Monday, August 1, 2016
.Common Cold Among the acute respiratory illness two-thirds to threefourths are caused by viruses. Most of these viral infections affect the upper respiratory tract, but lower respiratory tract can be involved in certain groups particularly in young age group and in certain epidemiological settings. The illness caused by respiratory viruses expressed into multiple distinct syndromes, such as common cold, pharyngitis, croup, tracheobronchitis, bronchiolitis, pneumonia, etc.Almost everybody suffers from common cold sometime in his life. It occurs more in winter and in cold climates. It is an acute infection of the respiratory tract characterized by sneezing, running nose, nasopharyngeal irritation and malaise lasting two to seven days. Fever is rare. The infectious agent is a rhinovirus with more than 100 serotypes. The patient is highly infective 24 hours preceding and five days following the onset of the disease. Transmission is by droplet method or through fomites such as handkerchief. Susceptibility is general. Immunity is shortlived and lasts for a month or so. Incubation period is
12 to 72 (usually 24) hours.There is no specific treatment. Cold vaccines have been used but the results are not encouraging.
Influenza. Influenza is an acute infectious respiratory disease caused by RNA viruses of the family orthomyxoviridae (the influenza viruses). The influenza virus, known to be circulating as a human pathogen since at least the 16th century is notable for its unique ability to cause recurrent epidemics and global pandemics. Genetic reassortments in the influenza virus cause fast and unpredictable antigenic changes in important immune targets leading to recurrent epidemics of febrile respiratory disease every one to three years. Each century has seen some pandemics rapidly progressing to all parts of the world due to emergence of a novel virus to which the overall population holds no immunity.
CLINICAL FEATURES(Symptoms).
Infection with influenza may be asymptomatic but usually gives rise to fever and typical prostrating disease, characteristic in epidemics. Usual symptoms are flushed
face, congested conjunctivae, cough, sore throat, fever for two to three days, headache, myalgia, back pains and marked weakness. Pneumonia due to secondary bacterial infection is the most common complication. Laboratory confirmation is made by recovery of virus from throat washings or by demonstration of significant rise of influenza antibodies in the serum in acute and convalescent stages of the disease or by direct identification of the virus in nasopharyngeal cells.
EPIDEMIOLOGY
A large number of cases are either missed or are unreported because of their mildness. Hence exact incidence cannot be assessed. Morbidity rate varies from 15 to 25 percent of the population exposed to risk in case of large communities. The rate may be as high as 40 percent in case of closed populations.1 Once an epidemic starts, its peak is reached in three to four weeks before declining.2
The disease was first recognized in 1173; since then 80 epidemics have occurred. The epidemic lasts for six to eight weeks at a place. It is not known what happens to the virus between the epidemics.3 However, there is evidence that transmission of the virus to extrahuman reservoirs (pigs, horses, birds, ducks) keeps the virus cycle alive.4
Immunity: The antibody to H type of antigen prevents initiation of the infection while that to N antigen prevents virus release and spread. The antibodies developed in the respiratory tract following an infection are mostly IgA. They appear in about seven days after an attack and peak in the blood by two weeks. The level drops to preinfection level by 8 to 12 months.Antibody against one influenza virus type or subtype confers limited or no protection against another type or subtype of influenza. Furthermore, antibody to one antigenic variant of influenza virus might not completely protect against a new antigenic variant of the same type or subtype. Frequent development of antigenic variants through antigenic drift is the virologic basis for seasonal epidemics and the reason for the usual incorporation of one or more new strains in each year’s influenza vaccine.
MODE OF TRANSMISSION
Influenza viruses predominantly transmitted through respiratory droplets of coughs and sneezes from an infected person. Influenza viruses may also spread through direct (skin to skin) or indirect contact with infected material, which ultimately enter through nasopharyngeal route. Transmission of viruses starts one day before the onset of symptoms and continue up to five to seven days after the symptoms subsides. Transmission is possible from asymptomatic carriers. Children may pass the virus for
longer than seven days. Influenza viruses can be inactivated by sunlight, disinfectants and detergents easily. Frequent hand washing reduces the risk of infection.
Incubation Period
The incubation time for influenza ranges from one to five days with an average of two days.
Diagnosis
Traditionally, the definitive diagnosis of influenza is made either on the basis of virus isolation or by serology. Virus is most frequently isolated from nasopharyngeal or throat swabs, nasal washings or sputum obtained within three days of onset of illness. Number of tests can help in confirming the diagnosis of influenza. During an outbreak of respiratory illness, however, testing can be very helpful in determining if influenza is the cause of the outbreak. Following laboratory tests that can be
carried out are:
• Detection of antigen in nasal secretions by: – Rapid test: It can be used to detect influenzaviruses within 30 minutes.
– Immunofluorescence test
– Antigen capture ELISA with monoclonal antibody to the nucleoprotein
– Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)
• Virus isolation:
– Cell line Madin-Darby Canine Kidneycells
(MDCK)
– Egg inoculation
• Serological test in paired serum samples
Treatment: 1. Antibiotics for bacterial complications of influenza 2. Antiviral therapy 3. Management of contacts may include-antiviral prophylaxis and advice about relevant vaccination (e.g. pandemic strain vaccine if available) Prevention and control strategies: People with respiratory infection symptoms should practice the following respiratory etiquette. All symptomatic people should: 1. Avoid close contact (less than 1 meter) with other people. 2. Cover their nose and mouth when coughing or sneezing. 3. Use disposable tissues to contain respiratory secretions. 4. Immediately dispose off used tissues.
RECOMMENDED DRUGS AND DOSAGE FOR PROPHYLAXIS OF INFLUENZA
• Amantadine 5 mg/kg/day up 5 mg/kg/day
• Rimantadine
• Oseltamivir
• Zanamivir
12 to 72 (usually 24) hours.There is no specific treatment. Cold vaccines have been used but the results are not encouraging.
CLINICAL FEATURES(Symptoms).
Infection with influenza may be asymptomatic but usually gives rise to fever and typical prostrating disease, characteristic in epidemics. Usual symptoms are flushed
face, congested conjunctivae, cough, sore throat, fever for two to three days, headache, myalgia, back pains and marked weakness. Pneumonia due to secondary bacterial infection is the most common complication. Laboratory confirmation is made by recovery of virus from throat washings or by demonstration of significant rise of influenza antibodies in the serum in acute and convalescent stages of the disease or by direct identification of the virus in nasopharyngeal cells.
EPIDEMIOLOGY
A large number of cases are either missed or are unreported because of their mildness. Hence exact incidence cannot be assessed. Morbidity rate varies from 15 to 25 percent of the population exposed to risk in case of large communities. The rate may be as high as 40 percent in case of closed populations.1 Once an epidemic starts, its peak is reached in three to four weeks before declining.2
The disease was first recognized in 1173; since then 80 epidemics have occurred. The epidemic lasts for six to eight weeks at a place. It is not known what happens to the virus between the epidemics.3 However, there is evidence that transmission of the virus to extrahuman reservoirs (pigs, horses, birds, ducks) keeps the virus cycle alive.4
Immunity: The antibody to H type of antigen prevents initiation of the infection while that to N antigen prevents virus release and spread. The antibodies developed in the respiratory tract following an infection are mostly IgA. They appear in about seven days after an attack and peak in the blood by two weeks. The level drops to preinfection level by 8 to 12 months.Antibody against one influenza virus type or subtype confers limited or no protection against another type or subtype of influenza. Furthermore, antibody to one antigenic variant of influenza virus might not completely protect against a new antigenic variant of the same type or subtype. Frequent development of antigenic variants through antigenic drift is the virologic basis for seasonal epidemics and the reason for the usual incorporation of one or more new strains in each year’s influenza vaccine.
MODE OF TRANSMISSION
Influenza viruses predominantly transmitted through respiratory droplets of coughs and sneezes from an infected person. Influenza viruses may also spread through direct (skin to skin) or indirect contact with infected material, which ultimately enter through nasopharyngeal route. Transmission of viruses starts one day before the onset of symptoms and continue up to five to seven days after the symptoms subsides. Transmission is possible from asymptomatic carriers. Children may pass the virus for
longer than seven days. Influenza viruses can be inactivated by sunlight, disinfectants and detergents easily. Frequent hand washing reduces the risk of infection.
Incubation Period
The incubation time for influenza ranges from one to five days with an average of two days.
Diagnosis
Traditionally, the definitive diagnosis of influenza is made either on the basis of virus isolation or by serology. Virus is most frequently isolated from nasopharyngeal or throat swabs, nasal washings or sputum obtained within three days of onset of illness. Number of tests can help in confirming the diagnosis of influenza. During an outbreak of respiratory illness, however, testing can be very helpful in determining if influenza is the cause of the outbreak. Following laboratory tests that can be
carried out are:
• Detection of antigen in nasal secretions by: – Rapid test: It can be used to detect influenzaviruses within 30 minutes.
– Immunofluorescence test
– Antigen capture ELISA with monoclonal antibody to the nucleoprotein
– Reverse Transcriptase Polymerase Chain Reaction (RT-PCR)
• Virus isolation:
– Cell line Madin-Darby Canine Kidneycells
(MDCK)
– Egg inoculation
• Serological test in paired serum samples
Treatment: 1. Antibiotics for bacterial complications of influenza 2. Antiviral therapy 3. Management of contacts may include-antiviral prophylaxis and advice about relevant vaccination (e.g. pandemic strain vaccine if available) Prevention and control strategies: People with respiratory infection symptoms should practice the following respiratory etiquette. All symptomatic people should: 1. Avoid close contact (less than 1 meter) with other people. 2. Cover their nose and mouth when coughing or sneezing. 3. Use disposable tissues to contain respiratory secretions. 4. Immediately dispose off used tissues.
RECOMMENDED DRUGS AND DOSAGE FOR PROPHYLAXIS OF INFLUENZA
• Amantadine 5 mg/kg/day up 5 mg/kg/day
• Rimantadine
• Oseltamivir
• Zanamivir
