Published Date: 2004-01-06 23:50:00
Subject: PRO/AH/EDR> Avian cholera, cormorants - South Africa
Archive Number: 20040106.0059
AVIAN CHOLERA, CORMORANTS - SOUTH AFRICA
A ProMED-mail post
ProMED-mail, a program of the
International Society for Infectious Diseases
Date: 6 Jan 2004
Source: Capetown Times [edited]
An outbreak of avian cholera has hit the seabird breeding colony on Dyer
Island, off Gansbaai on the southern Cape coast, killing more than 4000
birds in the past 2 weeks.
Conservation staff from several agencies have pooled resources to try to
contain the killer disease, which has swept through the breeding colony 3
times since winter 2003.
Several times a day, staff walk through the colony to pick up dead birds
and burn their carcasses in bonfires in an attempt to halt the spread of
the virus. They wring the necks of ill or dying birds, whose carcasses are
The disease has affected the cormorant population in particular, which is
already classified as "near-threatened".
In the past 2 weeks, 4115 birds, mainly cormorants, have died on the
island, which is a Cape Nature Conservation reserve.
Gail Cleaver, Cape Nature Conservation's manager for the Overberg region,
said yesterday: "The previous outbreaks of cholera affected adults, but
coming at this time of year, this outbreak is affecting the fledglings as
well. We are trying to get the dead out of the colony as quickly as
possible and are burning them on the island to try to stop the spread of
Cleaver said this was the 3rd year in a row that had seen avian cholera
outbreaks on Dyer Island. In the 2002 epidemic, 7800 birds died.
There was an outbreak on the island during the winter of 2003 and another
smaller outbreak in October 2003.
She said a joint operations team had been set up to deal with the cholera
outbreak and comprised staff from Cape Nature Conservation, the Department
of Environment Affairs' Marine and Coastal Management, and Overstrand
Municipality's nature conservation department.
Kevine Shaw, ornithologist for Cape Nature Conservation, said avian cholera
was spread through the birds' feces and mucous. Shaw said: "Obviously bird
colonies are more susceptible to the rapid spread of the disease because
the birds are so close together. The only way to fight it is to go through
the colony a couple of times a day and collect the dead birds and burn
them. I don't think an inoculation exists against avian cholera, but even
if it did it would be impossible to inoculate thousands of birds.
"Avian cholera is a natural thing and it's been around for years, but
because both the Cape cormorant and crowned cormorant populations have been
steadily decreasing over the years, every outbreak of the disease has more
of an effect than it would normally have."
Cormorant populations have been in decline because of a variety of factors,
he said, including human disturbance and declining fish stocks.
[Byline: Melanie Gosling]
[Gansbaai is located approximately 100 miles (160 KM) southeast of
Capetown, South Africa.
Avian Cholera is caused by the bacterium _Pasteurella multocida_. Cholera
in wild birds, such as the cormorants, is probably Type 1. Although many
species of birds and mammals can become infected with different strains of
this bacteria, Type I is most common. The species of birds most commonly
affected are ducks and geese, coots, gulls, and crows.
Avian cholera can spread very rapidly as it is highly contagious. Immediate
action is necessary to minimize or prevent the spread of the disease.
Careful carcass collection and disposal helps reduce the amount of bacteria
in the environment. Although human beings are not at high risk of
contracting this disease, it is a wise idea for the workers to wear gloves
when removing the carcasses.
Large die-offs are seen primarily in wild ducks and geese, which the
disease affects peracutely. The most common early sign is the sudden
appearance of large numbers of dead birds in good body condition. Few if
any birds are observed as sick.. Death can be be so rapid the birds will
literally fall out of the sky. They may die while eating, with food still
in the bills or oral region, with no previous signs of disease. Sick birds
appear lethargic and die within minutes when captured. Other clinical signs
are convulsions; swimming in circles; throwing the head back between the
wings; erratic flight, such as flying upside down or trying to land a foot
or more above the water; mucous discharge from the mouth; soiling or
matting of the feathers around the vent, eyes, and bill; pasty,
fawn-colored or yellow droppings; or blood-stained droppings or nasal
On necropsy, hemorrhages may be seen on the heart, liver, gizzard, and
intestines. Areas of tissue death appear as white or yellow spots on the
liver and spleen. The liver may appear darkened or copper in color, and may
be swollen and rupture when handled. These particular lesions are not
unique to avian cholera, but rather to an acute disease process. The upper
digestive tract may contain recently ingested food, while lower digestive
tract may contain a thick yellowish viscous fluid, filled with large
numbers of _P. multocida_ bacteria. - Mod.TG]