The American Journal of Tropical Medicine and Hygiene - Volume 81, Issue 3, 2009

Dengue is a mosquito-borne viral disease that affects 40% of the world’s population. Nearly four million U.S. citizens live in dengue-endemic areas; the most affected population resides in Puerto Rico. Data from a dengue surveillance system were used to describe all suspected cases reported in Puerto Rico in 2007. Rates of infection per 10,000 residents were calculated by age, sex, and residence. Rates and clinical outcomes were compared with those from outbreaks in 1994–1995 and 1998. In 2007, 10,508 suspected cases were reported; 52.5% persons were hospitalized, 31.8% reported hemorrhage, 2.2% had dengue hemorrhage fever, and 44 died. A total of 3,293 (33.0%) of processed specimens were laboratory positive for dengue virus (DENV); DENV-3 (1,342, 61.7%) and DENV-2 (677, 31.1%) were detected most often. The overall incidence of laboratory-positive dengue was 8.6 infections per 10,000 population. Rates were highest among persons 10–14 years of age (19.0), followed by persons 15–19 years of age (17.9) and infants (10.9). Higher rates of hospitalization and hemorrhage were reported in 2007 than in 1994–1995 or 1998. United States citizens residing in Puerto Rico are at risk of acquiring dengue. Data suggest that the severity is worsening, and persons 10–19 years of age and infants continue to be most affected.

We conducted a study at four hospitals from June 2003 to July 2005 to investigate the etiologies of bacterial meningitis in Bangladesh. A total of 2,609 patients met the clinical case definition, and 766 had cerebrospinal fluid tested by at least one of the following methods: latex agglutination, 16S rRNA gene sequencing, or real-time polymerase chain reaction for Neisseria meningitidis A and C, Streptococcus pneumoniae, and Haemophilus influenzae type b (Hib); culture results were noted from patient records. In total, 189 patients (24%) of those tested, representing all age groups, were diagnosed with bacterial meningitis; 136 (18%) had meningococcal, 23 (3%) had pneumococcal, and 25 (3%) had Hib infection. Twenty percent of patients with Hib meningitis (5/25) were > 15 years old. Case-fatality ratios were 10% for N. meningitidis, 22% for S. pneumoniae, and 24% for Hib. Bacterial meningitis from vaccine-preventable pathogens causes significant morbidity and mortality in Bangladesh in adults and children.

Scrub typhus is a potentially fatal infectious disease. However, to this date, no epidemiologic study on mortality of complicated scrub typhus has been reported. We reviewed the clinical records of 302 patients with diagnosis of scrub typhus who were admitted to our institute between January 2000 and December 2006. In total, 297 patients with scrub typhus were analyzed and the mortality rate of this study group was 6.1%. Multivariate logistic regression analysis revealed absence of eschar, event of intensive care unit admission and higher APACHE II score were independent predictive variables. Identification of these risk factors leading to fatal outcome may help physicians to start early intensive management of complicated scrub typhus.

Long-term planning to prevent malaria epidemics requires in-depth understanding of immunity to Plasmodium falciparum in areas of unstable transmission. Cytokine responses to immunodominant epitope peptides from liver stage antigen 1 (LSA-1) and thrombospondin-related adhesive protein (TRAP) were evaluated over a nine-month interval in adults and children in Kenya from a malaria epidemic–prone highland area after several years of low transmission. The proportion and magnitude of interferon-gamma ELISPOT responses and the proportion of interleukin-10 responders to LSA-1 and TRAP peptides tended to be higher in adults than children. Frequencies of interferon-gamma responders to these peptides were similar at the two time points, but responses were not consistently generated by the same persons. These results suggest that T cell memory to pre-erythrocytic stage malaria antigens is maintained but may be unavailable for consistent detection in peripheral blood, and that these antigens induce both pro-inflammatory and anti-inflammatory cytokine responses in this population.

We evaluated the cost-effectiveness of distributing insecticide-treated bed nets (ITNs) for malaria prevention at antenatal clinics in Kinshasa, Democratic Republic of the Congo. A decision tree model was used to estimate costs, outcomes, and incremental cost-effectiveness for 17,893 pregnant women attending 28 antenatal clinics who received long-lasting ITNs free of charge. Costs including purchase, transportation, storage, and distribution of ITNs were derived from program records. The ITN efficacy and other parameters were derived from peer-reviewed literature. Outcomes modeled included low birth weight (LBW) deliveries, infant deaths averted, life-years saved (LYs), and disability-adjusted life-years (DALYs) averted. Deterministic and probabilistic sensitivity analyses were conducted. For the 17,893 women in our program, ITN distribution would be expected to avert 587 LBW deliveries and 414 infant deaths. The incremental cost-effectiveness was US $17.22 per DALY averted (95% confidence interval [CI] = US $8.54–$30.90), US $15.70 per LY saved (95% CI = US $7.65–$27.68), and US $411.13 per infant death averted (95% CI = US $353.95–$1,085.89). If resources were constrained, the greatest benefit would be among women in their first through fourth pregnancies. Thus, ITN distribution is a cost-effective addition to antenatal services.

The spatio-temporal distribution pattern of malaria in Yunnan Province, China was studied using a geographic information system technique. Both descriptive and temporal scan statistics revealed seasonal fluctuation in malaria incidences in Yunnan Province with only one peak during 1995–2000, and two apparent peaks from 2001 to 2005. Spatial autocorrelation analysis indicated that malaria incidence was not randomly distributed in the province. Further analysis using spatial scan statistics discovered that the high risk areas were mainly clustered at the bordering areas with Myanmar and Laos, and in Yuanjiang River Basin. There were obvious associations between Plasmodium vivax and Plasmodoium falciparum malaria incidences and climatic factors with a clear 1-month lagged effect, especially in cluster areas. All these could provide information on where and when malaria prevention and control measures would be applied. These findings imply that countermeasures should target high risk areas at suitable times, when climatic factors facilitate the transmission of malaria.

The major malaria vector Anopheles funestus belongs to a group of morphologically similar species that are commonly distinguished from one another through the use of chromosomal and molecular techniques. Indoor resting collections of mosquitoes from Malawi were initially identified as An. funestus by morphology, but failed to have this confirmed by the species-specific polymerase chain reaction assay. Sequence analysis of the internal transcribed spacer region 2 identified variations within the An. funestus-specific primer binding site and showed a sequence variation of 4.5% compared with An. funestus. Domain 3 analysis showed sequence variation of 1.5% from An. funestus. Cytogenetic analysis of the polytene chromosome banding arrangements showed that the specimens were homosequential with An. funestus, with fixed inverted arrangements of the 3a, 3b, and 5a inversions commonly polymorphic in An. funestus. The chromosomes of hybrid females showed levels of asynapsis typical of inter-species crosses. These molecular and cytogenetic observations support the conclusion that this Malawi population is a new species and it has provisionally been named An. funestus-like.

We previously developed a real-time polymerase chain reaction (PCR) assay for detection of the four Plasmodium species that infect humans. Recent studies have shown that natural transmission of the simian parasite Plasmodium knowlesi to humans occurs frequently in Southeast Asia. We have expanded our PCR assay to include detection of P. knowlesi.

Does scaling up of malaria control by combining indoor residual spraying (IRS) and long-lasting insecticidal nets (LLIN) enhance protection to populations? Results from a literature search and from recent household surveys in Bioko, Equatorial Guinea, and Zambezia, Mozambique are presented. Five out of eight previous studies reported a reduced risk of infection in those protected by both interventions compared with one intervention alone. Surveys in Bioko and Zambezia showed strong evidence of a protective effect of IRS combined with nets relative to IRS alone (odds ratio [OR] = 0.71, 95% confidence interval [CI] = 0.59–0.86 for Bioko, and OR = 0.63, 95% CI = 0.50–0.79, for Zambezia). The effect of both interventions combined, compared with those who had neither, was OR = 0.46, (95% CI = 0.76–0.81) in Bioko and 0.34 (95% CI = 0.21–0.56) in Zambezia. Although the effects of confounding cannot be excluded, these results provide encouragement that the additional resources for combining IRS and LLIN are justified.

To study drug resistance in Bannu district, a malaria-endemic area in Pakistan, molecular-based analyses were undertaken. In Plasmodium vivax, antifolate resistance mutations were detected in pvdhfr gene codons 57, 58, and 117, with a 117N mutation frequency of 93.5%. All P. falciparum isolates exhibited double 59R + 108N mutations in pfdhfr, whereas the triple mutant 59R + 108N + 437G haplotype was found in 31.8% isolates. Furthermore, all (100%) P. falciparum isolates exhibited the key chloroquine resistance mutation, pfcrt 76T, which is also associated with resistance to amodiaquine. Additionally, pfmdr1 86Y and D1042Y mutations were, respectively, detected in 32% and 9% isolates. These results indicate an emerging multi-drug resistance problem in P. vivax and P. falciparum malaria parasites in Pakistan.

Of 1,004 positive lots of mosquitoes fed on 229 humans infected with Plasmodium falciparum, 46.2% had 1–10 oocysts/(+)gut, 21.2% had 10–30 oocysts/(+)gut, 22.2% had 30–100 oocysts/(+)gut, and 10.4% had > 100 oocysts/(+) gut. The highest levels of infection occurred between 6 and 15 days after the peak in the asexual parasite count. Of 2,281 lots of Anopheles freeborni mosquitoes fed on splenectomized Aotus monkeys infected with the Santa Lucia strain of P. falciparum, 1,191 were infected (52.2%). The highest intensity infections ranged from 2.78 oocysts per positive gut in mosquitoes fed on Aotus vociferans to 6.08 oocysts per positive gut for those fed on A. lemurinus griseimembra to 10.4 oocysts per positive gut for those fed on A. nancymaae. The pattern of infection for mosquitoes fed on splenectomized Aotus monkeys was similar to that obtained by feeding on humans, but the intensity, based on oocyst/(+)gut, was much lower.

The role that different age classes of birds play in the amplification of arthropod-borne viruses depends critically on the feeding choices made by mosquitoes. To determine if mosquitoes are more likely to feed on nestling or adult birds, we introduced Culex quinquefasciatus mosquitoes into eastern bluebird Sialia sialis nest boxes after dark and recaptured them the following morning. We collected blood from each nestling and brooding mother and used molecular genotyping methods to trace the blood meals of individual mosquitoes to the individual bird fed upon (mothers or chicks). Of the 14 recaptured mosquitoes, whose blood meals were identified to the species level, 10 fed only on nestlings, three fed only on an adult, and one mosquito fed on an adult and two nestlings. These preliminary data show that microsatellite genotyping may be used to answer important questions concerning mosquito feeding patterns on different age classes of birds.

Giardia intestinalis is comprised of two major genotypes, A and B, which may vary in their propensity to cause disease. We tested for the presence of these two genotypes in stool samples from patients with gastrointestinal symptoms in Nepal. A total of 1,096 clinical specimens were screened by microscopy, and 45 samples with G. intestinalis were identified. Giardia infection was confirmed in 35 of 45 samples by a Giardia specific real-time polymerase chain reaction (PCR) assay. Genotyping of the Giardia PCR product by restriction fragment length polymorphism indicated that 74% (26 of 35) were assemblage B, 20% (7 of 35) were assemblage A, and 6% (2 of 35) were mixed assemblages.

In this study, we report the imaging findings in two Japanese monkeys (Macaca fuscata) diagnosed with alveolar echinococcosis. Both monkeys were treated with albendazole for 10 years, without surgery. Radiography, computed tomography, and contrast-enhanced ultrasonography were performed under general anesthesia. This is the first report on contrast-enhanced ultrasonographic imaging for alveolar echinococcosis wherein perflubutane was used as the contrast medium. The findings of the imaging analyses were similar to those reported for alveolar echinococcosis in humans, such as snowflake sign and worm-eaten sign. In addition, the serology correlated well with the imaging data in these two monkeys. Therefore, we propose that the imaging findings of alveolar echinococcosis in nonhuman primates may be used to accumulate data on this condition in human alveolar echinococcosis.