Factoid - Avian Influenza

Key diagnostic tags
Influenza, Sudden death, Zoonosis, Avian, Respiratory

Risk to human health: HIGH

Overview

Avian influenza (AI) also known as “bird flu” is an infectious viral disease of birds (especially wild water fowl such as ducks and geese), often causing no apparent signs of illness. AI is very contagious among birds and can cause a wide spectrum of symptoms, ranging from mild illness (which may pass unnoticed), to a rapidly fatal disease that can cause epidemics of severe illness and death. The virus normally spreads from bird’s saliva, nasal secretions, and faeces. Susceptible birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces or materials that have been contaminated with the virus. Link to pictures

Humans - Avian influenza viruses do not normally infect humans. However, there have been instances of certain highly pathogenic strains causing severe respiratory disease in humans. In most cases, the people infected had been in close contact with infected poultry or with objects contaminated by their faeces. Nevertheless, there is concern that the virus could mutate to become more easily transmissible between humans, raising the possibility of an influenza pandemic. In 2005 there was an outbreak of a strain of avian influenza known as H5N1, and in the last month there have been reports from China of human deaths from a new strain, H7N9. Link

Signs

Poultry infected with avian influenza viruses causes two main forms of disease that are distinguished by low and high extremes of virulence. The "low pathogenic" form may go undetected and usually causes only mild symptoms (such as ruffled feathers and a drop in egg production). However, the highly pathogenic form spreads more rapidly through flocks of poultry. This form may cause disease that affects multiple internal organs and has a mortality rate that can reach 90-100% often within 48 hours.

Humans - Initial symptoms include a high fever, usually with a temperature higher than 38C, and other influenza-like symptoms. Diarrhoea, vomiting, abdominal pain, chest pain, and bleeding from the nose and gums have also been reported as early symptoms in some patients. One feature seen in many patients is the development of lower respiratory tract early in the illness. On present evidence, difficulty in breathing develops around five days following the first symptoms. Respiratory distress, a hoarse voice, and a crackling sound when inhaling are commonly seen. Sputum production is variable and sometimes bloody. Link

Diagnosis

Clinical signs are normally indicative of the disease.

Samples taken from dead birds should include intestinal contents (faeces) or cloacal swabs and pharyngeal swabs. Samples from trachea, lungs, air sacs, intestine, spleen, kidney, brain, liver, and heart may also be collected and processed either separately or as a pool. Samples from live birds should include both tracheal and cloacal swabs, although the latter are most likely to yield virus. Because small, delicate birds may be harmed by swabbing, the collection of fresh faeces may serve as an adequate alternative. To optimize the chances of virus isolation, it is recommended that at least 1 gm of faeces be processed either as faeces or coating the swab.

Haemoagglutination inhibition (HI) should be performed on serological samples to detect a fourfold increase in the viral antibodies. Samples should be taken at the acute phase, when the virus is first suspected and then a convalescent stage sample taken around two weeks later to detect an increase in antibodies. Further information

Humans – infections cannot be diagnosed by clinical signs and symptoms alone; laboratory testing is required. Avian influenza A virus infection is usually diagnosed by collecting a swab from the nose or throat of the sick person during the first few days of illness. This specimen is sent to a lab; the laboratory looks for avian influenza A virus either by using a molecular test (RT-PCR), by trying to grow the virus, or both. (Growing avian influenza A viruses should only be done in laboratories with high levels of protection).

For critically ill patients, collection and testing of lower respiratory tract specimens may lead to a diagnosis. For some patients who are no longer very sick or who have fully recovered, it may be difficult to find the avian influenza A virus in the specimen that was collected, using these methods. It can take several weeks to verify the results, and testing must be performed in a special laboratory, such as at CDC. Further information

Treatment and prevention

For highly pathogenic avian influenza, there is no current treatment. All birds must be slaughtered immediately and all birds on the premises must also be destroyed. The premises must be isolated and mass disinfection should occur before new stock are brought in.

Prevention is by proper hygiene and preventing contact with the wild bird population, such as ensuring housing is of good quality and there is proper fencing to stop contact with wild birds. Vaccination can be used either as a tool to support eradication or as a tool to control the disease and reduce the viral load in the environment.

Humans – Humans in contact with suspected sick birds need to be montiored for signs of developing influenza symptoms. In case of this, supportive therapy is needed. Evidence suggests that some antiviral drugs, notably oseltamivir, can reduce the duration of viral replication and improve prospects of survival. In suspected cases, oseltamivir should be prescribed as soon as possible (ideally, within 48 hours following symptom onset) to maximize its therapeutic benefits. However, given the significant mortality currently associated with H5N1 infection and evidence of prolonged viral replication in this disease, administration of the drug should also be considered in patients presenting later in the course of illness. In cases of severe infection with the H5N1 virus, clinicians may need to consider increasing the recommended daily dose or/and the duration of treatment. In severely ill H5N1 patients or in H5N1 patients with severe gastrointestinal symptoms, drug absorption may be impaired. This possibility should be considered when managing these patients. Further information

Diseases with similar signs

Any mild to severe contagious respiratory disease (i.e. Newcastle Disease, infectious bronchitis, infectious laryngotracheitis, acute fowl cholera, acute Escherichia coli infections)

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