Avian metapneumovirus subtype C in wild waterfowl in Ontario, Canada

Claire Jardine, Jane Parmley, Tore Buchanan, Larissa Nituch, Davor Ojkic

Reprinted from Transbound Emerg Dis 2018;65:1098-1102.

Avian metapneumovirus (aMPV) is an emerging poultry pathogen that has a significant economic impact on poultry production worldwide. The geographic range of the virus continues to expand, and wild birds have been implicated as reservoirs of aMPV that have the potential to spread the virus over long distances. Our objective was to determine the apparent prevalence of aMPV subtype C in wild waterfowl in Ontario, Canada. Wild waterfowl were captured in August and September, 2016, as part of routine migratory waterfowl population monitoring by the Ontario Ministry of Natural Resources and Forestry. Oropharyngeal and cloacal swabs were collected from each bird and placed together for aMPV testing using real-time RT-PCR. A total of 374 live wild birds from 23 lakes were sampled and tested for aMPV. Among all ducks tested, 84 (22%) were positive for aMPV. The proportion of samples that tested positive ranged from 0% in ring-necked ducks (Aythya collaris) and green-winged teal (Anas carolinensis) to 44% (8 of 18) in American black ducks (A. rubripes). Waterfowl positive for aMPV were found at 14 of 23 lakes in the study area and the percent positive at these 14 lakes ranged between 5% and 84%. Although subtype C aMPV has been detected in a variety of wild birds in North America, this is the first report of aMPV in wild ducks in Ontario, Canada. The high apparent prevalence, particularly in mallards and American black ducks (37 and 44%, respectively), suggests that these species may be important reservoirs of aMPV. Given the potential impact of aMPV on domestic poultry and the potential role of wild birds as reservoirs of the virus, further investigation of the geographic distribution, risk factors associated with aMPV carriage in wild waterfowl, and potential role of other birds in the epidemiology of aMPV in Canada is warranted. 

Reovirus in Ontario: an overview since 2012

Emily Martin, Marina Brash, Davor Ojkic

Reovirus has been an ongoing issue in Ontario since 2012. Since the reovirus AHL Newsletter article in December 2012, there have been multiple outbreaks and the following is a summary of these outbreaks.

In the summer and fall of 2012, increased leg problems were noted in Ontario broilers (Fig. 1) including slight difficulty walking as well as splay leg or leg deformity. Flocks as young as 6 d were affected and losses were up to 16% as a result of culling. Histologic lesions included nonsuppurative synovitis or tenosynovitis and epicarditis. On PCR, closed hock samples were positive for avian reovirus (ARV). Clinical signs may or may not have been evident even if there were histologic lesions in the tendons/heart and if the reovirus PCR was positive. Clinically unaffected flocks could have been 300-400 g behind at processing (poor feed conversion) with increased ARV ELISA titers at processing. In order to further investigate this reovirus, 43 ARV isolates were genotyped using S1 segment sequencing, and 33 formed 2 distinct clusters: 40-50% different from ARV isolates in previous years (variant A and variant B). ARVs are transmitted vertically and horizontally (fecal-oral route), resistance to infection increases with age, they survive well in the environment, and control is by decreasing viral load (e.g. increased down time, total clean out, etc.).

Reovirus cases declined from 2012 to 2015, and cases spiked again in the summer of 2016 (Fig. 1). There was an increase in lameness cases (May-July), with an inconsistent number of cases and outcomes among Ontario poultry practitioners. Clinical signs included splayed legs, slipped tendons, tenosynovitis, and affected broilers were 7-30-d-old. Increased numbers of birds were unsuitable for loading at the end of the grow-out. Increased culling was the main concern, was highly variable; elevated mortality was less of an issue. Flocks of non-domestic chicks were at higher risk. When sequencing was performed on these isolates, both variant A and a new variant C were identified.

Overall, 8 new “variant” ARV groups that are associated with viral arthritis/tenosynovitis have been introduced since 2012. New viruses show low similarity to vaccines and historical ARVs. The origin of variant ARVs could not be determined, but suggested sources included other species or other countries.

In 2017 another spike in reovirus cases occurred (Fig. 1), but this time there was a mix of clinical signs in each case: variable age of onset, leg problems (lameness, leg deformities - splay legs, tenosynovitis), runting, stall in growth, percent of culls through life increased (culling rate 2-50%). More birds were unsuitable for loading at the end of grow-out. This outbreak was also confusing as in some cases it was difficult to establish whether there was vertical transmission or horizontal transmission or both. There was evidence of horizontal transmission in some broiler cases, however, the severity was not always proportional to the presence of source flock, there was a history of reovirus in the previous flock (barn carryover), there was close proximity to other infected barns (later age clinical signs) and affected barns were close to manure spreading. Geographically there was clustering of cases and there was geospatial risk to neighbors (both high-density broilers and breeders). In broilers, the total end-of-flock mortality ranged from close to normal (4%) to 80% affected, and there was depopulation of entire floors or barns. There were no clinical signs at breeder level (no changes in ELISA serology). Over the course of the 2017 outbreak, the source varied because early in year the higher risk flocks were from non-domestic egg source origin (i.e., eggs and chicks), whereas in the fall the case clusters were associated with imported or domestic breeder flock sources. Both horizontal and vertical transmission were noted.

In 2017 the actions taken for mitigation included stopping placements from affected breeder flocks, increased sanitation procedures at hatcheries (used quaternary and glutaraldehyde products), and destruction of associated hatch. However, broiler chicks from suspect breeders continued to be placed 6 wk after the first case was identified as the literature indicated that breeders develop immunity and reduce shedding at 3-8 wk. Testing of embryos was negative suggesting that there was low risk of vertical transmission. In addition, placements were grouped to minimize the number of potentially affected farms, and grower services worked with producers to monitor and identify affected flocks. The reovirus from broilers was typed as predominantly group D (50 isolates were 98.4-99.3% similar to the 2016 isolates and 99-99.8% similar to each other). A genotyping project was implemented to identify predominant genotypes, determine industry impact, examine geospatial mapping and epidemiology, and to investigate whether to pursue autogenous vaccine. It was decided to pursue autogenous vaccination with variant D strains, and the first chicks from vaccinated breeders will be available in the spring of 2019.   AHL

number of positive reovirus cases per year

Figure 1. Number of positive reovirus cases per year; 2018 is to date, August, 2018.