Serious Invasive Saffold Virus Infections in Children, 2009

Alex Christian Yde Nielsen

, Blenda Böttiger, Jytte Banner, Thomas Hoffmann, and Lars Peter Nielsen

Author affiliations: University of Southern Denmark, Odense, Denmark (A.C.Y. Nielsen); Statens Serum Institut, Copenhagen, Denmark (A.C.Y. Nielsen, B. Böttiger, L.P. Nielsen); University of Aarhus, Aarhus, Denmark (J. Banner); Hvidovre Hospital, Copenhagen (T. Hoffmann)

Abstract

The first human virus in the genus Cardiovirus was described in 2007 and named Saffold virus (SAFV). Cardioviruses can cause severe infections of the myocardium and central nervous system in animals, but SAFV has not yet been convincingly associated with disease in humans. To study a possible association between SAFV and infections in the human central nervous system, we designed a real-time PCR for SAFV and tested cerebrospinal fluid (CSF) samples from children <4 years of age. SAFV was detected in 2 children: in the CSF and a fecal sample from 1 child with monosymptomatic ataxia caused by cerebellitis; and in the CSF, blood, and myocardium of another child who died suddenly with no history of illness. Virus from each child was sequenced and shown to be SAFV type 2. These findings demonstrate that SAFV can cause serious invasive infection in children.

Molecular biology has revolutionized the diagnostics of infectious diseases through the introduction of more sensitive and specific diagnostic tests. Despite these advances, the etiologic agents of many apparent infections are still unidentified. For example, the etiologic agent is unknown for many cases of apparent pneumonia (1); in a study conducted in California, USA, despite extensive testing and evaluation, an underlying cause of encephalitis was unidentified for 207 (62%) of 334 patients (2).

During the past few years, intensive searches for new viruses, using conventional virologic methods and metagenomics, have resulted in the discovery of several new viruses. During the past decade, the family Picornaviridae has grown as the number of recognized genera has increased from 6 to 12 (3,4); the numbers of species, types, and subtypes have increased even more. However, only viruses from 3 genera (Enterovirus, Hepatovirus, and Parechovirus) have been firmly established as being capable of causing clinically significant disease in humans. Viruses from other genera (Cardiovirus, Cosavirus, and Kobuvirus) have so far been detected only in noninvasively collected human sample material such as fecal and respiratory samples, and their clinical significance remains to be fully elucidated. (Invasively collected sample material is that from tissues considered sterile, i.e., devoid of microorganisms.)

Figure 1

Figure 1. Phylogenetic tree based on full-genome sequences of all known human picornavirus species, represented with 1 virus strain each. The tree was constructed by the neighbor-joining method by using MEGA4 software (<>

The phylogenetic relationships of human picornaviruses are shown in Figure 1. Most picornaviruses that are pathogenic to humans are ubiquitous viruses capable of causing a variety of diseases, from monosymptomatic febrile infection to severe infection in the central nervous system and myocardium. However, most infections with these viruses are asymptomatic (5).

Saffold virus (SAFV) was discovered by Jones et al. in 2007 by sequence-independent genomic amplification of virus isolated from a fecal sample (6). The sample had been obtained in 1981 from an 8-month-old child with fever of unknown origin. The genetic sequence of the virus indicated that the virus belonged to the species Theilovirus of the genus Cardiovirus, which contains 3 other members: Theiler’s murine encephalomyelitis virus (TMEV), Vilyuisk human encephalomyelitis virus (VHEV), and Thera virus.
In mice, TMEV is capable of causing infection in the central nervous system, and some variants of this virus cause a persistent infection and even multiple sclerosis–like disease (7). VHEV was isolated in the 1950s from cerebrospinal fluid (CSF) from a patient with Vilyuisk encephalomyelitis, a progressive neurologic disorder that occurs in indigenous populations of an isolated part of eastern Siberia (8). However, the correlation between VHEV and Vilyuisk encephalomyelitis is still uncertain because VHEV has been isolated by multiple passages in mice and thus may represent a highly divergent strain of TMEV. Thera virus (previously named Theiler-like rat virus) has been isolated from rats, but the clinical significance of infections with this virus is unknown (9,10). The genus Cardiovirus also contains a second species called encephalomyocarditis virus. Only 1 serotype is known, and it is capable of causing encephalitis and myocarditis in various animals (11,12).

Since the discovery of SAFV, several articles have provided insight into its epidemiologic and, to a minor degree, clinical significance. Saffold viruses are distributed worldwide (6,13–19), and 2 serologic studies have demonstrated that infection occurs early in life (14,20). However, finding an association with human disease has thus far been elusive. Most studies (13,15,17,20–22) have tried to associate SAFV with gastroenteritis, but no convincing results have been produced. A few studies (16,18,21,23) analyzed the clinical significance of SAFV virus in the respiratory system, but no substantial association between the virus and respiratory symptoms or disease has been made. Only 1 study (21) reports having tested invasively collected sample material (CSF samples), but no findings were positive.

To investigate the possible invasive potential of SAFV in humans, we developed a diagnostic PCR and tested CSF samples from a group of children. SAFV was detected in 2 of these children.