Multiplicity of infection of Plasmodium knowlesi in Malaysia: an application of Pkmsp-1 block IV

In Malaysia presently, the main cause of human malaria is by the zoonotic monkey parasite Plasmodium knowlesi. A previous study has suggested that the P. knowlesi merozoite surface protein 1 (Pkmsp-1) block IV to be a suitable multiplicity of infection (MOI) genotyping marker for knowlesimalaria. This study therefore aimed to investigate the usefulness of Pkmsp-1 block IV in assessing the MOI of P. knowlesi in clinical isolates from Malaysia. Two allele-specific PCR primer pairs targeting the two allelic families of block IV (T1 and T2) were designed, and used to genotype P. knowlesi in 200 blood samples (100 from Peninsular Malaysia and 100 from Malaysian Borneo). Results showed that the mean MOI in Malaysian Borneo was slightly higher as compared to Peninsular Malaysia (1.58 and 1.40, respectively). Almost half of the total blood samples from Malaysian Borneo (52%) had polyclonal infections (i.e., more than one allele of any family type) as compared to Peninsular Malaysia (33%) samples. The T1 allelic family was more prevalent in Peninsular Malaysia (n=75) than in Malaysian Borneo (n=60). The T2 allelic family, however, was more prevalent in the Malaysian Borneo (n=87 vs n=53 respectively). This study shows that the single locus Pkmsp-1 block IV can serve as a simple alternative genetic marker for estimating knowlesi malaria MOI in a population. Future MOI studies should focus on macaque populations as macaques are the natural host of P. knowlesi.

Plasmodium knowlesi circumsporozoite protein: genetic characterisation and predicted antigenicity of the central repeat region

Circumsporozoite protein (CSP) central repeat region is one of the main target regions of the RTS,S/AS01 vaccine for falciparum infection as it consists of immunodominant B cell epitopes. However, there is a lack of study for P. knowlesi CSP central repeat region. This study aims to characterise the CSP repeat motifs of P. knowlesi isolates in Peninsular Malaysia. CSP repeat motifs of 64 P. knowlesi isolates were identified using Rapid Automatic Detection and Alignment of Repeats (RADAR). Antigenicity of the repeat motifs and linear B cell epitopes were predicted using VaxiJen 2.0, BepiPred-2.0 and BCPred, respectively. A total of 35 dominant repeat motifs were identified. The repeat motif "AGQPQAQGDGANAGQPQAQGDGAN" has the highest repeat frequency (n=15) and antigenicity index of 1.7986. All the repeat regions were predicted as B cell epitopes. In silico approaches revealed that all repeat motifs were antigenic and consisted of B cell epitopes which could be designed as knowlesi malaria vaccine.

Experimental Study on Plasmodium knowlesi Normocyte Binding Protein Xa Region II (PkNBPXaII) for Erythrocyte Binding

Normocyte binding protein Xa (NBPXa) has been implied to play a significant role in parasite invasion of human erythrocytes. Previous phylogenetic studies have reported the existence of three types of NBPXa for Plasmodium knowlesi (PkNBPXa). PkNBPXa region II (PkNBPXaII) of type 1, type 2 and type 3 were expressed on mammalian cell surface and interacted with human and macaque (Macaca fascicularis) erythrocytes. The binding activities of PkNBPXaII towards human and macaque erythrocytes were evaluated using erythrocyte-binding assay (EBA). Three parameters were evaluated to achieve the optimal protein expression of PkNBPXaII and erythrocyte binding activity in EBA: types of mammalian cells, post transfection time and erythrocyte incubation time. COS-7, HEK-293, and CHO-K1 cells showed successful expression of PkNBPXaII, despite the protein expression is weak compared to the positive control. COS-7 was used in EBA. All three types of PkNBPXaII showed rosette formation with macaque erythrocytes but not with human erythrocytes. Future studies to enhance the PkNBPXaII expression on surface of mammalian cells is indeed needed in order to elucidate the specific role of PkNBPXaII in erythrocytes invasion.

Detection of mutated Plasmodium vivax Kelch Propeller Domain (PvK12) in Malaysian isolates

Malaysia is located near the borders of countries where artemisinin resistant Plasmodium falciparum (mutations in the P. falciparum Kelch propeller domain [PfK13]) have been reported. Plasmodium vivax Kelch propeller domain, PvK12, the ortholog of PfK13, could assess resistance towards artemisinin in vivax malaria. Polymorphisms in PvK12 gene were determined by PCR and sequencing was done in 300 clinical isolates collected in recent years (2012-2017) from hospitals within the country. Among 48 P. vivax samples, all were Sal-1 wild type alleles except for two isolates, a synonymous and nonsynonymous mutation respectively. The nonsynonymous (V552I) isolate was collected from an immigrant. P. vivax with mutated PvK12 is speculated to be an imported case and is likely to be circulating at very low frequency in Malaysia. An in-depth drug resistance surveillance among immigrants needs to be investigated to provide information that may be crucial for drug policy changes.

Evaluation of codon optimized recombinant Plasmodium knowlesi merozoite surface protein-119 (pkMSP-119) expressed in Pichia pastoris

Malaria causes high global mortality and morbidity annually. Plasmodium knowlesi has been recognised as the fifth human Plasmodium sp. and its infection is widely distributed in Southeast Asia. Merozoite surface protein-119 (MSP-119) appears as a potential candidate for malaria blood stage vaccine as it could induce protective immunity. In this study, codon optimized P. knowlesi MSP-119 (pkMSP-119) was expressed and purified in yeast Pichia pastoris expression system. The purified recombinant protein was further evaluated using Western blot assay using knowlesi malaria, non-knowlesi human malaria, non-malarial parasitic infections and healthy serum samples (n = 50). The sensitivity of purified pkMSP-119 towards detection of knowlesi infection was as 28.6% (2/7). pkMSP-119 did not react with all non-malarial parasitic infections and healthy donor sera, yet reacted with some non-knowlesi human malaria sera, therefore lead to a specificity of 86.0% (37/43).

Computed tomography and ultrasound diagnosis of mycotic aneurysm of the abdominal aorta due to Salmonella

The case of a 56 year old diabetic Chinese male, with a Salmonella bovismorbificans (serogroup C) mycotic aneurysm of the abdominal aorta is presented. The lesion was seen by computed tomography and ultrasound and the patient was successfully treated by primary resection, debridement and grafting. Computed tomography criteria for the diagnosis of mycotic aneurysms of the abdominal aorta are discussed. Ultrasound identified the aortic aneurysm correctly but was unable to demonstrate the associated psoas abscess in this case.