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Why does Plasmodium falciparum cause severe illness in some but not all infections? How is clinical immunity acquired? These questions have intrigued investigators since the clinical epidemiology of malaria was first described. The search for answers to both questions has highlighted the changes that take place at the surface of infected red blood cells during the last half of the erythrocytic cycle. These changes specify the antigenic and adhesive or cytoadherence phenotypes for the infected cell. Now the antigenic and adhesive phenotypes appear to be linked and together undergo clonal variation. In this article David Roberts, Beverley-Ann Biggs, Graham Brown and Christopher Newbold explain how clonal phenotypic variation and the linkage between adhesive and antigenic types contribute to our understanding of naturally acquired immunity and of pathogenesis of severe malaria.

Erythrocytes (E) infected with asexual forms of malaria parasites exhibit surface antigenic variation. In Plasmodium falciparum infections, the variant Ag is the P. falciparum E membrane protein 1 (PfEMP1). This molecule may also mediate the adherence of infected E to host venular endothelium. We show here that parasite lines selected for increased adherence to endothelial cells have undergone antigenic variation. Three adherent lines selected from the same P. falciparum clone reacted with the same agglutinating antiserum that failed to agglutinate the parental clone. Immunoprecipitation experiments with the agglutinating anti-serum demonstrated that the selected lines expressed cross-reactive forms of PfEMP1 that were of higher m.w. and antigenically distinct from PfEMP1 of the parental clone. When one of the adherent lines was cloned in the absence of selection, a range of variant antigenic types emerged with differing cytoadherence phenotypes. These findings show that selection for cytoadherence in vitro favors the emergence of antigenic variants of P. falciparum and suggest that the requirement for cytoadherence in vivo may restrict the range of antigenic variants of P. falciparum in natural infections.

Antigenic variation of infectious organisms is a major factor in evasion of the host immune response. However, there has been no definitive demonstration of this phenomenon in the malaria parasite Plasmodium falciparum. In this study, cloned parasites were examined serologically and biochemically for the expression of erythrocyte surface antigens. A cloned line of P. falciparum gave rise to progeny that expressed antigenically distinct forms of an erythrocyte surface antigen but were otherwise identical. This demonstrates that antigenic differences on the surface of P. falciparum-infected erythrocytes can arise by antigenic variation of clonal parasite populations. The antigenic differences were shown to result from antigenic variation of the parasite-encoded protein, the P. falciparum erythrocyte membrane protein 1.

We have previously described a colorimetric test, designated an amplified DNA assay (ADA), for specific segments of DNA amplified by polymerase chain reactions (PCRs), suited to diagnostic applications. This relied on binding the amplified DNA via a sequence in one oligodeoxyribonucleotide (oligo) to the DNA-binding protein GCN4 coated on the wells of a microtiter dish. Avidin-peroxidase was then bound to biotin at the 5' end of the other oligo and detected colorimetrically. Two successive PCRs with nested oligos were utilized. We describe here several modifications that greatly simplify the ADA. First, we bind the DNA to a glutathione S-transferase-GCN4 fused polypeptide (GST-GCN4) and avidin-peroxidase simultaneously, rather than successively. Second, we carry out the two successive PCRs in the one reaction mixture, using the thermal stabilities of oligos of differing lengths to separate the two reactions. Third, PCRs can be performed in the wells of a microtiter dish and the amplified DNA captured and detected via GST-GCN4 immobilized on beads attached to the lid of the microtiter dish. Hence it is only necessary to pipette the DNA sample once, and up to 96 samples can then be handled simultaneously.

The survival of Plasmodium falciparum-infected erythrocytes is enhanced by the sequestration of mature trophozoites and schizonts from the peripheral circulation. Cytoadherence of infected erythrocytes in vivo is associated with the presence of knobs on the erythrocyte surface, but we and others have shown recently that cytoadherence to C32 melanoma cells may occur in vitro in the absence of knobs. We show here that a knobless clone of P. falciparum adheres to the leukocyte differentiation antigen, CD36, suggesting that binding to CD36 is independent of the presence of knobs on the surface of the infected erythrocyte. This clone showed little cytoadherence to immobilized thrombospondin or to endothelial cells expressing the intercellular adhesion molecule 1. Furthermore, an Mr approximately 300-kD trypsin-sensitive protein doublet was immunoprecipitated from knobless trophozoite-infected erythrocytes. Finding a P. falciparum erythrocyte membrane protein 1 (PfEMP1)-like molecule on these infected erythrocytes is consistent with a role for PfEMP1 in cytoadherence to CD36 and C32 melanoma cells.

We show that chromosome 9 in all isolates and clones of Plasmodium falciparum examined so far exists as one of two distinctly different forms, a large form about 1.9 megabases long or a smaller form about 25% shorter. Physical maps of chromosome 9 from independent clones with large and small forms of chromosome 9, and from an isolate with the large form and 3 derived clones with the small form reveal the underlying structural basis of this size polymorphism. The small form differs from the large only in that there are subtelomeric deletions at each end, one of these deletions involving about 0.45 megabases. Remarkably, the breakpoints map within about +/- 1% of the total chromosome length for each of these populations. We discuss some possible mechanisms for this.

Malaria continues to be a major international public health problem but many Australians who travel overseas are ill-informed of the risk of infection and have inadequate protection against this potentially fatal disease. Management is complicated by the resurgence of malaria in areas that have previously had satisfactory control programmes, and the emergence of resistance to chloroquine and other drugs. This article focuses on prevention of malaria in travellers. The more important issue of malaria control for populations residing in endemic areas is beyond the scope of this review.

A man with acute Q fever developed hyponatraemia associated with inappropriate secretion of anti-diuretic hormone. The pyrexial illness lasted for 9 weeks and failed to respond to tetracycline, erythromycin and intravenous lincomycin. Subsequently seroconversion indicated chronic Q fever.

Sequestration of Plasmodium falciparum-infected erythrocytes is crucial to parasite survival as it prevents destruction in the liver and spleen. Knobs have been considered necessary but not sufficient for cytoadherence to vascular endothelial cells in vivo and to melanoma or umbilical vein endothelial cells in vitro. We describe here a knobless clone that cytoadheres strongly to C32 melanoma cells. This clone cannot express the knob-associated histidine-rich protein (KAHRP) due to the deletion of the KAHRP gene. Our results raise the possibility of an alternative mechanism for in vitro cytoadherence and suggest that the use of long term cultured isolates and melanoma cells as a model for cytoadherence in vivo may be misleading.

The problems associated with pulmonary aspergilloma were assessed retrospectively in 23 patients presenting from 1953 to 1982. Haemoptysis occurred in over half the patients and in two it was fatal. Invasive aspergillosis occurred in five patients, a higher proportion than in earlier reports, and two of these died. Amphotericin B in combination with either flucytosine or natamycin and, more recently, ketoconazole have proved useful in the treatment of this condition.

Gastrointestinal Kaposi's sarcoma is a well described and usually asymptomatic manifestation of the acquired immune deficiency syndrome. We report a patient who had extensive colonic Kaposi's sarcoma and presented with an ulcerative colitis like illness. Total colectomy was subsequently required as an emergency procedure for toxic megacolon. The patient remains well on maintenance interferon therapy 21 months after surgery.

The relative prednisolone-sparing effects of inhaled budesonide 400 micrograms daily and beclomethasone dipropionate (BDP) 400 micrograms daily were compared in a double-blind crossover study of 26 patients with chronic asthma requiring treatment with BDP and oral prednisolone in a daily dose of 5 mg or greater. During each period of the trial budesonide and BDP were inhaled via conventional pressurized inhalers in a dose of 100 micrograms four times daily. Prednisolone was reduced by 1 mg per month from the patient's normal maintenance dose to zero or to the point at which asthmatic symptoms became unacceptable. The mean reduction in prednisolone dose during BDP treatment was 2.65 mg compared with 1.8 mg at the end of the budesonide period. The difference between the prednisolone-sparing properties of BDP and budesonide assessed in this way in this group of patients was statistically significant in favour of BDP. The mean minimum prednisolone doses at the end of the treatment periods were 3.46 mg for BDP and 4.3 mg for budesonide. Since inhaled steroids were not withdrawn the absolute prednisolone-sparing properties of the two drugs were not assessed, and thus a pharmacological potency ratio cannot be derived from the results. It is concluded that BDP is marginally more potent than budesonide in its prednisolone-sparing properties.

Twenty-four patients who were known to develop bronchoconstriction in response to isocapnic hyperventilation (IH) took part in a double-blind, placebo-controlled trial to assess the effects of verapamil (5 mg) and sodium cromoglycate (SCG) 20 mg in the prevention of IH-induced bronchoconstriction. Both drug and placebo were inhaled in dry powder form and responses were assessed by serial measurements of forced expiratory volume in 1 sec (FEV1). Sodium cromoglycate was shown to offer significant protection whereas verapamil powder provoked bronchoconstriction in over 40% of patients and these patients appeared to be those with more marked degrees of bronchial reactivity.

We describe the isolation and the sequence of the gene for the bifunctional enzyme dihydrofolate reductase-thymidylate synthase (DHFR-TS; EC 1.5.1.3 and EC 2.1.1.45, respectively) from two pyrimethamine-resistant clones of Plasmodium falciparum, HB3 and 7G8. We have also derived the sequence of the DHFR portion of the gene, by amplification using polymerase chain reaction, for the pyrimethamine-sensitive clone 3D7 and the pyrimethamine-resistant strains V-1, K-1, Csl-2, and Palo-alto. The deduced protein sequence of the resistant DHFR portion of the enzyme from HB3 contained a single amino acid difference from the pyrimethamine-sensitive clone 3D7. It is highly likely that this difference is involved in the mechanism of drug resistance in HB3. The sequence of the DHFR gene from other pyrimethamine-resistant strains contains the same amino acid difference from the sensitive clone 3D7. However, they all differ at one other site that may influence pyrimethamine resistance. The DHFR-TS gene is present as a single copy on chromosome 4 in all pyrimethamine-sensitive and pyrimethamine-resistant isolates tested. Therefore, the molecular basis of pyrimethamine resistance in the parasites tested is not amplification of the DHFR-TS gene.

Subtelomeric deletions are responsible for the loss of expression of several Plasmodium falciparum antigens, including the knob-associated histidine-rich protein (KAHRP). Such deletions are detectable by two-dimensional pulsed-field gradient electrophoresis (PFGE) in which the chromosomes separated in dimension 1 are cleaved with Apa I, and the sizes of telomeric fragments are determined in dimension 2. This sensitive technique has enabled us to examine the role of subtelomeric deletions in two aspects of the biology of Plasmodium falciparum. First, we show that similar subtelomeric deletions to those that occur in vitro also occur in field isolates. Second, we demonstrate a correlation between subtelomeric deletions and loss of the phenotype of "cytoadherence" in cultured isolates. Subclones were generated from the cytoadherent cloned isolate ItG2F6, and their phenotypes were examined with respect to cytoadherence, the expression of "knobs," and agglutination of infected erythrocytes with rabbit antiserum. The only chromosomal change detectable by two-dimensional PFGE among subclones that differ from wild type in each of these three characteristics is a deletion of approximately 100 kilobases at one end of chromosome 2. This deletion includes the gene coding for KAHRP and the subtelomeric repeat designated rep20.

We report the findings of a two-year survey of faecal specimens for the protozoal pathogen, Cryptosporidium. Of the 2248 patients who were tested, 55 (2.5%) patients were found to have cryptosporidial infection. Transmission of the parasite appeared mainly to occur from person to person. In immunocompetent patients it caused an acute and sometimes severe gastroenteritis. Immunoincompetent patients experienced a variable illness that ranged from asymptomatic carriage to severe diarrhoea, causing malabsorption and ultimately death. Cryptosporidium is an important cause of gastroenteritis and may be the presenting feature of the acquired immunodeficiency syndrome. Therefore, it is pertinent to screen for this pathogen in all patients with acute diarrhoea.

Acquired Immunodeficiency Syndrome (AIDS) has received much publicity and medical attention. Interest has focused on education, epidemiology, treatment and prevention of the syndrome. This paper raises other issues for consideration, including problems associated with HIV testing, confidentiality, informed consent and the dilemmas facing those involved in the treatment of patients suffering from HIV infection.