Enzootic bovine leucosis

Alert

Enzootic bovine leucosis is category 1 restricted matter.

Under Queensland legislation, if you suspect the presence of this disease in any species of animal, you must report it to Biosecurity Queensland on 13 25 23 or contact the Emergency Disease Watch Hotline on 1800 675 888.

Cattle and buffalo are the only animals infected naturally with this virus. A small proportion of infected cattle develop lymphoid tumours affecting all body systems. There is no evidence of any human health risk.

Cause

Bovine leukaemia virus

Other names

  • EBL

Distribution

Enzootic bovine leucosis (EBL) is found worldwide and is widespread in dairying areas. In 1983, it was estimated that around 70% of Queensland's dairy herds and 14% of animals in the herds were infected. Since then, a voluntary control scheme has eliminated most infection from Queensland and Australian dairy herds. Ongoing monitoring of dairy herd by milk testing confirm the national industry's freedom from EBL.

Surveillance activities have identified the disease in beef cattle at a low prevalence.

Affected animals

  • cattle
  • buffalo

Symptoms

Infected cattle may show no clinical signs during their lifetime. Once infection is established, it is permanent and no spontaneous recovery has been shown. In animals that develop clinical signs, the main signs are:

  • loss of condition
  • lack of appetite
  • anaemia
  • weakness.

The animal's temperature is usually normal unless tumour growth is rapid. Tumours often involve the superficial lymph nodes and are easily visible. Once signs are observed and tumour growth is detectable, death normally occurs in 2-3 weeks.

How it is spread

Dairy herds are most at risk of entry of EBL through the introduction of untested beef animals (eg. a beef bull to join dairy heifers) to the herd, or sharing equipment (eg. dehorners, vaccinating needles) between beef and dairy herds.

Within a dairy herd, the primary method of transmission of the virus from infected cows is multiple suckling of calves or pooling of milk to feed calves.

About 4-8% of infections can be accounted for by transmission of the virus from a cow to her calf before birth.

The disease also spreads between animals whenever there is contact with the blood of an infected animal, for example blood from wounds. Biting insect vectors are known to spread the disease. Blood sampling and vaccination using common syringes and needles, dehorning and other procedures which re-use the same equipment and rectal examination of a group of cows may all spread infection.

Semen from infected bulls is not infective but a traumatised genital tract of an infected bull could transmit disease at natural service. No transmission to 6-day or 7-day embryos has been found. If embryos are well washed, no transmission to the recipient occurs.

Control

EBL has been eradicated from the national dairy herd, and Queensland supports an ongoing program to maintain dairy freedom. This include separating the dairy herds from untested beef cattle, and responding to eradicate infection and risk of spread if EBL is detected or suspected through milk testing.

There are no controls on EBL in the beef and buffalo industries, for which the incidence and impacts of EBL are negligible.

Further information