Sunday 15 April 2012

Novel adenovirus isolated from sea lions

Viruses of the family Adenoviridae have genomes consisting of double stranded DNA. They infect various species of vertebrates, including humans. Adenoviruses were first isolated in 1953 from human adenoids. Two types of canine adenoviruses are well known, type 1 and 2. Type 1 causes infectious canine hepatitis, a potentially serious disease involving vasculitis and hepatitis. Type 1 infection can also cause respiratory and eye infections. Canine adenovirus 2 (CAdV-2) is one of the potential causes of kennel cough. Viral hepatitis associated with adenoviral infection has been previously seen in free-ranging California sea lions Zalophus californianus. However previous isolation of viruses were unsuccessful and identification of this virus was ceased and no specific virus was documented. However because the morphological features seen under the microscope were quite similar to that of canine infectious hepatitis and since the virus has a wide host range, it was thought that perhaps the virus responsible for disease was CAdV-1.

The presence of adenoviral DNA was examined in tissue samples from 2 live stranded California sea lions that were admitted to the rehabilitation facility at Californian Marine Mammal Centre. The two rescued animals died with serious symptoms , first was diagnosed with arteritis , pneumonia and pulmonary haemorrhage. Also eosinophilic intranuclear inclusion bodies (sign of adenoviral infection) were discovered in few organs including lymph nodule and lungs. The other case died from severe viral hepatitis with intranuclear eosinophilic inclusions found within hepatocytes.

Tissues from both animals were first examined under electron microscope and then analysed using PCR with the use of specific primers (sense: 5’-GCG CAC TTA CTC ATC CAT TTC C-3’, antisense: 5’-GCT ATT TCT CCA CGC AGC GG-3’). The virus was isololated and compared with known adenoviruses.

The examination of lymph node from first animal and liver of the second one revealed the presence of adenoviral-like particles (70 to90 nm icosahedral) , within the nucleus of affected endothelial cells .The sera from both animals were negative for antibodies against both CAdV-1 and 2. The PCR to detect CAdV-1 and 2 was also negative. Sequencing confirmed the presence of a fragment of the DNA polymerase gene of a novel adenovirus and comparison of the sequence to known adenoviruses in GenBank showed that this was a novel virus from the Mastadenovirus genus. This virus was similar in 77% to tree shrew adenovirus 1 (TSAdV-1) CAdV-1 (72%) and 2 (74%) however in overall is was treated as independent lineage and species.

This was very interesting study and quite exciting that they managed to find new virus , although the more analysis is needed in order to establish if this virus is a primary pathogen causing death. It is quite surprising that although the symptoms of this disease were quite similar to those reported in many other cases , nobody actually managed to identify this virus before.

A review of Goldstein et al.2011 . Isolation of a novel adenovirus from California sea lions Zalophus californianus. Dis Aquat Org. 94: 243–248.

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