Investigation of animal caliciviruses related to Norwalklike caliciviruses

Until recently, the NLVs were considered to be pathogens with humans as the sole host. However, recent publications from Japan and the UK reported the presence of NLVs in some pigs and in some historic stool samples from calves (Sugieda et al 1998, Liu et al 1999, Dastjerdi et al 1999). The calf viruses, named Newbury agent and Jena virus, had been shown to be pathogenic for young calves under

FIG. 3. Distribution of genotypes of NLV in outbreaks of gastroenteritis reported to municipal health services in The Netherlands in 1997, 1998 and 1999 (until October).
FIG. 4. Proportion of outbreaks associated with the Lordsdale-like 'common' strain as percentage of all NLV outbreaks investigated in The Netherlands from 1994—1999.

experimental conditions and in field studies (Liu et al 1999, Dastjerdi et al 1999). The two bovine enteric caliciviruses were genetically distinct, but were most closely related with GGI NLVs, while the swine viruses were closely related with GGII NLVs. In a pilot study, we found that NLVs were widespread in cattle farms in The Netherlands, with 45% of the 74 calf herds testing positive for NLV by the generic RT-PCR designed for detection of NLV in humans. All Netherlands calf strains were tightly clustered and most closely related to the Newbury strains. The differences at the polymerase gene sequences, however, suggest that these viruses may be a distinct lineage of bovine NLV. This needs to be confirmed by capsid sequencing. All dairy herd samples were negative (n=20), and one pig herd out of 63 was found positive for a virus, which clustered with the published pig calicivirus sequences from Japan (van der Poel et al 2000). Preliminary data from

TABLE 6 Average proportion of the three most prevalent genotypes NLV in outbreaks (1997-1999), the NIVEL study (1996-1998), and the SENSOR study (1999) in The Netherlands

Study population Genotypes A verage proportion (%)

Outbreaks 1997-1999

LDV

40

LDV+Mx

53

LDV+Mx +

- R'dam

66

NIVEL 1996-1998

LDV

32

LDV+Mx

49

LDV+Mx +

Leeds

80

SENSOR 1999

LDV

25

LDV+Mx

43

LDV+Mx +

Leeds

6i

a three year surveillance of calf herds suggests that our initial observation reflects a common situation.

At this stage it is unclear if the animal NLVs form genetically distinct stable lineages, or are in fact part of a common pool of viruses circulating between animals and humans, although the finding of highly related strains in animals in different countries suggests the former. Studies are needed to solve this issue.

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