Human parvovirus (genus Erythrovirus) is a blood borne, non-enveloped virus that has a single-stranded DNA (ssDNA) genome of about 5.5 kb (Shade et al., 1986, J. Virol. 58(3): 921-936, Brown et al., 1997, Ann. Rev. Med. 48: 59-67). Individual virions contain one copy of either the plus or minus strand of the genome, represented in approximately equal numbers. The ssDNA genome has inverted terminal repeats that form 5′ and 3′ hairpins of about 350 nt, which are essential for viral replication. The genome includes two open reading frames on the plus strand, which code for structural proteins (VP1 and VP2) and non-structural protein (NS1).
At one time it was believed that human parvovirus was highly conserved at less than 2% genetic diversity. More recently, though, it has been discovered that a human Erythrovirus isolate, originally termed V9, has a greater than 11% divergence in genome sequence compared to B19, with the most striking DNA dissimilarity is >20%, observed within the p6 promoter region. The V9 isolate was determined to have a clinical presence of greater than 11%, as well. Now the human Erythrovirus group is divided into three distinct virus genotypes: genotype 1 (B19), genotype 2 (A6- and LaLi-like), and genotype 3 (V9-like). (Servant et al., 2002, J. Virol. 76(18): 9124-34; Ekman et al., 2007, J. Virol. 81(13): 6927-35). Servant et al., refer to genotype 1 as viruses corresponding to parvovirus B19 and refer to genotypes 2 and 3 as viruses corresponding to parvovirus V9-related. Ekman et al., refer to genotypes 1-3 as all corresponding to parvovirus B19. For convenience herein, genotypes 1, 2 and 3 are referred to as parvovirus genotypes 1, 2 and 3 or human parvovirus genotypes 1, 2 and 3.
Current nucleic acid detection assays do not accurately detect all parvovirus genotypes. As a result of these deficient assays, many plasma pools remain contaminated with human parvovirus. Similarly, many cases of parvovirus infection are not properly diagnosed. Thus, there is a need for a nucleic acid test that detects human parvovirus genotypes 1, 2 and 3.
Infection with human parvovirus can occur via respiratory transmission or through infected blood or blood products. Viremia reaches high levels at about a week after inoculation, and is generally cleared within about two weeks following infection. Infected individuals may exhibit no symptoms, or have erythema infectiosum symptoms that include mild flu-like symptoms, rash, and/or temporary arthritis-like joint pain (arthropathy). Children are more likely than adults to develop the rash (called “fifth disease”), whereas arthropathy is a common symptom in adults. More serious problems occur in susceptible patients, including aplastic crisis in patients with hemolytic anemias, and persistent parvovirus infection and other hematologic changes in immunosuppressed patients. In women, human parvovirus infections have been associated with loss of about 10% of early pregnancies due to fetal death. Thus, the failure to detect parvovirus in a pooled plasma sample or for diagnosis of infection has serious consequences.
Parvovirus is a relatively resistant to viral inactivation, e.g., by chemical or heat-treatment methods used to destroy infective particles in blood, serum or plasma. Also, high viral concentrations in a sample may overwhelm viral depletion methods used to remove viral contaminants from the sample. Parvovirus in blood, plasma or plasma-derived products can infect additional individuals who receive contaminated transfusions or products. Plasma derivatives are often made from pooled donations (e.g., a pool of thousands of individual donations) resulting in the risk that a single contaminated donation could contaminate the pool and products derived from it. Thus, there is a need to detect the presence of human parvovirus types 1, 2 and 3 in biological samples, such as donated blood or plasma to prevent further infection. Further, there is a need that detection assays provide a detection sensitivity that allows for detection of low titers of virus, as may occur early in an infection or in diluted or pooled samples. Parvovirus nucleic acid detection assays that can detect an appropriate level of contamination may facilitate removal of infected donated units from the blood supply or contaminated lots of pooled plasma before use.
Many immunodiagnostic methods detect anti-parvovirus antibodies (IgM or IgG) present in an individual's serum or plasma (e.g., see PCT Nos. WO 96/09391 by Wolf et al. and WO 96/27799 by Hedman et al.). These methods have limitations in detecting recent or current infections because they rely on detecting the body's response to the infectious agent. The rapid rise in viremia following infection results in high levels of parvovirus in an individual's blood without corresponding detectable levels of anti-parvovirus antibodies (See, e.g., U.S. Pat. No. 7,094,541 to Bentano et al at Example 4). Thus, immunological-based detection assays are susceptible to false negative results. Furthermore, viremia is often quickly cleared, yet a person may remain antibody-positive in the absence of these infective particles, thusly leading to false positive results. As many as 90% of adults are seropositive for parvovirus, making accurate immunological detection of recent or current infections difficult. Other similar assays detect the presence of parvovirus by detecting the virus or empty viral capsid bound to a purified cellular receptor (U.S. Pat. No. 5,449,608 to Young et al.), and these immuno-based assays experience similar problems.
DNA hybridization and amplification methods have also been used to detect human parvovirus, though these tests are generally directed to the detection of genotype 1 only. Yet, U.S. and European regulatory bodies have promulgated standards specifying that plasma pools used for manufacturing anti-D immunoglobulin and other plasma derivatives can contain no more than 10,000 IU/ml (10 IU/microliter in Europe) of any human parvovirus. As discussed above, therapeutic plasma pools and diagnostic tests need similarly to reliably identify human parvovirus types 1, 2 and 3. Thus, there is a need in the art for compositions, kits and methods useful in the in vitro nucleic acid detection of human parvovirus types 1, 2 and 3.