Description of Disease
Botulism or lamsiekte is primarily a disease of cattle.
Under some circumstances horses, sheep, goats, chickens,
ostriches and other birds may also be affected. The disease
occurs sporadically in sheep in the dry areas of the NorthWestern
Cape and Namibia. It is essentially a paralytic condition,
which is usually followed by death.
Botulism is caused by the toxins of bacteria known as
Clostridium botulinum types C and D. The bacteria
form resistant spores and are widespread in the soil in
most parts of the world. They multiply in decomposing
protein-rich animal or plant material eg carcasses of
rats, tortoises, hares and birds as well as bean and lucerne
hay. In these types of material the bacteria produce very
potent toxins which are taken in by mouth and absorbed
through the intestine.
In general the symptoms of botulism are as follows: the
animals walk unsteadily as if afraid, lie down and stand
only with difficulty, and eventually become completely
paralyzed. Saliva dribbles from the mouth because the
animals are unable to swallow, the tongues become paralyzed,
can easily be pulled out and cannot readily be retracted.
The tails also become paralyzed and the faeces hard. Animals
usually die within a day or two after lying down, but
they may survive for up to 10 days. If an animal ingests
a large amount of toxin it can die within 12 hours. In
other animals the symptoms are essentially the same as
in cattle, namely paralysis with abnormal muscle movements.
There are no typical postmortem lesions.
Botulism occurs under the following circumstances:
1. In areas that are subject to prolonged droughts
the phosphorus and protein content of the grass during
winter is very low and animals grazing on such veld develop
severe deficiencies. Phosphate deficiency is characterized
by poor growth, general weakness of the bones, a stiff
gait and an abnormal appetite known as pica. Pica is worsened
by the protein deficiency. Such animals chew old bones
and will eat any decomposed carcass material. If such
carcasses or bones are contaminated with Clostridium
botulinum, the toxin taken in will initiate the disease.
2. If a small animal, such as a cat or a rat, dies
in a drinking trough, in a silo or a place where fodder
is stored, the bacteria may multiply in such a carcass
and contaminate the surrounding feed. When such contaminated
feed is ingested by dairy cows or horses, they will contract
botulism. Sometimes a rotting carcass may lie in drinking
water and animals which consume this water may also die.
Decomposing protein- rich hay, such as bean or lucerne
hay, may occasionally produce botulism in cattle and sheep.
3. Poultry litter that contains decomposing carcasses
and which is fed to cattle or sheep may be a major source
of botulism, particularly if it becomes wet.
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Description of Disease
Tetanus or lockjaw is a disease which affects virtually
all animals and man. Horses and humans are the most sensitive
victims of the disease while cattle are less susceptible.
Young lambs are frequently affected. The disease is caused
by the toxin of Clostridium tetani. The bacteria
multiply in the dead tissue of a wound. The potent toxin
is absorbed from the wound and moves along the nerves
to the brain and spinal cord, causing typical nervous
symptoms.
The most common wounds in which the bacteria multiply
are caused by castration and docking. The bacteria may
also occasionally contaminate and infect the navel. The
use of rubber bands for docking is particularly dangerous
and must be avoided in unprotected lambs. These bands
cause necrosis of the skin which creates ideal conditions
for the bacteria to multiply and extensive losses have
been incurred with this procedure. Clostridium tetani
is extremely common in faeces and in the soil of kraals
and stables and readily infects wounds.
A lamb suffering from tetanus shows typical nervous symptoms.
It lies down and has great difficulty in standing. Later
the animal may become so stiff that it falls over and
cannot rise again. The legs are stiffly extended and the
whole body is tense. The neck is drawn backward and the
jaw is closed tightly. When such an animal is disturbed
it may go into a tetanic spasm.
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Description of Disease
There are various causes of abscesses in sheep and goats
but the bacterium Corynebacterium pseudotuberculosis
or Corynebacterium ovis is the most common.
This organism is mainly responsible for abscessation of
the lymph nodes. The disease is also known as caseous
lymphadenitis or Preisz-Nocard abscessation.
In exceptional cases abscesses may also occur in other
organs such as the liver, lungs or spinal cord, but abscesses
in these organs are usually the result of other bacteria,
particularly Actinomyces (Corynebacterium) pyogenes.
If an abscess is cut or opens of its own accord, the environment,
e.g. kraals, dipping tanks and shearing sheds, is contaminated
with pus. The bacteria can survive in moist places such
as manure and soil for many years and such contaminated
premises are a permanent source of infection. Sheep become
infected through shearing, castration and docking wounds
from where the infection spreads to the local lymph nodes.
The most common sources of infection are dirty, dusty
shearing sheds and contaminated clothing of shearers and
labourers. Unsterilized instruments which are used for
docking and castration also serve as a source of infection.
The organisms may enter through wounds caused by thorns,
grass seeds (steekgras-Aristida) and ticks.
Synthetic dips that are commonly used have little antibacterial
activity and dipping tanks can therefore be a source of
infection of wounds. The bacteria can also penetrate unbroken
skin, particularly after dipping and in wet conditions.
As the disease is chronic, the symptoms only appear long
after infection has taken place. There is a gradual loss
of condition with the development of superficial abscesses
which may break open. The pus from such abscesses is thick,
sticky, caseous and has a green-yellow colour.
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Description of Disease
The causative organism of brucellosis in cattle is
Brucella abortus. This disease is characterized by
abortions which usually occur in the later stages of pregnancy.
The infected cow sheds the bacteria with the aborted fetus,
the afterbirth, genital discharge or in the milk. A cow
or heifer becomes infected by inhaling the organisms from
or by licking the after- birth or mucous secretions of
infected animals which have calved or aborted. Man becomes
infected by contact with infected material or infected
animals and drinking infected raw milk.
In animals, Brucella abortus has a special affinity
for the fetal tissues during pregnancy. Therefore, the
sexually mature cow or the pregnant heifer is most susceptible
to such infection. When a pregnant animal becomes infected,
the cotyledons of the fetal membranes are affected. This
causes a disturbance in the blood supply to the fetus
which consequently dies and is expelled. The bacteria
may also localize in the udder and related lymph nodes.
Bulls occasionally become infected, but do not play an
important role in the spread of the disease.
There are many other causes of abortion and infertility
and a veterinarian should therefore be consulted for a
definite diagnosis.
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Description of Disease
Pasteurellosis of sheep and goats is a sporadic disease
characterized by various forms of pneumonia differing
in severity. The disease is also known as "bontlong" or
"harslagsiekte". Occasionally sheep develop a liver infection
which causes a severe icterus and which has been termed
bacterial hepatitis.
Pasteurellosis is caused by 2 bacteria, namely Pasteurella
multocida and Pasteurella haemolytica. These
bacteria occur in the respiratory tract of normal sheep,
but under abnormal conditions such as cold weather, malnutrition
during droughts or other stress factors, the bacteria
may multiply and produce pneumonia. It may also spread
to other organs and cause a fatal infection. Special care
must be taken if animals from a different area are introduced
into an infected area.
In many instances pasteurellosis is preceded and aggravated
by other infections such as Chlamydia or mycoplasma and
viruses and is often a com- plication of jaagsiekte. There
are also other bacterial and viral causes of pneumonia
in sheep and goats.
P. haemolytica may cause meningitis, joint infections
and particularly mastitis (a form of blue udder-see further
on).
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Description of Disease
Colibacillosis is a disease of young animals and occurs
during the first few days of life. It is characterized
by severe diarrhea. A more acute septicemia condition
may also occur which is characterized by meningitis and
sudden death (diarrhea absent). In piglets of a few days
old the main symptom is diarrhea. The causative organism
is the bacterium Escherichia coli of which there are a
vast number of different strains. Only a few of these
strains are primary pathogens and some of them only cause
disease in a particular species of animal while others
may affect a variety of species. All animals carry various
strains of E. coli in their intestines. These are usually
the nonpathogenic strains, but a few pathogenic types
may be present without causing disease. If conditions
in the intestines are favorable pathogenic types of E.
coli will attach to the intestinal wall by means of their
hairlike fimbriae. Colonization and multiplication take
place and enterotoxins are produced. Certain E. colitypes
may even penetrate the tissues and cause acute death by
septicemia. Favorable circumstances for the growth of
pathogenic types are often caused by unsatisfactory feeding
practices. Feeding times and the composition of the food,
especially milk, is of critical importance. For instance,
the disease may be precipitated if a young animal is fed
cold milk at irregular intervals or if sudden changes
in the composition of the ration occur. In these cases
the normal digestive process ceases and excessprotein
and carbohydrates accumulate in the intestine to form
an ideal medium for the growth of the bacteria. This can
also happen if young animals are affected by other debilitating
diseases or if they do not ingest sufficient colostrum
in time. The incidence of colibacillosis is increased
appreciably if piglets are exposed to extremely cold weather
and sudden changes in the diet. Control of the disease
is so dependent on good feeding and management that complete
reliance should not be placed on immunization alone. Oedema
disease in pigs is caused by only 3 serotypes of E. coli
capable of producing a unique toxin (probably a neurotoxin)
which is responsible for oedema of the gut and nervous
symptoms when it is absorbed into the bloodstream.
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VACCINES
AGAINST VIRAL DISEASES
Description of Disease
Rift Valley fever is an acute insect-transmitted
viral disease of sheep, goats, cattle and man. It is caused
by a virus which belongs to the family Bunyaviridae.
RVF last appeared in SA in 1974 and was associated with
he occurrence of heavy rains.
Rift Valley fever is transmitted by mosquitoes (Culex,
Aedes) and therefore appears in summer in hot,
humid conditions which favours the hatching of these insects.
There are high numbers of insects in low lying areas near
water and there is a large possibility that susceptible
animals grazing in these areas may contract Rift Valley
fever.
The duration of the disease in lambs under the age of
2 weeks is between 24 and 72 hours. They show a high fever
(41 to 42 °C), are depressed and lose their appetite.
The mortality rate may be 95 % or higher. In addition
to the above-mentioned signs, older sheep show a bloody,
foetid diarrhoea. The sheep frequently vomit and there
is a mucopuruient nasal discharge. The mortality rate
in older sheep is about 15 to 30 % with 40 to 60 % ewes
aborting. Clinical signs in calves are mild with 10 to
15 % mortalities, but in adult cattle abortion (10 to
40 %) is sometimes the only clinical sign. In goats clinical
signs are less severe than in sheep.
People are usually infected through handling of blood
and organs from animals which died of the disease. Care
must therefore be taken whenever a postmortem examination
is done on an animal which died of Rift Valley fever.
Transmission can occasionally occur direct from mosquitoes.
Clinical signs in humans include influenza-like symptoms,
headache, vomiting, bloody urine, dark stool, photosensitivity
(light sensitivity) and impaired vision.
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Description of Disease
Orf is caused by a poxvirus, namely
Paravaccinia
and it affects sheep, goats as well as man. Young lambs
are more susceptible and therefore show more severe clinical
signs than adult animals. The virus is widely distributed
in South Africa.
Orf virus is very stable on exposure to environmental conditions
and it can remain on a farm for up to 1 year. The virus
is transmitted from infected to susceptible sheep by direct
contact or indirectly through wounds. Animals grazing on
thornbushes and spiky grasses have wounds and scratches
which provide places of entry for the virus. The virus infects
small wounds and initially (after 2 to 6 days) a reddening
and slight swelling can be seen. A scab later develops which
eventually becomes wart-like.
The affected areas are typically the lips, ears, feet, reproductive
organs, flanks or upper legs. The lip form is more common
and the lesions can spread to the muzzle, eyelids, gingiva,
oesophagus and rumen. The wart-like lesions are single or
multiple. The foot form is seen where animals graze on long
spiky grass and in wet conditions. Lesions develop on the
coronet and between the toes. In severe cases the foot bones
can be affected. Lesions can spread to the udder and reproductive
organs of ewes when lambs suckle. Secondary bacterial infection
of the lesions may occur and could give rise to complications
such as mastitis or septicaemia, resulting in mortalities,
especially in young lambs.
Animals never show a fever because the virus remains localised
in the lesions. Orf lesions are painful, therefore animals
refuse to eat and this leads to weight loss and loss of
condition. It is a serious problem in the north-western
Cape where large economic losses occur annually.
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