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 haracterized 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 ource 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
Actinomyces (Corynebacterium) pyogenes is by far the most
common cause of abscesses in cattle. In contrast to C.
ovis the lymph nodes are seldom affected, but abscesses
usually develop under the skin on any part of the body
and are characterized by a soft yellow pus. If the navel
is infected at birth, the bacteria penetrate the liver.
They spread rapidly through the bloodstream and cause
a septicemia with resultant death within a few days. The
bacteria may also establish themselves in the liver and
produce numerous abscesses or spread to the joints and
tendon sheaths where abscesses may also be formed with
consequent lameness. The lungs may become infected through
inhalation of bacteria which give rise to acute pneumonia
or abscesses. When an abscess is formed in the lung the
bacteria spread and cause pneumonia and pleuritis, which
may result in adhesion of the lungs to the pleural tissues.
In cases where abscesses break open, the whole chest cavity
may become filled with pus. Abscesses may also occur in
the spinal cord and result in paralysis. The bacteria
may affect the brain and, depending on the position of
the abscess, blindness, complete loss of balance or circling
movements may be seen. Continued loss of condition is
observed in an animal in which multiple abscesses are
present. Anemia, weakness and death may follow. Mastitis
and udder abscesses are also very common. As in the case
of C. ovis infections, contamination of a farm builds
up gradually and eventually the whole environment including
dips, crushes, feeding troughs, etc., becomes contaminated.
All possible measures should therefore be taken to avoid
the development of such a state of affairs. If this is
not done the incidence will gradually increase and cause
greater losses. Cattle may also become infected through
small wounds and through the naval cord. Consequently
cows hould be allowed to calve in a clean camp or preferably
in the veld and newborn calves should be kept away from
drinking places and other areas where animals congregate
until the umbilical cord has healed completely. Moreover,
careful tick control is essential to avoid penetration
of bacteria. Similarly, thorn bushes should be controlled
and other causes of injuries such as wire, old tins, food
troughs with sharp edges, etc., should be removed.It should
be noted, however, that Actinomyces is not the only cause
of abscesses and other bacteria such as Staphylococcus,
Actinobacillus and Pasteurella are frequently involved.
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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 lood 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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| Name of disease |
Calf paratyphoid
(Salmonella dublin, S typhimurium and S.bovis-morbificans)
|
| Name of vaccine |
Salmonella dublin vaccine
|
| |
Product code: 1093 |
Description of Disease
Calf paratyphoid is a common disease of young calves between
the age of 4 to 6 weeks, especially when they are kept
under conditions of poor hygiene in cold and inadequate
housing. The disease may also sometimes occur in younger
or older animals. It is caused primarily by 2 bacteria
species, namely Salmonella dublin and S. typhimurium but
infection as a result of Salmonella bovis-morbificans
occasionally occurs. The majority of cases are the result
of S. dublin, whereas S. typhimurium occurs less frequently
and is inclined to infect younger calves. In exceptional
instances other Salmonella types may also be responsible
for the disease. Calves become infected from carrier animals
or from the contaminated environment. There are 3 forms
of the disease, namely septicemia, acute enteritis and
chronic enteritis. The septicemia form usually affects
young calves and is of short duration with death occurring
within a few ours up to 2 days. Many calves are found
dead without previously appearing to be ill. Calves showing
symptoms are usually weak, feeling cold and depressed
with or without colic and diarrhea. Calves which die quickly
may not show any lesions. Lesions observed are usually
insufficient for a definite diagnosis. Acute enteritis
will affect calves and older cattle. Once infected they
stop feeding, develop fever and have a foul smelling progressive
diarrhea, which begins watery and later becomes mucoid
and bloody. Chronic enteritis usually affects animals
older than 3 months of age. They grow poorly and have
watery faeces or a mild diarrhea. These symptoms result
from a severely damaged intestinal tract which can- not
properly digest or absorb ingested food. These cases showing
chronic infection may have active infections in several
organs and are continually shedding virulent bacteria
into the environment. Paratyphoid sometimes occurs simultaneously
with other diseases which aggravate the symptoms. There
e also many other causes of enteritis and diarrhea in
calves such as coccidiosis, Escherichia coli, chlamydiosis
and a variety of viruses as well as management factors.
In cases where immunized calves become ill, it is advisable
to consult a veterinarian to establish the true cause
of the disease. It should also be remembered that the
vaccine will only afford protection against S. dublin,
and that problems will be encountered if infection on
a farm is the result of S. typhimurium, or any other type
of Salmonella. In such instances the inactivated vaccine
must be used. Salmonella typhimurium commonly infects
cattle as well as sheep, goat, pigs, horses and man.
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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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Description of Disease
Vibriosis of cattle is a typical venereal disease and
is spread from one animal to another during mating. The
bacterium which causes the disease is a comma- shaped
organism known as Campylobacter fetus of which there are
a number of subspecies. Bulls usually become infected
when they serve infected cows. When infected bulls serve
susceptible heifers or cows the infection is transmitted
and an inflammatory reaction results in the female genital
organs. Conception usually does not take place or the
embryo is resorbed or aborted at a very early age. The
result is that cows come on heat repeatedly and this is
eventually manifested as a low calving percentage in the
herd. It is important to remember that there are also
many other causes of infertility in which feeding, management
and other infectious diseases such as trichomoniasis may
play a prominent role. All cases of infertility should
therefore not be ascribed to vibriosis. In herds with
infertility problems a veterinarian should always be consulted.
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Description of Disease
As in the case of sheep, pasteurellosis of cattle may
assume many forms. Pasteurella multocida and Pasteurella
haemolytica strains are important organisms in the bovine
respiratory disease complex, also known as "shipping
fever". Pasteurella bacteria change virus initiated
catarrhal inflammations of the mucosa of the respiratory
tract into mostly purulent bronchopneumonia with development
of abscesses. In feedlots, where animals are under stress
because of overcrowding, wind, heat, cold and adaptation
problems, risks of infection are higher and favour the
outbreak of the disease. Under such circumstances the
disease is usually preceded by infections with infectious
bovine rhinotracheitis (IBR) or parainfluenza 3 virus
(P13). In certain feedlots Pasteurella bacterins alone
may give rise to problems. It is therefore recommended
that feedlot cattle also be inoculated against ISR and
P13 to minimize the risk of respiratory disease. Acute
septicemic pasteurellosis (hemorrhagic septicemia) is
caused by P. multocida type E and occurs in Namibia and
the Northwest Province.
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VACCINES AGAINST VIRAL DISEASES
Description of Disease
Lumpy skin disease is an acute, sub-acute or subclinical
viral disease caused by a poxvirus (Neethling strain).
All breeds of cattle are sus- ceptible but the clinical
signs are most prominent in imported breeds such as Friesland
and Jerseys. Animals develop a biphasic fever response
within a week after exposure to the virus and may remain
febrile for 4 to 14 days. During this time animals may
show symptoms such as lack of appetite, a mucopuruient
nasal discharge and increased salivation. Typical raised
nodules on the skin (5 to 50 mm-diameter) appear before
or during the second increase in body temperature. Nodules
may involve both the skin and subcutaneous tissue and
in some cases even the underlying musculature. The number
of nodules may vary from a few to several hundreds occurring
over the whole body. During convalescence the skin lesions
either resolve rapidly, become indurated and persist as
hard lumps known as "sitfasts" for a few months
or in some cases early rejection of the skin lesions often
leaves purulent, raw ulcers and abscesses. Soft yellow-grey
ulcers also occur in the mucous membranes of the mouth,
the nose, the respiratory tract, forestomachs and the
reproductive organs. Subcutaneous swelling of the legs
may be seen which is often misdiagnosed as snakebite.
Although the mortality rate of the disease is comparatively
low, it causes appreciable economic losses because of
emaciation, mastitis which is the cause of temporary and
even permanent loss of milk production, sterility in bulls
and damage to the hide. Lumpy skin disease should be distinguished
from a benign superficial skin disease caused by bovine
herpesvirus type 2 (Allerton strain) which is also characterised
by the formation of skin nodules. This disease is called
"pseudo lumpy skin disease" and causes flat,
round or irregular swellings in the skin. They are 5 to
50 mm in diameter, but are flat and often centrally depressed
and often only noticed on teats. Animals are never ill
and after approximately 1 week the superficial layers
of the skin slough off. The disease is of no economic
importance and there is no commercially produced vaccine
against it. Although lumpy skin disease usually occurs
sporadic-early, in some years it may spread rapidly and
give rise to a severe epidemic (e.g. in the summer of
1989 to 1990). Circumstantial evidence suggests that biting
insects play a major role in spreading the infection.
The virus is present in the saliva and skin lesions and
consequently the disease spreads by direct contact, through
common drinking and feeding troughs. However this is not
the main means of transmission.
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Description of Disease
Three-day stiffsickness is an acute disease
of cattle which is transmitted by insects. The virus is
a member of the family Rhabdoviridae and there is only
one known serotype in South Africa. The disease is prevalent
in late summer and autumn, particularly when weather conditions
are favourable for hatching of insects. Outbreaks of the
disease usually terminate suddenly, soon after the first
severe cold or frost and may disappear throughout the
winter and only reappear the next summer or a few seasons
later.The disease symptoms are characteristic. Affected
animals are reluctant to walk and are stiff and lame.
They will later lie down and only rise with difficulty,
or not at all. (One or more limbs may be affected simultaneously.)
The back is usually arched, the neck stretched out and
muscle tremors as well as slight swelling of the joints
may be observed. Other symptoms include a pronounced flow
of saliva (usually because of paralysis of the oesophagus),
lacrimation, and a phasic fever reaction. Two or more
phasic febrile reactions of 12 to 24 hours may occur and
pass unobserved. The most important clinical signs and
economic effects of the disease are the severe loss in
condition and sudden drop in milk production. If the drop
occurs in the first trimester of lactation, milk production
will return to normal levels after recovery. A continuous
low milk production after the initial drop may occur in
cows that contract the disease in the second and third
trimester of lactation. Production levels in these dairy
cows will return to normal in the following lactation
period. Temporary sterility and abnormal sperm may occur
in bulls. As the name indicates, animals usually recover
after 3 days. Sometimes the recovery period may be longer,
especially in the case of heavy stud bulls, high producers,
heavily pregnant cows and older animals. These animals
may be down for several weeks. Severe complications such
as bedsores and pneumonia may occur and cause death. Animals
suffering from three-day stiffsickness have difficulty
in swallowing, and dosing by mouth should be avoided because
of the danger of introducing material into the lungs,
causing pneumonia. Cattle which have recovered from the
disease develop good immunity and seldom contract the
disease a second time.
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Description of Diseas
e 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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VACCINES AGAINST PROTOZOAL AND RICKETTSIAL DISEASES
Description of Disease
Anaplasmosis, commonly known as gallsickness,
is a tick-transmitted disease of cattle caused by a rickettsia-like
organism which occurs in the red-blood corpuscles of infected
animals. The disease is generally characterized by a variable
fever, anaemia, jaundice, rumen stasis and constipation.
In dairy cows, a drop in milk yield may precede any of
these symptoms. Two species of the causative organism
occur, viz. Anaplasma marginale and Anaplasma centrale.
The former is the most important, often causing serious
disease and mortality in susceptible cattle. A. centrale
is less harmful and seldom responsible for any serious
disease symptoms. Once animals are infected with A.marginale
or A.centrale, they probably remain carriers of the parasite
for life and this carrier state is accompanied by long-term
immunity to the disease. Since immunity to A. centrale
also protects cattle against serious disease and mortality
caused by A.marginale, A. centrale-infected blood is used
in the form of a live blood vaccine for immunization of
cattle against anaplasmosis The term gallsickness is often
erroneously used by farmers to describe a variety of disease
conditions, including ordinary constipation (dry gallsickness),
certain plant intoxications, or any condition in which
a distended gall-bladder filled with bile may be found
upon postmortem examination. Strictly speaking, however,
gallsickness in cattle only refers to the disease caused
by A. marginale or A. centrale, ie anaplasmosis.Anaplasmosis
occurs throughout most of South Africa and Namibia (except
in the very low-rainfall areas where few ticks occur)
and in many areas it is permanently established (endemic).
The distribution of anaplasmosis often corresponds to
that of babesiosis (Babesia-infection or redwater of cattle),
but it may also occur in areas free of babesiosis. Under
natural conditions, anaplasmosis is transmitted?by at
least 5 tick species. Ticks pick up the infection when
they feed on cattle having the disease or which have recovered
(which remain carriers of the parasite). Weather conditions
which favour tick survival may also lead to disease outbreaks
if ticks are carried into areas normally free of anaplasmosis.
The one-host blue tick (Boophilus decoloratus) is generally
regarded as probably the most important vector (transmitter)
of A. marginale, despite the fact that the infection is
not transmitted transovarially (from the female tick to
her progeny).Although ticks are the most important vectors
of anaplasmosis, the disease can also be transmitted mechanically
via small quantities of infected blood. Blood-sucking
flies, which often feed intermittently on a number of
animals, can transmit the infection between cattle via
minute quantities of blood remaining on their mouthparts.
In this regard it has been proven in South Africa that
anaplasmosis can be transmitted by stable flies (Stomoxys
spp.) and horseflies (Tabanus spp.), and in other parts
of the world it has also been found that midges and mosquitoes
can act as mechanical vectors of the disease. Mechanical
transmission by blood-sucking flies probably does not
play an important role in maintaining anaplasmosis under
extensive field conditions. However, where cattle are
maintained in close association with one another, such
as in dairy herds and feedlots, the risk of mechanical
transmission by blood-sucking flies is much greater. Furthermore,
it should be noted that the disease can also be transmitted
among cattle by the use of instruments, such as those
used for vaccination, ear-notching, tattooing, dehorning,
etc. on which fresh infected blood is found. Intra-uterine
transmission (infection of the unborn calf) occasionally
occurs, in which case the calf may already be a carrier
of the parasite at birth. In exceptional cases infection
of the unborn calf may lead to abortion or mortality of
the calf soon after birth. Anaplasmosis often shows a
strong seasonal incidence, and outbreaks of the disease
occur more frequently during the warmer summer and autumn
months. Increased incidence of the disease is related
to the greater abundance and activity of ticks and blood-sucking
flies during this period. Climate (especially rainfall)
and tick-control measures (eg dipping) will therefore
also influence the incidence of anaplasmosis in an area
or herd. All cattle which have not previously been infected
or vaccinated are susceptible to anaplasmosis. How- ever,
all calves are born with non specific resistance to the
disease, irrespective of whether the dam is immune or
not. The degree of resistance to the disease, however,
diminishes with age. This non specific resistance is probably
greatest at approximately 6 months of age, but calves
up to the age of 9 months seldom show any symptoms of
disease, or only develop a mild form of the disease. On
the other hand, the disease is much more severe in mature
animals which contract the disease for the first time.
In such cases disease and mortality may result in severe
losses. In areas where sufficient infected ticks occur,
all calves should become infected at a young age (up to
9 months). Calves will be "naturally immunized"
at a young age, and consequently no outbreaks of the disease
should occur in older animals in such areas. A situation
such as this, where no clinical cases of the disease occur
in an anaplasmosis endemic area, is referred to as a stable
disease situation. On the other hand, an unstable disease
situation arises when too few infected ticks occur in
an area, either as a result of too severe tick control
measures, or as a result of natural influences (eg droughts).
Consequently, not all calves are exposed to the infection
and outbreaks of the disease can thus be expected in these
animals during the following year (when they are older
and more susceptible). Although calves should ideally
be immunized against anaplasmosis by natural infection
(ie tick-transmitted infection), natural influences (rainfall)
on tick populations cannot be controlled. Therefore, anaplas-
mosis vaccine is usually used as an adjunct to natural
infection to protect animals which may have escaped infection
as calves against the serious consequences of natural
infection at a later age. For more details of the disease
symptoms, diagnosis and treatment of the disease, postmortem
findings, as well as control measures consult the technical
paper (information circular) Anaplasmosis (tick-transmitted
gallsickness) of cattle which is published by OVI. For
more information, Onderstepoort Biological Products may
also be contacted.
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Description of Disease
Babesiosis, commonly known as redwater, is a tick-transmitted
disease of cattle caused by a protozoal organism which occurs
in the red-blood corpuscles of infected animals. The disease
is generally characterized by a high fever, a light to dark
red or brown discoloration of urine, anaemia and even jaundice
in advanced cases. Two important species of the causative
organism occur in South Africa, viz. Babesia bigemina (which
causes African redwater) and Babesia bovis (which causes
Asiatic redwater). To protect cattle against serious disease
and mortality caused by the more virulent tick-transmitted
parasites, less harmful "vaccine strains" of Babesia
bigemina and/or Babesia bovis are used in the form of a
live blood vaccine to immunize cattle against babesiosis.
Infected recovered cattle usually develop an immunity to
that specific type of redwater, but there is no cross-immunity
between the African and Asiatic types. Babesiosis occurs
widespread in South Africa (except in the very low rainfall
areas where few ticks occur) and in many areas it is permanently
established (endemic). The distribution of babesiosis often
corresponds to that of anaplasmosis (Anaplasma- infection
or tick-transmitted gallsickness of cattle), but the latter
generally has a wider distribution. Of the 2 types of redwater,
African redwater (B. bigemina-infection) has the widest
distribution, coinciding with the distribution of the 2
tick vectors (transmitters). viz the one-host blue ticks
Boophilus microplus and Boophilus decoloratus. These ticks
are absent in the drier parts of the Western and Northern
Cape Provinces, western Free State and higher lying parts
of the Drakensberg and Lesotho. Asiatic redwater, however,
has a more limited distribution because it is transmitted
only by B. microplus, which occurs mainly in high rainfall
areas. These include parts of the Eastern Cape Province,
KwaZulu-Natal and Mpumalanga. Clinically it is difficult
to distinguish between the 2 types of redwater, since the
symptoms are very similar. In the case of Asiatic redwater,
however, the red discoloration of the urine is not always
present and nervous symptoms such as an increased or decreased
reaction to stimuli, poor coordination, muscle tremors,
convulsions and even coma may be observed, especially in
advanced cases. When these symptoms occur, the disease is
referred to as cerebral babesiosis which may, amongst others,
be confused with heartwater. Under natural conditions, babesiosis
is transmitted only by ticks, which become infected when
they feed on cattle having the disease or which have re-
covered (they remain carriers of the parasite for variable
periods). Weather conditions which favour tick survival
may also lead to disease outbreaks if ticks are carried
into areas normally free of babe- siosis. Intra-uterine
transmission (infection of the unborn calf) occasionally
occurs, which may lead to abortion or mortality of the calf
soon after birth. Babesiosis often shows a strong seasonal
incidence, and outbreaks of the disease occur more frequently
during the warmer summer and autumn months. In- creased
incidence of the disease is related to the greater abundance
and activity of ticks during this period. Climate (especially
rainfall) and tick-control measures (eg dipping) will therefore
also influence the incidence of babesiosis in an area or
herd. All cattle which have not previously been infected
or vaccinated are susceptible to babesiosis. However, all
calves are born with a nonspecific resistance to both forms
of the disease, irrespective of whether the dam is immune
or not. The degree of resistance to the disease, however,
diminishes with age. This nonspecific resistance is probably
greatest at approximately 6 months of age, but calves up
to the age of 9 months seldom show any disease symptoms
or only develop a mild form of the disease. On the other
hand, the disease is much more severe in animals which contract
the disease as adults for the first time. In such cases
disease and mortality may result in severe losses. In areas
where sufficient numbers of infected ticks occur, all calves
should become infected at a young age (up to 9 months of
age). Calves will thus be "naturally immunized"
at a young age, and no out- breaks of the disease should
occur in older animals in such areas. A situation such as
this, where no clinical cases of the disease occur in a
babesiosis endemic area, is referred to as a stable disease
situation. On the other hand, an unstable disease situation
arises when too few infected ticks occur in an area, either
as a result of too severe tick control measures, or natural
influences (eg droughts). Consequently, not all the calves
are exposed to the infection and outbreaks of the disease
can be expected in these animals during the following year
(when they are older and more susceptible). Al- though calves
should ideally be immunised against babesiosis by natural
infection (ie tick-transmitted infection) the natural influences
(rainfall) on tick populations cannot be controlled. Therefore,
babesiosis vaccine is usually used as an adjunct to natural
infection to protect those animals which may not have been
infected as calves against the serious consequences of natural
infection at a later age. For more details on the disease
symptoms, diagnosis and treatment of the disease, postmortem
findings, as well as control measures, consult the technical
paper (information circular) Babesiosis (redwater) of cattle
which is published by OVI. For more information, Onderstepoort
may also be contacted directly
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Description of Disease
Heartwater is an acute infectious disease responsible
for severe losses among susceptible cattle, sheep and goats.
Its causal organism, Cowdria ruminantium, is transmitted
by the bont tick, Amblyomma hebraeum. In nature the disease
can be transmitted only by this tick in its nymphal and
adult stages and occurs only where this tick is present.
The bont tick prefers warm and moist lowveld and bushveld
areas and is found in Mpumalanga, Kwa-Zulu-Natal, the Northern
and Northwest Provinces, Eastern and Western Cape Provinces,
as far south as Mossel Bay. It also occurs in parts of Swaziland
and Botswana. Affected animals have a fever of between 40
and 42 °C, are listless, loose their appetite and lag
behind the rest of the herd. As the disease progresses,
movement becomes more impeded. Animals often develop a high-stepping
gait. Breathing becomes more laboured and animals may push
their heads up against firm objects. The affected animals
eventually lie on their side with the head pulled backwards
and the legs extended. They are sensitive to intensive light
and twitch their eyelids rapidly when exposed to it. The
eyes roll from side to side in the orbita. The body temperature
rapidly drops to below normal prior to death. A postmortem
examination reveals varying quantities of straw-coloured
fluid, which may sometimes be blood-tinged, in the chest
cavity and the heart sac (hence the name of the disease).
The lungs are heavy and have a soaked appearance. White
foam is often abundant in the air passages. Some or all
of these changes may, however, also be observed in animals
dying from other causes and only a veterinarian can make
a final diagnosis by microscopical examination of a smear
prepared from brain tissue. Heartwater occurs throughout
the year. The incidence varies according to the tick population
and its activity and the disease is therefore less frequently
encountered during winter. The disease occurs when an infected
tick feeds on a susceptible animal. Bont ticks become infected
with the heartwater organism when they feed on an infected
animal in which the organism is circulating in the blood
at that particular time. Engorged larval and nymphal ticks
drop from the host, moult within 4 to 6 weeks and are ready
to seek new hosts on which they can feed as nymphae and
adults, respectively. If such a host is susceptible to heartwater
they will transmit the infection to it. Infected adult female
ticks play no further role after having engorged, dropped
and laid their eggs, because they then die and the heartwater
organisms are not transmitted through the eggs to the next
generation of ticks. Only 2 to 5 % of bont ticks found in
heartwater areas are infected. The movement of animals carrying
infected ticks into or through an area free from the disease,
can result in losses among susceptible stock if they are
infected by ticks which drop from the infested animals.
The ticks, however, seldom survive longer than one season
in an area which is climatically unsuitable for them. Apart
from cattle and small stock, large and small game animals,
hares and some ground dwelling birds (eg guineafowl) can
also become subclinically infected with heartwater, and
although they may show no clinical signs of the disease,
they may have the organism circulating in their blood and
therefore be able to infect ticks that feed on them. As
healthy carriers of the infection, these animals and birds
play an important role in the maintenance of the infection
in ticks and consequently also in the occurrence of the
disease. Because they cannot be dipped like cattle, these
animals and birds also regularly serve as hosts on which
the ticks can feed. It is clear that the bont tick, and
therefore heartwater, cannot readily be exterminated on
a farm where large and small game are present. Cattle, particularly
indigenous breeds, older than 1 year and newborn calves
up to an age of 4 to 6 weeks, have nonspecific resistance
to the disease and when infected many of them show no clinical
signs, or at most develop a mild fever reaction. This phenomenon
in newborn calves is exploited during vaccination (see below).
Cattle and small stock may be resistant to infection by
infected ticks for two reasons: animals may be immune (either
as a result of an earlier infection or through vaccination)
or they may have a varying degree of natural resistance
against the disease. Animals born in a heartwater area are
usually, but not necessarily always, exposed to infected
ticks (and become infected) when they are still young and
have an inborn natural resistance. In this way they acquire
an early immunity which is thereafter boosted by regular
reinfection by ticks. Losses as a result of heartwater most
often occur when animals born and reared in areas free from
the tick and the disease are moved into areas where the
disease occurs (endemic areas) or when animals in endemic
areas loose their immunity because they are not exposed
to reinfection by ticks (eg as a result of a too intensive
dipping programme).
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