HomeIdentifying Tick Borne Diseases and Conditions in Cattle
Identifying Tick Borne Diseases and Conditions in Cattle
Disease identification
In Australia, the tick-borne diseases of significance in cattle are tick fever (caused by Babesia bovis, Babesiabigemina andAnaplasma marginale) and theileriosis (bovine anaemia caused by variants of Theileria orientalis).
Preliminary suspicion of tick-borne disease may be obtained by noting clinical signs in the cattle. It is not possible to use clinical signs alone to identify the different tick-borne diseases. Similar clinical signs may also be present with other diseases. Pale and/or yellow mucous membranes (gums, eyes/conjunctiva, vulva), fever, weakness, urine colour changes and lack of appetite are possible clinical signs of all these diseases. There are some differences in clinical signs caused by these diseases: nervous signs are possible with Babesia bovis; red urine possible with Babesia bovis and Babesiabigemina; and brown urine more usual with Anaplasma marginale.
Diagnosis of tick fever and theileriosis is normally confirmed by finding the parasite in blood smears when using a microscope (Figure 1). Laboratory examination of blood smears prepared from the tip of the tail or ear is the most common method of diagnosis. In the case of dead animals, organ smears (including brain smears for Babesia bovis) and blood smears can be taken. Theileriosis can be difficult to diagnose as the organisms are readily seen in blood smears taken from healthy animals, so assigning significance to the finding can be challenging. Molecular techniques to detect the organisms, and serology to detect previous exposure, are also useful tests.
Ixodes ticks may cause paralysis, which is diagnosed by clinical signs and/or evidence of paralysis ticks. Normal evidence would be the presence of paralysis ticks or craters left in the skin where paralysis ticks have been (Figure 2). Occasionally, very heavy burdens of the cattle tick itself may cause weakness by sucking large amounts of blood.
Figure 1. Microscopic comparison of the different species that cause tick fever. Image courtesy of Lyn Knott (Common Parasites of Veterinary importance).
Figure 2. Paralysis tick feeding. Image courtesy of Lex Turner
Tick fever
Figure 1. Tick fever is transmitted by cattle tick, naïve cattle which are introduced into the cattle tick zone are at greatest risk. Image courtesy of Virbac
(Babesiosis and anaplasmosis)
Tick fever is caused by infection with Babesia and Anaplasma organisms transmitted by the cattle tickRhipicephalus australis (formerly known as Boophilus microplus). All cattle in tick infested areas are at risk of developing tick fever. Breed and age are key risk factors.
British, European and other Bos taurus breeds are more susceptible to tick fever caused by Babesia than Brahman/Bos indicus breeds. All breeds, including Bos indicus breeds, are highly susceptible to disease caused by Anaplasma marginale.
There is a strong link between age and resistance. Calves exposed to tick fever organisms between 3–9 months of age rarely show clinical symptoms and develop a solid, long-lasting immunity. Once infected with Babesia or Anaplasma organisms, the animals become carriers and the infection and immunity is likely to persist for many years. A tick fever vaccine is available in Australia.
The single biggest risk for disease caused by infection with tick fever is in cattle that are introduced from outside the cattle tick areas. However, even cattle born and raised within the tick area are not guaranteed to have developed immunity by the time age-related resistance wanes at 9–10 months of age.
Babesiosis
Figure 1. Schematic of a blood smear from a cow infected with Babesia bovis. Image courtesy of the Tick Fever Centre
Babesiosis (also known as red water) is caused by either of the organisms Babesia bovis or Babesia bigemina, both of which are transmitted by the cattle tick. Babesia bovis is only transmitted by cattle tick larvae on pasture; Babesia bigemina is transmitted by the nymph or adult stages of cattle tick.
Babesia bovis (Figure 1) is the most important cause of tick fever disease in Australia; it is responsible for more than 80% of tick fever outbreaks. The course of the disease is quite rapid, and death can occur within a day or two of first observing clinical signs.
Signs
Fever, lethargy, depression and weakness.
Pale and/or yellow mucous membranes (anaemia and/or jaundice).
Loss of appetite.
Staggered gait.
Muscle tremors.
Red urine (especially with B. bigemina; in latter stages with B. bovis).
Nervous signs such as charging or head pressing may be a feature of the later stages of Babesia bovis infection.
Abortion may occur in cows.
Temporary infertility in bulls.
Diagnosis
Many of these clinical signs are non-specific and can be associated with other conditions, so it is important to confirm the diagnosis by examination of blood smears under a microscope.
Figure 1. Schematic of a blood smear from a cow infected with Anaplasma marginale (dark spots on the edge of the red blood cells). Image courtesy of the Tick Fever Centre
Anaplasmosis is caused by the organism Anaplasma marginale (Figure 1). It is transmitted by the cattle tick and is thought to be transferred mainly by direct movement of male ticks from carrier animals to other animals when they are in close contact. The course of the disease is more gradual than that associated with babesiosis, and the animals may be quite anaemic and jaundiced by the time clinical illness is noted.
Signs
The main clinical signs are pale and/or yellow mucous membranes (anaemia and/or jaundice); note that the urine does not turn red with anaplasmosis but may appear as a dark brown colour. Other clinical signs of anaplasmosis may include fever, loss of appetite, lethargy and depression, weakness and loss of condition.
Diagnosis
As with babesiosis, many of these clinical signs are non-specific and can be associated with other conditions, so it is important to confirm the diagnosis by examination of blood smears under a microscope.
The parasite infection is transmitted by bush ticks, wallaby ticks and bandicoot ticks (all in the genus Haemaphysalis).
The disease is most common in eastern, coastal Australia.
Young calves, heavily pregnant and recently-calved cows are most susceptible.
Immunity usually develops by 6 months of age and adults in endemic regions are rarely sick.
In adults, the most susceptible are those with no prior exposure (naïve) that are moved to endemic areas (signs typically appear 6–8 weeks after introduction).
Currently, no vaccine or specific treatment is available.
Follow best practice herd management and biosecurity protocols to minimise risk.
The protozoan parasite Theileria orientalis can cause theileriosis (bovine anaemia) in cattle and is transmitted by bush ticks, wallaby ticks and bandicoot ticks which feed on cattle and inject the parasite into their bloodstream. Parasites enter red blood cells, multiply and destroy them, eventually resulting in anaemia.
The parasite has been present in Australia for more than 100 years and although it causes lifelong infection, it was rarely associated with disease. Since 2005, reports of theileriosis outbreaks have greatly increased with up to 30% mortalities in some herds attributed to Theileria. This change is associated with a new parasite strain and is sometimes referred to as BATOG or ‘bovine anaemia due to Theileria orientalis group’.
It is important to distinguish BATOG from highly pathogenic East Coast Fever, which is caused by exotic strains of Theileria and is confined to eastern Africa.
Theileria has been detected in all states and territories. It is commonly detected in wet coastal areas where Haemaphysalis ticks are prevalent and is considered endemic (repeatedly found in a region) in much of coastal Queensland, New South Wales and Victoria. Theileriosis cases in South Australia and Western Australia have only been reported within the last decade.
The Theileria parasite is mainly spread by Haemaphysalis ticks and signs can occur with less than 10 ticks, which can easily be missed when inspecting cattle. Cattle that have recovered from the disease continue to be carriers remaining as Theileria parasite sources in endemic zones. A recent study from New Zealand has shown that sheep can carry detectable levels of Theileria infection, although the levels of infection were much lower than those found in cattle. Research is needed in Australia to determine if species other than cattle could be involved in transmission. Not all Haemaphysalis ticks carry Theileria.
Signs
Fever, lethargy (reluctance to walk), weakness.
Laboured or heavy breathing.
Pale or yellow mucous membranes (gums, eyes/conjunctiva, vulva).
Brown urine.
Reduced appetite and weight loss.
Decreased milk production in dairy cows.
Abortion, premature births, stillbirths.
Sudden death (highest rates seen in heavily pregnant cows).
Diagnosis
The signs of theileriosis can also be linked to other conditions so it is important to confirm a diagnosis with your veterinarian. This involves examination of blood under a microscope for the presence of Theileria parasites. It can also be confirmed using other laboratory based molecular tests too, if necessary.
Treatment and control
No registered drugs or vaccines are currently available for the specific treatment or control of theileriosis. The effect theileriosis may have can be minimised through appropriate management practices to maintain a healthy herd.
Figure 1. Theileria stains dark pink inside the round, red blood cells of an infected cow. Image courtesy Tick Fever Centre
Figure 2. Theileria has the same coastal distribution as its Haemaphysalis tick host (bush tick distribution shown). Image adapted from Virbac.
Tick paralysis
The paralysis tick, Ixodes holocyclus, is the main cause of tick paralysis of cattle. Paralysis tick is native to Australia’s east coast from Cape York Peninsula in Queensland to southern Victoria. Other paralysis tick species are not as common but do extend into Tasmania (Figure 1).
Paralysis ticks are a 3-host tick and the most common host is the bandicoot although many native species are infested.
Adult paralysis ticks, which are responsible for causing paralysis, are more active in late winter to mid-summer (August to December) but cases can be seen all year round in some areas. A drop in barometric pressure and rain events can stimulate activity in pasture-based unattached adults resulting in movement to areas (higher parts of plants) that increase likelihood of attachment to a host.
The adult tick is found mainly in areas that are less likely to get rubbed off, so most attach to the head, neck, ventral abdomen and escutcheon (under the tail area) of the host. As the tick feeds on the blood of the host, saliva from the tick is injected into the host animal (Figure 2). The saliva contains toxins that cause paralysis. Paralysis does not occur immediately. Sufficient tick toxin may be injected to cause signs in the host after an adult tick has fed for about 3 days. Young calves are more prone to the effects of the toxin. Natural immunity to the toxin can develop with repeated exposure.
Signs
Paralysis starting with hind limb ataxia (weakness) is usually the first symptom.
Paralysis is ascending (progressively moving forward) until the animal is unable to rise.
Increased respiratory effort and difficulty swallowing may become evident as paralysis increases.
As paralysis continues to increase, an animal may not be able to maintain sternal recumbency (sitting up) and death is usually from aspiration of gut contents and pneumonia complications.
Mis-adventure and an inability to move from environmental extremes may also contribute to the death toll.
Diagnosis
Diagnosis is based on the presence of signs of paralysis as described above and the presence of paralysis ticks, or craters left in the skin where paralysis ticks have been.
Figure 1. Distribution of Australian paralysis ticks. Image courtesy of Virbac.
Figure 2. Paralysis ticks feeding on the blood of a cow. Image courtesy of Lex Turner.
Tick fever diagnosis advice and laboratory services
Samples to collect
Blood and organ smears
Microscopic examination of blood and organ smears from sick or dead animals is the most commonly used procedure to confirm tick fever. These smears are best included as part of general sample submission after examination by a veterinarian or Biosecurity Officer. Clinical examination and submission of a broad range of appropriate samples give the best chance of making an accurate and useful diagnosis.
You can, however, prepare your own smears from affected animals and have them sent to our Biosecurity Sciences Laboratory by a veterinarian or Biosecurity Officer for a quick diagnosis of tick fever see ‘Submit samples to the Biosecurity Sciences Laboratory’ below).
Organ smears are also a valuable aid to diagnosis and can be made from animals that have been dead for up to 24 hours.
Blood and serum samples
Occasionally it is helpful to provide other blood samples in addition to smears if you are investigating disease in vaccinated animals. Please contact the Tick Fever Centre to discuss whether additional samples are required and which samples to collect (see ‘Diagnostic services and advice’ below).
In general, if you are investigating a:
potential vaccine breakdown (disease in animals previously vaccinated) – a serum sample is useful to assess vaccination status. It may also be worth collecting sera from a number of cattle vaccinated at the same time as the sick animals to assess vaccine ‘take’ across the group. Heparin or EDTA blood samples may also be useful to isolate a virulent strain if there is evidence of a number of vaccinated animals becoming sick.
potential vaccine reaction (disease in animals vaccinated within the last month) – an EDTA blood sample may be useful to distinguish vaccine organisms from naturally transmitted field organisms.
Contact the Tick Fever Centre for advice
You can contact the Tick Fever Centre for advice about:
Withholding periods are mandatory with all registered veterinary products used to treat animals for internal and external parasites. These limits are set in Australia to ensure that meat and milk are safe to eat and to ensure that they do not exceed maximum residue limits (MRLs) for Australian and overseas markets. It is extremely important to ensure that cattle treatments are timed so that WHP can be observed and MRLs are not exceeded. There are three main withholding periods of concern in cattle:
Meat Withholding Period (Meat WHP) is the time from chemical application to when an animal can be slaughtered for domestic use.
Export Slaughter Interval (ESI) is the time from chemical application to when an animal can be slaughtered for export.
Milk Withholding Period (Milk WHP) is the time from chemical application to when milk can be taken from the animal for human consumption.
These withholding periods are stated on the labels of all registered veterinary products and on the APVMA website. Note that very occasionally in the case of older registered veterinary products there may not be an ESI listed on the label. In this case consult the APVMA website. When cattle are sold it is necessary for the owner to certify on the National Vendor Declaration (NVD) whether or not they are within the meat withholding period (WHP) or export slaughter interval (ESI) after treatment with veterinary drugs or chemicals.
Check with your processor to determine which withholding period to use as some processors export products such as offal so require ESI.
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