Sunday, 20 October 2013

Possible human zoonosis of herpes simplex-like virus to a bottlenose dolphin

Herpes simplex-like infection found in a stranded bottlenose dolphin.

In 2001 a deceased stranded bottlenose dolphin was found in the Canary Islands. It exhibited non-suppurative encephalitis (an inflammation of the brain without pus,) and the aim of this paper was to discover the cause. Tissue samples from the brain, liver and lungs were frozen at -80ᵒC, and in order to determine the presence of viral agents, a RT-PCP was carried out for morbillivirus and a PCR for herpesvirus.

Products of the PCRs were electrophoresed, and specific bands  were excised and sequenced. The RT-PCR amplifies 426bp within a conserved region in the phospoprotein gene, and the PCR amplifies between 215-315bp in the polymerase gene (this technique produces sequences which are unique to each herpesvirus species). The sequenced products were then compared to sequences already available in GenBank using the BLAST search.

A specific band was not observed in the RT-PCR for morbillivirus, and therefore we may conclude morbillivirus was not the reason for the non-suppurative encephalitus. However, a herpesviral specific band of 250bp was found in the lungs and brain. This sequence, referred to as EU003440, obtained 98% homology (with a p-distance of 0.02) with Human herpesvirus 1 (herpes simplex virus 1, or HSV-1.) There were also similarities between EU003440 and Human herpesvirus-2 (p-distance of 0.13), and the F-strain of HSV-1 (p-distance of 0.14)

The findings of this paper are spectacular, given that previous occurrences of bottlenose dolphin herpesvirus show a large genetic difference to EU003440 (with p-distance of between 0.45-0.69). I have (attempted to) attach the phylogram given in the paper, and it shows the surprising similarities between this virus (known as EU003440) and human herpesvirus.

It is interesting to note that normally, instances of herpesvirus which show high genetic relatedness to the human herpesvirus, have been those which target non-human primates such as Baboon herpesvirus 2 and Cercopithecine herpes 1.

This paper was coy in drawing a firm conclusion, vaguely suggesting that “it could be concluded that [EU003440] may be considered a HSV-like sequence.” Again, most of the reports about HSV-like sequences (HSV being the Human herpes virus), are restricted to non-human primates – and “the presence of an HSV-like sequence of possible human origin in a bottlenose dolphin has not been previously described.”

Whilst this paper was the first to demonstrate the potential of human herpes virus 1 zoonosis to the bottlenose dolphin, and zoonosis was one of the key words of the paper – it was never again mentioned. I personally think that this paper could have better explored the idea that EU003440 was of a human herpes origin, which had been transmitted to a different species – that of the bottlenose dolphin. Saying this, it was still an informative and interesting paper to read.

Possibly, the proximity of the Canary Islands to the surrounding marine environment, could predisposition bottlenosed dolphins to greater expose to pesticides, industrial pollutants and urban wastes. The release of human micro-organisms through urban sewage to other environments has already occurred with species such as the norovirus, and it appears that the herpesvirus has taken the same route.

Esperon, F., Fernandez, A., & Sanchez-Vizcaino, J. M. (2008). Herpes simplex-like infection in a bottlenose dolphin stranded in the Canary Islands.Diseases of aquatic organisms, 81(1), 73.

1 comment:

  1. Hi Caz. Do you know how the herpes virus would cause non-suppurative encephalitis? Is there a particular product that causes swelling or is it an immune response within the dolphin?