Epidemiological characteristics of infectious hematopoietic necrosis virus (IHNV): a review
Dixon et al. Vet Res
Epidemiological characteristics of infectious hematopoietic necrosis virus (IHNV ): a review
Peter Dixon 0
Richard Paley 0
Raul Alegria‑Moran 1
Birgit Oidtmann 0
0 Centre for Environment, Fisheries and Aquaculture Science , Weymouth, Dorset , UK
1 Faculty of Veterinary and Animal Sciences, University of Chile , Santiago de Chile , Chile
Infectious hematopoietic necrosis virus (IHNV, Rhabdoviridae), is the causative agent of infectious hematopoietic necrosis (IHN), a disease notifiable to the World Organisation for Animal Health, and various countries and trading areas (including the European Union). IHNV is an economically important pathogen causing clinical disease and mortalities in a wide variety of salmonid species, including the main salmonid species produced in aquaculture, Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). We reviewed the scientific literature on IHNV on a range of topics, including geographic distribution; host range; conditions required for infection and clinical disease; minimum infectious dose; subclinical infection; shedding of virus by infected fish; transmission via eggs; diagnostic tests; pathogen load and survival of IHNV in host tissues. This information is required for a range of purposes including import risk assessments; parameterisation of disease models; for surveillance planning; and evaluation of the chances of eradication of the pathogen to name just a few. The review focuses on issues that are of relevance for the European context, but many of the data summarised have relevance to IHN globally. Examples for application of the information is presented and data gaps highlighted.
1 Introduction
Infectious hematopoietic necrosis virus (IHNV) is an
economically important pathogen causing clinical disease
(Figure 1) and mortalities in a wide variety of salmonid
species, including the main salmonid species produced
in aquaculture, Atlantic salmon (Salmo salar) and
rainbow trout (Oncorhynchus mykiss). In 2013, the
worldwide production of all farmed salmonids exceeded three
million tonnes, with a value of $17.5 billion [
1
].
Salmonid production, particularly Atlantic salmon, increased
dramatically from 299 000 tonnes in 1990 to 1.9 million
tonnes in 2010, at an average annual rate near 10% [
2
].
Infectious diseases are one of the main constraints to
further expansion of aquaculture production [
3
]. Two
epizootics of IHNV in Canada (from 1992 to 1996 and 2001
to 2003) caused a combined estimated economic loss to
the salmon industry of CDN$40 million in inventory
representing CDN$200 million in lost sales [4]. Infection of
fish with IHNV is notifiable to the World Organisation
for Animal Health, and various countries and trading
areas (like the European Union) have particular
legislation in place for the control of the disease. Initially
identified in western North America, the pathogen spread to
Europe and Asia [5, 6]. Data on the characteristics of a
given pathogen are relevant for several purposes. In the
epidemiological context such data are required for the
preparation of import risk assessments (e.g. to
evaluate the risk of introducing a given pathogen to support
animal health policy with regards to trade and
biosecurity); the parameterisation of disease models (e.g. to
predict disease spread in the case of an introduction of the
pathogen); to evaluate the chances of eradication of the
pathogen; for surveillance planning (e.g. following a
disease outbreak or to demonstrate freedom from disease)
to name just a few.
The review focuses on issues that are of relevance for
the European context, but many of the data summarised
have relevance to IHN globally.
The scope of the review covers characteristics of the
pathogen, the hosts and the likelihood of detection, all
of which provide information towards the likelihood of
pathogen transfer and establishment.
It is often relevant to understand some details of the
studies referred to in order to evaluate the information
provided and use it for risk assessments. For this reason,
we provided information on the context and/or methods
of the referenced papers. This makes this review a
relatively detailed document; however, this was done with
the view to provide a reference document that allows
scientists to refer to the summarised (but not too
summarised) information without necessarily having to refer
to all the original sources. An overview of the interaction
between the various epidemiological factors covered in
this review and their impact on disease control is
presented in Figure 2.
2 Aetiological agent, agent strains
The causative agent of IHN, IHNV, is classified in the
family Rhabdoviridae, and is one of three rhabdoviruses
of finfish listed by the OIE (World Organisation for
Animal Health). The IHNV virion is bullet shaped (Figure 3)
and contains a single stranded, non-segmented,
negative sense RNA genome of approximately 11 000 bases
which encodes six proteins (...truncated)