Influenza A Zoonosis

Saad Gharaibeh BVM, PhD, Dip ACPVDept. of Pathology and Animal Health

Faculty of Veterinary MedicineJordan University of Science and Technology

Irbid 22110, Jordan

Jong et al., 2000, Journal of Infection

HI test

NI test

ELISA test

AGP test

Dr. Gary Butcher specializing in avian diseases, and has a Ph.D. in poultry virology.

"The threat is basically zero,“

"We're spending all of our attention on this [virus], and another one may sneak up on us."

http://news.bbc.co.uk/2/hi/americas/8021547.stm

Influenza History

• Avian influenza was first described in 1878 as fowl plaque disease in Italy. The causative agent was isolated in 1902 (A/chicken/Brescia/1902 [H7N7]). By 1955, it was characterized as influenza virus.

• In 1930, influenza virus, A/swine/Iowa/30, was isolated.

• In 1933, the first human virus was isolated in London, England.

Previous Influenza Pandemics

• Spanish flu (1918-1919): H1N1

Asian flu (1957): H2N2

Hong Kong flu (1968): H3N2

Russian flu (1977): H1N1

http://en.wikipedia.org/wiki/Swine_influenza

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Pig Involvement

A number of findings have suggested a role for pigs in the emergence of pandemic influenza viruses:

1. Pigs can be naturally or experimentally infected with avian viruses.

2. Epithelial cells in pig trachea contain both human- and avian-type receptors

3. In nature, continued replication of an avian virus in pigs leads to variants that preferentially recognize human-type receptors

4. Swine viruses and avian-human reassortant viruses can infect humans and, in some cases, cause fatal disease

5. Interspecies transfer and reassortment events have led to the establishment of two new lineages of pig viruses since 1979, demonstrating that pigs can host genetically diverse viruses

Pig Involvement

• Swine influenza is enzootic in pigs and is the most prevalent respiratory disease in these animals

• in 1918 and 1919, pigs presented with symptoms similar to those observed in humans, that is, nasal discharge, coughing, fever, labored breathing, and conjunctivitis.

• Phylogenetic analyses indicated that the 1918/1919 human and swine viruses were genetically similar and likely originated from a common ancestor.

Main Influenza Groups in Pigs

• Classical swine viruses H1N1 (1918-1976) America and Europe

• Avian-like H1N1 (after 1979) America and Europe• Human-like viruses H3N2 after 1970 in Taiwan. • Reassortant Viruses H1N2 viruses (after 1978 in Japan)

that resulted from reassortment of classical H1N1 swine viruses and human H3N2 viruses

• H3N2 triple human/avian/swine reassortant viruses emerged in North America (1998)

Field’s virology, 5th ed

Swine-Human Virus Exchange

• 1938, serologic evidence for the transmission of a human virus to pigs.

• 1976, an H1N1 swine virus was isolated from a soldier who had died of influenza at New Jersey. This virus was subsequently isolated from five other soldiers, and serologic studies suggest that more than 500 personnel were infected.

• Numerous other reports have described the transmission of swine viruses to humans, and transmission of human viruses to pigs.

• Avian H9N2 and H5N1 viruses have from Southeast Asia.

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Pathogenesis in Pigs

• Morbidity may be up to 100% • Mortality rate is low and recovery is rapid• Secondary bacterial infections can increase the severity of

illness and may result in complications such as pneumonia.

• Once a herd is infected, the virus is likely to persist through the production of young susceptible pigs and the introduction of new stock.

• Outbreaks of disease occur throughout the year but usually peak in the colder months.

Pathogenesis in Pigs

• Infection is often subclinical and typical signs are seen in only 25 to 30% of a herd.

• Disease transmission is primarily direct and occurs via the nasopharyngeal route through the dispersal of aerosols.

• Nasal secretions are laden with virus during the acute febrile stages of infection and virus excretion lasts for approximately 6 days.

• The severity of clinical disease is influenced by many factors but most importantly by:

• maternal immunity• virus strain• route of inoculation • secondary bacterial infections.

Clinical Signs in Pigs

• Influenza is an acute febrile, respiratory disease characterised by:

• Fever • Apathy• Anorexia • Laboured breathing• Coughing may be apparent during the later stages of disease• Clinical signs seen less frequently include sneezing, nasal

discharge and conjunctivitis.

Pathological Lesions

• Typical viral pneumonia (interstitial)• Most often limited to the apical and cardiac lobes of the

lungs, although in severe cases more than half of the lung may be affected.

• The altered lung areas are depressed and consolidated and are dark red or purple-red in color, contrasting sharply with normal tissue.

• The airways are likely to be dilated and filled with blood-tinged, fibrinous exudate.

• The associated bronchial and mediastinal lymph nodes are usually enlarged.

Histopathological Lesions

• Microscopic lesions usually consist of airways filled with exudate.

• Widespread alveolar atelectasis, interstitial pneumonia and emphysema.

• Peribronchial and perivascular cellular infiltration is also seen.

Avian Influenza Infections in Humans

http://www.mayoclinicproceedings.com/

Public health

(Capua & Alexander, 2005)

H5N1 AI in Human

Courtesy of Dr. Hafez

Thank You