Evaluation of an intragastric challenge model for Shigella dysenteriae 1 in rhesus monkeys (Macaca mulatta) for the pre‐clinical assessment of Shigella vaccine formulations

Shigellosis is a worldwide disease, characterized by abdominal pain, fever, vomiting, and the passage of blood‐ and mucus‐streaked stools. Rhesus monkeys and other primates are the only animals that are naturally susceptible to shigellosis. A suitable animal model is required for the pre‐clinical evaluation of vaccines candidates. In this study, the minimal dose of Shigella dysenteriae1 1617 strain required to produce dysentery in four of five (80% attack rate) monkeys using an escalating dose range for three groups [2 × 10⁸, 2 × 10⁹ and 2 × 10¹⁰ colony forming unit (CFU)] was determined. In addition, the monkeys were re‐infected. The identified optimal challenge dose was 2 × 10⁹ CFU; this dose elicited 60% protection in monkeys when they were re‐challenged with a one log higher dose (2 × 10¹⁰ CFU). The challenge dose, 2 × 10¹⁰ CFU, produced severe dysentery in all monkeys, with one monkey dying within 24 h, elicited 100% protection when re‐challenged with the same dose. All monkeys exhibited immune responses. This study concludes that the rhesus monkey model closely mimics the disease and immune response seen in humans and is a suitable animal model for the pre‐clinical evaluation of Shigella vaccine candidates. Prior infection with the 1617 strain can protect monkeys against subsequent re‐challenges with homologous strains.     

Immune responses to Campylobacter (C. jejuni or C. coli) infections: a two‐year study of US forces deployed to Thailand

Campylobacter spp. is a leading cause of diarrheal disease among US troops deployed to Thailand for exercise. We investigated the importance of immunological analysis and immune responses against Campylobacter infection in US troops deployed to Thailand. Blood and fecal samples were collected from volunteered soldiers with diarrhea and from healthy controls. Stool culture was performed to identify the pathogens. Campylobacter‐specific antibodies, antibody secreting cells and cytokines were measured. Several bacterial protein fragments in the outer membrane extract of Campylobacter spp., were identified by an immunoblot analysis with plasma and fecal antibodies. Among all of the diarrheal cases, 35% were Campylobacter‐positive. Based on antibody titers in plasma and in fecal extract and antibody secreting cells: 6% of healthy controls, 32% of the Campylobacter culture‐negative diarrheal cases, and 85% of the Campylobacter culture‐positive diarrheal cases were positive for Campylobacter. Our results indicate that the measurement of Campylobacter‐specific antibodies in plasma and fecal extract samples is a good marker of exposure to Campylobacter, and this test may be a useful diagnostic tool for seroepidemiological studies. Elicited antibodies against several bacterial outer membrane protein fragments suggest that these protein fragments are vital in providing protective immunity against Campylobacter.     

Epidemiologic study of Kawasaki disease and cases resistant to IVIG therapy in Thailand

The incidence of Kawasaki disease (KD) in Thailand has never been studied before. We reviewed the data from the National Registry of Thai Children who had KD between 1998-2002 to evaluate the incidence of KD and cases resistant to treatment with intravenous immunoglobulin (IVIG). Resistance to IVIG was defined as remaining febrile at least 48 hours after initial IVIG therapy. There were 710 KD patients in the registry. The incidence of KD was from 2.14 to 3.43 cases per 100,000 children aged 0-5 years. During the acute phase 15.6% of 435 patients were considered as resistant cases. Resistant cases of KD in Thai children are quite common (15.6%) even after IVIG treatment. We found that patients who had high white blood cell counts (> 16,500 cells/mm3) had a higher likelihood of being resistant.     

Dengue myocarditis

We report a 13-year-old boy who developed bradycardia and hypotension a day after recovery from dengue hemorrhagic fever. His electrocardiogram, during the bradycardia, showed a junctional rhythm with a rate of 50 beats/minute. This is the first reported case of sinus node dysfunction following dengue infection.     

Hepatosplanchnic circulatory dysfunction in acute hepatic infection: the case of dengue hemorrhagic fever

The mechanism of shock in patients with dengue hemorrhagic fever (DHF) has not yet been fully understood. In this study, we investigated the possibility of splanchnic venous pooling as a contributor for circulatory dysfunction in these patients. Ultrasonographic studies of portal vein and inferior vena cava were done in 45 patients with serologically or PCR-confirmed diagnosis of dengue virus infection. The size of portal vein and inferior vena cava, mean blood flow velocity in the right portal vein, and modified portal vein congestion index were compared between patients with dengue fever (DF, n = 20), DHF without shock (n = 14), and dengue shock syndrome (DSS, n = 11) during the toxic stage, convalescent stage, and at follow-up. The portal vein was significantly more dilated in patients with shock (DSS) than DHF without shock and than DF during the toxic and convalescent stages (P < 0.05), but not at follow-up. The change in the size of inferior vena cava followed the opposite trend (not statistically significant). Portal vein blood flow velocity was lower and congestion index was higher in shock cases (DSS) than DHF without shock and than DF at toxic and convalescent stages (P < 0.01). The differences disappeared at follow-up. Hepatosplanchnic venous pooling and/or dysfunction occur and correlate with the severity of circulatory derangement and shock in patients with DHF. The cause(s) and significance of hepatosplanchnic circulatory dysfunction in DHF and possibly other viral hepatic diseases deserve further study.     

The Presence of Epsilon Waves in All Precordial Leads (V1–V6) in a 13‐Year‐Old Boy with Arrhythmogenic Right Ventricular Dysplasia (ARVD)

Electrocardiographic feature is included in the diagnostic criteria for arrthythmogenic right ventricular dysplasia (ARVD) based on the Revised Task Force criteria 2010. The epsilon wave, which reflects delayed conduction of the right ventricle, is considered to be one of the major diagnostic criteria. We reported a 13‐year‐old Thai boy with ARVD who presented with ventricular tachycardia. The presence of epsilon wave in all precordial leads (V₁–V₆) was observed in standard 12‐lead EKG. Extensive scarring of the right and left ventricle was seen on cardiac MRI. The extensive Epsilon wave found in this patient may reflect the extensive ventricular wall involvemen.     

Emergence and properties of fluoroquinolone resistant Salmonella enterica serovar Typhi strains isolated from Nepal in 2002 and 2003

A total of 171 Salmonella enterica serovar Typhi strains isolated from Nepal, mostly from patients with typhoid fever in 2002-2003, were tested for antimicrobial susceptibility by disk diffusion assay. Selected S. enterica serovar Typhi isolates were tested for MICs by E-test for ceftriaxone, ciprofloxacin and ofloxacin. Mutations of DNA gyrase gyrA and gyrB and topoisomerase IV parC and parE were identified by sequencing of PCR amplicons. By disk diffusion assay, 75/171 S. enterica serovar Typhi isolates were resistant to nalidixic acid, ampicillin, choramphenicol, streptomycin, tetracycline, sulfisoxazole, and trimethroprim/sulfamethoxazoles. Multiple drug resistance to the 7 antimicrobials was most predominant among S. enterica serovar Typhi isolates in this study. Resistance to nalidixic acid was detected in 76/111 and 56/60 of total isolates collected in 2002 and 2003, respectively. Nalidixic acid-resistant isolates in 2002 and 2003 showed MIC range for ciprofloxacin of 0.125-0.250 mg/l. Nalidixic acid-resistant isolates contained point mutations in gyrA and parC but not gyrB and parE. The gyrA mutation of nalidixic acid-resistant isolates obtained in 2002 and 2003 had amino acid substitution at position 83 of Serine-->Tyrosine and Serine-->Phenylalanine, respectively. Two different mutations of gyrA were detected among nalidixic acid-resistant isolates. Thus it is necessary to monitor mutation in DNA topoisomerase associated with increases in quinolones resistance.