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Biomedical subjects

D Strickman

Publications and source records attributed to D Strickman.

At least 19 recordsLinked to original sources
PubMed2001

A live attenuated recombinant dengue-4 virus vaccine candidate with restricted capacity for dissemination in mosquitoes and lack of transmission from vaccinees to mosquitoes.

2Adelta30 is a live dengue-4 virus vaccine candidate with a 30-nucleotide deletion in its 3'-untranslated region. To assess the transmissibility of 2Adelta30 by mosquitoes, we compared its in vivo replication in mosquitoes with that of its wild type DEN-4 parent. Both the vaccine candidate and wild type virus were equally able to infect the mosquito Toxorhynchites splendens after intrathoracic inoculation. Relative to its wild type parent, 2Adelta30 was slightly restricted in its ability to infect the midgut of Aedes aegypti mosquitoes fed on an artificial blood meal and was even more restricted in its ability to disseminate from the midgut to the salivary glands. Thus, the 30-nucleotide deletion rendered the vaccine candidate more sensitive than its wild type parent to the mosquito midgut escape barrier. Most significantly, 2Adelta30 was not transmitted to 352 Ae. albopictus mosquitoes fed on 10 vaccinees, all of whom were infected with the vaccine candidate.

Adult↗
PubMed2001

Soldier acceptability of a camouflage face paint combined with DEET insect repellent.

Under operational conditions, current doctrine requires separate application of the standard military insect repellent and camouflage face paint. Working with an industrial partner, Amon Re, Inc., we developed a combined camouflage face paint and insect repellent that offers excellent protection from arthropod disease vectors. We undertook a study to determine whether the new product was acceptable to soldiers under field conditions. A new formulation of camouflage face paint containing the insect repellent N,N-diethyl-3-methyl-benzamide (DEET) was tested for user acceptability during a joint-service, multinational, military field training exercise (Operation Cobra Gold 1999) in Thailand. Soldiers testing the camouflage face paint were members of one of three companies (A, B, and C) of 1st Battalion, 21st Infantry Regiment, 25th Infantry Division. Soldiers in A company (N = 98) received standard military camouflage face paint and the U.S. military's Extended Duration Topical Insect and Arthropod Repellent containing 33% DEET, soldiers in B company (N = 75) received a new formulation of camouflage face paint without DEET, and soldiers in C company (N = 88) received the new formulation of camouflage face paint containing 30% DEET. Every soldier who volunteered to participate completed the study and submitted responses to the questionnaire. The different treatments were evaluated while soldiers spent 4 days conducting simulated combat exercises in a hot, tropical environment in central Thailand. Soldiers were provided the test materials, given a briefing on the study, and completed an initial questionnaire on May 19, 1999. Soldiers completed a final questionnaire after they returned from the training exercise on May 24, 1999. Results of the study indicated that soldiers found the new formulation of 30% DEET camouflage face paint easier to apply (88% of respondents) and remove (77%) than the current standard issue camouflage face paint. Soldiers liked the new 30% DEET camouflage face paint formulation better (61%) and were more likely to recommend it (67%) than the old camouflage face paint formulation. Although the addition of DEET to the camouflage face paint occasionally caused minor irritation after application for a short period (less than 15 minutes), the new camouflage face paint formulation with 30% DEET was evaluated most often (72%) as either good or excellent. The new 30% DEET camouflage face paint formulation offers significant operational advantages: protection from disease-transmitting arthropods, elimination of the need to carry separate insect repellent and camouflage face paint, and reduction in the time required to apply repellent and camouflage face paint separately.

Adolescent↗
PubMed2000

Doxycycline and rifampicin for mild scrub-typhus infections in northern Thailand: a randomised trial.

BACKGROUND: Some strains of scrub typhus in northern Thailand are poorly responsive to standard antirickettsial drugs. We therefore did a masked, randomised trial to compare rifampicin with standard doxycycline therapy for patients with scrub typhus. METHODS: Adult patients with strictly defined, mild scrub typhus were initially randomly assigned 1 week of daily oral treatment with 200 mg doxycycline (n=40), 600 mg rifampicin (n=38), or doxycycline with rifampicin (n=11). During the first year of treatment, the combined regimen was withdrawn because of lack of efficacy and the regimen was replaced with 900 mg rifampicin (n=37). Treatment outcome was assessed by fever clearance time (the time for oral temperature to fall below 37.3 degrees C). FINDINGS: About 12,800 fever patients were screened during the 3-year study to recruit 126 patients with confirmed scrub typhus and no other infection, of whom 86 completed therapy. Eight individuals received the combined regimen that was discontinued after 1 year. The median duration of pyrexia was significantly shorter (p=0.01) in the 24 patients treated with 900 mg daily rifampicin (fever clearance time 22.5 h) and in the 26 patients who received 600 mg rifampicin (fever clearance time 27.5 h) than in the 28 patients given doxycycline monotherapy (fever clearance time 52 h). Fever resolved in a significantly higher proportion of patients within 48 h of starting rifampicin (900 mg=79% [19 of 24], 600 mg=77% [20 of 26]) than in patients treated with doxycycline (46% [13 of 28]; p=0.02). Severe gastrointestinal events warranted exclusion of two patients on doxycyline. There were two relapses after doxycycline therapy, but none after rifampicin therapy. INTERPRETATION: Rifampicin is more effective than doxycycline against scrub-typhus infections acquired in northern Thailand, where strains with reduced susceptibility to antibiotics can occur.

Adolescent↗
PubMed2000

Longitudinal studies of Aedes aegypti (Diptera: Culicidae) in Thailand and Puerto Rico: population dynamics.

Aspiration collections of adult Aedes aegypti (L.) were made weekly from inside and outside of houses for 3 yr in a rural Thai village (n = 9,637 females and n = 11,988 males) and for 2 yr in a residential section of San Juan, Puerto Rico (n = 5,941 females and n = 6,739 males). In Thailand, temperature and rainfall fell into distinct seasonal categories, but only temperature was correlated with fluctuations in female abundance. Average weekly temperature 6 wk before mosquitoes were collected and minimum weekly temperature during the week of collection provided the highest correlations with female abundance. Accounting for annual variation significantly improved Thai models of temperature and mosquito abundance. In Puerto Rico, temperature, but not rainfall, could be categorized into seasonal patterns. Neither was correlated with changes in female abundance. At both sites the vast majority of females were collected inside houses and most contained a blood meal. Most teneral females were collected outside. Wing length--an indicator of female size--and parity, egg development or engorgement status were not correlated, indicating that feeding success and survival were not influenced by female size. At both sites, females fed almost exclusively on human hosts (> or = 96%), a pattern that did not change seasonally. In Puerto Rico more nonhuman blood meals were detected in mosquitoes collected outside than inside houses; no such difference was detected in Thailand. Gut contents of dissected females indicated that females in the Thai population had a younger age distribution and fed more frequently on blood than did Ae. aegypti in Puerto Rico. Our results indicated that aspects of this species' biology can vary significantly from one location to another and 1 yr to the next.

Aedes↗
PubMed2000

Longitudinal studies of Aedes aegypti (Diptera: Culicidae) in Thailand and Puerto Rico: blood feeding frequency.

We used a histologic technique to study multiple blood feeding in a single gonotrophic cycle by engorged Aedes aegypti (L.) that were collected weekly for 2 yr from houses in a rural village in Thailand (n = 1,891) and a residential section of San Juan, Puerto Rico (n = 1,675). Overall, mosquitoes from Thailand contained significantly more multiple meals (n = 1,300, 42% double meals, 5% triple meals) than mosquitoes collected in Puerto Rico (n = 1,156, 32% double meals, 2% triple meals). The portion of specimens for which frequency of feeding could not be determined was 31% at both sites. We estimated that on average Ae. aegypti take 0.76 and 0.63 human blood meals per day in Thailand and Puerto Rico, respectively. However, frequency of multiple feeding varied among houses and, in Puerto Rico, the neighborhoods from which mosquitoes were collected. In Thailand 65% of the mosquitoes fed twice on the same day, whereas in Puerto Rico 57% took multiple meals separated by > or = 1 d. At both sites, the majority of engorged specimens were collected inside houses (Thailand 86%, Puerto Rico 95%). The number of blood meals detected was independent of where mosquitoes were collected (inside versus outside of the house) at both sites and the time of day collections were made in Puerto Rico. Feeding rates were slightly higher for mosquitoes collected in the afternoon in Thailand. Temperatures were significantly higher and mosquitoes significantly smaller in Thailand than in Puerto Rico. At both sites female size was negatively associated with temperature. Rates of multiple feeding were associated positively with temperature and negatively with mosquito size in Thailand, but not in Puerto Rico. Multiple feeding during a single gonotrophic cycle is a regular part of Ae. aegypti biology, can vary geographically and under different climate conditions, and may be associated with variation in patterns of dengue virus transmission.

Aedes↗
PubMed2000

Field evaluation of deet and a piperidine repellent against Aedes communis (Diptera: Culicidae) and Simulium venustum (Diptera: Simuliidae) in the Adirondack Mountains of New York.

Repellent efficacy of N,N-diethyl-3-methyl-benzamide (deet), the piperidine, 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine (AI3-37220), and a 1:1 ratio of deet + AI3-37220 were evaluated topically (0.25 mg/cm2 applied in ethanol solution) on human volunteers against the mosquito Aedes communis (DeGeer) and the black fly Simulium venustum Say. The average repellency of all three formulations was > 95% at 4 h. For both mosquitoes and black flies, deet alone provided < 90% protection at 6 h, whereas AI3-37220 provided > 95% protection. Although repellent treatments were not significantly different overall, the contrasts between AI3-3720 versus deet were significant at 6 and 8 h. The 95% confidence interval on percent repellency at 6 h ranged from 90.1 to 98.9% for AI3-37220 versus 64.3 to 82.2% for deet, and at 8 h ranged 76.1 to 88.5% for AI3-37220 versus 47.8 to 64.0% for deet. Similarly, the confidence interval for protection against black flies at 6 h by (AI3-37220 ranged from 86.3 to 99.5% and did not overlap with the confidence interval provided by deet alone (51.2 to 78.8%). There was no evidence of synergistic repellency from a combination of the two compounds; i.e., protection from combined compounds was no better than either repellent used alone.

Aedes↗
PubMed2000

Serologic responses of Korean soldiers serving in malaria-endemic areas during a recent outbreak of Plasmodium vivax.

Anti-Pv200 antibody levels were assessed in samples from endemic areas of Plasmodium vivax malaria in the Republic of Korea (ROK), using an indirect enzyme-linked immunosorbent assay (ELISA) method. Asymptomatic carriers of P. vivax were detected using nested polymerase chain reaction (PCR) of blood samples. Anti-Pv200 antibody levels in 20 vivax malaria patients (optical density +/- standard deviation [OD +/- SD] values 1.85 +/- 0.29 of IgG isotype and 1.33 +/- 1.33 of IgM isotype) were markedly higher than those of uninfected, malaria-naive controls (0.08 +/- 0.16 of IgG isotype and 0.04 +/- 0.04 of IgM isotype). Antibody levels for 7 out of 8 soldiers with a recent malaria infection were sustained above the cut-off values for 4 months after successful treatment. Analysis of serum collected from 40 healthy, asymptomatic soldiers who had a P. vivax malaria attack within 3 months after our sampling, revealed 11 antibody-positive samples (27.5%), compared to 5 positive samples (12.5%) collected from a random selection of 40 soldiers. Among a larger pool of 1,713 soldiers who had served in high-risk areas for P. vivax transmission, 15% were antibody positive. Among 1,000 blood samples from asymptomatic soldiers who had served in the high-risk areas, 4 samples (0.4%) were parasite positive, as determined by nested PCR. Our results show that anti-Pv200 antibody levels can provide useful information in the late diagnosis of P. vivax malaria infection in a previously naive population and also in large seroepidemiologic studies. Furthermore, our results suggest that asymptomatic P. vivax carriers could be important in the current outbreak of malaria in Korea.

Animals↗
PubMed2000

Mosquito surveillance in the Demilitarized Zone, Republic of Korea, during an outbreak of Plasmodium vivax malaria in 1996 and 1997.

Since 1993, more than 2,000 cases of vivax malaria have occurred in the Republic of Korea in an epidemic that ended nearly 20 malaria-free years. Most malaria has occurred in the northwestern part of the country, mainly affecting Korean military personnel. As a part of an operational surveillance effort, we sampled mosquitoes in and near the Demilitarized Zone (Paju County, Kyonggi Province) during the last 2 wk of July in 1996 and from May 15 to September 10 in 1997. The 1st year, landing collections were done at 5 different sites; the 2nd year, carbon-dioxide-baited light traps at 5 sites, larval collections in 10 adjacent fields, and landing collections at 1 site in the Demilitarized Zone were performed weekly. Of 17 species collected, Anopheles sinensis was consistently the most abundant mosquito, comprising 79-96% of mosquitoes. The diel pattern of biting by An. sinensis varied by location and season, with the majority of individuals biting late at night during warm weather (>20 degrees C) and early at night during cool weather. In contrast, Aedes vexans nipponii (the 2nd most abundant species) bit in the greatest numbers at the same time all season, from 2000 to 2300 h. Among the correlates with abundance of An. sinensis were average nighttime temperature 2 wk previous to the night in question, wind late at night (negatively correlated), and apparent size of the moon (negatively correlated). The data showed that the exact number of An. sinensis biting could not be estimated from numbers collected in carbon-dioxide-baited light traps. On the other hand, a threshold of 15 An. sinensis per trap night corresponded (88% accuracy) to a threshold of 12 mosquitoes biting 2 adjacent collectors per night. Larval collections were also significantly correlated with landing collections, despite inexact sampling methods and separation of the larval habitat from the site where landing collections were performed. Operational entomology assets using nighttime temperature records, carbon-dioxide-baited light traps, and larval collections should be able to target their efforts in Korea more efficiently.

Animals↗
PubMed2000

Effects of magnetic fields on mosquitoes.

Phylogenetically diverse organisms, including some insects, are able to detect and respond to magnetic fields comparable to the Earth's magnetic field. Because of their tremendous importance to public health, mosquitoes were tested for the presence of remanent ferromagnetic material indicative of a biological compass and also tested for behavioral responses to magnetic fields. Using a superconducting quantum interferometry device, we found that significant remnant was probably due to attraction of ferromagnetic dust onto the surface of live or dead mosquitoes. Most mosquitoes placed in a 1.0-gauss, uniform magnetic field moved until they were oriented parallel to the field. Two of 3 species of mosquitoes tested took fewer blood meals in a rotating magnetic field than in the Earth's normal magnetic field.

Animals↗
PubMed2000

Mosquito collections following local transmission of Plasmodium falciparum malaria in Westmoreland County, Virginia.

A 63-year-old woman from Colonial Beach, Westmoreland County, VA, was diagnosed with Plasmodium falciparum malaria on July 19, 1998. The woman had no history of international travel, intravenous drug use, blood transfusion, or other risk factor for contracting the disease. She seldom left the county and generally spent her evenings indoors, leading to the conclusion that she had been bitten locally by an infected mosquito. Colonial Beach is host to a population of migrant agricultural laborers from areas in which malaria occurs, but a blood survey of 89 Haitians and Mexicans failed to find Plasmodium parasites, specific antibodies, or clinical cases of malaria. Mosquito surveys were conducted during 2 days (July 22 and 28, 1998) with carbon-dioxide-baited light traps, larval and pupal collections, and landing collections. Thirteen species of mosquitoes were identified morphologically, including 4 potential vectors: Anopheles crucians, An. punctipennis, An. smaragdinus (new state record), and An. quadrimaculatus s.s. (new state record). Identifications of the latter 2 species were confirmed by sequencing of the ITS2 DNA region from adults reared from locally collected larvae. Anopheles smaragdinus was the most common biting species among the potential vectors, although An. crucians was the most abundant in other kinds of collections. In addition, Ae. albopictus was collected in Westmoreland County for the 1st time.

Aedes↗
PubMed1999

Response to chloroquine of Plasmodium vivax among South Korean soldiers.

The response to standard chloroquine treatment was evaluated, by microscopical examination of blood-smears, among 81 soldiers diagnosed with Plasmodium vivax malaria in South Korea in 1996. The smears were prepared pre-treatment and 3, 14 and 28 days after starting chemotherapy. Parasitaemias were determined after staining the smears with Giemsa's stain. Blood samples from the patients who were not smear-negative by day 3 were carefully checked for parasites, by staining smears with Acridine Orange and by a PCR-based assay. Only two of the patients appeared to be parasitaemic on day 14 and were therefore considered treatment failures. Although both were apparently cured after additional therapy with the same regimen, one had a recurrence 8 months later. Most cases of recent, resurgent malaria in South Korea therefore appear to sensitive to chloroquine.

Adult↗
PubMed1999

Laboratory evaluation of AI3-37220, AI3-35765, CIC-4, and deet repellents against three species of mosquitoes.

Four repellents, N,N-diethyl-3-methyl-benzamide (deet), 2-hydroxy-methyl-cyclohexyl acetic acid lactone (CIC-4), and 2 piperidines (1-[3-cyclohexen-1-ylcarbonyl] piperidine [AI3-35765] and 1-[3-cyclohexen-1-ylcarbonyl]-2-methylpiperidine [AI3-37220]) were evaluated alone and in combination against Aedes aegypti, Anopheles stephensi, and Culex quinquefasciatus using a modified in vitro test system. This method was a valuable tool for comparing effective concentrations of the new compounds. Because of the controlled conditions of the test, it was possible to use the results of assays that had been conducted over a 5-year period and to perform the many replications necessary to evaluate combinations of compounds. The new candidate repellents were generally as effective as deet. Although speculative at this time, there was some evidence of synergistic interaction. Repellent combinations of CIC-4/AI3-37220/AI3-35767, deet/AI3-35765, and deet/AI3-37220/AI3-35765 against An. stephensi and CIC-4/AI3-35765, deet/AI3-37220/AI3-35765, AI3-37220/AI3-35765, and CIC-4/AI3-37220 against Ae. aegypti were more effective than the component compounds alone.

Aedes↗
PubMed1999

Evaluation of the malaria threat at the multipurpose range complex, Yongp'yong, Republic of Korea.

As part of an operational effort to control the transmission of malaria after its reemergence in the Republic of Korea, a number of U.S. military and Korean civilian health workers assessed the situation at a large training site where two cases had been transmitted. The vector mosquitoes (Anopheles sinensis) probably had a limited flight range (< 1 km) in this situation based on low numbers in permanent light traps and biting collections at the billeting area compared with collections from light traps and larval surveys where the mosquito was abundant. The threat of malaria was proven by the presence of infected local Korean residents (13 of 105 sampled). However, only a small proportion of U.S. soldiers (39 of 78 surveyed) at the training site used personal protective measures. Further efforts should include improved techniques for informing and motivating soldiers to use personal protective measures and cooperation with Korean authorities to perform vector control in civilian areas bordering the training area.

Animals↗
PubMed1998

Recovery and viability of Orientia tsutsugamushi from packed red cells and the danger of acquiring scrub typhus from blood transfusion.

BACKGROUND: The purpose of this study was to determine whether infective Orientia tsutsugamushi, the etiologic agent of scrub typhus, could survive normal blood banking processing and storage procedures. STUDY DESIGN AND METHODS: Mononuclear cells isolated from whole blood by density gradient centrifugation were inoculated with O. tsutsugamushi, Karp strain. Infection of the mononuclear cells was confirmed by Giemsa stain, direct fluorescent antibody assay, and polymerase chain reaction using primers specific for the groESL operon of O. tsutsugamushi. The quantity of rickettsial particles in each preparation was determined by direct counts from the Giemsa-stained preparations. Infected mononuclear cells were returned to their respective aliquots of packed red blood cells, which were then either stored at 4 degrees C or glycerolized and frozen at -70 degrees C. RESULTS: Rickettsiae survived up to 10 days (but not 30 days) of refrigerated storage and 45 days of frozen storage, as determined by inoculation of mice with 0.5-mL aliquots of the blood components. Infection of the mice was determined by illness, death, direct fluorescent antibody assay of peritoneal smears, polymerase chain reaction of blood, and enzyme-linked immunosorbent assay detection of antibodies in plasma. CONCLUSION: Because the quantity of rickettsiae injected into the mice was comparable to the quantity reported in the literature for human blood during natural infections, scrub typhus could present a risk in blood collected from donors in endemic areas. This may especially be true, because people can be rickettsemic before illness, after successful antibiotic treatment, and chronically after resolution of disease.

Animals↗
PubMed1998

Performance of a dot blot immunoassay for the rapid diagnosis of scrub typhus in a longitudinal case series.

A rapid dipstick test for scrub typhus was prospectively evaluated in Chiangrai, northern Thailand. Sera from 162 patients with fever of unclear etiology were tested by a dot blot immunoassay using two different antigen concentrations. Dipsticks coated with lower concentration of antigen lacked sensitivity compared with the indirect immunoperoxidase test. Dipsticks with higher antigen concentration had increased sensitivity that was equivalent to that of the immunoperoxidase test. By increasing the antigen concentration on the dipstick, sensitivity increased from 67% to 100%, positive predictive value increased from 90% to 93%, and negative predictive value rose from 92% to 100%. The specificity of both antigen concentrations was 98%. This study establishes that scrub typhus can be confirmed serologically by use of a dipstick assay and that serodiagnosis can be effectively tailored to a target population.

Adult↗
PubMed1998

Effect of size and geographic origin of Aedes aegypti on oral infection with dengue-2 virus.

Differences in larval habitats cause variation in the size of Aedes aegypti (L.) adults. We suspected that such size variation was related to the ease with which the mosquitoes could be infected with dengue virus. Using a rearing procedure that produced three distinct size classes of mosquitoes, we determined the percentage of mosquitoes that developed disseminated dengue-2 infection following oral feeding with a suspension containing 3.3 x 10(7) plaque-forming units/ml. Mosquitoes were reared from eggs deposited by females captured in either of two villages in Chachoengsao Province or in Bangkok, Thailand. More of the larger mosquitoes (10.7%) were infected than the medium (5.6%) or small (5.7%) mosquitoes. Mosquitoes from Bangkok were less easily infected (5.0%) than mosquitoes from either of the two villages (8.5% and 10.7%). These results suggest that quantitative risk assessment of dengue transmission may be very difficult unless inoculation rate is measured directly. Also, control procedures that reduce density of larvae in individual containers may exacerbate dengue transmission by creating larger mosquitoes that are more easily infected.

Aedes↗
PubMed1997

Seroepidemiologic evidence for murine and scrub typhus in Malang, Indonesia.

Indonesian military personnel stationed in Malang, East Java were among troops deployed to central Cambodia as part of the United Nations' Transition Authority Cambodia peace-keeping operation in 1992. Predeployment blood samples obtained from a cohort of Indonesian soldiers indicated a high prevalence of antibodies to antigens of Rickettsia typhi or Orientia (formerly Rickettsia) tsutsugamushi, the etiologic agents for murine and scrub typhus, respectively. To evaluate the potential risk of these rickettsial diseases in the Malang area, a subsequent seroepidemiologic survey was conducted. This study involved civilian personnel residing within one of three Malang kelurahans (neighborhoods) representing urban, suburban, and rural communities. The heads-of-households from 197 homes completed a detailed epidemiologic survey. In addition, blood samples were collected from 464 individuals residing within the households surveyed. Examination of civilian blood samples disclosed that 34.7% and 1.3% of the study participants were seroreactive to R. typhi and O. tsutsugamushi, respectively. These results were similar to those obtained earlier from the military samples. In addition, assessment of 78 blood samples obtained from peridomestic rodents trapped from within or near the households surveyed showed that 28 were reactive to R. typhi antigens and four were reactive to O. tsutsugamushi antigens. These data indicate that military and civilian personnel living in the Malang area of East Java are at risk of infection with rickettsiae that are antigenically indistinguishable from those that cause murine and scrub typhus.

Adolescent↗