TABLE 4.
Immunogenicity and protective efficiency of rHMPV/AMPV chimeras in AGMs
Immunizing virusa | Mean serum neutralizing antibody titer (reciprocal log2 ± SE)b
|
HMPV replication following challenge on day 28
|
|||||||
---|---|---|---|---|---|---|---|---|---|
Preimmunization | 28 days postimmunization and statistical groupingc | 28 days postchallenge | Nasopharyngeal swab
|
Tracheal lavage specimen
|
|||||
Mean peak titer (log10 PFU/ml ± SE)d | Duration of sheddinge (day ± SE) | No. of animals shedding virusf | Mean peak titer (log10 PFU/ml ± SE) | Duration of shedding (day ± SE) | No. of animals shedding virus | ||||
None (mock) | ≤1.5 | ≤1.5 | 6.8 ± 0.3 | 2.9 ± 0.6 | 6.0 ± 1.0 | 2/2 | 3.6 ± 1.2 | 5.0 ± 0.0 | 2/2 |
rHMPV | ≤1.5 | 6.0 ± 0.7 A | 6.0 ± 0.7 | 0.8 | 0.5 ± 0.3 | 2/4 | <0.7 | 0.0 ± 0.0 | 0/4 |
rHMPV-NA | ≤1.5 | 5.4 ± 0.4 A | 5.8 ± 0.3 | <0.7 | 0.0 ± 0.0 | 0/4 | <0.7 | 0.0 ± 0.0 | 0/4 |
rHMPV-PA | ≤1.5 | 5.0 ± 0.5 A | 6.7 ± 0.4 | <0.7 | 0.0 ± 0.0 | 0/4 | <0.7 | 0.0 ± 0.0 | 0/4 |
The groups of AGMs are identified by the virus used in the initial immunizing infection as described in Table 3, footnote a. The mock-infected group is an additional group of two animals shown in Fig. 4 that had been mock infected in parallel with the other groups.
Sera were collected on days 0 and 28 following the first infection and 28 days following the challenge, and the neutralizing antibody titer against HMPV was determined using an endpoint dilution assay (8).
Mean antibody titers were assigned to statistically similar groups by the Tukey-Kramer post hoc test. Values within a column that share a common letter are not significantly different (P < 0.05).
On day 28, AGMs from each group were challenged intranasally and intratracheally with 106 PFU of CAN97-83 in 1 ml per site. Nasopharyngeal swabs and tracheal lavage specimens were collected on days 2, 4, 6, and 8 postchallenge, and virus titers were determined by plaque assay. The level of virus replication is expressed as the geometric mean of the peak virus titers (log10 PFU/ml ± standard error) for the animals in each group irrespective of sampling day. The lower limit of detection is 0.7 log10 PFU/ml. A value of 0.7 log10 PFU/ml was assigned to samples without detectable virus.
The period of days from the first to the last day on which virus was recovered, including negative days (if any) in between.
Number of animals from which virus was detected out of the total number of animals in that group.