Two Cases of Herpes Zoster Following Varicella Vaccination in Immunocompetent Young Children:One Case Caused by Vaccine-Strain

Herpes zoster (HZ) has been reported in immunocompetent children who received the varicella vaccine. In vaccinated children, HZ can be caused by vaccine-strain or by wild-type varicella-zoster virus (VZV). Like wild-type VZV, varicella vaccine virus can establish latency and reactivate as HZ. We report two cases of HZ in otherwise healthy 16- and 14-month-old boys who received varicella vaccine at 12 months of age. They presented with a vesicular rash on their upper extremities three to four months after varicella vaccination. In one case, a swab was obtained by abrading skin vesicles and VZV was detected in skin specimens by polymerase chain reaction. The VZV open-reading frame 62 was sequenced and single nucleotide polymorphism analysis confirmed that the virus from skin specimen was vaccinestrain. This is the first HZ case following varicella vaccination confirmed to be caused by vaccine-strain VZV in the immunocompetent children in Korea. Pediatricians should be aware of the potential for varicella vaccine virus reactivation in vaccinated young children.

Detection of Toxoplasma gondii Infections using Virus-Like Particles Displaying T. gondii ROP4 Antigen

Toxoplasma gondii ME49 infections are typically diagnosed by serological tests. However, serological diagnosis of RH strain-induced toxoplasmosis remains unknown. In order to develop seradiagnosis of above 2 kinds of infections, we generated recombinant virus-like particles (VLPs) displaying the T. gondii rhoptry protein 4 (ROP4) and evaluated their potential in T. gondii ME49 or RH strain infection diagnostics. Mice were orally infected with either the tachyzoites of T. gondii (RH) or cysts of T. gondii (ME49) at various dosages, and sera were collected at regular intervals. ELISA-based serological tests were performed to assess IgG, IgM, and IgA antibody responses against ROP4 VLP antigen and tissue lysate antigen (TLA). Compared to TLA, IgG, IgM, and IgA levels to ROP4 VLP antigen were significantly higher in the sera of T. gondii RH-infected mice 1 and 2 week post-infection (PI). T. gondii-specific IgG antibody was detected at 1, 2, 4, and 8 week PI in the T. gondii ME49-infected mice with infection dose-dependent manner. These results indicated that the ROP4 VLP antigen was highly sensitive antigens detecting T. gondii RH and ME49 antibodies at an early stage.

Virus-like Particle Vaccine Containing Toxoplasma gondii Rhoptry Protein 13 Induces Protection against T. gondii ME49 Infection in Mice

Toxoplasma gondii can infect humans worldwide, causing serious diseases in pregnant women and immunocompromised individuals. T. gondii rhoptry protein 13 (ROP13) is known as one of the key proteins involved in host cell invasion. In this study, we generated virus-like particles (VLPs) vaccine expressing T. gondii rhoptry ROP13 and investigated VLPs vaccine efficacy in mice. Mice immunized with ROP13 VLPs vaccine elicited significantly higher levels of T. gondii-specific IgG, IgG1, IgG2a, and IgA antibody responses following boost immunization and challenge infection, whereas antibody inductions were insignificant upon prime immunization. Differing immunization routes resulted in differing antibody induction, as intranasal immunization (IN) induced greater antibody responses than intramuscular immunization (IM) after boost and challenge infection. IN immunization induced significantly higher levels of IgG and IgA antibody responses from feces, antibody-secreting cells (ASCs), CD4⁺ T, CD8⁺ T cells and germinal center B cell responses in the spleen compared to IM immunization. Compared to IM immunization, IN immunization resulted in significantly reduced cyst counts in the brain as well as lesser body weight loss, which contributed to better protection. All of the mice immunized through either route survived, whereas all naïve control mice perished. These results indicate that the ROP13 VLPs vaccine could be a potential vaccine candidate against T. gondii infection.

Low Levels of Polymorphisms and Negative Selection in Plasmodum knowlesi Merozoite Surface Protein 8 in Malaysian Isolates

Human infections due to the monkey malaria parasite Plasmodium knowlesi is increasingly being reported from most Southeast Asian countries specifically Malaysia. The parasite causes severe and fatal malaria thus there is a need for urgent measures for its control. In this study, the level of polymorphisms, haplotypes and natural selection of full-length pkmsp8 in 37 clinical samples from Malaysian Borneo along with 6 lab-adapted strains were investigated. Low levels of polymorphism were observed across the full-length gene, the double epidermal growth factor (EGF) domains were mostly conserved, and non-synonymous substitutions were absent. Evidence of strong negative selection pressure in the non-EGF regions were found indicating functional constrains acting at different domains. Phylogenetic haplotype network analysis identified shared haplotypes and indicated geographical clustering of samples originating from Peninsular Malaysia and Malaysian Borneo. This is the first study to genetically characterize the full-length msp8 gene from clinical isolates of P. knowlesi from Malaysia; however, further functional characterization would be useful for future rational vaccine design.

Previous Infection with Plasmodium berghei Confers Resistance to Toxoplasma gondii Infection in Mice

Both Plasmodium spp. and Toxoplasma gondii are important apicomplexan parasites, which infect humans worldwide. Genetic analyses have revealed that 33% of amino acid sequences of inner membrane complex from the malaria parasite Plasmodium berghei is similar to that of Toxoplasma gondii. Inner membrane complex is known to be involved in cell invasion and replication. In this study, we investigated the resistance against T. gondii (ME49) infection induced by previously infected P. berghei (ANKA) in mice. Levels of T. gondii-specific IgG, IgG1, IgG2a, and IgG2b antibody responses, CD4+ and CD8+ T cell populations were found higher in the mice infected with P. berghei (ANKA) and challenged with T. gondii (ME49) compared to that in control mice infected with T. gondii alone (ME49). P. berghei (ANKA) + T. gondii (ME49) group showed significantly reduced the number and size of T. gondii (ME49) cysts in the brains of mice, resulting in lower body weight loss compared to ME49 control group. These results indicate that previous exposure to P. berghei (ANKA) induce resistance to subsequent T. gondii (ME49) infection.

Virus-Like Particles Expressing Toxoplasma gondii Rhoptry Protein 18 Induces Better Protection Than Rhoptry Protein 4 against T. gondii Infection

Toxoplasma gondii is a ubiquitous protozoan parasite responsible for causing toxoplasmosis. Preventive measures for toxoplasmosis are currently lacking and as such, development of novel vaccines are of urgent need. In this study, we generated 2 virus-like particles (VLPs) vaccines expressing T. gondii rhoptry protein 4 (ROP4) or rhoptry protein 18 (ROP18) using influenza matrix protein (M1) as a core protein. Mice were intranasally immunized with VLPs vaccines and after the last immunization, mice were challenged with ME49 cysts. Protective efficacy was assessed and compared by determining serum antibody responses, body weight changes and the reduction of cyst counts in the brain. ROP18 VLPs-immunized mice induced greater levels of IgG and IgA antibody responses than those immunized with ROP4 VLPs. ROP18 VLPs immunization significantly reduced body weight loss and the number of brain cysts in mice compared to ROP4 VLPs post-challenge. These results indicate that T. gondii ROP18 VLPs elicited better protective efficacy than ROP4 VLPs, providing important insight into vaccine design strategy.

Seroprevalences of Specific IgG Antibodies to Measles, Mumps, and Rubella in Korean Infants

In this study, the seroprevalences of measles, mumps, and rubella antibodies in infants were determined to assess the immunization strategy and control measures for these infectious diseases. Serum samples from infants < 1 year of age and their mothers were collected to measure the concentrations of specific IgG antibodies to measles, mumps, and rubella by enzyme-linked immunosorbent assay. For selected infant serum samples, measles-specific neutralizing antibody levels were determined by using the plaque reduction neutralization test. The sera from 295 of infants and 80 of their mothers were analyzed. No infants had past measles, mumps, or rubella infections. Almost all infants < 2 months of age were positive for measles and rubella IgG antibodies. However, seroprevalence of measles and rubella antibodies decreased with age, and measles IgG and rubella IgG were barely detectable after 4 months of age. The seroprevalence of mumps antibodies was lower than that of measles and rubella antibodies in infants ≤ 4 months old, and mumps IgG was barely detectable after 2 months of age. The seropositivity of measles-specific neutralizing antibody was 63.6% in infants aged 2 months and undetectable in infants ≥ 6 months old. Because the seropositivity rates of measles, mumps, and rubella antibodies were low after the first few months of age in Korean infants, active immunization with vaccines is strongly recommended for infants aged 6–11 months when measles is epidemic. Timely administration of the first dose of measles-mumps-rubella vaccine at 12 months of age should be encouraged in non-epidemic situations.

An Outbreak of Mumps in a High School, Seoul, 2013

PURPOSE: This study investigated an outbreak of mumps affecting students in a high school (S high school) in Seoul, with an evaluation of the diagnostic utility of the mumps polymerase chain reaction (PCR) assay. METHODS: S high school students that presented to health care providers with mumps symptoms between April 2013 and July 2013 were surveyed for the monthly distribution of symptom onset and their grade level. Mumps PCR assays were performed using buccal swabs from some of these students. RESULTS: During the survey period, 77 students presented with suspected cases of mumps. The monthly distribution of symptom onset was as follows: one in April, 17 in May, 54 in June, and five in July. With regard to grade level, 26 students were in their first year, 28 were in their second year, and 23 were in their third year. Of the 18 students tested with PCR assays, five had positive results. Samples were collected within 3 days of symptom onset in 15 of the 18 students, and positive PCR results were obtained in five of these 15 students. The PCR results of the remaining three students from whom samples were collected more than 3 days after the onset of symptoms were negative (P=0.24). CONCLUSIONS: We evaluated the epidemiological aspects of an outbreak of mumps in a high school. Mumps PCR might be epidemiologically useful if performed within 3 days of the onset of symptoms in suspected cases.

Molecular Epidemiology of Mumps Virus Circulated in Gwangju

The recent mumps epidemic in South Korea has generated a large amount of public concern. This study has attempted to analyze molecular epidemiological changes of mumps virus circulating in Gwangju metropolitan area, South Korea. 953 throat swab samples were collected from patients with parotitis from May 2013 to July 2014. The majority (71.5%) of these cases have occurred in middle or high school students aged from 15 to 19 years. All samples were tested using a reverse transcription polymerase chain reaction (RT-PCR) that targets the short hydrophobic (SH) gene of the virus. Mumps virus SH gene was detected in 39.2% (374/953) of samples. And 82 RT-PCR products were randomly selected for nucleotide sequencing analysis. All of these sequences were determined as genotype I by phylogenetic analysis and showed the highest nucleic acid similarity (99%) with Dg1062/Korea/98 (GenBank accession no. AY309060). These results suggested that appearance of new genotype or genetic variation at the nucleotide level could be ruled out to evaluate main cause of recent mumps outbreak in Gwangju metropolitan area.