June 11, 2019 Jason EMMONS

Health and Safety Series: Nidovirus

What are nidoviruses?

Nidoviruses are a group of related viruses known to cause a severe and sometimes fatal respiratory disease in snakes. These viruses are cousins of SARS and MERS coronaviruses that affect humans, which can also cause severe respiratory disease.

What snakes are susceptible to nidovirus infection and disease?

This is one of the primary questions The Stenglein Lab is trying to answer. So far, nidoviruses have been detected predominately in pythons and some boas, but it is their goal to determine all the snake species that are susceptible and how severely the disease affects them. There is no evidence that this virus can infect or cause disease in humans. Below is a list of some of the animals that nidovirus has been found in.

Ball python (Python regius)
Green tree python (Morelia viridis)
Carpet python (Morelia spilota)
Diamond python (Morelia spilota spilota)
Rough scaled python (Morelia carinata)
Blood python (Python curtus brongersmai)
Sumatran python (Python curtus)
Borneo python (Python breitensteini)
Angolan python (Python anchietae)
Indian rock python (Python molurus)
Anthill python (Antaresia perthensis)
Stimson’s python (Antaresia stimsoni)
Woma python (Aspidites ramsayi)
Dumeril’s boa (Acrantophis dumerili)
Emerald tree boa (Corallus caninus)
Amazon tree boa (Corallus hortulanus)
Honduran milksnake (Lampropeltis triangulum hondurensis)
Corn snake (Pantherophis guttatus)

How many strains of virus are there and how do they differ in virulence?

Viruses that have complete genome sequencing data (a method for determining different strains of virus) have been isolated from ball pythons, an Indian rock python, and green tree pythons. The nidoviruses from ball and Indian rock pythons are relatively similar, but are quite different from those isolated from green tree pythons. Although these viruses have not been taxonomically categorized, it is likely there are multiple strains and these may affect snake species differently. The Stenglein lab's research will attempt to address this question through the sampling of high numbers and a wide range of snakes of species.

What are the clinical signs of nidovirus infection?

The clinical signs can vary from mild and non-specific to severe respiratory signs or sudden death. Typically, snakes will begin to have increased amounts of clear mucus in the mouth and nose and the gums may become reddened. This can progress to wheezing, breathing with the mouth open, more rapid breathing, or coughing. Other signs include a poor or non-existent appetite, weight loss, decreased activity level, dehydration, and spending more time on the bottom of the cage (if a perching snake). Secondary bacterial infections may also play a role in disease, so mouth rot could be evidence of an underlying nidovirus infection (although there are many other causes for this as well).

How long are snakes usually infected?

This is currently unknown. Some snakes remain nidovirus positive for over a year. Other snakes succumb to disease and die within 6-12 months of being infected. There is also evidence in the Stenglein lab that some snakes can clear the infection following 6-12 months of infection, but the data to support this remains anecdotal and this is not clearly established. Overall, this disease is chronic and usually results in long-term infection in snakes.

How is this disease transmitted?

The Stenglein lab has found virus in the oral/nasal cavity, lungs, and feces. Therefore, transmission is thought to occur by direct or indirect exposure to respiratory secretions (similar to the common cold) or to feces from infected snakes.

How can nidovirus infection be treated?

Currently, there is no specific treatment for nidovirus infection in snakes, nor is a vaccine available. This is similar to other viral diseases of snakes, and in fact in most species, including humans. Only rare viral diseases have been treated with anti-viral therapy and with varying success. Also, there are no effective commercially available vaccines for any snake diseases, despite attempts at vaccine production. Typical treatment includes supportive care and antibiotics to prevent secondary bacterial infections.

How long does the virus stay infectious in the environment?

This has not been tested for snake nidoviruses. However, SARS coronavirus, a closely related virus, is relatively stable outside of the host for up to 4 days. For SARS, heating and UV irradiation can eliminate infectious virus in the environment, as can common disinfectants (e.g. accelerated hydrogen peroxide, alcohol-based disinfectants with greater than 79% ethanol, and solutions with at least 0.050% of triclosan, 0.12% of Chloroxylenol (PCMX), 0.21% of sodium hypochlorite bleach, 0.23% of pine oil, or 0.10% of a quaternary compound with 79% of ethanol). It is unknown if snake nidoviruses are similarly affected by these disinfectant and antiseptic methods, but compounds listed above are good places to start when sterilizing cages and areas that have been exposed to nidovirus positive snakes or their excreta. These viruses may also be carried as fomites on hands, clothes, and instruments, therefore, it is important to use appropriate protective gear and washing of items before using between infected and uninfected snakes. Ideally, nidovirus positive snakes would be isolated/quarantined in a separate area and have designated instruments and protective gear only used with these snakes.