Import risk analysis: Llamas (Lama glama) and alpacas (Vicugna ...

Stallknecht 2000). Culicoides spp. are also possible vectors and have been infected
experimentally (Nunamaker et al 2000). Blackflies (Simulium spp.) have also been
incriminated in the transmission of the disease (Mead et al 2000). The virus can also be
transmitted by teat cups during milking of cows with teat lesions or by infection of wounds
and abrasions (Wilks 1994).
The maintenance hosts of the virus have not yet been conclusively established, but deer,
raccoon (Stallknecht 2000) and the cotton rat, Sigmodon hispidus (Jimenez et al 1996),
have been found to have antibody to the virus. The white tailed deer has shown signs of
infection and many other species of animals can be infected or develop antibodies against
the virus (Hanson & McMillan 1990).
VS is zoonotic and people are infected by direct contact or as a result of laboratory
accidents (Letchworth et al 1999).
The incubation period is 1-3 days (Wilks 1994), but for the purposes of international trade
a period of 21 days is recommended by the Code.
Lesions on teats and feet are primary lesions caused by entry of the virus directly at these
sites (Wilks 1994). Similarly, in experimental infection of pigs, lesions occurred at the
injection sites but there was no viraemia (Howerth et al 1997). In a description of the
pathogenesis of the disease it is stated that virus replicates in the lower layers of the
epidermis and there is no description of viraemia (Mare & Mead 2004). Mead states that
viraemia does not occur in mammalian hosts but demonstrated transmission of the virus to
non-infected blackfly when infected and non-infected blackfly co-fed on the same host
(Mead et al 2000). If viraemia does not occur in mammals, introducing the disease through
trading clinically healthy animals would not be possible. This may account for the failure
of the disease to spread beyond the Americas.
Serotype specific antibody develops within 5-8 days of infection. Blocking and
competitive ELISAs, virus neutralisation and complement fixation tests are recommended
for international trade (Swenson 2008).
17.1.5. Hazard identification conclusion
VS virus is an important exotic pathogen of cattle, horses and pigs and more rarely of other
animals including llamas and alpacas. Therefore, it is considered to be a potential hazard in
the commodity.
17.2. RISK ASSESSMENT
17.2.1. Entry assessment
There is a considerable body of opinion that suggests that viraemia does not occur in VS.
Despite this, it is has been stated that “subclinical infection is frequent and subsequent
excretion of the virus can occur with no clinical signs” (Mare & Mead 2004). The Code
suggests that the incubation period for international trade “shall be 21 days” and
recommends that a quarantine period of 30 days should be imposed on animals for export
from infected countries. As many facts relating to the transmission, pathogenesis and
excretion of the virus remain unknown for South American camelids, it is prudent to
assume that llamas and alpacas could introduce the virus to New Zealand, while in the
58 ● Import risk analysis: Llamas and alpacas from specified countries MAF Biosecurity New Zealand