In addition to the well-known differences among the four dengue serotypes, intra-serotypic antigenic diversity has been proposed to play a role in viral evolution and epidemic fluctuation. A replacement of genotype II by genotype III of dengue virus serotype 3 (DENV3) occurred in Thailand during 2007–2014, raising questions about the role of intra-serotypic antigenic differences in this genotype shift. We characterized the antigenic difference of DENV3 of genotypes II and III in Thailand, utilizing a neutralizing antibody assay with DENV3 vaccine sera and monotypic DENV3 sera. Although there was significant antigenic diversity among the DENV3, it did not clearly associate with the genotype. Our data therefore do not support the role of intra-serotypic antigenic difference in the genotype replacement. Amino acid alignment showed that eight positions are potentially associated with diversity between distinct antigenic subgroups. Most of these amino acids were found in envelope domain II. Some positions (aa81, aa124, and aa172) were located on the surface of virus particles, probably involving the neutralization sensitivity. Notably, the strains of both genotypes II and III showed clear antigenic differences from the vaccine genotype I strain. Whether this differencewill affect vaccine efficacy requires further studies.

The pathogenic Theileria species Theileria parva and T. annulata infect bovine leukocytes and erythrocytes causing acute, often fatal lymphoproliferative diseases in cattle. The parasites are of interest not only because of their economic importance as pathogens, but also because of their unique ability to transform the leukocytes they infect. The latter property allows parasitized leukocytes to be cultured as continuously growing cell lines in vitro, thus providing an amenable in vitro system to study the parasite/host cell relationship and parasite-specific cellular immune responses. This paper summarizes important advances in knowledge of the immunobiology of these parasites over the last 40 years, focusing particularly on areas of relevance to vaccination.

Theileria sergenti Shintoku stock consists of 2 parasite populations bearing 2 atlelic forms of p33/32, an immunodominant piroplasm surface protein. Parasite population changes during parasite passages among cattle and tick vectors, and during persistent infection in individual calves were analysed by using allele-specific polymerase chain reaction (PCR). The parasite DNAs were prepared from piroplasms from calves which had been infected with Shintoku stock by inoculation of sporozoite stabilates or parasitized erythrocytes, and from sporozoite stabilates which had been prepared from Shintoku stock-infected ticks. Changes in a dominant parasite population were demonstrated during transmission from calves to vector ticks and from infected ticks to calves. Parasite population changes were also apparent during persistent infection in cattle over several months, and this change is thought to occur under host immune pressure. The results of this study indicate that expression of diverse forms of p33/32 may play a role in parasite persistence within mammalian hosts and its transmission from tick vector.

A key issue relating to developing multi-component anti-malarial vaccines, lies in studying Plasmodium vivax surface proteins' genetic variation. The present work was aimed at amplifying, cloning and sequencing the gene encoding P. vivax merozoite surface protein 5 (PvMSP5) in samples obtained from infected patients from Colombian areas having varying malaria transmission rates.Nucleotide sequence data reported in this paper are available in the GenBank, EMBL and DDBJ databases under Accessions numbers DQ341586 to DQ341601. Our results have revealed that PvMSP5 is one of the P. vivax surface proteins having greater polymorphism, this being restricted to specific protein regions. The intron and exon II (which includes the GPI anchor and EGF-like domain) were both highly conserved when compared to exon I; exon I displayed the greatest variation and most of the recombination events occurred within it. No geographical grouping was observed. The Nei-Gojobori test revealed significant positive selection in the samples analysed here, whereas Tajima and Fu and Li tests presented a neutral selection pattern. The results reflected a localized variation pattern, recombination between PvMSP5 alleles and also functional and immune pressures, where stronger selective forces might be acting on exon I than on exon II, suggesting that the latter could be an important region to be included in an anti-malarial vaccine.

The study of genetic diversity in malaria populations is expected to provide new insights for the deployment of control measures. Plasmodium falciparum diversity in Africa and Asia is thought to reflect endemicity. In comprehensive epidemiological surveys reported here the genetic and antigenic structure of P. falciparum in the Venezuelan Amazon were studied over a 2-year period. DNA polymorphisms in glutamate-rich protein (GLURP), merozoite-surface protein 1 (MSP1) and MSP2 genes, in a multicopy element (PfRRM), all showed low diversity, 1 predominant genotype, and virtually no multi-clonal infections. Moreover, linkage disequilibrium was seen between GLURP, MSP1 and MSP2. Specific antibody responses against MSP1 and MSP2 recombinant antigens reflected the low genetic diversity observed in the parasite population. This is unexpected in a mesoendemic area, and suggests that the low diversity here may not only relate to endemicity but to other influences such as a bottleneck effect. Linkage disequilibrium and a predominant genotype may imply that P. falciparum frequently propagates with an epidemic or clonal population structure in the Venezuelan Amazon.

Using surface immunofluorescence isolate-specific antigens were detected on the membrane of erythrocytes infected with Babesia parasites. In addition, the strains reacted differently with Plasmagel in that the European isolate (B.c. canis) could be purified on Plasmagel effectively, whereas infected erythrocytes of the South-African isolate (B.c. rossi) could not. Experimental infection of dogs with Babesia canis isolates from geographically different areas revealed different pathology. The European isolate obtained from France exhibited transient parasitaemia, usually below 1%, associated with low PCV values and congestion of internal organs. Clinical disease was correlated with an effect on the coagulation system, and not with peripheral parasitaemia. Infection of dogs with South-African-derived isolate induced high parasitaemia usually much higher than 1%, which required chemotherapeutic treatment. In these animals clinical disease was correlated with peripheral parasitaemia and not with parameters of the coagulation system. The results show that the etiology of disease caused by these isolates of B.c. canis and B.c. rossi is different. This might have implications for the development of vaccines against these infections.