The waterborne route of transmission is traditionally not
considered to be relevant for respiratory viruses.
Scenarios describing the possible pathways avian influenza viruses e and
especially highly pathogenic H5N1 e may adapt to transmission
in humans and cause a new pandemic have been rehearsed
frequently.[119] Transmission pathways and target
tissues play a central role in these scenarios. For instance,
the pathogenesis of H5N1 in mammals raises some new concerns
about the waterborne route; in cats, H5N1 replicates
in multiple extra-respiratory tissues, including cells in the
small intestine.[120] Alternatively, birds like the quail may
act as the ‘‘route modulator’’ that changes the pathway
from fecal-oral to airborne transmission.
In this context of speculative scenarios, the influenza related
risk posed by water resources, water supplies and
sanitation has received some limited attention.[122]
There is apparently no quantitative information on the inactivation
The most recent work on low- and high pathogenic
avian influenza virus inactivation in water investigates
8 subtypes of low-pathogenic avian influenza (LPAI)
viruses and two strains of high-pathogenic H5N1 (Anyang/01
and Mongolia/05).[124] Virus inactivation depends on pathogenicity,
salinity and temperature (see Table 3): survival
decreases with salinity and temperature and LPAI survive
longer than HPAI.
It is unclear how significant a role persistence of influenza
A in water may play in the transmission dynamics
during an epidemic or pandemic. However, inactivation in
water could affect the long-term epidemiology and evolution
of avian influenza viruses. The fact that avian influenza
viruses can potentially persist several months in water
affects the way the concept of a reservoir for influenza is
defined. A reservoir can be defined Áñas one or more
epidemiologically connected populations or environments
in which the pathogen can be permanently maintained and
from which infection is transmitted to the defined target
populationÃò.[125] Like soil is an important environmental reservoir
of insect-pathogenic viruses,[126] ponds, or sediments
of ponds[127] and lakes could act as environmental reservoirs
for avian influenza viruses.
References
119. Webster RG, Peiris M, Chen H, Guan Y. H5N1 outbreaks and
enzootic influenza. Emerg Infect Dis 2006;12:3e8.
120. Rimmelzwaan GF, van Riel D, Baars M, Bestebroer TM, van
Amerongen G, Fouchier RAM, et al. Influenza A virus (H5N1)
infection cats causes systemic disease with potential novel
routes of virus spread within and between hosts. Am J Pathol
2006;168:176e83.
121. Liu M, Guan Y, Peiris M, He S, Webby RJ, Perez D, et al. The
quest of influenza A viruses for new hosts. Avian Dis 2003;
47:S849e56.
122. World Health Organization. Review of latest available evidence
on risks to human health through potential transmission
of avian influenza (H5N1) through water and sewage.
Geneva: The Organization; 2006. WHO/SDE/WSH/06.1.
123. Zhang G, Shoham D, Gilichinsky D, Davydov S, Castello JD,
Rogers SO. Evidence of influenza A virus RNA in Siberian
lake ice. J Virol 2006;80:12229e35.
124. Brown JD, Swayne DE, Cooper RJ, Burns RE, Stallknecht DE.
Persistence of H5 and H7 avian influenza viruses in water.
Avian Dis 2007;51:285e9.
125. Haydon DT, Cleaveland S, Taylor LH, Laurenson MK. Identifying
reservoirs of infection: a conceptual and practical challenge.
Emerg Infect Dis 2002;8:1468e73.
126. England LS, Holmes SB, Trevors JT. Persistence of viruses and
DNA in soil. World J Microbiol Biotechnol 1998;14:163e9.
127. Lang AS, Kelly A, Runstadler JA. Prevalence and diversity of
avian influenza viruses in environmental reservoirs. J Gen Virol
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128. Smith AW, Skilling DE, Castello JD, Rogers SO. Ice as a reservoir
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