Page 547 - The Veterinary Laboratory and Field Manual 3rd Edition

484 Susan C. Cork

anthrax of these can be found in birds but H17 N10 and
H18 N 11 have only been isolated from bats.
Cause: Bacillus anthracis Most mammalian species have common strains
of influenza but can occasionally be infected by
Epidemiology: The spores of the organism sur- avian strains. Many infections are asymptomatic.
vive for long periods in the soil. If the soil is Virulent strains, known as ‘highly pathogenic
later disturbed by ploughing or grazing stock avian influenza’ (HPAI) are usually subtypes H5
there may be an outbreak of the disease. Such or H7 and are associated with disease outbreaks
outbreaks usually occur in areas where animals in domestic poultry. The virus is transmitted
have previously died of anthrax and the vegeta- by aerosol but can also be transmitted through
tive organisms have been exposed to the air and the oral-faecal route. Although there are vac-
dispersed by scavengers.
cines available against influenza A viruses in
Signs in animals: Sudden death. Swollen carcass. humans and animals these are not always fully
Bloody discharges from body orifices (that is, protective due to changes in the antigenic struc-
mouth, nostrils, rectum). ture of the virus. This can occur as a result of
antigenic drift (common over time) or due to
Diagnosis: If anthrax is suspected, do not ‘antigenic shift’ (more rapid but less common)
open the carcass or spore formation will occur as a result of genetic reassortment between
resulting in long term contamination of the sur- viruses infecting the same host. Poultry and pigs
rounding area. Send a blood smear, taken from are considered to be potential ‘mixing vessels’
an ear vein, to the laboratory. It is important for the development of strains that can infect
to ask specifically for anthrax to be looked for humans, this is because strains adapted to pigs
(microscopy +/– culture) and if possible speak (including H9N2) have characteristics that allow
to the nearest veterinary unit about the case. attachment to the epithelial lining of the human
PCR can also be used to confirm a diagnosis respiratory tract. In 2003, pan-zoonotic strains
of anthrax. Control: Where and when feasible/ of avian influenza H5N1 resulted in a number of
desirable vaccination is available for livestock. If human deaths across Asia.
the diagnosis of anthrax is confirmed the carcass
should be buried in a deep pit and the hole filled Signs in animals: May be clinically in apparent. In
in with lime. domestic poultry, the virus can act locally caus-
ing mild disease (for example, ruffled feathers,
off food) but virulent strains are more invasive
avian Influenza causing systemic infections with neurological,
respiratory and gastrointestinal signs.
Cause: Orthomyxovirus, influenza A Diagnosis: Diagnosis can be confirmed at nec-
ropsy using PCR or traditional virological
Epidemiology: Influenza A viruses cycle natu-
rally in wild aquatic birds, especially waterfowl. techniques. There are also a number of serologi-
Many strains are non-pathogenic. The avian cal tests including kit tests for rapid diagnosis.
influenza viruses are divided into subtypes Egg inoculation is used to culture strains. Typing
based on the structure of two proteins on the is often done using either PCR or HI. (See also
surface of the virus: haemagglutinin (HA) and Chapter 6.)
neuraminidase (NA). To date, there have been Control: Quarantine poultry flocks sus-
18 HA and 11 NA proteins identified and these pected to have highly virulent avian influenza.
can occur in a wide range of combinations. Most Vaccinations are available for poultry and other

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