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Rosetting of Plasmodium falciparum-infected red blood cells (parasitized RBC [pRBC]) with uninfected RBC has been associated in many studies with malaria morbidity and is one form of cytoadherence observed with malarial parasites. Rosetting is serum dependent for many isolates of P. falciparum, including the strains FCR3S1.2 and Malayan Camp studied here. We identified the three naturally occurring components of sera which confer rosetting. Complement factor D alone induced 30 to 40% of de novo rosetting. Its effect was additive to that of 0.5 mg/ml albumin and to that of 15 ng/ml of naturally occurring antibodies to the anion transport protein, band 3. The three components together mediated rosetting as effectively as 10% serum. De novo rosetting experiments showed that naturally occurring anti-band 3 antibodies as well as factor D were effective only when added to pRBC. Factor D appeared to cleave a small fraction of a protein expressed on the surface of pRBC.Cerebral malaria occurs from infections with Plasmodium falciparum, the parasite species that shows sequestration in the periphery. Sequestration is a means by which parasitized red blood cells (pRBC) escape from their clearance from the reticuloendothelial system. It is mediated by cytoadherence and rosetting of pRBC with uninfected RBC. Clinical studies and autopsies have indeed revealed rosettes in blood vessels from malaria victims (19,20,40,43), and parasites isolated from patients with severe disease formed more and larger rosettes than those from uncomplicated cases (4, 47). For many parasite isolates, in vitro rosetting is dependent on serum factors that are also present in nonimmune, healthy persons. Thus, it is more than a coincidence that the mortality from cerebral malaria is highest in very young children, who have not developed immunity against the parasite but have partially established their innate immune systems. The serum factors that have been shown to mediate rosetting are immunoglobulins (15,43,45), albumin (48), and a third so far unidentified small component which does not bind to concanavalin A (45). We embarked on a study of these serum factors in more detail because neither the specificities of the involved innate immunoglobulins (naturally occurring antibodies [NAbs]) nor the role of complement has been investigated. . When the parasitemia reached 5 to 10%, the culture was diluted to achieve 0.2 to 0.5% parasitemia and culture was continued. Twice a month, cultured parasites were enriched for the rosetting phenotype (49). MATERIALS AND METHODSRosette disruption. A rosetting parasite culture containing P. falciparum late stages at a parasitemia of 5 to 10% was centrifuged for 5 min at 500 ϫ g. Cells were washed twice with phosphate-buffered saline (PBS)-glucose (pH 7.4) and resuspended to a 20% hematocrit in PBS-glucose containing 5 mM sodium citrate, and rosettes were disrupted by passing the resuspended cells 20 times through a 23-gauge 0.6-mm-diameter needle. Cells were then washed once with PBS-glucose containing 5 mM sodium ...

Necrotizing enteritis in piglets is caused by the spore-forming anaerobe Clostridium perfringens type C. The pathology is believed to be due to the production of beta-toxin by the agent and the infection tends to persist in affected herds despite appropriate hygiene measures. During the period 1989 to 2001, 35 outbreaks were observed in 15 herds in a limited geographic region in northwestern Switzerland in the canton of Fribourg. Initial outbreaks of acute disease were followed by chronic manifestations of necrotizing enteritis in eleven herds. Since clinical symptoms in case of chronic necrotizing enteritis and of mixed infections were rather non-specific, diagnosis in all herds was confirmed by gross pathological analysis, intestinal histology and bacteriological culture. After initial evaluation in 135 litters (1500 piglets), metaphylaxis consisted of penicillin for outbreaks of acute disease or of amoxycillin-clavulanic acid pending results of laboratory confirmation. Vaccination with a C. perfringens toxoid vaccine (Gletvax 6, also containing E. coli pilus antigens) together with penicillin chemoprophylaxis was used in 2400 litters (27,000 piglets). In 12 to 17% of litters disease recurred during this combined prophylaxis. Necrotizing enteritis persisted in all affected herds throughout the follow-up period.

Investigations were performed on shedding of C. perfringens in sows from four different pig farms. In two farms where no outbreaks of necrotizing enteritis had been observed, no strains of C. perfringens producing beta-toxin were detected in the faeces of sows. In contrast, C. perfringens strains producing beta-toxin were detected in sows on both farms suffering outbreaks of acute necrotizing enteritis. Strains of C. perfringens producing beta-toxin were invariably positive for the beta 2-toxin gene. However, strains carrying the beta 2-toxin gene only (i.e. negative for beta-toxin) were present in animals on all farms with roughly similar frequencies (mean 28.2% carriers). Some sows carried C. perfringens strains of both toxin genotypes simultaneously. Whereas these data further support the role of betatoxin as a cause of necrotizing enteritis, the role of beta 2-toxin in intestinal disease of piglets remains unclear. To establish the role of faecal shedding vs. environmental contamination as reservoirs of C. perfringens type C, strains were isolated from teats and feedlot trough swabs (toxin genotype beta/beta 2), as well as from fodder (genotype beta 2). However, sows carried this pathogen intermittently and in small numbers. This renders an individual, reliable diagnosis of carrier sows very difficult. Ribotyping of 34 C. perfringens isolates of different toxin genotypes showed five distinct profiles. Different toxin genotypes can belong to the same ribotype, and the same toxin genotype can be present in different ribotypes. Thus, even if a majority (79.4%) of strains investigated in a limited geographic region belonged to ribotype 1, ribotyping offered discrimination of strains beyond toxin typing.

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