The American Journal of Tropical Medicine and Hygiene - Current Issue

Gametocytes are sexual stage malaria parasites responsible for transmission to mosquitoes. Multiple gametocyte-producing clones may be present in natural infections, but the molecular characterization of gametocytes is challenging. Because of their magnetic properties, gametocyte enrichment can be achieved by magnetic fractionation. This increases detection sensitivity and allows specific genotyping of clones that contribute to malaria transmission. Here, we determined the percentage of Plasmodium falciparum gametocytes successfully bound to magnetic activated cell sorting (MACS) LS columns during magnetic fractionation and assessed whether columns can be reused without risking contamination or affecting column binding efficiency. Bound column fractions were quantified using multiplex quantitative reverse transcription polymerase chain reaction (qRT-PCR) for male (pfMGET) and female (CCp4) gametocytes and ring-stage asexual parasites (SBP1). To investigate cross contamination between columns, parasite strain identity was determined by merozoite surface protein 2 genotyping followed by capillary electrophoresis fragment sizing. A reproducible high percentage of gametocytes was bound to MACS LS columns with < 5% gametocytes appearing in the flow-through and < 0.6% asexual ring-stage parasites appearing in the gametocyte fraction. A high yield (> 94%) of gametocyte enrichment was achieved when columns were used up to five times with lower binding success after eight times (79%). We observed no evidence for cross contamination between columns.

Forty-five Schistosoma mansoni egg–negative/circulating cathodic antigen (CCA) low (Trace-1+) positive children in areas of very low prevalence were followed up daily for 30 days. Stool and urine specimens were collected and examined each day from each child. At the midpoint of the study, three egg-positive control persons with light intensity infection were included in the protocol. Stool samples were examined by the Kato–Katz (four slides/stool sample) technique and all S. mansoni egg–negative stools were further tested by the “miracidia hatching test” (MHT). Urine samples were examined by the point-of-care CCA assay (POC-CCA). Over 30 days, only one of 1,338 consecutive stool samples from study subjects was S. mansoni egg and MHT positive (0.07%). Egg counts fluctuated daily in stools from positive controls and S. mansoni miracidia were detected in all but two samples by the MHT. Point-of-care–circulating cathodic antigen bands were scored from G1 to G10 and then translated to standard Trace, 1+, 2+, 3+ banding patterns. In two districts, the POC-CCA assays were Trace or 1+ for both the study children and the positive controls. In the third district, the POC-CCA assays were Trace or 1+ for the study children and 1+ or 2+ for the positive control. We conclude that in areas with extremely low prevalence S. mansoni egg–negative and CCA-Trace or 1+ children are unlikely to pose substantial risks to continued transmission of schistosomiasis. In this setting, POC-CCA Trace or 1+ readings are likely to be false positives or perhaps represent low-level single-sex schistosome infections.

Mitochondrial genome analysis of Schistosoma japonicum suggests that diversity of intermediate host snails drove intra-species divergence during its expansion in Asia. We applied the knowledge of this genomic variation to study an unusual patient we recently diagnosed with schistosomiasis. The patient had not visited any schistosomiasis-endemic countries for more than 35 years and had no idea where she became infected. Unusual clinical features of this patient included the absence of egg granulomas in tissue and persistent noncalcified eggs despite multiple praziquantel (PZQ) treatments over 7 years. A digital droplet polymerase chair reaction (PCR) assay that specifically targets the schistosome 1,4 dihydronicotinamide adenine dinucleotide-1 (NADH1) dehydrogenase-1 mitochondrial gene successfully amplified parasite DNA extracted from colon biopsies. DNA sequence analysis of parasite DNA revealed that it was a Philippine strain of S. japonicum. Future molecular studies using stored DNA from patients such as this may provide new insight into why some persons do not respond well to PZQ treatment.

A 23-year-old recent emigrant from Afghanistan presented in August 2017 with severe wheezing and dyspnea that required hospital admission. Her illness was associated with marked peripheral blood eosinophilia (9,900–15,600/µL; 45.2–68%), as well as mild nausea, epigastric pain, and decreased appetite. She had lived until 3 months earlier in close proximity to cattle in her home in Kabul and did not recall eating watercress or other leafy plants associated with Fasciola hepatica transmission. Computerized tomography scanning showed bilateral ground-glass lung consolidations and multiple distinctive hypo-attenuating linear, tubuliform, and nodular liver lesions, including a large subcapsular hematoma. Numerous tests for rheumatological and malignant disorders were negative. Fasciola hepatica infestation was suspected on epidemiological, clinical, and radiographic grounds, and was confirmed by immunoblotting at the Centers for Disease Control (CDC). Multiple stool ova and parasite examinations were negative and endoscopic retrograde cholangiopancreatography did not identify trematodes. Her acute respiratory illness resolved with asthma-targeted therapies and her eosinophilia resolved with triclabendazole, which was obtained from CDC via an FDA Investigational New Drug application. Fascioliasis is uncommon in the United States, but the prolonged warfare and civil strife in Afghanistan and adjacent areas may lead to increased incidence outside the endemic region. Her case also demonstrates how hepatic imaging features of fascioliasis can be pathognomonic in clinical scenarios with eosinophilia and appropriate epidemiology and clinical features. We also highlight her relatively unusual presentation with symptoms of Loeffler-like syndrome alone.

Fascioliasis, caused by Fasciola hepatica and Fasciola gigantica infection, is a major food-borne trematodiasis in many places of the world, with the central region of Vietnam being reported as a highly endemic area. Stool examination for Fasciola eggs is not a sensitive method, and immunodiagnostic methods are preferable. We investigated various enzyme-linked immunosorbent assays (ELISAs) to evaluate their efficacy for fascioliasis diagnosis. Test sera used are primarily screened using an ELISA kit produced in Vietnam (VN kit; Viet Sinh Chemical Producing & Trading Co. Ltd., Ho Chi Minh City, Vietnam): Seropositive individuals having symptoms compatible with fascioliasis were regarded as clinically diagnosed fascioliasis cases. A commercial Fasciola IgG ELISA kit from Diagnostic Automation/Cortez Diagnostics, Inc. (USA kit; Woodland Hills, CA), which has been commonly used in Vietnam, was assessed and compared with in-house ELISA systems, including a cystatin-capture (CC) ELISA using crude worm extract (CWE) and an indirect ELISA using a synthetic peptide Ac-TPTCHWECQVGYNKTYDEE-NHMe designed from the F. gigantica cathepsin B (FgCB5) molecule. The USA kit was suitable for routine diagnosis after recalibration of the manufacturer’s suggested cutoff point. Cystatin-capture ELISA with CWE provided good sensitivity and specificity with perfect agreement to the results of the USA kit. In dot-blot ELISA, recombinant FgCB5 reacted more strongly with human antisera than did other F. gigantica antigens tested. Enzyme-linked immunosorbent assay using the synthetic peptide fragment of the FgCB5 exhibited nearly 80% sensitivity and specificity, but the test results showed low agreement with CC-ELISA or the USA kit. In conclusion, the commercially available Fasciola IgG ELISA kit from the United States and the in-house CC ELISA using CWE are suitable for practical diagnosis for fascioliasis.

Cholangiocarcinoma (CCA) is a cancer with high mortality owing to its aggressiveness and resistance to therapy. The liver flukes of the Opisthorchiidae family have been recognized as risk factors of CCA. Opisthorchis felineus infection occurs in Western Siberia, the biggest endemic area in the Russian Federation, and is associated with chronic inflammation of the bile ducts, which may be linked to severe hepatobiliary morbidity. We report two cases of confirmed CCA who had a chronic O. felineus infection. Both cases presented unspecific symptoms at the onset of the disease, a stage when severe pathological changes already had occurred. Both patients were living in endemic areas but did not receive any antihelminthic treatment. This report underlines the need for assessment of O. felineus infection as a causative factor of CCA. The results will provide further arguments for control of O. felineus in the Russian Federation.

The pig is the natural intermediate host of Taenia solium, a parasite causing significant burden of disease in both humans and pigs. Porcine cysticercosis is traditionally detected via tongue palpation and slaughterhouse meat inspection, both with limited sensitivity. Serum antibody detection has a better performance; however, it does not discriminate past from present infection. Serum antigen detection can demonstrate viable infection and gives a good estimate of parasitic load. This study evaluated a sandwich antigen-detection ELISA using monoclonal antibodies (MoAbs) 158C11 and 60H8 for the diagnosis of viable cysticercosis in pigs. Serum samples were used from 35 naturally T. solium cysticerci–infected pigs, 31 cysticercosis-negative pigs, and 22 pigs with Taenia hydatigena infection (to assess cross-reactions). Positive cysticercosis samples were subcategorized at necropsy according to parasitic burden as mild (1–10 viable cysts, n = 10), moderate (11–100 cysts, n = 5), or severe infection (more than 100 cysts, n = 20). This Ag-ELISA showed a sensitivity of 82.9% and a specificity of 96.8% when not considering cross-reactions with T. hydatigena. Hundred percentage of severely infected, 80% of moderately infected, and 50% of mildly T. solium–infected pigs tested positive. Twenty of 22 pigs with only T. hydatigena infections were positive, with 13 reaching saturating levels in the ELISA. The Ag-ELISA revealed the presence of live cysts and is, thus, a fairly reliable test to monitor experimental infection, response to treatment, and follow-up in animal models of cysticercosis. It should, however, be carefully interpreted when used in regions where T. hydatigena is endemic in pigs.

Manifestations of neurocysticercosis (NCC) are primarily due to host inflammatory responses directed at drug-damaged or naturally degenerating metacestodes (cysts) of the tapeworm Taenia solium. Prolonged high-dose corticosteroids are frequently required to control this inflammation in complicated disease, often causing severe side effects. Studies evaluating alternatives to corticosteroids are lacking. Here, we describe the clinical course of NCC in 16 patients prescribed etanercept (ETN), a tumor necrosis factor-alpha inhibitor to control inflammation resulting from anthelmintic treatment. Twelve patients with extraparenchymal NCC were administered ETN with corticosteroids (11/12, 91.7%) and/or methotrexate (9/12, 75.0%). The median age of the subgroup with extraparenchymal NCC was 40 years (range 26–57 years) and 66.7% were male. They were administered ETN for a median period of 311 days (range 31–461 days) and then followed for a median of 3.4 years (range 0.3–6.6 years). Among nine assessable patients, all improved clinically after starting ETN and one deteriorated transiently. Of the remaining three, one was lost to follow-up and two patients have improved but had not completed their assigned course. Four additional persons with recurrent perilesional edema (PE) episodes were given ETN for a median of 400.5 days (range 366–854 days) and followed post-ETN for a median of 1.7 years (range 0.2–2.4 years). All PE patients improved and two successfully tapered corticosteroids. Etanercept administration was associated with clinical improvement, stable disease, absence of recurrence, and lack of serious side effects. Etanercept appears to contribute to the control of inflammation and facilitate corticosteroid taper.

Cystic echinococcosis (CE) is a zoonosis caused by the larval stage of the tapeworm Echinococcus granulosus. In humans, the infection induces the formation of parasitic cysts mostly in the liver and lungs, but virtually any organ can be affected. CE of the bone is one of the rarest forms of the disease, yet it is also extremely debilitating for patients and hard to manage for clinicians. Unlike abdominal CE, there is currently no expert consensus on the management of bone CE. In this study, we conducted a survey of the clinical records of seven European referral centers for the management of patients with CE and retrieved data on the clinical management of 32 patients with a diagnosis of bone CE. Our survey confirmed that the patients endured chronic debilitating disease with a high rate of complications (84%). We also found that diagnostic approaches were highly heterogeneous. Surgery was extensively used to treat these patients, as well as albendazole, occasionally combined with praziquantel or nitaxozanide. Treatment was curative only for two patients, with one requiring amputation of the involved bone. Our survey highlights the need to conduct systematic studies on bone CE, both retrospectively and prospectively.

Acute undifferentiated febrile illness (AUFI) has been a diagnostic dilemma in the tropics. Without accurate point-of-care tests, information on local pathogens and clinical parameters is essential for presumptive diagnosis. A prospective hospital-based study was conducted at the Bangkok Hospital for Tropical Diseases from 2013 to 2015 to determine common etiologies of AUFI. A total of 397 adult AUFI cases, excluding malaria by blood smear, were enrolled. Rapid diagnostic tests for tropical infections were performed on admission, and acute and convalescent samples were tested to confirm the diagnosis. Etiologies could be identified in 271 (68.3%) cases. Dengue was the most common cause, with 157 cases (39.6%), followed by murine typhus (20 cases; 5.0%), leptospirosis (16 cases; 4.0%), influenza (14 cases; 3.5%), and bacteremia (six cases; 1.5%). Concurrent infection by at least two pathogens was reported in 37 cases (9.3%). Furthermore, characteristics of dengue and bacterial infections (including leptospirosis and rickettsioses) were compared to facilitate dengue triage, initiate early antibiotic treatment, and minimize unnecessary use of antibiotics. In conclusion, dengue was the most common pathogen for AUFI in urban Thailand. However, murine typhus and leptospirosis were not uncommon. Empirical antibiotic treatment using doxycycline or azithromycin might be more appropriate, but cost–benefit studies are required. Physicians should recognize common causes of AUFI in their localities and use clinical and laboratory clues for provisional diagnosis to provide appropriate treatment while awaiting laboratory confirmation.

We assessed carotid intima-media thickness (cIMT) and arterial stiffness in 28 children and adolescents with previous dengue hemorrhagic fever (DHF) (mean interval between DHF and cardiovascular assessment, 8.4 years), and 34 controls in a low-resource setting. Participants with previous DHF had an adjusted increased cIMT of 42.6 µm (95% confidence interval [CI]: 10.0–75.3, P = 0.01), and 61.7 µm (95% CI: 21.5–102.0, P < 0.01) in a subgroup analysis on dengue shock syndrome. There were no differences in arterial stiffness. In this first exploratory study, children and adolescents with a history of DHF had an increased cIMT, which may be modulated by dengue severity.

Scrub typhus (ST, Orientia tsutsugamushi), murine typhus (MT, Rickettsia typhi), and dengue virus (DENV) are important causes of childhood morbidity in Cambodia. This prospective, cross-sectional seroprevalence study determined the proportion of Cambodian children infected by these pathogens and the ages at which initial infection is likely to occur. A total of 993 patient serum samples were tested for MT- and ST-specific IgG, and 837 samples tested for DENV-specific IgG. Overall, ST, MT, and DENV seroprevalence was high, estimated at 4.2%, 5.3%, and 50.7%, respectively. Scrub typhus and MT seropositivity peaked in children aged 8–11 and 12–15 years, respectively, suggesting initial infection occurs in these ages. Dengue virus seroprevalence steadily increased with age, indicating constant DENV exposure. The results of this study suggest that in Cambodian children presenting with undifferentiated febrile illness, dengue should be considered high in the list of differential diagnoses, and empirical anti-rickettsial antimicrobial therapy may be more indicated in 8- to 15-year-olds.

Zika virus (ZIKV) has been presumed to be endemic in Southeast Asia (SEA), with a low rate of human infections. Although the first ZIKV evidence was obtained in the 1950s through serosurveys, the first laboratory-confirmed case was only detected in 2010 in Cambodia. The epidemiology of ZIKV in SEA remains uncertain because of the scarcity of available data. From 2016, subsequent to the large outbreaks in the Pacific and Latin America, several Asian countries started reporting increasing numbers of confirmed ZIKV patients, but no global epidemiological assessment is available to date. Here, with the aim of providing information on ZIKV circulation and population immunity, we conducted a seroprevalence study among blood donors in Vientiane, Laos. Sera from 359 asymptomatic consenting adult donors in 2003–2004 and 687 in 2015 were screened for anti-ZIKV IgG using NS1 ELISA assay (Euroimmun, Luebeck, Germany). Positive and equivocal samples were confirmed for anti-ZIKV–neutralizing antibodies by virus neutralization tests. Our findings suggest that ZIKV has been circulating in Vientiane over at least the last decade. Zika virus seroprevalence observed in the studied blood donors was low, 4.5% in 2003–2004 with an increase in 2015 to 9.9% (P = 0.002), possibly reflecting the increase of ZIKV incident cases reported over this period. We did not observe any significant difference in seroprevalence according to gender. With a low herd immunity in the Vientiane population, ZIKV represents a risk for future large-scale outbreaks. Implementation of a nationwide ZIKV surveillance network and epidemiological studies throughout the country is needed.

This study was conducted to find the burden of dengue virus (DENV) and Japanese encephalitis virus (JEV) among children under the age of 13, who presented with acute encephalitis syndrome at Mandalay Children Hospital in Myanmar in 2013. Molecular and serological investigations were performed on 123 cerebrospinal fluid (CSF) samples collected from these patients. By neutralization tests and/or virus isolation, four (3.3%) JEV- and one DENV-associated encephalitis cases (0.8%) were confirmed. Antibody titer against JEV Genotype 3 was the highest among the laboratory-confirmed JEV cases. One strain of DENV-1 with Genotype 1 was isolated from the CSF sample of the dengue encephalitis patient; this was similar to the virus circulating in the study area and neighboring countries. This study shows that flaviviruses are important pathogens causing encephalitis in Myanmar. Active disease surveillance, vector control, and vaccination programs should be enforced to reduce the morbidity and mortality caused by flavivirus encephalitis.

The largest epidemic of Lassa fever in recent history occurred in Nigeria in 2018. We assessed the potential for cases of Lassa fever originating in Nigeria to arrive at international destinations via air travel using a probabilistic model. We estimated no exported cases in 62% of 1,000 model simulations. In 30% of simulations, a single exported case was projected. Greater than 40% of outbound travelers from Nigeria arrived in the United States, the United Kingdom, and Ghana, placing these countries at greatest risk for receiving an exported case. There was a wide range in the capacity of highly connected countries to respond to infectious disease threats, as measured by the Infectious Disease Vulnerability Index. Although we quantified a low probability of case exportation during this outbreak, countries with the greatest connectivity to Nigeria should be alert to the potential risks of Lassa fever importation and be prepared to manage infected individuals.

This study aimed to assess baseline knowledge, attitudes, and practices about severe fever with thrombocytopenia syndrome (SFTS) and identify the target population for health education programs in endemic areas of Anhui, China. This cross-sectional study was conducted from May to June 2017. Of 752 participants, 383 (50.9%) were from Nanqiao District, 397 (52.8%) were female, and 430 (57.2%) were farmers; 37.4% had heard about SFTS, but knowledge of symptoms and signs including fever (34.2%), leukopenia (8.0%), and thrombocytopenia (10.1%) was low. Only 12.1% knew that SFTS virus is transmitted by ticks, 9.4% realized that the blood and body fluid of SFTS are infectious, and only 38.2% thought that the tick should be paralyzed using medical alcohol or iodine. Meanwhile, 61.3% wore long-sleeve clothes, whereas 20.2% used repellents. Median scores for knowledge, attitudes, and practices, and the total score were 4.0, 6.0, 5.0, and 16.0, respectively. Knowledge was influenced by region (OR = 0.632, 95% CI: 0.399–0.999), education (OR = 0.516, 95% CI: 0.434–0.612), gender (OR = 1.865, 95% CI: 1.165–2.987), and age (OR = 3.406, 95% CI: 2.345–4.947). Education was a predictor of lack of appreciation of infection risk (OR = 0.519, 95% CI: 0.449–0.599) and practice (OR = 0.481, 95% CI: 0.396–0.584). Our findings indicate that SFTS-related health education programs are required for females; participants from Qianshan Prefecture; those with an occupation of farmer, retiree, houseworker, or unemployed; elderly participants; and those with low education. Large-scale sustainable health education programs focusing on the target populations are urgently needed in endemic areas.

In March 2016, an outbreak of Rift Valley fever (RVF) was identified in Kabale district, southwestern Uganda. A comprehensive outbreak investigation was initiated, including human, livestock, and mosquito vector investigations. Overall, four cases of acute, nonfatal human disease were identified, three by RVF virus (RVFV) reverse transcriptase polymerase chain reaction (RT-PCR), and one by IgM and IgG serology. Investigations of cattle, sheep, and goat samples from homes and villages of confirmed and probable RVF cases and the Kabale central abattoir found that eight of 83 (10%) animals were positive for RVFV by IgG serology; one goat from the home of a confirmed case tested positive by RT-PCR. Whole genome sequencing from three clinical specimens was performed and phylogenetic analysis inferred the relatedness of 2016 RVFV with the 2006–2007 Kenya-2 clade, suggesting previous introduction of RVFV into southwestern Uganda. An entomological survey identified three of 298 pools (1%) of Aedes and Coquillettidia species that were RVFV positive by RT-PCR. This was the first identification of RVFV in Uganda in 48 years and the 10th independent viral hemorrhagic fever outbreak to be confirmed in Uganda since 2010.

The contribution of respiratory viruses to acute febrile illness (AFI) burden is poorly characterized. We describe the prevalence, seasonality, and clinical features of respiratory viral infection among AFI admissions in Sri Lanka. We enrolled AFI patients ≥ 1 year of age admitted to a tertiary care hospital in southern Sri Lanka, June 2012–October 2014. We collected epidemiologic/clinical data and a nasal or nasopharyngeal sample that was tested using polymerase chain reaction (Luminex NxTAG, Austin, TX). We determined associations between weather data and respiratory viral activity using the Spearman correlation and assessed respiratory virus seasonality using a Program for Appropriate Technology definition. Bivariable and multivariable regression analyses were conducted to identify features associated with respiratory virus detection. Among 964 patients, median age was 26.2 years (interquartile range 14.6–39.9) and 646 (67.0%) were male. One-fifth (203, 21.1%) had respiratory virus detected: 13.9% influenza, 1.4% human enterovirus/rhinovirus, 1.4% parainfluenza virus, 1.1% respiratory syncytial virus, and 1.1% human metapneumovirus. Patients with respiratory virus identified were younger (median 9.8 versus 27.7 years, P < 0.001) and more likely to have respiratory signs and symptoms. Influenza A and respiratory viral activity peaked in February–June each year. Maximum daily temperature was associated with influenza and respiratory viral activity (P = 0.03 each). Patients with respiratory virus were as likely as others to be prescribed antibiotics (55.2% versus 52.6%, P = 0.51), and none reported prior influenza vaccination. Respiratory viral infection was a common cause of AFI. Improved access to vaccines and respiratory diagnostics may help reduce disease burden and inappropriate antibiotic use.

In rural agricultural communities in Africa, particularly those with a single annual harvest, the preharvest period has been associated with increased food insecurity. We estimated the association between seasonal food insecurity and childhood malnutrition in Haydom, Tanzania. Children enrolled in a birth cohort study were followed twice weekly to document food intake and monthly for anthropometry until the age of 2 years. Household food insecurity was reported by caregivers every 6 months. We modeled the seasonality of food insecurity and food consumption, and estimated the impact of birth season on enrollment weight and subsequent malnutrition. Finally, we described the seasonality of admissions for acute malnutrition at a local referral hospital (Haydom Lutheran Hospital) from 2010 to 2015. Food insecurity was highly seasonal, with a peak from December to February. Children born during these 3 months had an average 0.35 z-score (95% CI: 0.12, 0.58) lower enrollment weight than children born in other months. In addition, weight-for-length z-scores measured in these months were on average 0.15 z-scores lower (95% CI: 0.10, 0.20) than that in other months, adjusting for enrollment weight and seasonal infectious diseases, and this disparity was sustained up to the age of 2 years. Correspondingly, the number of admissions with acute malnutrition at the local hospital was highest at this time, with twice as many cases in December–February compared with June–August. We identified acute and chronic malnutrition associated with seasonal food insecurity and intake. Targeting of prenatal care and child-feeding interventions during high food insecurity months may help reduce child malnutrition.

Bacillus pumilus has rarely been reported as a cause of human infections. We report a case of a B. pumilus causing food poisoning in an adult male. A 51-year-old Japanese man complained of severe abdominal cramps, fever with chills, diarrhea, dizziness, and loss of appetite after eating reheated rice with stewed minced meat purchased from a Kenyan restaurant. Bacillus pumilus was isolated from blood culture and was identified using a biochemical test and 16S rRNA gene sequencing analysis. The patient was treated with probiotics and ciprofloxacin and recovered after 3 days. To our knowledge, this is the first report describing the potential role of B. pumilus as a foodborne pathogen in Kenya and highlights the importance of good hygiene and food preparation practices.