Theileriosis - an emerging disease problem?

Graham Bailey

Graham Bailey
Veterinary Research Officer
NSW Department of Primary Industries[DPI]

Summary

  • A specific project will cover lab charges for the investigation of suspect cases of theileriosis (testing to confirm /exclude Theileria as detailed below)
  • The samples needed for Theileria investigation are blood (clotted and EDTA), fresh blood smears and standard autopsy samples if PM sampling
  • Epidemiological information (cases, duration, ticks, property introductions etc) is needed on the specimen advice

Background

In 2008 there was an increase in the number of outbreaks of theileriosis in NSW, due to infection by the protozoan parasite, Theileria buffeli. T. buffeli is part of the Theileria buffeli/sergenti/orientalis group. This group is regarded as benign when compared to T. parva (east coast fever) and T. annulata (mediterranean fever) - highly pathogenic strains that are exotic to Australia.

The reason for the increased number of outbreaks is unknown and is being investigated. It is possible that differing pathogenicity of strains as demonstrated by Japanese veterinarians is responsible.

We are providing the following information to veterinary practitioners to increase awareness of the disease and to provide a guide for investigation and diagnosis of outbreaks. NSW DPI is encouraging veterinarians to submit samples to its veterinary laboratory at Menangle to investigate suspect cases.

Charges for tests to confirm/exclude theleriosis will be paid by NSW DPI under its "Better understanding of theileriosis in NSW cattle herds" project. Charges for other tests will be as normal - that is, paid for by the submitter unless there is an existing project which would pay all/part of test charges.

Clinical signs

Clinical signs are those associated with severe anaemia and include: lethargy, inappetence, exercise intolerance, tachycardia, tachypnoea, pale to jaundiced mucous membranes, transient pyrexia, abortions, and in dairy cows a drop in milk production. No visual evidence of haemoglobinuria though on occasions urinary dipstick positive. Mortality rate is highest in heavily pregnant cows. Cases have been noted in all age groups.

Postmortem findings

Commonly see jaundice of carcase, in particular the liver may appear yellow.

Diagnostic aids

Severe regenerative anaemia, blood smear examination reveals Theileria piroplasms within erythrocytes, and hyperbilirubinaemia. There is often elevated GLDH, GGT and AST associated with anoxic liver damage. Fibrinogen levels are generally normal. Theileria infection may be seen as an incidental finding, so other causes of haemolytic anaemia should also be considered and excluded where necessary.

Differential diagnoses for haemolytic anaemia

Differentials include: Brassica poisoning (kale anaemia), tick fever (babesiosis and anaplasmosis which are notifiable diseases in NSW), bacillary haemoglobinuria (Clostridium haemolyticum), leptospirosis in calves, post-parturient haemoglobinuria (hypophosphataemia), chronic copper toxicity (mainly in sheep, rare in cattle). Other differentials exist but are less common.

Submission of specimens to the Veterinary Laboratory at Menangle

  • Complete a Laboratory Submission form (hard copies available from EMAI or can be downloaded from http://www.dpi.nsw.gov.au/agriculture/vetmanual/submission/specimen-submission-form
  • Document whether or not there were any cattle introductions to the property in the last 3 months, including where the introduced cattle came from. PIC and/or owner name, property address and town of origin are preferred. If this is not available, as a minimum, the town is required. If cattle were introduced, record whether introduced cattle/homebred cattle/both are affected.
  • Examine the affected mob for ticks, recording whether or not any ticks were seen. If ticks are found submit them for identification. Ticks are best preserved by placing in a small container of alcohol.
  • Veterinarians investigating a cattle production problem or disease that fits the suspect theileriosis case definition are requested to sample up to 5 affected animals and if present, up to 5 in-contact but healthy animals. If one or more affected animals are freshly dead, collect samples as per an autopsy ensuring that fixed liver and a fresh spleen or liver sample (held for subsequent PCR testing) are submitted.
  • Submit EDTA bloods and smears from affected cattle for haematology. Blood smears should be made at the time of sampling using clean dry slides. Distinguishing piroplasms becomes more difficult in smears made from stored EDTA blood. EDTA bloods will be retained by the laboratory for possible PCR testing (not routinely available).
  • Submit clotted blood. Sera will be retained by the laboratory for serology (not routinely available).
  • Submit other samples as required for differential diagnosis.

Testing to be performed

On receipt of samples, a PCV will be performed on EDTA blood and smears (either supplied or made in the laboratory), stained and examined. Additional tests eg full blood count, biochemistry will be at the job manager's discretion. If submitted, ticks will be identified. The cost of these tests will be paid by NSW DPI provided instructions regarding submission of samples are followed.

If one or more affected animals have died and post mortem(s) are performed, testing of EDTA blood from live animals and ticks from any animal will be paid by NSW DPI. Testing of samples from dead animals or samples to exclude other than notifiable diseases, will be charged according to the normal guidelines.

Case Definition

For the purposes of the "Better understanding of theileriosis in NSW cattle herds" project, the following case definition applies.

Suspect theileriosis:

  • cattle in NSW with clinical evidence of severe anaemia (with associated signs), and
  • case occurs between 1 May 2009 and 30 June 2010, and
  • clinical examination and history fails to detect any other obvious cause of the anaemia, or other causes have been excluded.

Further Information

For further information contact
Graham Bailey
02 63913870 or
graham.bailey@dpi.nsw.gov.au