Ophidian Paramyxovirus

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Species predisposition

Ophidian paramyxovirus (OPMV), also called Fer-de-Lance virus of reptiles (FDLV), is an important viral pathogen of snakes, principally Viperidae and it has also been isolated from Elapidae, Colubridae and Boidae. The natural host for OPMV is unknown but may be a non-viperid. Disease may be associated with decreased immunocompetence. Transmission may be by droplet, fomites and vectors such as mites. Congenital infection may be involved.

Examination

Anorexia may be seen several weeks before presentation. Clinical signs are often related to the respiratory system. Presentation is frequently a moribund snake, although the progression may be chronic. There may be a discharge from the glottis that is sometimes bloody (haemorrhagic pneumonia). Central nervous system signs (including writhing, torticollis, loss of righting reflex) are occasionally seen. Chronic paramyxovirus shows clinical progression from mild respiratory disease to severe respiratory disease and pneumonia, followed by progressive neurologic disease.

Consider paraxmyxovirus in snakes with the following clinical signs:

  • Emaciation
  • Loss of muscle tone
  • Unwillingness to move
  • CNS signs including head tremors, stargazing)
  • Seeking heat
  • Recurring unresponsive bacterial or fungal pneumonia
  • Mucoid diarrhoea
  • Malodorous stools
  • Distended bowel
  • Severe protozoal infections

For more information on the respiratory system of snakes, see Snake Respiratory System.

For more information on examination of a snake, see Snake Physical Examination.

Diagnosis

OPMV should be suspected in Viperidae presented with signs associated with immunodeficiency. There are several methods of diagnosis:

Antemortem

A haemaglutination inhibition test (HI) for specific antibodies to OPMV has been developed (titre < 1:20 - negative, 1:40 to 1:80 - suspect and > 1:80 - positive). A positive titre means exposure and not disease or shedding status. Two samples for HI at a 2-4 week interval are advisable. Negative staining electron microscopy of faecal or lung samples is possible. A polymerase chain reaction (PCR) test would be very useful.

For more information on sample collection, see Lizard and Snake Specimen Collection and Evaluation.

Postmortem

  • Gross necropsy - Lesions are usually subtle to non-existent but may include pulmonary (pneumonia - congestion, oedema, haemorrhage or inflammatory exudate) and pancreatic (necrosis, hyperplasia, interstitial oedema or fibrosis) lesions. The liver may be involved.
  • Histopathology - There may be characteristic histopathological lesions in lung and pancreas and occasionally CNS. Sections from cranial, mid and caudal lung should be examined. Immunoperoxidase and immunofluorescent staining is possible (formalined-fix tissues in 10% formalin for 48 hours then store in 70% ethanol).
  • Virus isolation is the definitive diagnostic tool. Tissue (lung, liver, kidney, spleen and heart) is placed in individual sterile bage and frozen. Seroconversion (requiring a minimum of 8 weeks) determines that a snake has been previously exposed to the virus and has been infected.

For more information on postmortem of a snake, see Snake Necropsy.

Therapy

There is no specific treatment for snakes showing clinical signs of OPMV infection. Antibiotics are indicated because most affected snakes die with gram-negative respiratory tract infections.

Infected snakes should be isolated. Snakes suspected to be infected should remain in isolation until definitive diagnostic tests have been carried out. Reptiles that have been in direct or immediate indirect contact should be placed in isolation and serologically tested immediately with repeat testing in 4-6 months time.

Prevention

The best control is a sound preventative medicine programme. All new specimens should be quarantined for ninety days. Hygiene is very important because of the possibility of spread by fomites and mites. Geriatric snakes may be more susceptible to paramyxovirus than young conspecifics. Modified-live and inactivated vaccines have had mitigated the spread of paramyxovirus in birds and mammals, however there is currently no vaccine available for protecting snakes against OPMV.

Literature Search

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Ophidian Paramyxovirus publications

References

Mader, D.R. (2005). Reptile Medicine and Surgery. Saunders. pp. 401. ISBN 072169327X

Richie, B.W. (1995). Avian viruses: function and control, Lakeworth, Fla, Wingers Publishing. ISBN 0963699636