PEG-precipitation and complement fixation by circulating immune complexes

Circulating immune complexes have been studied in 152 sera with PEG-precipitation nd with measurement of the complement activating capacity in a complement binding reaction with 51Cr-labelled indicator cells. A correlation was found between the results of both methods.     

Population genomic structure and adaptation in the zoonotic malaria parasite Plasmodium knowlesi

Malaria cases caused by the zoonotic parasite Plasmodium knowlesi are being increasingly reported throughout Southeast Asia and in travelers returning from the region. To test for evidence of signatures of selection or unusual population structure in this parasite, we surveyed genome sequence diversity in 48 clinical isolates recently sampled from Malaysian Borneo and in five lines maintained in laboratory rhesus macaques after isolation in the 1960s from Peninsular Malaysia and the Philippines. Overall genomewide nucleotide diversity (π = 6.03 × 10⁻³) was much higher than has been seen in worldwide samples of either of the major endemic malaria parasite species Plasmodium falciparum and Plasmodium vivax. A remarkable substructure is revealed within P. knowlesi, consisting of two major sympatric clusters of the clinical isolates and a third cluster comprising the laboratory isolates. There was deep differentiation between the two clusters of clinical isolates [mean genomewide fixation index (F_ST) = 0.21, with 9,293 SNPs having fixed differences of F_ST = 1.0]. This differentiation showed marked heterogeneity across the genome, with mean F_ST values of different chromosomes ranging from 0.08 to 0.34 and with further significant variation across regions within several chromosomes. Analysis of the largest cluster (cluster 1, 38 isolates) indicated long-term population growth, with negatively skewed allele frequency distributions (genomewide average Tajima’s D = −1.35). Against this background there was evidence of balancing selection on particular genes, including the circumsporozoite protein (csp) gene, which had the top Tajima’s D value (1.57), and scans of haplotype homozygosity implicate several genomic regions as being under recent positive selection.The zoonotic malaria parasite Plasmodium knowlesi is a significant cause of human malaria, with a wide spectrum of clinical outcomes including high parasitemia and death (1–4). Long known as a malaria parasite of long-tailed and pig-tailed macaques (5), the first large focus of human cases was described only in 2004 in the Kapit Division of Sarawak in Malaysian Borneo (6). Since then infections have been described from almost all countries in Southeast Asia (2, 7). Travelers to the region from Europe, North America, and Australasia also have recently acquired P. knowlesi malaria (7, 8). Until the application of molecular assays for specific detection, human P. knowlesi malaria was largely misdiagnosed as Plasmodium malariae, a morphologically similar but distantly related species (1, 6, 9, 10). Studies in the Kapit Division of Sarawak in Malaysian Borneo have indicated that P. knowlesi malaria is primarily a zoonosis with macaques as reservoir hosts (11) and that the forest-dwelling mosquito species Anopheles latens is the local vector for P. knowlesi (12). Other members of the Anopheles leucosphyrus group are vectors in different parts of Southeast Asia and may determine the geographical distribution of transmission (13, 14).Although P. knowlesi malaria is regarded as an emerging infection, there clearly have been increased efforts in detection made since its existence as a significant zoonosis was discovered, and specific detection has been enhanced by the declining numbers of human cases caused by other malaria parasites in Southeast Asia (15). Aside from the first two human cases described several decades ago (5), there is direct evidence of human P. knowlesi infections from ∼20 y ago in Malaysian Borneo and Thailand obtained by retrospective molecular analysis of material from archived blood spots and slides (10, 16), and molecular population genetic evidence indicates the zoonosis has been in existence for a much longer time (11). The genetic diversity of P. knowlesi is high within humans as well as macaques, with sequence data on three loci [the circumsporozoite protein (csp) gene, 18S rRNA, and mtDNA genome] indicating extensive shared polymorphism and no fixed differences between P. knowlesi parasites from humans and monkeys sampled in the same area in Sarawak, Malaysian Borneo (6, 11). Analysis of samples from a smaller number of humans and monkeys in Thailand showed alleles of the P. knowlesi merozoite surface protein 1 (msp1) gene to be similarly diverse in both hosts (16), and there were shared polymorphisms of the csp gene in parasites from a few infections examined in humans and macaques in Singapore (17). Recent multilocus microsatellite analysis has indicated a deep population subdivision in P. knowlesi associated with long-tailed and pig-tailed macaques; both major types infect humans and occur sympatrically at most sites in Malaysia, but the two types show some additional geographical differentiation across sites (18).Human populations have grown very rapidly in the Southeast Asian region and encroach on most of the wild macaque habitats, so it is vital to know if P. knowlesi parasites are adapting to human hosts or to anthropophilic mosquito vector species, either of which could cause human–mosquito–human transmission. Initial analysis of the P. knowlesi reference genome sequence (strain H) highlighted some unique features of the genome of this species (19), namely, schizont infected cell agglutination variant (SICAvar) and knowlesi interspersed repeat (KIR) variant antigen genes, which were widely dispersed instead of being predominantly localized in subtelomeric regions as seen in large gene families in Plasmodium falciparum and Plasmodium vivax (20). Here, we analyzed genomewide diversity in P. knowlesi and conducted scans for signatures of balancing and directional selection, revealing extremely high genetic diversity and significant structuring of this species into subpopulation clusters that appear to be reproductively isolated as well as loci that show evidence of recent strong selection.     

Imported Plasmodium knowlesi malaria in a French tourist returning from Thailand

We report a case of imported Plasmodium knowlesi malaria in a French tourist following a vacation in Thailand. This case shows, first, tourists may contract knowlesi malaria even only staying on the beach and second, the diagnosis remains difficult, even with polymerase chain reaction methods.     

人体自然感染诺氏疟原虫(Plasmodium knowlesi)--形态学描述、分子鉴定和msp-1片段表达

疟疾是威胁人类健康的重要传染病之一。全球每年有3.5亿~5亿临床病例,100万~300万人死于该病,其中大部分是儿童。由于原虫及媒介均已对药物产生抗药性,疟疾控制面临重重困难。此外,在东南亚国家屡有报道灵长类疟原虫在人体寄生,这种情况有可能引发严重的公共卫生问题:首先,对感     

Plasmodium knowlesi malaria in humans is widely distributed and potentially life threatening.

BACKGROUND: Until recently, Plasmodium knowlesi malaria in humans was misdiagnosed as Plasmodium malariae malaria. The objectives of the present study were to determine the geographic distribution of P. knowlesi malaria in the human population in Malaysia and to investigate 4 suspected fatal cases. METHODS: Sensitive and specific nested polymerase chain reaction was used to identify all Plasmodium species present in (1) blood samples obtained from 960 patients with malaria who were hospitalized in Sarawak, Malaysian Borneo, during 2001-2006; (2) 54 P. malariae archival blood films from 15 districts in Sabah, Malaysian Borneo (during 2003-2005), and 4 districts in Pahang, Peninsular Malaysia (during 2004-2005); and (3) 4 patients whose suspected cause of death was P. knowlesi malaria. For the 4 latter cases, available clinical and laboratory data were reviewed. RESULTS: P. knowlesi DNA was detected in 266 (27.7%) of 960 of the samples from Sarawak hospitals, 41 (83.7%) of 49 from Sabah, and all 5 from Pahang. Only P. knowlesi DNA was detected in archival blood films from the 4 patients who died. All were hyperparasitemic and developed marked hepatorenal dysfunction. CONCLUSIONS: Human infection with P. knowlesi, commonly misidentified as the more benign P. malariae, are widely distributed across Malaysian Borneo and extend to Peninsular Malaysia. Because P. knowlesi replicates every 24 h, rapid diagnosis and prompt effective treatment are essential. In the absence of a specific routine diagnostic test for P. knowlesi malaria, we recommend that patients who reside in or have traveled to Southeast Asia and who have received a "P. malariae" hyperparasitemia diagnosis by microscopy receive intensive management as appropriate for severe falciparum malaria.     

Naturally occurring plasmodia-specific circulating immune complexes in individuals of malaria endemic areas in India

Blood samples collected from individuals belonging to malaria endemic areas were assayed for antigen-specific circulating immune complexes in polyethylene glycol precipitates of serum by enzyme immunoassay. Sera were tested from patients with acute P. vivax and P. falciparum infections, from clinically immune individuals and also from healthy normals. Circulating immune complexes (CICs) containing immunoglobulin G and M isotypes were found to be abundant in individuals with ongoing and past infections and also in clinically immune donors. In patients with acute infection but without any past history of malaria, CICs of IgM type were found to be significantly higher. Demonstration of antigen/antibody specific CICs could be a useful indicator of active, ongoing and recent/past infection, also of the status of immune responses of individuals belonging to various endemic areas.     

A simple method for detecting HIV antibodies hidden in circulating immune complexes

A method previously used for studying the specificity of antibody components of circulating immune complexes in different diseases has been applied to analyse circulating immune complexes in HIV-infected patients. Antibodies against HIV antigens hidden in circulating immune complexes were studied in 14 sera from 13 patients with asymptomatic HIV infection (group 1) and in 11 sera from seven patients with HIV symptoms (group 2). HIV antigen-coated wells from the Vironostika kit as well as core and envelope antigen-coated beads from the Abbott confirmatory kit were used as solid-phase antigen. Using the Vironostika plates, HIV antibodies were demonstrated in circulating immune complexes in three and five sera in groups 1 and 2, respectively. Anti-core antibodies hidden in circulating immune complexes were present in three out of eight and two out of nine sera, respectively, in groups 1 and 2, whereas anti-envelope antibodies were present in circulating immune complexes in one out of eight and six out of nine sera in the same groups. These findings demonstrate that not only core-anti-core but also envelope-anti-envelope immune complexes are present in the sera of HIV infected patients.     

Associations between clinical disease, circulating antibodies and C1q-binding immune complexes in human onchocerciasis

Onchocerciasis is a disease where often there are high levels of serum antibodies and high parasitic loads. The role of immune complexes in the development of the disease is investigated here by studying non-specific and Onchocerca volvulus specific immune complex levels, as well as the antibody concentrations, in the sera of 372 people living in either Southern (199) or Northern (173) Sudan; sera from Sudanese individuals (31) and Caucasians (21) living outside the onchocerciasis endemic area were also tested. The levels of non-specific immune complexes (NS-IC) in these sera were measured by a solid phase radio-immunoassay and those of O. volvulus-specific immune complexes (OV-IC) by an assay measuring antibody-excess complexes using C1q-coated plates. The concentrations of O. volvulus IgG antibodies were measured by ELISA. Immune complex and antibody levels of the serum donors were compared with regard to their clinical status due to onchocerciasis. These clinical changes were classified according to onchocercal lesions related to either the active destruction of microfilariae (acute changes), or the long term tissue alterations (chronic changes). Data was analysed using the Odds Ratio method. A negative association between microfilarial load and immune complex level was found, with the higher levels of OV-IC present in patients with the lower levels of dermal microfilariae (i.e., less than 10 mf/mg). Significant associations between immune complex levels and the severity of onchocercal disease were also found. Levels of OV-IC specific immune complexes were higher in infected individuals carrying dermal onchocercal lesions than in those without such clinical changes; there was no apparent relationship between these levels and the presence of ocular lesions. OV-IC levels varied considerably within each age group and from age to age. A weak positive association was detected between microfilarial load and parasite-specific IgG antibody concentration in the sera. On average younger individuals (less than 25 years) had the higher antibody levels with a gradual reduction in mean concentrations with age. The significance of these serological findings in terms of the pathogenesis of onchocerciasis is discussed.