ShapeShapeauthorShapechevroncrossShapeShapeShapeGrouphamburgerhomeGroupmagnifyShapeShapeShaperssShape

Avian influenza: 2018 and beyond

12 December 2018, at 12:00am

Avian influenza causes vast economic losses throughout the world. Since the emergence of the highly pathogenic avian influenza viruses, they have already become enzootic in some countries, infecting domestic and wild birds, and continue to cause outbreaks in poultry, as well as sporadic human infections. These viruses are diversifying genetically and antigenically, calling for new research developments towards better control of the disease

Words Matthew Wedzerai

Background

Avian influenza is caused by influenza A viruses. These viruses are naturally carried by wild aquatic birds such as ducks, geese, swarms, or seagulls, and can infect local poultry and other bird and animal species (Modnak and Wang, 2018). There are two categories of influenza A viruses that may cause illness in birds: low pathogenic avian influenza (LPAI) and high pathogenic avian influenza (HPAI). Wild birds usually spread LPAI viruses to domestic birds and, under suitable conditions, LPAI undergoes mutation and evolves into HPAI that causes failure of internal organs and leads to death rates as high as 90 to 100 percent rates among domestic birds within 48 hours of infection (Modnak and Wang, 2018).

Why focus on avian influenza

Influenza A viruses can spread from infected birds to humans. Person-to-person transmission has also been documented. Humans infected by avian influenza exhibit symptoms such as fever, coughing, sore throat and muscle aches, and in severe cases can have breathing difficulty, pneumonia, acute respiratory distress and respiratory failure.

Across Europe in the past 12 months there have been a number of outbreaks of different avian influenza viruses. Between 16 November 2017 and 15 February 2018, one highly pathogenic avian influenza A(H5N6) and five HPAI A(H5N8) outbreaks in poultry holdings were reported within the EU (European Food Security Authority, EFSA, 2018), along with two HPAI A(H5N6) outbreaks in captive birds and 22 HPAI A(H5N6) wild-bird events.

From 16 November 2017 to 15 February 2018 a total of 29 outbreaks of A(H5) HPAI occurred in the EU, and from 16 May to 15 August 2018 a total of nine outbreaks of AI – six A(H5) HPAI, two A(H5) LPAI and one A(H7) LPAI – occurred (EFSA, 2018) as shown in the tables below.

Table 1. Number of A(H5) HPAI outbreaks by country from 16 November 2017 to 15 February 2018 in Europe (EFSA, 2018)

Table 2. Number of HPAI and LPAI outbreaks in Europe by virus subtype and country, from 16 May to 15 August 2018 (EFSA, 2018)

How to spot avian influenza

Anyone who keeps poultry must keep a close watch on their birds for any signs of disease and must seek prompt advice from veterinarians if they have any concerns.

Highly pathogenic avian influenza is the more serious type. It is often fatal in birds. The main clinical signs of HPAI in birds are:

  • Swollen head
  • Blue discolouration of neck and throat
  • Loss of appetite
  • Respiratory distress such as gaping beak, coughing, sneezing, gurgling, rattling
  • Diarrhoea
  • Fewer eggs laid
  • Increased mortality

New developments relating to avian influenza

New micro?amount of Virion Enrichment Technique (MiVET)
Detecting micro?amounts of pathogens in environmental samples is rarely successful due to the very low contamination level. The Virion Enrichment Technique is a simple and highly sensitive method that combines the use of various chemicals and equipment. In the study of Yamazaki et al (2018), the MiVET system successfully concentrated avian influenza A viruses (AIVs) in faecal samples with significantly greater efficacy than conventional extraction methods.

The MiVET is expected to enable early diagnoses and to help in the implementation of appropriate control measures, as well as shed light on how these viruses circulate in the environment. The ability to detect micro?amounts of virus using the MiVET will be especially valuable for precise diagnosis in the early phase in human?positive cases and asymptomatic carriers, as well as for identifying the sources of the viruses’ spread (Yamazaki et al., 2018).

Advanced biosensors

With the complexity of the commonly used methods for detecting pathogens, and time needed to conduct the procedures, there is strong interest in developing new, swifter point?of?care biosensing systems for detecting animal diseases early. Colorimetric sensors have proved effective in detecting influenza A viruses. In this method, gold nanoparticles are stabilised with gold nanoparticles are stabilised with sialic/sialic acid (a substance found in saliva) to bind with a protein on the surface of the influenza virus. Aside from this technique, current developments are focused on miniaturising and automating micro?array biosensors for building portable diagnostic platforms (Vidic et al., 2017).

New candidate vaccine viruses (CVVs)

Established influenza viruses continue to be identified in regions around the world, and evolve both genetically and antigenically, leading to the need for additional candidate vaccine viruses (CVVs) so governments and industry can be prepared for potential pandemics (EFSA, 2018). Changes in the genetic and antigenic characteristics of these viruses relative to existing CVVs, and their potential risks to public health, justify the need to select and develop new CVVs (WHO, 2018). It is important to know that institutions interested in receiving these CVVs should contact the World Health Organization (WHO) or the institutions listed in announcements published on the WHO website (WHO, 2018).

Avian influenza mathematical model

Since the virus can spread from birds to humans, a mathematical model for the spread of avian influenza has been formulated by Modnak and Wang (2018), which includes bird-human interaction and incorporates the effects of infection latency and human vaccination. The essential dynamics of the model are being investigated through an equilibrium analysis to explore effective vaccination strategies for controlling avian influenza outbreaks using optimal control theory. This model-study indicates that strategically deployed human vaccination could significantly reduce the numbers of exposed and infectious people in the event of a major outbreak among people.

Editor at The Poultry Site

Ryan worked in conservation from 2007-2017, during which time he operated a rainbow trout hatchery in Canada for the Toronto and Region Conservation Authority. As editor of The Poultry Site, he now writes about challenges and opportunities in the global poultry industry and agri-food chain.

More from this author