INTRODUCTION

Rabbit haemorrhagic disease (RHD) is a highly contagious, infectious viral disease with a high mortality rate, usually affecting both domestic and wild rabbits.

WHAT IS VIRAL HAEMORRHAGIC DISEASE?

Rabbit haemorrhagic disease (RHD) is an infectious disease of viral origin, highly contagious and with a high mortality rate, which usually affects both domestic and wild rabbits.

The causative agent is an RNA virus of the genus Lagovirus of the Caliciviridae family. It is highly resistant to inactivation when protected by organic material and has the ability to agglutinate red blood cells.

EVH affects only domestic and wild members of the species Oryctolagus cuniculus. Other rabbit species, as well as free-ranging rabbits and other animals, are not susceptible. As it does not affect humans, it does not cause public health problems.

It is endemic in Australia, New Zealand, Cuba, parts of Asia and Africa and most of Europe.

SYMPTOMATOLOGY OF VIRAL HAEMORRHAGIC DISEASE

Symptoms usually appear in animals over 8 weeks of age. In domestic rabbits, acute or over-acute disease is most frequently described, but sub-acute and chronic disease can also be observed.

In the superacute form, infected rabbits develop fever and die. In the over-acute form infected rabbits develop fever and die suddenly within 12 to 36 hours after the onset of symptoms, which may be only terminal squeaking followed rapidly by collapse, convulsions, opisthotonos and death - in the acute form depression, fever, anorexia, ocular haemorrhages, epistaxis or prostration may be observed. In addition, neurological signs (excitation, convulsions...) and respiratory signs (dyspnoea, rhinorrhoea...) may develop. Some animals recovering from acute disease develop severe jaundice, with weight loss and lethargy, and die within a few weeks. In these animals, diarrhoea and abdominal dilatation may occur just before death.

In the subacute form, similar but milder symptoms are observed (hypertension, depression, anorexia...), and most rabbits survive.

• AT CIRCULATORY LEVEL: DIC, semi-clotted blood, haemorrhages in various tissues and organs, serohemorrhagic exudate and hyperemia (generalised circulatory dysfunction).
  
  

• AT LIVER LEVEL:
  Necrotic hepatitis: At liver level (marked tropism).
  Multifocal necrotic hepatitis: The liver may be pale with a fine reticular pattern of necrosis demarcating each lobe. In acute forms the liver appears yellow and very friable.
  
  

• PULMONARY: serohaemorrhagic pneumonia, congestion and oedema.
  
  

The trachea appears hyperemic, with bloody content, the trachea appears hyperemic, with bloody content (haemorrhage) and oedema. In the spleen we can find splenomegaly, congestion, a blackish colour, rounded edges and engorged organ. In the kidney we see congestion and a dark brown colour. Generalised congestion and infarcts are also common in most organs. Haemorrhages are common in the thymus, and petechiae may be found in the serous membranes or viscera. In subacute disease, catarrhal enteritis of the small intestine and jaundice may be observed. Congestion of the meninges has also been reported.

HOW IS THE DISEASE TRANSMITTED?

• MAIN SOURCES: The main reservoir is the wild rabbit, although any excretion or secretion of affected animals may contain the virus (urine, faeces, saliva, etc.) and can survive in carcasses for up to several months.
  
  

• ROUTES OF TRANSMISSION: Rabbits can acquire the disease by oral, nasal or conjunctival routes.
  
  

• DIRECT CONTAGION: By close contact between healthy and sick animals.
  
  

• INDIRECT CONTAGION: The virus persists for some time in the environment and is spread by fomites (hair, personnel, cages, etc.); and by vectors (flies and other insects), which transmit the virus from one farm to another.
  
  

HOW TO PREVENT VIRAL HAEMORRHAGIC DISEASE?

Prevention is fundamental and that same prevention includes specific vaccination (every 12 months), putting mosquito nets on windows, ensuring good ventilation and cleanliness and being cautious when going to the countryside or visiting farms, catteries or the homes of companions who keep rabbits.

There is no cure for this disease and it is potentially fatal.