Avian Influenza Shedding Patterns in Waterfowl: Implications for Surveillance, Environmental Transmission, and Disease Spread

Abstract

Despite the recognized importance of fecal/oral transmission of low pathogenic avian influenza (LPAI) via contaminated wetlands, little is known about the length, quantity, or route of AI virus shed by wild waterfowl. We used published laboratory challenge studies to evaluate the length and quantity of low pathogenic (LP) and highly pathogenic (HP) virus shed via oral and cloacal routes by AI-infected ducks and geese, and how these factors might influence AI epidemiology and virus detection. We used survival analysis to estimate the duration of infection (from virus inoculation to the last day virus was shed) and nonlinear models to evaluate temporal patterns in virus shedding. We found higher mean virus titer and longer median infectious period for LPAI-infected ducks (10-11.5 days in oral and cloacal swabs) than HPAI-infected ducks (5 days) and geese (7.5 days). Based on the median bird infectious dose, we found that environmental contamination is two times higher for LPAI- than HPAI-infectious ducks, which implies that susceptible birds may have a higher probability of infection during LPAI than HPAI outbreaks. Less environmental contamination during the course of infection and previously documented shorter environmental persistence for HPAI than LPAI suggest that the environment is a less favorable reservoir for HPAI. The longer infectious period, higher virus titers, and subclinical infections with LPAI viruses favor the spread of these viruses by migratory birds in comparison to HPAI. Given the lack of detection of HPAI viruses through worldwide surveillance, we suggest monitoring for AI should aim at improving our understanding of AI dynamics (in particular, the role of the environment and immunity) using long-term comprehensive live bird, serologic, and environmental sampling at targeted areas. Our findings on LPAI and HPAI shedding patterns over time provide essential information to parameterize environmental transmission and virus spread in predictive epizootiologic models of disease risks.

Flock-Based Surveillance for Low Pathogenic Avian Influenza Virus in Commercial Breeders and Layers, Southwest Nigeria

“…Since influenza virus is excreted continuously in faeces for only about 12 days in birds (Henaux and Samuel, 2011;Couacy-Hymann et al, 2012), it is possible that the period of virus shedding could have been missed in the birds sampled. It could also be due to too low titres of the virus in faeces which makes it undetectable by RT-PCR.…”

Reassortant influenza A viruses in wild duck populations: effects on viral shedding and persistence in water

“…[15] for synthesis) with the highest probability of virus isolation success in the cloaca during the first 8 days of infection. The potential effect of sampling time on the probability to detect viruses has been previously discussed along with aspects related to sampling technique, sample conservation and detection method, which all influence IAV detection [50 -52].…”

Replication of 2 Subtypes of Low-Pathogenicity Avian Influenza Virus of Duck and Gull Origins in Experimentally Infected Mallard Ducks

“…8 Viral shedding decreased markedly after 10 days, based on RRT-PCR results from pharyngeal and cloacal swabs; this corresponds to the period of shedding generally observed in other experimental infections. 14,22,38 The marked contrast in the occurrence of inflammation among the infected organs in H2N3-infected birds is notable. On the basis of the results of IHC, the pulmonary parenchyma, intestinal mucosal epithelium, and cloacal bursal epithelium all contained many infected cells at some point in the course of infection.…”