Prevention and Control Methods and Technical Key Points for Porcine High Fever Syndrome

"Porcine unknown high fever," also known as porcine high fever syndrome, is a disease with high morbidity and mortality rates, occurring mainly in growing-finishing pigs and some sows. The main clinical manifestations in affected pigs are elevated body temperature, depression, loss of appetite or complete anorexia, difficulty breathing, panting, with some pigs showing symptoms such as reddened to purplish skin, and a few having hemorrhagic spots at the hair follicles. The pathogens are mainly mixed infections and secondary infections involving multiple viruses, bacteria, and parasites, including classical swine fever virus (HCV), porcine reproductive and respiratory syndrome virus (PRRSV), swine influenza virus (SIV), pseudorabies virus (ADV), porcine circovirus type 2 (PCV-II), and mixed infections with bacteria such as Actinobacillus pleuropneumoniae (APP), Streptococcus suis type 2 (SS-II), Haemophilus parasuis (HP), Pasteurella multocida (PM), Mycoplasma hyopneumoniae (MH), Toxoplasma, Eperythrozoon, and Salmonella choleraesuis (SC).

Because the etiology of this disease is complex, generally involving mixed infections of multiple pathogens, it is difficult to control clinically, and treatment results are often unsatisfactory, causing slowed or stunted growth in pig herds, an increase in diseased and dead pigs, reduced feed efficiency, growth rate, and overall uniformity of the herd, increased treatment costs, and causing severe losses to @#@227@#@ production.

I. Disease Characteristics

1. It occurs in seasons with higher temperatures, with a long disease course, generally about 5 to 20 days, and a high mortality rate.

2. Pig farms that do not pay attention to disease prevention work, whose technical personnel have poor health care concepts, that do not strictly seal off the pig farm, and that do not carry out systematic health care for the herd, experience severe outbreaks.

3. The body weight of affected pigs is generally 20 to 80 kg, with the highest incidence, and weaned piglets may also be affected.

4. Drug treatment results are not ideal, and pig farms that use drugs indiscriminately have higher mortality rates.

II. Clinical Symptoms

Affected pigs show elevated body temperature rising to 40 to 42.5°C, depression, decreased feed intake or complete anorexia, reddened skin, cyanosis of the ear margins behind the ears, and patchy purplish-red skin lesions in multiple areas of the body such as the ventral abdomen and extremities of the limbs; difficulty breathing, preference for lying prone, with some pigs showing severe abdominal breathing and rapid panting, and some exhibiting panting or irregular breathing; some affected pigs have nasal discharge, sneezing, coughing, and increased ocular discharge, with most pigs having tear stains and showing symptoms of conjunctivitis; some herds have constipation, with dry, ball-shaped feces, and yellow, scanty, turbid, darkened urine. Pigs with a slightly longer disease course become pale all over, showing anemia, with rough and messy hair coat, some affected pigs have weakness in the hind limbs, and individual affected pigs cannot stand before dying, finally dying with generalized convulsions. The mortality rate in affected herds is very high, in some farms even reaching 50 to 90%. Some sows in late pregnancy (100 to 110 days) experience abortion, giving birth to stillborn fetuses, weak piglets, and mummified fetuses.

III. Necropsy Changes

All dead pigs showed varying degrees of pneumonia, and the following symptoms can be seen on necropsy:

1. Lungs swollen and hardened; presenting as non-collapsible rubber-like lungs, with obvious interstitial pneumonia symptoms, and the lungs showing mottled to brown lesions (marbled appearance); most are mixed-infection pneumonia with suppurative foci, some pig lungs have hemorrhage, hemorrhagic pneumonia, with markedly widened interstitium.

2. Extensive lymph node enlargement, especially the inguinal lymph nodes and hilar lymph nodes.

3. Some dead pigs have swollen livers with pale color, and some livers are loess-colored and friable; individual pigs have hemorrhagic spots on the kidneys, bladder, larynx, fat of the coronary groove of the heart, and endocardium and epicardium; some dead pigs have swollen kidneys with darkened color, presenting as brown or earthy yellow, relatively friable, with congestion. Some affected pigs have swollen spleens that are friable.

4. Multiple serofibrinous pleurisy and peritonitis, with fibrinous exudation in the thoracic and abdominal cavities. Individual pigs have fibrinous adhesions between the pulmonary pleura and the pleura or pericardium.

IV. Prevention and Control Measures

The etiology of this disease is complex, and affected pigs generally have a poor prognosis. In prevention and control, the principle of prevention first should be maintained, and through measures such as strengthening feeding management, doing a good job in heat prevention and cooling, early health care and prevention, strengthening disinfection work, and symptomatic treatment, the morbidity and mortality rates can be reduced.

1. Maintain the principle of self-breeding and self-raising, and prevent the purchase of latently infected pigs.

2. Pay attention to the feeding and management of the herd, and minimize various stress factors as much as possible:

① In summer, do a good job in heat prevention and cooling, increase the ventilation volume of the pig house and use cooling measures such as spraying with cool water, promoting evaporation and heat dissipation through convection; all doors and windows of the pig house should be opened to allow air convection. When temperatures are higher, rinse the pigs' bodies with cold water or install spray devices, spraying 4 to 6 times per day;

② In summer, reduce stocking density; growing pigs should have more than 0.8 sq m of living space, and growing-finishing houses should preferably provide 1.2 sq m per pig, with the number of pigs per pen preferably around 10 to 12. Maintaining reasonable stocking density and cooling can effectively control porcine unknown high fever and respiratory diseases.

③ Strictly adopt the "all-in, all-out" feeding method from farrowing, nursery, to growing-finishing, avoid mixing pigs of greatly different ages in the same group, minimize the number of times pigs are moved between pens and mixed into groups, ensure that all pigs in the same pig house are moved out at the same time, and after each batch of pigs is sent to market, the pig house must undergo strict washing and disinfection and be left vacant for several days before new pigs are introduced.

3. Both the pig house and the environment need regular disinfection to reduce the content of pathogenic microorganisms.

Because viruses are not sensitive to ordinary disinfectants, especially porcine circovirus, which is unaffected by general disinfectants, new types of disinfectants with low irritation should be selected for disinfection, such as compound aldehyde disinfectant solutions. Within 10 days of the outbreak, the concentration of the disinfectant solution should be increased, and strict disinfection of the epidemic area and the external environment near the epidemic area should be carried out 4 to 6 times per day. Sows and large-to-medium pigs can be spray-disinfected together with the pigs at noon, and the living and management area of the pig farm should be disinfected once daily. Starting from the 10th day, the dilution can be doubled for disinfection, reducing the chance of healthy pigs being infected with influenza and other viruses through the respiratory tract, to prevent the spread and extension of this disease, which can achieve relatively good results in controlling the transmission of the epidemic.

4. Drug control measures:

This disease emphasizes prevention; when large-scale outbreaks occur in the herd, treatment results are generally unsatisfactory. Antibiotics should be added to feed or drinking water for prevention before the disease occurs, and medication should be added for prevention before the peak period of porcine unknown high fever. When the disease occurs, antibacterial drug treatment targeting bacteria and mycoplasma can reduce losses. Measures should be taken early to administer drugs simultaneously in drinking water and feed, combined with injection for treating affected pigs, to reduce deaths caused by secondary bacterial infections. Currently, drugs that are relatively sensitive in pig farm clinical practice include tiamulin, etc. Pig farms can adopt a combined medication approach according to their own conditions and formulate their own preventive health care medication plan. Start by controlling the source of bacterial diseases through medication and health care for sows.

① For herds that have already developed "porcine unknown high fever": add florfenicol + sulfamonomethoxine 300 g/ton to each ton of feed; because affected herds reduce feed intake and cannot ingest sufficient therapeutic doses of drugs, drugs should also be added to drinking water simultaneously, using a compound preparation of antibiotics and traditional Chinese medicine extracts effective against both bacteria and viruses, allowing the herd to drink freely for 5 to 7 days. Affected pigs should be isolated and raised, carefully cared for, and treated with injections of astragalus polysaccharide and long-acting sulfonamide preparations, 2 times per day for 3 to 5 consecutive days, while also adding drugs to drinking water for treatment. If affected pigs have mixed infection with viral diseases such as classical swine fever, the treatment results will be poor. For affected pigs with particularly severe conditions and poor treatment results, they should be promptly and decisively culled to prevent the spread of the disease.

② Growing-finishing period: Use effective drugs for prevention at 12 to 13 weeks of age and 17 to 18 weeks of age. Add florfenicol + doxycycline 250 g per ton of feed, or add soluble antibiotics to drinking water, using a pulse medication method, for 1 consecutive week, then stop for 1 week, then medicate for another 1 week.

③ In hot, high-temperature weather or when pigs are being moved between pens or vaccinated, anti-stress drugs such as multivitamin electrolytes should be added to drinking water to minimize the chance of disease caused by stress-induced decline in herd resistance.

④ Lactating sows: Add antibiotics to sow feed for 1 week before and after farrowing, adding florfenicol + lomefloxacin 1000 g per ton of feed for prevention; or add 80% tiamulin 125 g/ton + chlortetracycline 300 g/ton + amoxicillin 150 g/ton to reduce the shedding of pathogenic bacteria by sows contaminating the farrowing house and cut off horizontal transmission of diseases from sows to piglets.

⑤ Weaned piglets: Add antibiotics to piglet feed from 1 week before weaning to 4 weeks after weaning, adding florfenicol + doxycycline 200 g/ton per ton of feed; or use 80% tiamulin 125 g/ton + chlortetracycline 300 g/ton + amoxicillin 200 g/ton, to cut off horizontal transmission of diseases among piglets.

⑥ Regular deworming: Internal parasites such as Ascaris and whipworm damage the body's immune system and reduce herd resistance. Ascaris larvae migrating through the lungs and lungworms both aggravate the symptoms of respiratory diseases, so deworming with drugs is of certain significance for controlling the development of this disease. After weaned piglets are transferred to the nursery house for 2 weeks, deworming agents with obvious effects against internal and external parasites should be selected for deworming.