Plasmodium falciparum develops within the mature RBCs (red blood cells) of its human host in a PV (parasitophorous vacuole) that separates the host cell cytoplasm from the parasite surface. The pore-forming toxin, SLO (streptolysin O), binds to cholesterol-containing membranes and can be used to selectively permeabilize the host cell membrane while leaving the PV membrane intact. We found that in mixtures of infected and uninfected RBCs, SLO preferentially lyses uninfected RBCs rather than infected RBCs, presumably because of differences in cholesterol content of the limiting membrane. This provides a means of generating pure preparations of viable ring stage infected RBCs. As an alternative permeabilizing agent we have characterized EqtII (equinatoxin II), a eukaryotic pore-forming toxin that binds preferentially to sphingomyelin-containing membranes. EqtII lyses the limiting membrane of infected and uninfected RBCs with similar efficiency but does not disrupt the PV membrane. It generates pores of up to 100 nm, which allow entry of antibodies for immunofluorescence and immunogold labelling. The present study provides novel tools for the analysis of this important human pathogen and highlights differences between Plasmodium-infected and uninfected RBCs.

We have developed a new procedure (Vir typing) for typing Streptococcus pyogenes, by amplifying the entire $to 7-kb variable vir regulon by long PCR. The amplified DNA is then cleaved with Haelll and visualized by ethidlum bromide fluorescence after agarose gel electrophoresis. A simple procedure for preparing DNA of sufficiently high quality from 96 samples was employed simultaneously. This DNA was also used to develop a random amplified polymorphic DNA (RAPD) procedure. The discriminatory power of the two DNA-based procedures was compared with previous methods, M typing, and multilocus enzyme electrophoresis. Both procedures were highly discriminatory, but the stoichiometric yield of restriction fragments in Vir typing allows unambiguous interpretation of results.

Group A streptococcal infections among the Aboriginal communities of the Northern Territory of Australia are endemic, with a concurrently high rate of the postinfection sequelae of rheumatic fever and acute poststreptococcal glomerulonephritis. The majority of the group A streptococcal isolates from the Northern Territory are not typeable by M typing. We recently developed a novel genotyping method, Vir typing. A preliminary study using this method discriminated all the M-nontypeable (MNT) isolates. Vir typing is based on restriction fragment length polymorphisms of the 4-to 7-kb Vir regulon of group A streptococci, which contains a number of genes, including emm (the gene for M protein). A total of 407 isolates of group A streptococci obtained from four Aboriginal communities over a 4-year period were typed by this genotyping method. Forty-two distinct genotypes were found among the isolates, including 22 among the MNT isolates. The correlation between Vir type and M type was good. This genotyping method allows the characterization of all group A streptococcal isolates from Aboriginal communities in the Northern Territory. We also propose that Vir typing be used in conjunction with M typing for epidemiological surveillance in geographical regions where the majority of isolates are MNT. Streptococcus pyogenes, which constitutes the Lancefield group A streptococci (GAS), is the major causative agent of a number of human diseases, ranging from relatively benign conditions, such as pyoderma, to severe invasive diseases, such as toxic shock-like syndrome and necrotizing fasciitis (4). A resurgence of invasive group A streptococcal disease and the postinfection sequela of rheumatic fever in developed countries was reported in the 1980s (11, 16, 36). This resurgence prompted a renewed interest in GAS and its disease manifestations. GAS infections in Aboriginal communities of the Top End of northern Australia are endemic, with up to 70% of children having impetigo, due in part to infection of scabies lesions. The reported rates of acute rheumatic fever and rheumatic heart disease are some of the highest reported anywhere in the world (9, 23). The annual rate of acute rheumatic fever is 2.5 per 1,000 Aboriginal children, and the prevalence rate of rheumatic heart disease is 10.4 per 1,000 Aboriginal people (7). Epidemics of acute post-streptococcal glomerulonephritis (APSGN) occur frequently throughout Aboriginal communities in tropical Australia (13, 34). APSGN was diagnosed in 10% of the Aboriginal children in one community in an APSGN epidemic (34), and it is believed that APSGN is also endemic in the Aboriginal communities. Until recently, M protein serotyping (M typing) has been used extensively in an effort to understand the epidemiology of GAS infections in Aboriginal communities. The antiphagocytic M protein, encoded by the emm gene, is the major virulence factor of GAS, and the antigenic variation of this protein is the basis for the serological typing method. Currently, there are at least 74 characterized M ser...

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Drugs that kill or inhibit the sexual stages of Plasmodium in order to prevent transmission are important components of malaria control programmes. Reducing gametocyte carriage is central to the control of Plasmodium falciparum transmission as infection can result in extended periods of gametocytaemia. Unfortunately the number of drugs with activity against gametocytes is limited. Primaquine is currently the only licensed drug with activity against the sexual stages of malaria parasites and its use is hampered by safety concerns. This shortcoming is likely the result of the technical challenges associated with gametocyte studies together with the focus of previous drug discovery campaigns on asexual parasite stages. However recent emphasis on malaria eradication has resulted in an upsurge of interest in identifying compounds with activity against gametocytes. This review examines the gametocytocidal properties of currently available drugs as well as those in the development pipeline and examines the prospects for discovery of new anti-gametocyte compounds.