Jonathan P. Clewley

Human Parvovirus Infection in Pregnancy and Hydrops Fetalis

Abstract Human parvovirus is the causative agent of erythema infectiosum, a mild epidemic illness. In a recent outbreak in northeast Scotland, six women had serologic evidence of having contracted human parvovirus infection during pregnancy. Two of the women had midtrimester abortions, and both abortuses were grossly hydropic with anemia. They had similar microscopical histopathological features — a pronounced leukoerythroblastic reaction, hepatitis, excessive iron pigment in the liver, and eosinophilic changes in the hematopoietic cell nuclei. Dot hybridization with Radio-labeled human parvovirus DNA probes revealed viral DNA in several tissues from both fetuses, indicating that they had been infected by the virus in utero. The remaining four women had uncomplicated pregnancies and delivered apparently healthy babies, none of whom had human parvovirus–specific IgM antibody at delivery. We conclude that this common virus may pose a serious risk to the fetus after maternal infection. (N Engl J Med 1987; 31...

Detection of human parvovirus using a molecularly cloned probe

Half of the genomic DNA of the human parvovirus (B19) was cloned in the plasmid pBR322. The cloned DNA was used as a molecular probe for the detection of parvovirus in serum by means of a dot hybridization test. In an assay of 26 samples, the dot hybridization test was found to be of comparable sensitivity and to be as rapid as radioimmunoassay for viral antigen detection; it is potentially useful as a diagnostic test.

The polymerase chain reaction, a review of the practical limitations for human immunodeficiency virus diagnosis

The polymerase chain reaction (PCR) is a powerful method for the in vitro amplification of specific nucleic acid sequences. As very small amounts of a virus genome can be detected it has obvious diagnostic applications. The background to the reaction and its use for human immunodeficiency virus (HIV) detection are described. The problems likely to be encountered in using PCR as a diagnostic assay (false positives and negatives) and the practical measures which can be taken to overcome them are discussed.

The public health significance of HIV-1 subtypes.

Since the first descriptions of HIV/AIDS HIV-1 has emerged as the most significant pathogen worldwide with approaching 60 million infections to the end of 2000. Over 18 million deaths from AIDS have occurred and HIV/AIDS is now classed among the top five causes of global mortality [1]. As with other infectious pathogens that exhibit a high degree of genetic variation such as influenza the extensive genetic variability of HIV-1 poses significant challenges for disease control and epidemiological surveillance [2]. The genetic heterogeneity of HIV-1 isolates is one of the major characteristics of the virus and the epidemic. This diversity generated by the processes of mutation and recombination [3] has led to the development of a subtype nomenclature for the classification of isolates [4]. The major (M) group of HIV-1 responsible for the majority of infections in the epidemic contains several recognized non-recombinant subtypes and sub-sub-types and at least 10 circulating recombinant forms (CRFs) [4]. These subtypes show uneven regional distribution and past attempts have been made to use them to describe the global molecular epidemiology of HIV-1 [56]. In this context undertaking systematic sampling and monitoring of populations is important to determine the value of these studies. We review here the public health and clinical significance of HIV-1 genetic variability and the methods and rationale for public health surveillance of subtypes. (excerpt)

Surveillance of HIV-1 subtypes among heterosexuals in England and Wales, 1997-2000.

Summary:The molecular diversity and demographic characteristics among 976 anti-HIV-1-positive heterosexuals attending 15 sexually transmitted infection (STI) clinics participating in an unlinked anonymous HIV prevalence serosurvey in England and Wales during 1997–2000 were investigated. Subtypes were assigned by heteroduplex mobility assay or sequencing of the p17/p24 region of gag and the V3/V4 region of env and by sequencing of the protease gene. Overall, there was no significant change in the subtype distribution, with subtype C accounting for the majority (32%) of subtyped infections. Subtypes B (29%), A (12%), circulating recombinant forms (CRFs, 9%), unique recombinant forms (URFs, 8%), and subtypes D-H (8%) were also detected. Thirty-nine percent of infections in men were with subtype B, whereas subtype C was most common (38%) in women. Logistic regression analyses showed the relative risk (RR) of infection with a non-B subtype, compared with subtype B, to be greater in African-born individuals (RR = 28.9, P < 0.01), among newly diagnosed infections (RR = 3.4, P < 0.01), and in women (RR = 2.4, P < 0.01). These findings indicate a high level of genetic diversity among HIV-infected heterosexual STI clinic attendees in England and Wales. Recently, subtype C has become most prevalent, particularly in younger age groups, suggesting recent acquisition of this viral strain. The high proportion of non-B, CRF, and URF infections among UK-born individuals is consistent with mixing between migrants and UK-born individuals in England and Wales. As migration patterns change, continued monitoring of HIV genetic diversity will aid understanding of transmission patterns.

Biochemical characterization of a human parvovirus.

The buoyant density, nucleic acid, and proteins of the human serum parvovirus-like agent were investigated. Evidence is presented which suggests that the virus has genomic single-stranded DNA, and that complementary strands may be encapsidated in separate virions. Three proteins of 48 000, 68 000 and 80 000 mol. wt. were found to co-purify with viral antigen at a density of 1.43 g/ml on CsCl gradients. On the basis of these properties it is suggested that this virus is a parvovirus.

Early Evolution of the Human Immunodeficiency Virus Type 1 Subtype C Epidemic in Rural Malawi

ABSTRACT We have tracked the early years of the evolution of the human immunodeficiency virus type 1 (HIV-1) epidemic in a rural district of central east Africa from the first documented introductions of subtypes A, D, and C to the present predominance of subtype C. The earliest subtype C sequences ever reported are described. Blood samples were collected on filter papers from 1981 to 1984 and from 1987 to 1989 from more than 44,000 individuals living in two areas of Karonga District, Malawi. These samples included HIV-1-positive samples from 200 people. In 1982 to 1984, HIV-1 subtypes A, C, and D were all present, though in small numbers. By 1987 to 1989, 152 (90%) of a total of 168 sequences were subtype C and AC, AD, and DC recombinants had emerged. Four of the subtype C sequences from 1983 to 1984 were closely related and were found at the base of a large cluster of low diversity that by the late 1980s accounted for 40% of C sequences. The other two early C sequences fell into a separate and more diverse cluster. Three other clusters containing sequences from the late 1980s were identified. Each cluster contained at least one sample from a person who had recently arrived in the district. From 18 HIV-1-positive spouse pairs, 12 very closely related pairs of sequences were identified. We conclude that there were multiple introductions of HIV-1 with limited spread, followed by explosive growth of a subtype C cluster, probably arising from a single introduction in or before 1983.

Characterization of a highly divergent TT virus genome.

A novel TT virus (TTV)-like DNA sequence was detected in the serum of a patient (PM) with acute non-A-E hepatitis. The full-length genome sequence, referred to here as PM virus (PMV), was obtained and its relationship to other full or near full-length TTV sequences examined. Although it shares a common genomic arrangement and short conserved regions, the majority of the genome is extremely divergent, displaying an average genetic distance of 0.60 from all other TTV sequences. By comparing PMV with TTV genomes representing the most divergent types so far described, six major groups can be distinguished. The level of genetic diversity seen between these genomes is higher than would be expected within a single virus species. Indeed, PMV could be considered the prototype of an independent taxonomic group within the Circoviridae: family. A genoprevalence study of sera from blood donors and patients with acute hepatitis suggests that PMV is rare.

National surveillance of HIV-1 subtypes for England and Wales: Design, methods, and initial findings

Summary: The HIV‐1 infections detected in an ongoing national unlinked anonymous HIV surveillance program were subtyped and analyzed according to demographic and risk characteristics. Of the 893 anti‐HIV‐1‐positive specimens allocated to an exposure group, 70% could be subtyped. Almost 25% of infections subtyped were non‐B, mostly subtypes A, C, and D. Non‐B infections were rare in homosexual and bisexual men and in drug injectors. Forty percent of infections in heterosexual men attending genitourinary medicine clinics were non‐B subtypes; of these, 25% were subtype A infections and 59% were subtype C infections. For female clinic attendees, 61% were non‐B subtype infections, of which 48% were subtype A infections and 42% were subtype C infections. Of the clinic attendees born in the United Kingdom and Europe, 14% of the men and 35% of the women were infected with non‐B subtypes. In contrast, 78% of infections in antenatal patients were non‐B subtypes, of which 61% were subtype A and 29% were subtype C. Extrapolation to the estimated 29,700 prevalent adult infections in the United Kingdom indicates that approximately 8,100 (27%) such infections are non‐B subtypes and that these are found almost entirely in heterosexuals. The findings suggest spread of infection of non‐B subtypes to heterosexuals born in the United Kingdom from individuals infected in regions of high prevalence.

Viral genome characterisation by the heteroduplex mobility and heteroduplex tracking assays.

The heteroduplex mobility assay (HMA) is a means of comparing two PCR amplicons or, in the variation known as the heteroduplex tracking assay (HTA), a means of estimating the quasispecies diversity of a viral genome. Heteroduplex assays have many applications including subtyping viral genomes, screening for low frequency variants in a population, scanning the relative genetic diversity across a genome and screening for recombinant clones. They can be used to detect dual infections, superinfections, contaminated blood products and laboratory contaminations. PCR amplicons of about 65% sequence similarity or greater will form heteroduplexes under appropriate conditions, and phylogenetic trees can be drawn from heteroduplex mobility data. While homoduplexes indicate more than 98% similarity between two DNA sequences, heteroduplexes indicate at least seven mismatches in a 500‐bp amplicon, or a three‐base pair gap in 1000‐bp. Minority variants comprising 1% to 5% of the genome population can be detected and quantified by HTA. Thus far, heteroduplex assays have been described for HIV and other lentiviruses, hepatitis C and G viruses, Norwalk‐like viruses, influenza, measles and poliovirus. They could be applied to a wide range of other viral species. Copyright