Table 1.
Parameters used in the model to assess the risk of exposure of duck and goose hunters to avian influenza viruses in three US states
| Variable | Georgia | Louisiana | Minnesota | Assumptions | Ref. | |
|---|---|---|---|---|---|---|
| Exposure assessment | ||||||
| Duck hunting season: number of weekends open for hunting in each month (based on 2009 season) | Sept. | 3 | 3 | 0 | Number of weekends of open season is a good indicator of the proportional risk of contact with waterfowl from month to month | [8, 9, 11] |
| Oct. | 0 | 0 | 5 | |||
| Nov. | 2 | 3 | 4 | |||
| Dec. | 3 | 3 | 0 | |||
| Jan. | 5 | 4 | 0 | |||
| Goose hunting season: number of weekends open for hunting in each month (based on 2009 season) | Sept. | 4 | 0 | 3 | ||
| Oct. | 0 | 0 | 5 | |||
| Nov. | 2 | 3 | 4 | |||
| Dec. | 3 | 3 | 4 | |||
| Jan. | 5 | 5 | 0 | |||
| Average harvest per duck hunter-day | Poisson (λ) | Juv: λ=1 | Juv: λ=1·9 | Juv: λ=1 | The reported harvest per season can be averaged among all hunter-days to give the expected harvest. The proportion of adults/juveniles harvested does not vary from month to month within a season | [10]* |
| Adt: λ=0.8 | Adt: λ=1·4 | Adt: λ=0·3 | ||||
| Average harvest per goose hunter-day | Juv: λ=0.2 Adt: λ=0·8 | Juv: λ=0·5 Adt: λ=0·9 | Juv: λ=0·2 Adt: λ=0·4 | |||
| Prevalence of ducks shedding viruses | Sept. | Juv: 4·2% | Juv: 4·2% | No season | Prevalence of AIV in birds varies according to the time of the year. Spatial variation is more important during the end of breeding season and beginning of migration | [14–16]† |
| Adt: 1·2% | Adt: 1·2% | Expert opinion (see text for details) [28] | ||||
| Oct. | No season | No season | Juv: 9·1% | |||
| Adt: 1·5% | ||||||
| Nov. | Juv: 2·5% | Juv: 2·5% | Juv: 2·5% | |||
| Adt: 1·1% | Adt: 1·1% | Adt: 1·1% | ||||
| Dec. | Juv: 1·0% | Juv: 1·0% | Juv: 1·0% | |||
| Adt: 0·1% | Adt: 0·1% | Adt: 0·1% | ||||
| Jan. | Juv: 1·0% | Juv: 1·0% | Juv: 1·0% | |||
| Adt: 0·1% | Adt: 0·1% | Adt: 0·1% | ||||
| Prevalence of geese shedding viruses | Sept. | Juv: 2·0% | Juv: 2·0% | Juv: 2·0% | ||
| Adt: 0·5% | Adt: 0·5% | Adt: 0·5% | ||||
| Oct. | Juv: 2·0% | Juv: 2·0% | Juv: 2·0% | |||
| Adt: 0·5% | Adt: 0·5% | Adt: 0·5% | ||||
| Nov. | Juv: 1·0% | Juv: 1·0% | Juv: 1·0% | |||
| Adt: 0·1% | Adt: 0·1% | Adt: 0·1% | ||||
| Dec. | Juv: 1·0% | Juv: 1·0% | Juv: 1·0% | |||
| Adt: 0·1% | Adt: 0·1% | Adt: 0·1% | ||||
| Jan. | Juv: 1·0% | Juv: 1·0% | Juv: 1·0% | |||
| Adt: 0·1% | Adt: 0·1% | Adt: 0·1% | ||||
| Viral load in one dropping of faeces from ducks | [Normal(5·6, 2)] in log10 EID50/g (one dropping=4·4 g) | The normal distribution captures the variation in the viral load among individual birds, which are in different infection stages | J. Brown (unpublished) Equal to ducks (see text for details) | |||
| Hunter population | ||||||
| Duck hunter-days | Sept. | 27 785 | 189 623 | 0 | The number of hunter-days per season, for each waterfowl species, can be homogeneously distributed along all weekends open for waterfowl hunting | [10] |
| Oct. | 0 | 0 | 220 333 | |||
| Nov. | 18 523 | 189 623 | 176 267 | |||
| Dec. | 27 785 | 189 623 | 0 | |||
| Jan. | 46 308 | 252 831 | 0 | |||
| Total | 120 400 | 821 700 | 396 600 | |||
| Goose hunter-days | Sept. | 11 114 | 0 | 55 913 | ||
| Oct. | 0 | 0 | 93 188 | |||
| Nov. | 5557 | 13 255 | 74 550 | |||
| Dec. | 8336 | 13 255 | 74 550 | |||
| Jan. | 13 893 | 22 091 | 0 | |||
| Total | 38 900 | 48 601 | 298 201 | |||
Juv, Juvenile (hatching year) birds; Adt, adult birds; EID, egg infective dose.
*
Based on the proportion juveniles/adults reported for mallard ducks.
†
Prevalence in December and January was adjusted according to expert opinion (see text for details).