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Hong Kong Flu



This article is a sub-article of Influenza.

Hongkong flu

The influenza viruses that caused the Hong Kong flu. (magnified approximately 100,000 times)

Hong Kong flu is a pandemic of influenza A (H3N2) in 1968-69. This virus was first detected in Hong Kong in early 1968 and spread to the United States later that year. where it caused about 34,000 deaths, making it the mildest pandemic in the 20th century. It is also known as Hong Kong influenza.

Contents

Signs and Symptoms
Causative Agent
Mode of Transmission
Diagnosis
Incubation Period
Pathogenesis/Pathophysiology
Prevention
Treatment
Complications
References

Trivia

There could be several reasons why fewer people in the US died due to this virus. First, the Hong Kong flu virus was similar in some ways to the Asian flu virus that circulated between 1957 and 1968. Earlier infections by the Asian flu virus might have provided some immunity against the Hong Kong flu virus that may have helped to reduce the severity of illness during the Hong Kong pandemic.

Second, instead of peaking in September or October, like pandemic influenza had in the previous two pandemics, this pandemic did not gain momentum until near the school holidays in December. Since children were at home and did not infect one another at school, the rate of influenza illness among schoolchildren and their families declined.

Third, improved medical care and antibiotics that are more effective for secondary bacterial infections were available for those who became ill.

Signs and Symptoms

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The list of signs and symptoms mentioned in various sources for Flu includes the 20 symptoms listed below:

· Headache
· Fever
· Chills
· Sneezing
· Runny nose
· Nasal inflammation
· Blocked nose
· Dry cough
· Sore throat
· Sweating
· Body aches
· Muscle aches
· Limb pain
· Joint pain
· Loss of appetite
· Prostration
· Exhaustion
· Fatigue
· Weakness
· Myalgia

Note that Flu symptoms usually refers to various symptoms known to a patient, but the phrase Flu signs may refer to those signs only noticeable by a doctor.

Causative Agent

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Influenza A (H3N2)

Mode of Transmission

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H3N2 pandemic flu strains contained genes from avian influenza viruses. The new subtype arose in pigs co-infected with avian and human viruses and were soon transferred to humans. Swine were considered the original “intermediate host” for influenza, because they supported re-assortment of divergent subtypes. However, other hosts appear capable of similar co-infection (e.g., many poultry species), and direct transmission of avian viruses to humans is possible.

As an Influenza virus, it predominately transmitted by airborne spread in aerosols but can also be transferred by direct contact with droplets. Nasal inoculation after hand contamination with the virus is also an important mode of transmission.

Direct contact is important, as the virus will survive some hours in dried mucus particularly in cold and dry environments.

Diagnosis

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Laboratory diagnosis depends upon the demonstration of the virus or its components or a rising antibody titer. The following tests are available:

· Direct antigen detection
· RT-PCR for viral RNA
· Virus culture (nasal pharyngeal aspirate preferably within 3 days of onset, other specimens, such as stool and rectal swabs may be considered.)
· Serological tests for detection of specific antibody. (blood test within 7 days of onset and repeated at least 2 weeks after onset.)

Incubation Period

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The incubation period of a case will probably be one to four days.

Pathogenesis/Pathophysiology

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Influenza virus infection occurs after transfer of respiratory secretions from an infected individual to a person who is immunologically susceptible. If not neutralized by secretory antibodies, the virus invades airway and respiratory tract cells. Once within host cells, cellular dysfunction and degeneration occur, along with viral replication and release of viral progeny. Systemic symptoms result from inflammatory mediators, similar to other viruses.

Prevention

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Please see Flu -under Prevention.

Treatment

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Please see Flu -under Treatment.

Complications

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The most common complication of Influenza is Pneumonia. Other complications include Bronchitis, Sinus, Ear infections, Myocarditis, and Pericarditis. Myositis is among the complications but this one rarely occurs.

References

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1. “MedicineNet.com – Hong Kong Flu definition”

2. “Symptoms of Type A Influenza subtype H3N2 – WD”

3. “Hong Kong Flu – Wikipedia”

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