directly affect human health.
Toxoplasma can invade the pig body through the mouth, eyes, nose, respiratory tract, intestinal tract, skin and other routes. After pigs are infected with toxoplasmosis, the main disease characteristics are continuous fever, difficulty breathing, panting, reddening of the skin, accompanied by neurological symptoms and reproductive disorders in sows (its main disease characteristics are relatively similar to swine fever, swine pasteurellosis, swine eperythrozoonosis, etc., and it is very easily misdiagnosed; confirmation can only be made through veterinary laboratory diagnosis).
Swine toxoplasmosis can generally be seen clinically in three types: acute, subacute and chronic, and clinical cases are often accompanied by concurrent infection or secondary infection symptoms, leading to poor or even ineffective treatment results with ordinary antibiotic drugs and antiviral drugs. In mild cases, it affects the growth and development of affected suckling piglets and further affects the weight gain and growth uniformity of weaned piglets, thus very easily causing some affected piglets to become runt pigs; in severe cases, it causes the death of large numbers of affected piglets. This disease is a major stubborn problem for pig farms. If swine toxoplasmosis occurs on a pig farm, the morbidity and mortality rate of the entire pig farm can reach more than 60%. If it is not controlled promptly and effectively, it will cause huge economic losses to the pig farm and seriously threaten human health. In view of the harm of swine toxoplasmosis, a brief analysis of the diagnosis and prevention of swine toxoplasmosis is now provided, aiming to provide reference and guidance for pig farmers to effectively prevent and control swine toxoplasmosis.
I.Epidemiological Characteristics
The definitive hosts of Toxoplasma are cats and felines, and the intermediate hosts are various mammals and birds. Pigs are also one of the intermediate hosts of Toxoplasma. The sexual reproduction stage of Toxoplasma is completed in the intestinal epithelial cells of cats and felines, and oocysts are shed. Intermediate hosts become infected if they swallow oocysts and trophozoites; Toxoplasma mainly invades nucleated cells, especially reticuloendothelial cells, and undergoes division and reproduction. After the cells rupture, trophozoites are released, causing acute infection in pigs; if the cells do not rupture, cysts are formed, causing chronic infection or latent infection in pigs. There is no difference in the susceptibility of pigs to Toxoplasma by breed, age or sex. Generally, the morbidity and mortality rates are higher in piglets aged 2 months to 4 months. Older pigs and adult pigs mostly show latent infection due to stronger resistance; if pregnant sows become infected in late pregnancy, they often show abortion, stillbirth and reduced survival rate of the piglets born.
Swine toxoplasmosis mostly occurs in summer and autumn, and is especially likely to occur in seasons with warm, humid climates and rampant blood-sucking insect activity. Humans and various animals such as cats, pigs and chickens can all become infected through the digestive tract and respiratory tract by direct contact with food and drinking water containing oocysts, and during acute onset it can also be transmitted through the skin and mucous membranes, and can also infect the fetus through the placenta.
II.Clinical Symptoms
After pigs are infected with Toxoplasma (invasive oocysts), the incubation period is generally 3 days to 7 days. At the beginning of the disease, affected pigs show anorexia or reduced eating, listlessness, and congested and reddened conjunctiva; after 3 days to 4 days, affected pigs show high fever, with body temperature rising to as high as 40.5°C to 42.0°C, showing continuous fever, reduced or even complete loss of appetite, preference for lying down, preference for burrowing into haystacks or water pits, and pale and icteric conjunctiva; in the later stage, affected pigs mainly show difficulty breathing, with abdominal breathing, panting, coughing, runny nose, and defecation that is first dry then loose or alternating dry and loose, with the feces being grayish-green or coal tar-like; as the disease progresses, hemorrhagic purpura appears on the ear tips, vulva, tip of the prepuce and abdominal skin of affected pigs. Some affected pigs have petechial spots on the lower part of the body and ears. On palpation, enlargement of superficial lymph nodes can be felt, especially the inguinal lymph nodes, which are more obviously enlarged.
Infected suckling piglets often have neurological symptoms such as circling and ataxia. Some affected pigs show difficulty rising from sternal recumbency, and when driven by humans they have an unsteady gait. Individual affected pigs may even show joint swelling, and the inguinal lymph nodes are obviously enlarged. Affected pigs that survive generally take about 2 weeks to recover, but often have residual neurological symptoms such as coughing, difficulty breathing, hindquarter paralysis, torticollis and epileptiform spasms. If pregnant sows become infected with acute toxoplasmosis, they first develop high fever at onset, then complete loss of appetite, and the affected sows are drowsy. After several days, the sows abort or give birth to stillborn or weak piglets. Weak piglets die within a few days of birth, while the sows often recover on their own after abortion and generally do not have residual sequelae.
III.Pathological Changes on Necropsy
The ears, extremities of the limbs and nasal plane of dead pigs are blue-purple, and white foamy liquid is commonly seen around the nostrils and in the nasal cavity; most dead pigs have enlarged inguinal lymph nodes, and the mesenteric lymph nodes are enlarged and rope-like, pale red in appearance, with the cut surface everted and showing a sauce-red mottled appearance; the cecum and colon have scattered ulcers the size of millet or sorghum grains with depressed centers, and their surface is covered with grayish-yellow pseudomembranes; the heart shows right heart dilation, with blood clots in the heart chambers, and the myocardium is cloudy and friable in texture; the lungs are slightly enlarged in volume, with widened interlobular interstitium, and foamy liquid flows from the cut surface; the liver is enlarged and degenerated, and scattered or densely distributed hemorrhagic spots and grayish-white or grayish-yellow lesions ranging from needle-tip size to millet-grain size can be seen on the surface; the spleen is enlarged, with an indistinct structure on the cut surface, and in a small number of cases hemorrhagic infarcts can be seen on the capsule; the kidneys are degenerated, and in some cases scattered hemorrhagic spots can be seen on the capsule; needle-tip-sized hemorrhagic spots can be seen on the bladder mucosa; the fundic gland region of the stomach is congested or has hemorrhage and superficial ulcers; the intestines are congested or have catarrhal inflammation.
IV.Diagnosis
A preliminary diagnosis can be made based on the epidemiological characteristics, clinical symptoms and pathological changes on necropsy of swine toxoplasmosis. Confirmation requires finding the pathogen or specific antibodies through veterinary laboratory examination. Generally, veterinary laboratory examination can take materials such as blood, cerebrospinal fluid, lymph nodes, liver and feces from dead pigs, make compression preparations and smears, stain with Giemsa and examine under a microscope to look for Toxoplasma oocysts. Commonly used immunological diagnostic methods include the methylene blue staining method, biotin-avidin enzyme-linked immunosorbent assay, immunocyte adherence test and fluorescent antibody technique, etc.
Swine toxoplasmosis is easily confused with swine fever, swine pasteurellosis and swine eperythrozoonosis in terms of onset symptoms and pathological changes on necropsy. Therefore, attention should be paid to differential diagnosis to prevent misdiagnosis.
First, differential diagnosis between swine toxoplasmosis and swine fever:Both diseases show clinical symptoms such as depression, elevated body temperature, reddening of the skin and cyanosis after onset, but although swine fever can show generalized skin cyanosis in affected pigs, affected pigs do not show symptoms such as coughing and difficulty breathing; necropsy of pigs that died of swine fever shows punctate hemorrhage in the kidneys and bladder, and hemorrhagic infarction in the spleen; chronic swine fever cases show button-like ulcers at the ileocecal valve, no grayish-white necrotic foci in the liver, and no widening of the pulmonary interstitium, with no gelatinous material.
Second, differential diagnosis between swine toxoplasmosis and swine pasteurellosis:Both diseases show clinical symptoms such as depression, elevated body temperature, reddening of the skin, cyanosis and difficulty breathing after onset, but after the onset of swine pasteurellosis, rales and friction sounds can be heard on chest auscultation, percussion of the rib area is painful, and coughing intensifies; necropsy shows a rough pulmonary capsule with a fibrinous membrane, and the cut surface of the lung is dark red and pale yellow with a marble-like pattern.
Third, differential diagnosis between swine toxoplasmosis and swine eperythrozoonosis:Both diseases show clinical symptoms such as depression, elevated body temperature, reddening of the skin and difficulty breathing after onset, but after the onset of swine eperythrozoonosis, the main manifestations are coughing and panting, and the calls of affected pigs are hoarse; the visible mucous membranes of affected pigs are first congested and then pale, with mild icterus, and the blood is thin; necropsy of dead pigs shows poor blood coagulation, and 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 doing a good job in the routine prevention of swine toxoplasmosis. The environmental sanitation around the pig farm and in the pig houses should be cleaned frequently, and disinfection and deratization work should be done regularly. Pig farms should prohibit the use of slaughterhouse waste, kitchen garbage and raw meat broth to feed the pig herd. Raising cats and dogs, etc. in pig farms should be prohibited, and domestic and wild felines should be strictly prevented from contacting pig houses and the pig herd, strictly blocking contamination of pig houses, their feed and drinking water by feline excreta. At the same time, beetles, mosquitoes, flies and earthworms in and around the farm should also be killed as much as possible to guard against mechanical transmission vectors of swine toxoplasmosis.
Second, routine epidemic prevention supervision of the pig herd should be done well. Other animals suffering from toxoplasmosis and their excretions, as well as fetuses aborted by sows and their excretions, should be strictly subjected to harmless treatment, and the sites should be strictly disinfected to prevent them from contaminating the surrounding environment.
Third, in the high-incidence season of swine toxoplasmosis, in order to effectively control the prevalence of swine toxoplasmosis on pig farms, preventive medication should be given to the pig herd in a targeted manner. Per ton of feed for the pig herd, 500 grams of sulfadiazine and 25 grams of pyrimethamine can be added, and feeding can be continued for 7 days, to effectively prevent the occurrence of swine toxoplasmosis.
2. Treatment Measures
First, once suspected cases of swine toxoplasmosis occur on a pig farm, affected pigs should be isolated promptly, and decisive culling measures should be taken for severely affected pigs. Harmless treatment measures such as deep burial should be taken for dead pigs, and a 3% quicklime solution should be used daily to disinfect the environment inside and outside the pig houses.
Second, treatment measures should be taken promptly for pigs confirmed to have swine toxoplasmosis. For pigs with acute toxoplasmosis (treatment results are generally relatively obvious within 3 days of onset, but after 5 days of onset, the cure rate is relatively poor; even after treatment measures are taken and the onset symptoms of affected pigs disappear, Toxoplasma will still enter tissues and form cysts, causing affected pigs to become carriers), compound sulfadiazine sodium injection can be used at 0.3 milliliters per kilogram of body weight of affected pigs (each 10 milliliters contains 1 gram of sulfadiazine sodium and 0.2 grams of trimethoprim) by intramuscular injection, with the first injection dose doubled, injected 3 times a day for 3 consecutive days, and at the same time an equal amount of sodium bicarbonate injection should be given by intramuscular injection; for severely affected pigs, symptomatic treatment measures should be taken, such as antipyretics and fluid infusion, along with antibiotic drugs to prevent secondary infection. If the condition of affected pigs is brought under control, treatment should be continued for another 1 day to 2 days; for suspected affected pigs that have not yet shown clinical symptoms, a 0.1% preventive dose of sulfamonomethoxine can be mixed into the feed of all pig herds for prevention, or sulfadimidine sodium or Fuyangkang + TMP can be mixed and fed to the pig herd, with continuous feeding for 7 days.