How to Prevent and Treat Porcine Unknown High Fever Syndrome? A Detailed Guide to Practical Methods

"Porcine unknown high fever," also known as porcine high fever syndrome, is a disease with both high morbidity and high mortality, occurring mainly in growing-finishing pigs and some sows. The main clinical signs in affected pigs are elevated body temperature, listlessness, poor appetite or complete loss of appetite, difficulty breathing and panting; some pigs also show reddened to purplish skin, and a few have bleeding points 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 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 cause of this disease is complex and it generally involves mixed infection by multiple pathogens, it is relatively difficult to control in clinical practice, and treatment results are often unsatisfactory. This leads to slow or stalled growth in the herd, an increase in cull pigs and dead pigs, reduced feed efficiency, growth rate and overall uniformity of the herd, and higher treatment costs, causing serious losses to @#@227@#@ production.

I. Disease Characteristics

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

2. Pig farms that do not attach importance to epidemic prevention work, whose technical personnel have poor health-care awareness, that do not strictly close off the pig farm, and that do not carry out systematic health care for the herd have severe outbreaks.

3. Affected pigs generally weigh 20 to 80 kg, with the highest morbidity, and weaned piglets can also be affected.

4. Drug treatment results are not very satisfactory, and pig farms that misuse drugs have a higher mortality rate.

II. Clinical Symptoms

Affected pigs have body temperature rising to 40 to 42.5°C, are listless, and have reduced feed intake or complete loss of appetite. The skin of affected pigs is reddened; the skin behind the ears and at the ear margins is cyanotic, and multiple areas of the body such as the underside of the abdomen and the extremities of the limbs show patchy, purplish-red skin. They have difficulty breathing and prefer to lie prone; some pigs show severe abdominal breathing with rapid panting, and some show panting or irregular breathing. Some affected pigs have nasal discharge, sneezing, coughing and increased eye discharge; most pigs have tear stains and show symptoms of conjunctivitis. Some herds have constipation, with hard, ball-shaped feces, and yellow, scanty, turbid and darker urine. Pigs with a slightly longer course become pale all over, show anemia and have rough, messy hair coats; some affected pigs have weak hind legs, and individual affected pigs cannot stand before dying and finally die after generalized convulsions. Mortality in affected herds is very high, in some farms even reaching 50 to 90%. Some sows abort in late pregnancy (100 to 110 days), giving birth to stillborn piglets, weak piglets and mummified fetuses.

III. Necropsy Changes

All dead pigs show pneumonia of varying degrees, and necropsy reveals the following symptoms:

1. The lungs are swollen and hardened, appearing as rubbery lungs that cannot contract, with obvious signs of interstitial pneumonia; the lungs show mottled to brown lesions (marble-like). Most cases involve mixed-infection pneumonia with suppurative foci; some pig lungs show hemorrhage, hemorrhagic pneumonia, and markedly widened interstitium.

2. Lymph nodes are extensively enlarged, especially the inguinal lymph nodes and hilar lymph nodes.

3. Some dead pigs have a swollen liver with a paler color, and some livers are loess-colored and brittle; individual pigs have bleeding points in the kidneys, bladder, larynx, fat of the coronary groove of the heart, and the endocardium and epicardium. Some dead pigs have swollen kidneys that are darker in color, brown or earthy yellow, relatively brittle, and show congestion. Some affected pigs have a swollen and brittle spleen.

4. Multiple serofibrinous pleurisy and peritonitis, with fibrinous exudation in the thoracic and abdominal cavities. In individual pigs, the pulmonary serosa is fibrinously adhered to the pleura or pericardium.

IV. Prevention and Control Measures

Because the cause of this disease is complex and affected pigs generally have a poor prognosis, prevention and control should insist on prevention first. By strengthening feeding management, doing a good job in heat prevention and cooling, providing health care and prevention in advance, strengthening disinfection work, and providing symptomatic treatment and other measures, its morbidity and mortality can be reduced.

1. Adhere to the principle of self-breeding and self-raising to prevent the purchase of latently infected pigs.

2. Attach importance to the feeding management of the herd and minimize various stress factors:

① In summer, do a good job in heat prevention and cooling, increase the ventilation rate of the pig house and use measures such as cool-water spraying to lower the temperature; promote evaporation and heat dissipation through convection. All doors and windows of the pig house should be opened to allow air convection. When the temperature is relatively high, wash the pigs' bodies with cold water or install spraying equipment and spray 4 to 6 times a 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; the number of pigs per pen should preferably be about 10 to 12. Maintaining reasonable stocking density and cooling can effectively control porcine unknown high fever and respiratory diseases.

③ From farrowing, nursery to growing-finishing, strictly adopt the "all-in, all-out" feeding method, avoid mixing pigs of greatly different ages in the same group, and minimize the number of times pigs are moved between pens and mixed into groups. Make sure all pigs in the same pig house are moved out at the same time. After each batch of pigs is sent to market, the pig house must be strictly washed and disinfected, left empty for several days, and only then can new pigs be moved in.

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

Because viruses are not sensitive to ordinary disinfectants, especially porcine circovirus, which ordinary disinfectants have no effect on, new types of disinfectants with relatively 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 should be carried out 4 to 6 times a day in the epidemic area and the external environment near the epidemic area. Sows and medium and large pigs can be spray-disinfected at noon together with the pigs (including the pigs themselves), and the living and management area of the pig farm should be disinfected once a day. Starting from the 10th day, disinfection can be carried out with dilution increased by one fold, reducing the chance of healthy pigs being infected with influenza and other viruses through the respiratory tract, so as to prevent the spread of this disease and achieve a relatively good effect in controlling the transmission of the epidemic.

4. Drug control measures:

This disease emphasizes prevention. When the herd develops a large-scale outbreak, treatment results are generally unsatisfactory. Before the disease occurs, antibiotics should be added to feed or drinking water for prevention, and medication should be added before the peak period of porcine unknown high fever for prevention. When the disease occurs, antibacterial drug treatment against bacteria and mycoplasma can reduce losses. Measures should be taken early to administer drugs in both drinking water and feed, combined with injection to treat affected pigs, so as to reduce deaths caused by secondary bacterial infection. At present, drugs to which pig farms are relatively clinically sensitive include tiamulin and others. Pig farms can adopt a combined medication approach according to their own conditions and formulate their own preventive health-care medication plan. Start by providing health-care medication to sows to control the source of bacterial diseases.

① For herds that have already developed "porcine unknown high fever": add florfenicol + sulfamonomethoxine 300 g per ton of feed; because affected herds reduce their feed intake and cannot take in enough therapeutic doses of drugs, drugs should also be added to drinking water at the same time, using a compound preparation of antibiotics and traditional Chinese medicine extracts effective against both bacteria and viruses, and let the herd drink freely for 5 to 7 days. Affected pigs should be isolated and raised, carefully cared for, and treated by injection with astragalus polysaccharide and long-acting sulfonamide injections, 2 times a day for 3 to 5 consecutive days, while drugs are also added to drinking water for treatment. If affected pigs have mixed infection with viral diseases such as classical swine fever, the treatment effect is 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: use for 1 week, stop for 1 week, then use for another 1 week.

③ In hot, high-temperature weather or when pigs are 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 reduced herd resistance due to stress.

④ Lactating sows: add antibiotics to sow feed for 1 week before and after farrowing. Add 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 discharge of pathogenic bacteria by sows contaminating the farrowing house and cut off horizontal transmission of the disease 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 the disease among piglets.

⑥ Regular deworming: internal parasites such as roundworms and whipworms damage the body's immune system and reduce herd resistance. Roundworm larvae migrating through the lungs and lungworms both aggravate the symptoms of respiratory disease, so deworming with drugs is of certain significance for controlling the development of this disease. It should be carried out 2 weeks after weaned piglets are moved into the nursery house, selecting a dewormer with obvious effects on both internal and external parasites.