Pathogenesis of avian influenza A (H5N1) viruses in pigs

[sharon sanders]

Hat tip Treyfish


Research Project:

Application of Biological and Molecular Techniques to the Diagnosis and Control of Avian Influenza and Other Emerging Poultry Pathogens

Location: Exotic and Emerging Avian Viral Diseases Research Unit

Title: Pathogenesis of avian influenza A (H5N1) viruses in pigs

Authors

<table cellpadding="3" cellspacing="0"> <tbody><tr><td valign="top"></td><td align="left" background="/incme/images/spacer.gif" valign="top"> Lipatov, Aleksandr </td></tr> <tr><td valign="top"></td><td align="left" background="/incme/images/spacer.gif" valign="top"> Kwon, Yong Kuk - FAS/ICD/RSED VISITING SCI </td></tr> <tr><td valign="top"></td><td align="left" background="/incme/images/spacer.gif" valign="top"> Lager, Kelly </td></tr> <tr><td valign="top"></td><td align="left" background="/incme/images/spacer.gif" valign="top"> Suarez, David </td></tr> <tr><td valign="top"></td><td align="left" background="/incme/images/spacer.gif" valign="top"> Swayne, David </td></tr> </tbody></table>

<script> <!-- function showinfo(){ window.open('_pubinfo.js', 'pubinfo', 'height=150,width=150') pubinfo.document.write('hi

'); } // --> </script> Submitted to: Research Conference on Orthomyxoviruses
<!--Publication type added 03-02-06 --> Publication Type: Abstract
Publication Acceptance Date: July 1, 2007
Publication Date: September 21, 2007
<!--Removed abstract only flag 03-02-06 when pub_type_code was added to display --> <!-- --> <!-- To appease ARIS/NPS folks, the publisher's url that links to reprints hosted at ars.usda.gov were not displayed, as per PVL March 2006. We await the reprint field in ARIS --> <!-- Reprint URL field added to ARIS June 1, 2006, file modified June 6, 2006 --> <!-- June 6, 2006: To capture good data stored in the publisher's url field that links to a reprint uploaded in SP, the following clause is inserted to display that information as the 'reprint url' --> <!-- Edited Aug. 15, 2007 JCP to increase manuscript title comparison from 50 to 60 characters --> Citation: Lipatov, A.S., Kwon, Y., Lager, K.M., Suarez, D.L., Swayne, D.E. 2007. Pathogenesis of avian influenza A (H5N1) viruses in pigs [abstract]. In: Proceedings of the Research Conference on Orthomyxoviruses, September 21-24, 2007, Woods Hole, Massachusetts. p. 26.

Technical Abstract:

Background. Genetic reassortment of avian influenza H5N1 viruses with currently circulating human influenza A strains is one possibility that could lead to efficient human-to-human transmissibility. Domestic pigs which are susceptible to infection with both human and avian influenza A viruses are one of the natural hosts where such reassortment events could occur. To begin to study this possibility we characterized the pathogenesis of H5N1 influenza in a pig model. Methods. 3-week-old male domestic pigs (PIC 1050's, a cross between a Land Race x Large White Cross) were used in the experiments. Groups of 4 animals were intranasally inoculated with 10 6 EID50 of A/Vietnam/1203/04 (VN/04) or A/Muscovy duck/ Vietnam/209/06 (Dk/VN/06) viruses. Pigs were observed daily and 2 pigs from each group were euthanized on day 5 and day 14 after virus inoculation to collect organ samples. Body weight of infected pigs was measured daily; nasal and rectal swabs for virus detection were collected on days 1, 3, 5, 7, 9, and 11.

Results.

Inoculation of pigs with both H5N1 viruses did not result in disease with visible clinical signs or significant weight loss. VN/04 virus was detected in nasal swabs of inoculated pigs on days 1 (2 animals, titers 10 1.5 EID50 and 10 2.25 EID50/1.0 ml of collection fluid), 3 (1 pig, titer 10 2.25 EID50) and 5 (1 pig, titer 10 3.75 EID50). Dk/VN/06 virus was not detected in nasal or rectal swabs. VN/04 virus was not detected in any of organs samples collected on day 5. Dk/VN/06 virus was isolated from lungs of 1 pig (titer 10 5.75 EID50/g) and nasal turbinate of another animal (titer 10 2.5 EID50/g). Histological examination revealed lobular lymphocytic bronchopneumonia and focal alveolitis in the lungs of pigs infected with both H5N1 viruses.

Conclusions.

Pigs had limited susceptibility to infection with avian influenza H5N1 viruses. Inoculation of pigs with VN/04 and Dk/VN/06 viruses resulted in asymptomatic infection restricted only to the respiratory tract in contrast to mouse and ferrets animal models, where these viruses are highly pathogenic and replicate systemically.

http://ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=210959

[gsgs]

Re: Pathogenesis of avian influenza A (H5N1) viruses in pigs

strange, that pigs don't become sick.
Did the pigs have antibodies before/after the experiment ?

now doubly infect the pigs with H5N1 and
current pig-flu and look whether
reassortant viruses emerge.
This should have been done since long !
Well, maybe it was done but results kept secret ?!

[mixin]

Re: Pathogenesis of avian influenza A (H5N1) viruses in pigs

The complete study is here http://www.plospathogens.org/article...l.ppat.1000102

Shedding of H5N1 viruses
To detect viruses and determine infective titers, nasal and rectal swabs were collected from infected animals. None of the influenza A viruses were detected in rectal swabs. Differences were observed in nasal excretion among the H5N1 viruses: WS/Mong/05 virus was detected in all 4 pigs on days 1 and 3 after inoculation, 3 of 4 pigs shed Ck/Indo/03 virus on days 1 and 3, VN/04 virus was detected in nasal swabs of 3 pigs on day 1 and only in 1 pig on days 3 and 5, while MDk/VN/05 virus was not detected in nasal swabs of inoculated pigs. Swine H3N2 and H1N1 viruses were detected in all inoculated pigs on days 1, 3, and 5. In general, titers of H5N1 viruses in nasal samples collected on day 1 and 3 were similar, and were 2?3 log10 lower than those of swine H3N2 and H1N1 viruses which were detected at the similarly high titers.

Organ tropism of H5N1 viruses
To determine sites of viral replication, samples from 18 organs and tissues were collected from infected pigs on day 5 after virus inoculation. H5N1 influenza viruses as well as swine H3N2 and H1N1 viruses were detected only in tissues from the respiratory organs. All studied H5N1 viruses were detected in the lungs of inoculated pigs. Lung titers of WS/Mong/05 and MDk/VN/05 (detected in one of two pigs) viruses were high and comparable with those of swine H3N2 and H1N1 viruses, while lung titers of Ck/Indo/03 and VN/04 (detected in one of two pigs) viruses were remarkably lower. MDk/VN/05 virus was also detected in nasal turbinate of one infected pig. The replication sites and titers of WS/Mong/05 virus, which was detected in lungs, trachea and tonsils, were close to those of swine H3N2 and H1N1 influenza viruses which were detected at high titers in upper and lower respiratory tract.

Exposure of pigs to H5N1 virus through consumption of meat from infected chickens
To model this potential route of infection, piglets in one group of 4 were fed breast and thigh meat from chickens that died from infection with WS/Mong/05 H5N1 virus. The meat was chopped into small pieces approximately 4 cm?2 cm?0.5 cm in size and mixed with a limited amount of pelleted diet. Each animal consumed approximately 100 g of meat with infective virus titer 108 EID50/g. No disease signs such as significant weight loss, changes in food consumption or behavior abnormalities were observed in exposed pigs during the 14 day observation period. Virus was detected in nasal swabs from 2 of 4 pigs on day 3 only. No virus was detected in rectal swabs. Two pigs were euthanatized on day 5 after meat consumption and samples from 18 organs and tissues were harvested to determine virus distribution and histological lesion. Infective virus was detected in nasal turbinate and tonsils of both animals. Microscopically, the organs or tissues lacked histological lesions and viral antigen was not demonstrated. However, virus-neutralizing antibodies to WS/Mong/05 virus were detected in serum samples from both pigs collected on day 14 after consumption of infected meat indicating infection had occurred.

Experimental infection of pigs
Two to three weeks-old male castrated piglets were purchased from a local commercial farm. The pigs did not receive any vaccines on the production farm. In the BSL-3AG animal laboratory facilities pigs were housed in HEPA-filtered isolation units at a constant 27?C. Three to five days were taken to acclimatize animals to the facility. Piglets were feed with commercially available pelleted diet in amounts prescribed by the manufacturer to fulfill all dietary needs.

[HenryN]

Re: Pathogenesis of avian influenza A (H5N1) viruses in pigs

strange, that pigs don't become sick.
Did the pigs have antibodies before/after the experiment ?

now doubly infect the pigs with H5N1 and
current pig-flu and look whether
reassortant viruses emerge.
This should have been done since long !
Well, maybe it was done but results kept secret ?!

Why are asymptomatic H5N1 pigs "strange"? The initial H5N1 infected pigs in China and Indonesia were asymptomatic, as were many dogs and cats.
The only strage are expections that H5N1 reassortants with swine would be different than humans, which was a dismal failure.