Swine Influenza (Swine Influenza) is an acute, zoonotic respiratory infectious disease of pigs or humans caused by influenza A (type A) virus. The disease occurs frequently in pigs and rarely causes death in pigs (1-4% of pigs). Humans are rarely infected with swine influenza virus, but some cases of human infection with swine influenza have been found, mostly in people who have had direct contact with sick pigs. 2009 March, Mexico and the United States and other successive human infections with swine influenza virus, for influenza A virus, H1N1 subtype swine influenza virus strain, which contains genetic fragments of three influenza viruses, swine influenza, avian influenza and human influenza, is a new swine Influenza virus, can be human-to-human transmission. The early clinical symptoms of human swine influenza infection are similar to those of influenza, including fever, cough, fatigue, loss of appetite, etc. Symptoms such as diarrhea or vomiting can also occur. The disease can progress rapidly, with sudden high fever and pneumonia, and in severe cases, respiratory failure and multi-organ damage can occur, leading to death.
I. Pathogenesis
Swine influenza virus belongs to the family of orthomyxoviridae (0rthomyxoviridae), influenza A virus genus (Influenza virus A). Typical virus particles are spherical, 80 nm ~ 120 nm in diameter, with a capsule membrane. There are many radially arranged protruding glycoproteins on the capsid, which are hemagglutinin HA, neuraminidase NA and M2 protein. Swine influenza virus is a single-stranded negative-stranded RNA virus with a genome of approximately 13.6 kb, consisting of eight independent fragments of varying sizes. Although many influenza virus serotypes can be formed among different subtypes, the main serotypes that can cause human infection with swine influenza viruses are H1N1, H1N2 and H3N2.
Swine influenza virus is a vesicular virus, so it is sensitive to organic solvents such as ether, chloroform and acetone, and the infectivity of the virus was destroyed by 200 mL/L ether overnight at 4°C. It is also sensitive to oxidants, halogen compounds, heavy metals, ethanol and formaldehyde, and was treated with 10 g/L potassium permanganate, 1 mL/L mercury for 3 min, 750 mL/L ethanol for 5 min, 1 mL/L tincture of iodine for 5 min, 1 mL/ L hydrochloric acid for 3 min and 1 mL/ L formaldehyde for 30 min, all of which could inactivate swine influenza virus. Swine influenza virus is sensitive to heat and can be inactivated at 56 ℃ for 30 min; it is sensitive to ultraviolet light, but inactivation of swine influenza virus with ultraviolet light can cause multiple resurrection of the virus.
II. Epidemiology
In 1976, the United States occurred in the so-called “New Jersey incident”, about 500 people were infected with swine influenza H1N1 subtype virus, the virus and the virus isolated from pigs at that time, the first confirmed in natural conditions, swine influenza virus can be transmitted from pigs to humans. 1999 October, a 10-month-old baby girl in Hong Kong In October 1999, a 10-month-old baby girl in Hong Kong was infected with swine influenza virus H3N2 and has fully recovered. Over the years, human infections with different strains of swine influenza virus have been reported around the world, but there have been no large-scale epidemics. Recently there has been an outbreak of human swine flu in Mexico and some parts of the United States. The World Health Organization noted that the cases infected in Mexico and the United States belong to an identical strain of the H1N1 subtype of swine influenza virus.
(A) the source of infection.
Mainly sick pigs and pigs carrying the virus, people infected with swine flu virus have also been shown to transmit the virus. Animals infected with this virus can be transmitted.
(B) transmission route.
Mainly for respiratory transmission, but also through contact with infected pigs or their feces, the surrounding contaminated environment or aerosols and other means of transmission. Certain strains such as H1N1 can be spread between people, the transmission pathway is similar to the flu, usually through the infected person coughing or sneezing, etc..
(C) susceptible people.
Generally susceptible. Most patients are between the ages of 25 and 45 years old, currently reported to be mainly young adults, attention should be paid to the elderly and children.
(iv) High-risk groups.
People engaged in swine farming, people who have been to pig farming, sales and slaughter within 1 week before the onset of the disease, and laboratory workers who are in contact with swine influenza virus infected materials are high-risk groups.
Human swine influenza often occurs in winter and spring, and swine influenza usually occurs in summer and autumn.
III. Clinical manifestations
The incubation period is generally about 1 to 7 days, longer than the incubation period of influenza and avian influenza.
(A) clinical symptoms.
The early symptoms of human swine influenza infection are similar to those of ordinary human influenza, including fever, cough, sore throat, body pain, headache, chills and fatigue, etc. Some patients also have diarrhea or vomiting, muscle pain or fatigue, and red eyes.
In some patients, the disease may progress rapidly, with fierce onset, sudden high fever, temperature over 39℃, and even secondary severe pneumonia, acute respiratory distress syndrome, pulmonary hemorrhage, pleural effusion, complete blood cytopenia, renal failure, sepsis, shock and Reye’s syndrome, respiratory failure and multi-organ damage, leading to death.
(ii) Signs.
Pulmonary signs are often not obvious, and some patients may hear wet rales or have solid lung signs.
(c) Prognosis.
The prognosis of human swine influenza infection with the infected virus subtype, most of the prognosis is good; while the prognosis of those infected with H1N1 is poor, the mortality rate is about 6%.
(D) laboratory tests.
1. Peripheral blood picture: the total number of white blood cells is generally not high or reduced. Severely ill patients have more total white blood cells and lymphocyte reduction, and platelet reduction.
2. serological diagnosis: indirect ELISA, antigen capture ELISA, fluorescent immunoassay, etc. can be used.
3. reverse transcription-polymerase chain reaction (RT-PCR): because of the simplicity, rapidity, sensitivity and specificity of PCR technology, it has been used for the detection of swine influenza virus genes and molecular epidemiological investigation, etc.
4. Virus isolation: Swine influenza virus is isolated from respiratory specimens of patients (pharyngeal swabs, oral gargle, nasopharyngeal or tracheal aspirates, sputum or lung tissue). Commonly used methods include chicken embryo inoculation and cell culture methods. Among the available diagnostic methods, the virus isolation method is more sensitive, but it takes 2-3 weeks.
(v) Chest imaging.
Laminar images are seen in the lungs in the presence of combined pneumonia. In severe cases, the lamellar images are extensive.
IV. Diagnosis
The diagnosis of human swine influenza is mainly combined with epidemiological history, clinical manifestations and pathogenic examination, etc. Early clinical detection and early diagnosis is the key to treatment.
(A) the diagnostic criteria of human swine influenza infection.
1.Medical observation cases: those who have been to the swine flu infected area, or have a history of close contact with sick pigs and swine flu patients, and have clinical manifestations of flu within 1 week. Those who are classified as medical observation cases will be placed under medical observation for 7 days (depending on their condition, they can be isolated at home or in hospital).
2, suspected cases: have been to the infected area, or have a history of close contact with sick pigs and swine influenza patients (can also be epidemiological history is unknown), within 1 week of the clinical manifestations of influenza, respiratory secretions, pharyngeal test, sputum, positive serum H subtype virus antibody or positive nucleic acid test.
3.Clinically diagnosed cases: Those who are diagnosed as suspected cases and those who have a common exposure history with them are diagnosed as confirmed cases.
4.Confirmed cases: specific viruses isolated from respiratory specimens or serum; RT-PCR testing of the above specimens, the presence of swine influenza virus RNA, confirmed by sequencing, or two serum antibody titers 4 times higher, can confirm the diagnosis of human swine influenza infection.
See the annex for the diagnosis and treatment process of human swine influenza
(B) the differential diagnosis of human swine influenza.
Human infected swine influenza should be distinguished from influenza, avian influenza, epizootic, pneumonia, SARS, infectious mononucleosis, cytomegalovirus infection, Legionella pneumonia, chlamydia, mycoplasma pneumonia, etc.
V. Treatment
(a) Symptomatic support.
Suspected and confirmed patients should be treated in situ isolation, emphasizing early treatment.
For human swine influenza is currently mainly a comprehensive symptomatic support treatment. Pay attention to rest, drink more water, pay attention to nutrition, and closely observe changes in the condition; the first 48 hours of onset is the best treatment period, and for those with high fever and obvious clinical symptoms, chest X-ray should be taken and blood gas checked.
(B) Drug treatment.
1.Anti-viral treatment: Anti-viral drugs should be applied early, and oseltamivir (oseltamivir Tamiflu) can be tried. Tamiflu is a neuraminidase inhibitor, the swine influenza virus may have inhibitory effect, the dose of 75mg / d, a course of 5 days, children should be used with caution. Viruses isolated from recent swine influenza virus infections in the United States are susceptible to oseltamivir and zanamivir and resistant to amantadine and amantadine.
2. Antibiotics: Antibiotics can be used if bacterial infection is present.
(C) Chinese medicine evidence-based treatment.
1.Toxic attack on the lung guard.
Symptoms: fever, chills, sore throat, headache, muscle aches, cough.
Treatment: Clearing heat and detoxifying toxins, promoting the lung to penetrate the evil.
Reference formula: roasted ephedra, almonds, raw gypsum, Chai Hu, Scutellaria, burdock, Qiang Wu, raw licorice.
Commonly used Chinese medicines: Lotus Clear Fever Capsules, Yinhuang class preparation, Shuanghuanglian oral preparation.
2.Toxic attack on the lung and stomach.
Symptoms: fever, or chills, nausea, vomiting, abdominal pain and diarrhea, head and body, muscle pain.
Treatment: Clearing heat and detoxifying toxins, resolving dampness and harmonizing the middle.
Reference formula: Pueraria lobata, Scutellaria baicalensis, Huang Lian, Atractylodes macrocephala, Patchouli, Ginger and Semen, Su Ye, Hou Pu.
Commonly used Chinese medicines: Radix Scutellariae Scutellariae Weiwan, Huo Xiang Zheng Qi preparation, etc.
3. Toxic congestion in the Qi camp.
Symptoms: high fever, cough, chest tightness, shortness of breath, restlessness, or even delirium.
Treatment: Clear the Qi and cool the camp.
Reference formula: roasted ephedra, almonds, guavas, raw rhubarb, raw gypsum, red peony, water hyacinth.
If necessary, use Angong Niuhuang Pills, as well as phlegm-heat clearing, blood BJ, Qingkai Ling, waking brain Jing injection, etc.
Prevention
(A) control the source of infection.
Carry out human and swine influenza outbreak monitoring. Once found swine or other animals infected with swine influenza virus, should be in accordance with the “Animal Quarantine Law” relevant provisions, thorough disinfection of the epidemic source, the patient and suspected patients for isolation.
(B) cut off the transmission route.
Disinfect farms found with sick pigs, stalls that have sold sick pork, patients’ units and homes, etc. Waste such as sick and dead pigs should be immediately destroyed in place or buried deeply; outpatient clinics and wards for patients should be isolated and disinfected according to the standards of avian influenza and SARS; specimens should be transported and handled according to the requirements of cases of pneumonia of unknown origin.
(iii) Protect healthy people.
Avoid contact with respiratory patients with flu-like symptoms (fever, cough, runny nose, etc.) or pneumonia; pay attention to personal hygiene, wash hands frequently with soap and water, especially after coughing or sneezing; avoid contact with pigs or places where pigs are present; avoid crowded places; cover the nose and mouth with a tissue when coughing or sneezing, and then throw the tissue away. When coughing or sneezing, cover your mouth and nose with a tissue and then throw the tissue into the garbage; if you develop flu-like symptoms (fever, cough, runny nose, etc.) outside the country, seek medical attention immediately (wear a mask when seeking medical attention) and explain to the local public health agency and inspection and quarantine department.
(D) Strengthen hospitalization control measures.
For suspected or confirmed patients to isolate and wear surgical masks; medical staff should do personal protection, strengthen hand hygiene and use rapid hand disinfectant for hand disinfection; medical staff in key departments such as fever clinics and infectious disease departments should wear surgical masks and goggles or protective masks when necessary; indoor ventilation should be strengthened for key departments such as fever clinics and infectious disease departments.
Swine flu vaccine: Currently, there is only a swine flu vaccine for pigs, not yet specifically for humans. As of now, the common influenza vaccine has no significant effect on preventing swine flu in humans.