Blue tongue

From Cow
Ulcerative dermatits in the nares of a cow infected with BTV
Similar lesions in a BTV-infected cow

Blue tongue (Epizootic hemorrhagic disease) is an arthropod-borne orbivirus (Bluetongue virus - BTV) which only rarely causes neonatal deformities and acute oral disease in cattle worldwide[1].

A large number of Orbivirus serotypes have been recognised and numerous vectors are responsible for its transmission, primarily biting midges (Culicoides spp). Transmission can occur through bull semen. Transplacental transmission has been reported in cattle in Europe.

Clinical signs

Clinical signs in cattle are rare and presentations usually involve fever, conjunctivitis, dyspnea, ptyalism, salivation and joint stiffness. The characteristic swollen blue tongue is due to lesions of nasal mucosa, nasal discharge.

Examination of the affected animals sometimes reveals oral vesicles and ulcers and ulcerative dermatitis. Abortion has been recorded in pregnant cows. Birth defects occur in calves such as hydranencephaly or porencephaly, resulting in ataxia and blindness.

Diagnosis

A diagnosis is based on presenting clinical signs, prevalence of the orbivirus in the region and ancilliary testing. Ancillary tests include histopathological analysis of postmortem samples, ELISA and PCR tests[2].

Treatment

There is no specific treatment for cattle with bluetongue, although novel antiviral agents have been developed recently[3]. Supportive feeding, fluids and administration of broad-spectrum antimicrobials may assist recovery.

Mandatory vaccination protocols are required in some countries (e.g. france), using an inactivated vaccine[4]. Other countries routinely vaccinate cattle for this disease[5].

Prevention of outbreaks must address control of insect vectors.

References

  1. Boyle DB et al (2012) Genomic sequences of Australian bluetongue virus prototype serotypes reveal global relationships and possible routes of entry into Australia. J Virol 86(12):6724-6731
  2. Zientara S et al (2012) Difficulties in the interpretation of bluetongue RT-PCR results in France. Vet Rec 170(23):599
  3. Gu L et al (2012) Novel Virostatic Agents against Bluetongue Virus. PLoS One 7(8):e43341
  4. Hultén C et al (2012) Seroprevalence after Vaccination of Cattle and Sheep against Bluetongue Virus (BTV) Serotype 8 in Sweden.
  5. Gubbins S et al (2012) Scaling from challenge experiments to the field: Quantifying the impact of vaccination on the transmission of bluetongue virus serotype 8. Prev Vet Med 105(4):297-308