Canarypox

Canarypox virus (CNPV) is a member of the Poxviridae family. Canarypox viruses, as with other bird pox viruses, are in the genera of Avipoxvirus. Nine other species are also in the genus Avipoxvirus. These include: Fowlpox virus, Juncopox virus, Mynahpox virus, Psittacinepox virus, Sparrowpox virus, Starlingpox virus, Pigeonpox virus, Turkeypox virus and Quailpox virus. It has thus far been reported that around 232 bird species (from 23 disparate orders) are affected by avian pox virus. ==Structure and replication==

CNPV is an enveloped virus. They can be enveloped by double (external enveloped virion- EEV) or single (intracellular mature virion – IMV) membranes. The process which further characterises the poxvirus family is that replication occurs in the cytoplasm and utilises a specific virus-made structure for replication, the 'virosome'. Furthermore, gene expression is divided into three phases: early, intermediate and late. At each stage specific genes and promoters are expressed. The structure and replication of CNPV also characterise other members of the Poxviridae family. ==Transmission==

The most common form of spread of CNPV is by vectors such as mosquitoes and mites. These transmit the virus from infected birds to non-infected birds. Direct routes of transmission have also been observed, especially in closed environments such as aviaries or farms, where the contact rate of birds is high. When the virus is transmitted directly, this would usually occur through aerosols, consumption of infected bird tissue or by general contact with the diseased bird. Healthy birds are at increased risk of acquiring the disease through existing wounds or scabs when in close contact with diseased birds. ==Symptoms==

CNPV symptoms often show two main forms. That is either dry (cutaneous) and/or wet (diphtheritic) symptoms (both forms can occur at the same time). Observations under the microscope have shown that the lesions are characterised by epithelial proliferation and hypertrophy in the viral infected areas. Characteristics of avian pox include the formation of intracytoplasmic inclusion bodies ('Bollinger bodies') which are composed of mononuclear inflammatory cells and have been detected in the thymus, spleen, bone marrow, middle ear and air sac. Similar inclusion bodies which are associated with inflammation have also been seen in the epidermis, feather follicles, sinuses and oral mucosa lining. Apart from the symptoms mentioned above, more general signs of infection include weight loss, loss of feathers and scaly skin on the head, neck and back. Secondary bacterial infections are common with both forms of the disease, having the potential to cause pneumonia or other bacterial infections at the sites of blistering. ==Treatment==

Currently there is no treatment available. Diseased birds should however be admitted to a veterinary practice where suitable care will be provided. Care would normally consist of removing skin from the lesions and washing the infected area(s) with Lugol's iodine solution. Furthermore, swabbing of the mouth and throat areas to remove necrotic tissues is common. By keeping diseased birds in warmer temperatures and ensuring daily eye rinsing with 1-2% saline solution has also been shown to promote recovery. In some cases, the infected birds are prescribed antibiotics. This will not target the virus but its use is designed to prevent secondary bacterial and fungal infections which are often found in skin lesions. ==Medical==

Avian prevention A live attenuated CNPV vaccine has been developed and is the best preventive measure against canarypox for captive grown canary birds and other passerine birds. Mammalian medicine CNPV has been used recently as a mammalian expression vector in the vaccine industry. The expression system using CNPV is advantageous because it undergoes what is known as ‘abortive infection’ but at the same time displays the necessary antigens to the hosts immune system. The use of this strain has been involved in the expression of several key pathogen and tumour associated antigens. These include (but are not limited to) those found in rabies virus, hepatitis B and hepatitis C, leukaemia virus, HIV and cancers; such as melanoma and colorectal cancers. More information can be found in a review by Weli et al, 2011. ==Threats==

Canarypox virus remains a constant threat to wild birds. Those most vulnerable are passerine birds, endemic on islands such as Hawaii and the Galapagos. Here they have experienced dramatic losses in bird numbers. Many more have become classified as endangered species due to CNPV. The disease is mainly spread by mosquitoes and mites in these regions, which were introduced during European colonisation. Canarypox, together with avian malaria, are the most devastating diseases for birds on the island of Hawaii and surrounding regions. ==References==