Infectious Diseases 2017

Infectious Diseases 2017

FLI (Germany): Risk estimation on HPAI H5

14 February, 2017

The detection of HPAIV H5N8 in 26 European countries (listed chronologically by date of report: Hungary, Poland, Croatia, Switzerland, Austria, Germany, Denmark, the Netherlands, Sweden, Finland, France, Romania, Serbia, Great Britain, Greece, Bulgaria, Montenegro, Slovak Republic, Italy, Ireland, Czech Republic, Slovenia, Spain, Portugal, Macedonia, and Belgium) and the rapid distribution of the virus indicate a further highly dynamic spatial spread of the infection. The number of cases reported from various parts of Europe increases daily; often also birds kept in zoological gardens and animal parks are affected. In Germany, the case numbers in wild birds and the number of outbreaks in bird holdings (69) have reached an unprecedented level.
WILD BIRDS
While in the 2014/2015 outbreak HPAIV H5N8 was only sporadically detected in healthy appearing wild birds (three mallard ducks, one common teal and one sea gull), currently a large number of dead water birds and carrion-eating birds of prey, e.g. buzzards, white-tailed eagles and sea gulls, is found. So far, the virus has been detected in 47 different bird species including species belonging to the categories diving ducks, grebes, sea gulls, swans, in isolated cases dabbling ducks (mallard duck), geese, birds of prey and also carrion-eating songbirds (e.g. crows). The fact that HPAIV H5 has also been detected in healthy water birds or in their feces leads to the assumption that wild birds can excrete the virus without developing disease or dying. It must be concluded that there is an ongoing HPAI H5N8 epidemics among wild water bird species and that the dead birds found possibly represent no more than the tip of the iceberg.
Infected but asymptomatic wild birds as well as birds during the incubation period continue to be mobile virus carriers. Many water bird species (e.g. geese, swans, some duck species) move between cropland (particularly grassland, maize stubble and winter rapeseed and grains) where they feed during the day and waterbodies where they rest during the evening and night. They can excrete the virus with the feces and contaminate the respective surfaces and waterbodies. Furthermore, predators (mammals such as foxes and martens, but also birds of prey and crows) may break up carcasses of dead waterfowl and carry away parts of the carcasses or inner organs with high virus loads, thus causing a considerable contamination of the environment. Persons and vehicles accessing contaminated areas may spread the virus and introduce it into poultry holdings.
If the frosty weather continues, further dynamic migratory movements of birds must be expected. Most water bird species flee from the cold, i.e. they move to ice-free waterbodies. Such weather conditions can lead to a spread of the infection among wild birds in inland areas and in Southern Europe.
POULTRY AND ZOOS/ANIMAL PARKS
In Germany, HPAIV H5N8 so far has been introduced into 54 poultry holdings and 15 zoos/animal parks. Almost all of these holdings are located in areas where increased numbers of dead HPAIV-positive water birds have been found. In the affected animal parks, mostly water birds with possible contact to wild waterfowl were affected. In most poultry holdings, direct or indirect introduction via contaminated material (shoes, vehicles, objects) is the most likely route of infection. The risk of introduction by purchased poultry, feed and drinking water has been negligible in all outbreaks investigated epidemiologically by the FLI. Most outbreaks in affected holdings were primary outbreaks which did not spread any further; three cases however are highly likely to be secondary outbreaks. In all locations where contacts between wild birds and domestic poultry are possible infections can be introduced and distributed and new sources of infection can develop.
PHYLOGENETIC ANALYSES
Genetic analyses show a similarity to H5N8 viruses which were first detected in Southern Russia in the summer of 2016. These viruses show clear genetic differences to H5N8 viruses which occurred in Europe in 2014/2015. Therefore, the virus has been newly introduced, most likely by the same route as in 2014, i.e. via Russia by wild birds. Phylogenetic analyses lead to the assumption that on the way from Central Asia to Central Europe reassortment events with at least one other avian influenza virus have taken place. Direct introduction from China or the neighboring Asian countries by poultry and poultry products is very unlikely, as in this case other genetic patterns of the virus would have to be expected. The results of epidemiological outbreak investigations did not provide any indications for direct connections between the holdings affected in Germany and the endemic regions in East or Southeast Asia. (It must be mentioned that import bans on poultry and poultry products are in force for all countries affected from HPAI). The observed increased virulence in waterfowl correlates with the modified composition of the genome segments of the currently circulating H5N8 compared to the virus which circulated in 2014/2015.
Since mid-December 2016 a further subtype, H5N5, has been circulating in wild birds, which now has first been introduced into a poultry holding. This virus is a reassortant based on the original H5N8. Mixed viruses, so-called reassortants, of avian influenza viruses are generated, if several virus subtypes are present in one infected animal and exchange genetic material during replication. First analyses of the H5N5 virus also showed a relationship with HPAIV H5N8 precursor viruses from the Russian-Mongolian border region. It seems to have evolved in parallel with or shortly after HPAIV H5N8, but shows genetic differences and was then also introduced to Germany. Generation of reassortants always must be expected when different high and low pathogenic influenza viruses are circulating in one population. 
So far, no human cases of HPAIV H5N8 or HPAIV H5N5 infection have been reported.
Conclusions and recommendations
Due to the current spread of HPAIV H5N8 in wild birds in 26 European countries and in currently 15 affected German States the risk of introduction into domestic poultry holdings and captive bird holdings in zoological gardens through direct and indirect contacts between wild birds and domestic poultry is estimated to be high, particularly for holdings in the vicinity of resting and gathering areas of waterfowl, including agricultural cropland where wild birds gather.
Protection of domestic poultry holdings from infection with HPAIV H5N8 is the highest priority. Emphasis is put on the creation of a physical and functional barrier between wild bird habitats and domestic poultry holdings. Mandatory indoor housing of poultry and other biosafety measures minimize the risk of direct and indirect contact with infected wild birds. In particular, indirect introduction routes, e.g. by feed contaminated by wild birds, water or contaminated litter and objects (shoes, wheelbarrows, vehicles etc.) must be cut off and adequate disinfection measures must be taken. A spread of infections between poultry holdings must be prevented. This requires the implementation of strict biosafety measures, particularly consistent cleaning and disinfection of equipment and vehicles. Revision, optimization and strict implementation of biosafety measures are of utmost importance. Poultry farmers are obliged by law to observe basic biosafety rules.
In detail, the following recommendations are made:
- Observance of strict biosafety measures in all poultry holdings, also small-scale holdings, zoological gardens, animal parks and shelters, including change of shoes and clothing, disinfection measures
- After entering a poultry holding persons should refrain from visiting other poultry holdings for the following 72 hours
- Joint use of equipment and vehicles by poultry holdings should be avoided
- Access of vehicles and persons to poultry holdings should be limited as far as possible
- Risk-based restriction of free-range husbandry (mandatory indoor housing) of poultry (at least in regions with a high wild bird density, a high poultry density, in the vicinity of wild bird resting and gathering areas, or locations where HPAIV H5N8 has been detected)
- Indoor housing of zoo birds as far as possible, limited access to aviaries/bird shows
- Prevention of access of free-range poultry to natural bodies of water
- Increased investigations of poultry holdings; in galliform birds increased clinical examinations, in geese and ducks PCR testing of combined pharyngeal and cloacal swabs pursuant to the legal regulations
- Poultry holdings which have been exempt from mandatory indoor housing should be investigated clinically and virologically at three-week-intervals maximum
- Ban on live bird exhibitions of any kind until further notice
- Notification of the responsible veterinary authority in case of dead or ill wild birds and mammals in areas where increased numbers of dead wild birds have been found
- Increased investigation of dead wild birds or wild birds living on or around water for avian influenza viruses (passive and active wild bird monitoring, particularly by field-collected fecal samples)
- No contact of hunters who have been in contact with game birds with domestic poultry; in areas where fowl plague has been detected in wild birds ban on game bird hunting
- Avoidance of direct contact between humans and pet animals and dead or ill wild birds
- Assessment of practicability of the measures foreseen in the animal disease emergency plans and, if necessary, revision of plans.