Diagnosis and Treatment Methods for Swine Influenza and Case Report

Swine influenza is an acute, highly contagious infectious disease caused by swine influenza virus. It is characterized by sudden onset, high morbidity, rapid spread throughout the herd, but low mortality. Affected pigs mainly show symptoms such as fever, difficulty breathing, coughing, and mucous-purulent discharge from the eyes and nostrils. The following analysis is presented regarding the diagnosis and treatment of a case of swine influenza:

1 Outbreak Situation

A certain pig farm had 83 pigs on hand, including 55 piglets and 28 finishing pigs. Because our county is located in the mountainous area of southeastern Jilin Province, entering October, the weather alternated between warm and cold, with a large temperature difference between day and night. On October 19, 2004, 5 piglets were found to suddenly develop coughing, rapid breathing, and reduced feed intake, and even 2 of them showed symptoms such as anorexia, runny nose, and discharge at the corners of the eyes. By October 22, most pigs showed the above symptoms, and it was found that both large and small pigs had chills and huddled together. Immediately afterward, symptomatic treatment was given with drugs such as virus spirit and analgin, and the symptoms of most pigs were alleviated, but one piglet still died due to delayed treatment.

2 Clinical Symptoms

The affected pigs developed sudden onset of disease, with almost the entire group infected. Body temperature rose, often between 40.3 and 41.5 degrees C, and sometimes could rise to 42 degrees C. The pigs were highly depressed, with reduced or absent appetite. Affected pigs often lay on the ground unable to stand and crowded together, had difficulty breathing, coughing, or paroxysmal spasmodic coughing, and had thick purulent discharge from the eyes and nostrils. Individual pigs might turn into chronic, persistent coughing, with indigestion, emaciation, and weakness, and those with a long course of disease could die.

3 Necropsy Findings

Necropsy of the dead piglets found that the main pathological changes were in the respiratory organs. The laryngeal mucosa was congested and covered with thick white mucus. There was also a large amount of mucus in the trachea. The lung lesions were dark purplish red and firm, and the gastrointestinal mucosa was congested.

4 Diagnosis

4.1 A preliminary diagnosis can be made based on epidemiology, clinical symptoms, and necropsy pathology.

4.2 Laboratory diagnosis: Collect diseased material and inoculate chicken embryos to isolate the virus, then further perform hemagglutination tests and hemagglutination inhibition tests for identification. Tracheal and lung diseased material can also be inoculated intranasally into white mice, which usually develop disease in 3 to 4 d and finally die of viral pneumonia, allowing confirmation of the disease.

5 Prevention and Control Measures

5.1 Timely isolate affected pigs and infected pigs, and thoroughly disinfect contaminated sites and pig houses with 20% lime milk to keep the pig houses clean, warm, and dry.

5.2 There is still no effective therapeutic drug for this disease, so only symptomatic treatment is available. The treatment methods include the following:

5.2.1 Oral administration of amantadine hydrochloride, twice daily, 1 tablet each time.

5.2.2 Intramuscular injection of moroxydine hydrochloride 5 to 10 mL, twice daily.

5.2.3 Intramuscular injection of Banlangen injection 10 to 20 mL, twice daily.

5.2.4 If body temperature rises to 41 to 42 degrees C, intramuscular injection of 30% analgin 5 to 10 mL can be given.

5.3 For pig herds that have not developed the disease, feed a complete-price diet and add antibiotics to the feed to enhance the pigs' resistance.

6 Summary

6.1 The epidemic of this disease has obvious seasonality and mostly occurs in late autumn, early spring, and cold seasons. Affected pigs and virus-carrying pigs are the source of infection of this disease. This disease is epidemic, and once it occurs, all pigs develop the disease within 2 to 3 d, but the course is short and mortality is low. Under the effects of factors such as rainy and humid weather, cold weather, sudden climate changes, transport, and malnutrition, the resistance of pigs declines, which can promote the occurrence and epidemic of this disease.

6.2 This disease is often seen clinically, and laboratory diagnosis should be carried out when necessary; otherwise, it is easily confused with acute swine asthma and swine pasteurellosis, leading to misdiagnosis.

6.3 When infected pigs are found, they should be isolated promptly, and the pig houses should be thoroughly disinfected with 3% caustic soda, 5% bleaching powder, lime water, and so on. The pig houses should be dry and warm, and protected from drafts. If humans develop influenza, patients should be prohibited from contacting pigs to prevent secondary infection.

6.4 Strengthen feed management, feed easily digestible green and juicy feed, and supply enough clean drinking water, which can accelerate the recovery of affected pigs.