Outbreak of aplastic crises in sickle cell anaemia associated with parvovirus-like agent

Transmission of serum parvovirus-like virus by clotting-factor concentrates

The serum parvovirus-like virus (SPLV) is a ubiquitous human virus that suppresses the growth of bone-marrow stem cells in vitro. Antibody to it (anti-SPLV) was found in 28 (97%) of 29 children and young adults with haemophilia treated with clotting-factor concentrates but in only 36% of those who had received multiple blood transfusions and in 20% of age-matched controls. The increased anti-SPLV prevalence in haemophiliacs was significant and was not due to passive acquisition of antibody. Haemophiliacs in a residential school showed seroconversion and rises in anti-SPLV titre following the introduction of concentrate treatment. 10 days after receiving his first dose of factor-VIII concentrate a patient had viraemia and then an anti-SPLV IgM response. These observations show that SPLV is often transmitted in clotting-factor concentrates but not in transfused blood. Whether this transmission has any harmful effect is uncertain.

Diagnostic assays with monoclonal antibodies for the human serum parvovirus-like virus (SPLV)

Monoclonal antibodies to the serum parvovirus-like virus (SPLV) were prepared by the hybridoma technique. They provided an antibody reagent which was used to develop solid phase antibody-capture assays for anti-SPLV IgM and IgG and for SPLV antigen. These assays were more sensitive than those based on human convalescent antibody as a reagent, and were more economical in the use of SPLV antigen. Their use enabled the serological responses to SPLV to be studied more fully and their sensitivity revealed the extent of SPLV infection. SPLV antigen was detected in four patients by both counter-immuno electrophoresis (CIE) and radioimmunoassay (RIA) and in two others by RIA alone. Parvovirus particles were seen in all six by electron microscopy. The anti-SPLV IgM response was measured in patients infected by SPLV. It was strong 5-18 days after the onset of illness, then declined and was only detectable in trace amounts after 6 months. Anti-SPLV IgG was also formed early, and persisted for at least 6 months. In a survey of 310 blood donors anti-SPLV was detected in 134 (43%) by CIE, but in 190 (61%) by IgG antibody capture RIA.

Aplastic crisis due to parvovirus infection in pyruvate kinase deficiency

A thirteen-year-old boy with congenital haemolytic anaemia due to pyruvate kinase (PK) deficiency had an aplastic crisis. A serum parvovirus-like virus (SPLV) was demonstrated in the blood by electron microscopy and, subsequently, IgM and IgG antibodies to the prototype SPLV B19 were detected. In an attempt to define the level of erythropoiesis that is involved in parvovirus-induced bone marrow suppression, the levels of circulating early erythroid progenitors (burst forming units erythroid, BFU-E) were monitored during the crisis and recovery period. The virus-containing plasma inhibited the formation of BFU-Es from non-immune subjects and this effect was neutralised by convalescent serum. Colony forming units granulocyte-macrophage (CFU-GM) were also inhibited but this was probably non-specific since neutralisation did not reverse the effect. These experiments, together with the clinical data, suggest a selective effect of SPLV at the stage of erythroid progenitors.

Sickle cell disease and infection

Overwhelming infections caused by encapsulated bacteria, salmonella spp. and Plasmodium falciparum (in malarious areas) are an important cause of morbidity and death in patients with sickle cell disease. Bacterial infections afflicting these patients include fulminant meningitis and septicaemia caused by Str. pneumoniae and H. influenzae type b, and non-typhoid salmonellosis. Children less than five years of age are at greatest risk for meningitis and septicaemia, while salmonella osteomyelitis is probably common to all age groups. The most important contributing factors to this increased susceptibility to encapsulated bacteria are: a state of functional asplenia, an opsonophagocytic defect due to an abnormality of the alternative complement pathway, and a deficiency of specific circulating antibodies. Devitalisation of gut and bone due to repetitive vaso-occlusive crises, saturation of the macrophage system with red cell breakdown products of chronic haemolysis, and underlying splenic and hepatic dysfunction all predispose to salmonella infections. Seventy per cent of septicaemias and meningitis among under-fives with sickle cell disease is caused by Str. pneumoniae. Septicaemia frequently presents with sudden fever, few prodromal features, and a deceptive appearance of well-being, followed within hours by rapid relentless progression to shock and death. Adrenal haemorrhage is common, and mortality can be as high as 50 per cent, unless intravenous antibiotic, with or without steroid therapy, is promptly initiated. The clinical presentation of bacterial meningitis, its management and mortality follow the normal patterns, but recurrent meningitis and cerebrovascular morbidity are common in patients with sickle cell disease. An acute pulmonary involvement, indistinguishable from bacterial pneumonia (the 'chest syndrome') is the commonest single complication of sickle cell disease at any age. Str. pneumoniae is responsible for about half of the episodes. The protective values of the pneumococcal vaccine and long-term penicillin prophylaxis remain to be established in sickle cell disease. Over 70 per cent of haematogenous osteomyelitis in sickle cell disease is caused by salmonellae. The distinction from vaso-occlusive bone crisis is often difficult, but the presence of multiple, often symmetrical bone involvement, diaphyseal fissuring and involucrum should suggest osteomyelitis rather than bone infarction. Chloramphenicol remains the drug of choice and often has to be given in high doses for up to six weeks. The role of surgery is limited by the presence of multiple bone involvement and the known anaesthetic risks in this group.(ABSTRACT TRUNCATED AT 400 WORDS)

Hypothesis: the aplastic crisis of hereditary spherocytosis is due to a single transmissible agent

Aplastic crisis in sickle cell anaemia has been associated with infection by a serum parvovirus-like virus (SPLV). Reports of outbreaks of these crises in hereditary spherocytosis (HS) were investigated to see if the data were consistent with a single agent such as SPLV being their cause. The age distribution of the cases and the pattern of spread were compatible with an infectious aetiology. The symptoms and duration of the cases, and the intervals between them, were sufficiently uniform to indicate that they were caused wholly or predominantly by a single agent with an incubation period of about nine days. There were close similarities between these illnesses and recognised cases of SPLV infection. It is concluded that SPLV is probably the main cause of aplastic crisis in HS.

A human parvovirus-like virus inhibits haematopoietic colony formation in vitro

Viruses have been shown to cause bone marrow aplasia in animals and have been implicated in bone marrow failure in man; however, until recently, a specific link between human viral infection and bone marrow failure has not been proven. In 1975 Cossart and colleagues found a serum parvovirus-like virus (SPLV, sometimes referred to as B19) in human serum. Antibody to this virus is present in the sera of 30-45% of healthy adults (Y. E. Cossart, P. P. Mortimer, unpublished observations). However, evidence for a direct link came from work by Pattison et al. who found five children with transient aplastic crisis of sickle cell disease and evidence of active infection with SPLV. This association was later confirmed in a large series of children with sickle cell disease and aplastic crisis in Jamaica. We have studied the effects of virus-containing material on haematopoiesis, using in vitro colony-forming assays to look for direct evidence for a role of SPLV in bone marrow aplasia. We show here that SPLV-containing sera inhibit erythropoiesis in culture. Moreover, in a child with hereditary spherocytosis who developed transient aplastic crisis, a strong inhibitory effect of the patient's serum on erythropoiesis correlated with the presence of virus.

The emerging story of a human parvovirus-like agent

It is now seven years since Cossart and her co-workers reported finding a novel parvovirus-like agent (PVLA) infecting man. Although this virus was found as a systemic infection in both Dr Cossart's eleven subjects and a further four subjects described subsequently (Paver & Clarke, 1976; Schneerson, Mortimer & Vandervelde, 1980) it was not until 1981 that a clearly defined clinical syndrome was identified as attributable to infection with this agent. Work in the Departments of Microbiology and Haematology, King's College Hospital Medical School and collaboration with the MRC laboratory at Kingston, Jamaica has shown that infection with the PVLA is the major cause of aplastic crisis in children with sickle cell anaemia (Sergeantet al.1981, Andersonet al.1982a, b).

Occurrence of infection with a parvovirus-like agent in children with sickle cell anaemia during a two-year period

The occurrence of infection with a parvovirus-like agent during the period April 1979-May 1981 in children attending a single sickle cell clinic in London was investigated. Virus was detected in serum by counter-current immunoelectrophoresis (CIE) and immunoelectron microscopy (IEM). Viral antibody was detected by CIE and specific IgM antibody by an IgM-antibody capture assay. Of the 68 children studied nine presented in aplastic crisis and evidence of infection with the parvovirus-like agent at the time of the crisis was found in all nine. Eighteen of the other children were antibody-positive at some time during the study. In 11 children there was no evidence of recent infection; however, two of these had a history of aplastic crisis in previous years. The other seven seroconverted during the course of the study but did not show any haematological effects. Five of these had a primary infection, one appeared to have reinfection and in the seventh there were insufficient data to distinguish between the two. Possible explanations for the difference between those presenting with aplastic crisis and those with asymptomatic seroconversion are discussed.

The development and use of an antibody capture radioimmunoassay for specific IgM to a human parvovirus-like agent

An IgM-antibody capture radioimmunoassay (MACRIA) was developed for the detection of IgM antibody specific for the human parvovirus-like agent B19. Diagnosis of infection with this agent by either antigen detection or antibody seroconversion had been made by counter-current immunoelectrophoresis (CIE) in 18 cases of aplastic crisis occurring in children with homozygous sickle-cell disease. The MACRIA described here gave positive results in 17 of these 18 cases; in the remaining case only an acute specimen taken from the patient during viraemia and late convalescent specimens taken 184 and 247 days after onset of illness were available. The test was used to investigate 20 further cases of aplastic crisis in which neither viral antigen nor antibody seroconversion could be detected by CIE. Detection of virus-specific IgM permitted diagnosis of infection with this parvovirus-like agent in 17 of these cases. In the remaining three cases only single serum specimens taken late in convalescence, 82 days or more after the onset of symptoms, were available. In addition to these 34 cases of aplastic crisis in which primary infection with this agent was diagnosed by MACRIA, seven cases of apparent 'silent' infection detected by CIE were investigated. The test permitted the discrimination between primary infection and re-exposure to the virus in six of these patients. The use of this assay has added a considerable weight of evidence implicating primary infection with this parvovirus-like agent as an important cause of aplastic crisis in children with sickle-cell disease. Furthermore, MACRIA permits diagnosis of infection when only single serum specimens taken up to ten weeks after infection are available. Thus the use of this test will significantly facilitate the investigation of other clinical syndromes of presumptive infectious aetiology.