The American Journal of Tropical Medicine and Hygiene - Volume 53, Issue 6, December 1995

The publication of the Journal remains a collaborative effort of the Society's Editorial Board and Council, the Editor, Associate Editor and the staff in Atlanta, and the hundreds of professionals, many of them members of the Society, who took time from very busy schedules to review manuscripts, providing invaluable assistance to both the editorial office and to authors.

The following list of active reviewers is as of November 7th, 1995. Each one of the manuscripts published during 1995 was seen by two or more of those listed below. These refereees also have seen manuscripts that are still under review or have been rejected. Their considerable geographic diversity is exceeded by the extraordinary breadth in terms of subject matter, expertise, and experience that they bring to their important task. The Editor's office extends a warm thanks to everyone who contributed this year to supporting and strengthening the Journal.

Dear Sir:

We would like to thank Dr. McManus for his letter regarding his recently published method for distinguishing the four recognized species of Echinococcus using PCR and DNA sequencing. It is interesting to know that the modern genetic approaches confirm the morphological observations made by classical parasitologists. Although we do agree with Dr. McManus that the four “species are quite clearly distinct”, we are in slight disagreement with some of the minor points he raises in his letter.

We are not convinced that “morphological features alone must be open to considerable doubt.” Experienced helminthologists have no problems identifying any of the four species in either the larval or strobilar stages. However, admittedly, many physicians are unable to make reliable identifications. Therefore, the PCR-RFLP and RAPD-PCR methods of McManus may be useful in hospital situations when no experienced person is available to make the identification. Secondly, we question how simple and how inexpensive the PCR-RFLP method is to carry out.

Dear Sir:

Hydatid disease is medically and economically one of the most important of the zoonoses. There are four currently recognized species of Echinococcus: E. granulosus, E. multilocularis, E. vogeli and E. oligarthrus. The first three are commonly found in humans but E. oligarthrus had been recorded previously on one occasion only in the eye of a Venezuelan woman. Thus, I read with interest the recent paper by D'Alessandro and others which reviewed an earlier published case of hydatid disease in the heart of a Brazilian person who died of tetanus. Originally the case was described as being due to Echinococcus granulosus but this later paper considers that the infection was caused by E. oligarthrus and thus is the second reported human infection due to this species. As with the Venezuelan patient, both the cysts recovered from the Brazilian were unilocular—typical of E. granulosus, but untypical of E. vogeli and E. oligarthrus which are generally polycystic in nature—and diagnosis was based mainly on the morphological features of the hooklets of the protoscolex.

As part of a program to integrate schistosomiasis control into the primary health care system in northern Cameroon, an unexpected opportunity to undertake a controlled evaluation of the impact of interventions was recognized. Inadvertently, a large part of Mindjil, one of four assessment villages, had been essentially excluded from the program, creating a unique natural control. The prevalence of infection with Schistosoma hematobium in school-aged children was 7% in the areas where the control program was implemented, and 71% in the excluded areas (P < 0.0002). High intensity infection was 1% and 26% in the two areas, respectively (P < 0.0002). Children in the school where the control interventions were implimented had a significantly lower prevalence of infection with Schistosoma hematobium (P < 0.005). Subjects in intervention areas demonstrated greater knowledge about the transmission of schistosomiasis than those in the control area. This study documented and quantified program impact in a controlled manner not usually possible in field studies and also illustrated how unrecognized intracultural diversity (within culture differences) in target populations may effect disease control programs in communities.

A randomized trial was carried out from 1991 to 1993 among women attending an antenatal clinic in Ebolowa, Cameroon where malaria is hyperendemic and transmission occurs at a high level all year round. All pregnant women attending the clinic for their first prenatal visit between October 1991 and November 1992 were alternately assigned to chloroquine (CQ) or control (CT) groups. Chloroquine was given under observation at a weekly oral dose of 300 mg. At delivery, smears from maternal, cord, and placental blood were made and stained with Giemsa for parasites. An in vivo chloroquine sensitivity investigation was carried out on women attending the postnatal consultation to evaluate the level of chloroquine resistance in the target population. The efficacy of chloroquine was moderate in placental infection (39.2% infected in the CQ group versus 57.8% in the CT group: P = 0.05), probably because of a resistance to chloroquine estimated to be 10.9%. In the CQ group, the mean birth weight was significantly higher (P = 0.02) and the proportion of low birth weight newborns was lower (10.5% versus 27.7%; P = 0.02). A strong correlation between placental infection and birth weight was observed: the mean birth weight difference between infected and noninfected placentae was 359 g (P < 0.0001) and the proportion of low birth weight new born babies was 35.6% versus 5.9% (P = 0.0001). In Cameroon, in spite of a moderate resistance to chloroquine, this drug proved to be highly effective in increasing birth weight when administered to primigravidae. We therefore think such a prophylaxis should be recommended only to primigravidae in high transmission areas.

In 1995, 24 million travelers from the United States are anticipated to visit developing countries where hepatitis A is endemic. Passive immunization with immune globulin, before exposure or within two weeks following exposure to the hepatitis A virus, protects against clinical disease in < 70–90% of immunized individuals. The duration of protection, measured in months, is relatively short. Active immunization with a single dose of inactivated hepatitis A virus vaccine appears to provide greater protective efficacy and, based on the persistence of vaccine-induced protective antibodies, should provide protection for years. Booster doses given between six and 12 months are likely to provide immunity that may persist for at least a decade. The inactivated hepatitis A vaccine approved for use in the United States has been clinically well-tolerated; mild transient soreness at the injection site is the most frequently reported adverse reaction. Immunization with inactivated hepatitis A vaccine is a safe and effective method for travelers to endemic areas to protect themselves against this infection.

Premise inspections and treatment of the larval habitats of container-breeding Aedes aegypti are extremely labor intensive. Since this means of control is the only one available in relation to dengue fever, this report presents an effective approach for streamlining premise surveys in north Queensland, Australia. From a survey of 877 premises in Townsville, Charters Towers, and Mingela/Ravenswood in 1990, occupier and premise variables were collected to examine any relationships with the presence of Ae. aegypti. Statistical modeling of these parameters using multiple and simple Poisson regression indicated that for both adjusted and unadjusted models respectively, the degree of shade and tidiness of the yard had strong correlations with both the proportion of positive premises and the numbers of infested containers therein. Condition of the house was also a significant variable in the unadjusted model. On this basis, the Premise Condition Index is proposed as a rapid assessment tool that can increase efficiency of detecting positive premises and containers by 270–370%. Although habitat selection by Aedes varies throughout the world, this approach could be used as a model for control of vectors of both dengue and yellow fever.

The objective of this work was to define criteria that could be applied to achieve faster, more economical, and accurate assessment of vector populations for control of dengue viruses. During 1989–1990, 1,349 premises were surveyed in Townsville, Charters Towers and Mingela/Ravenswood, Queensland, Australia. In each locality, 1.9–8.4% of premises contained three or more containers with Aedes aegypti immature forms and were designated as key premises. Comparison of surveys in Townsville from 1989 to 1990 indicated that positive premises (i.e., those with at least one container with Ae. aegypti present) were 3.22 times more likely to remain positive than negative houses to become positive the following year. The Ae. aegypti population in Townsville was seen to be totally associated with garden receptacles, discarded household items, and trash but one well and one rainwater tank were responsible for 28% of all immature forms recorded in the 1,349 premises inspected. These breeding sites of high productivity were designated as key containers. At Charters Towers, Mingela, and Ravenswood, rainwater tanks were seen as the most important key container because although they constituted 13–29% of positive containers, they supported 60–63% of the immature forms. This study demonstrates that there is a certain degree of stability with regard to positive premises and that some of these, or some container types, contribute disproportionately to the Ae. aegypti population. Control programs could be made more efficient if efforts were concentrated on these sites of key vector productivity.

Recent unpublished reports from northern Thailand of severe and sometimes fatal cases of scrub typhus, despite appropriate antibiotic therapy, suggest that resistance may occur. Current antibiotic susceptibility methods that use direct microscopic counts of Giemsa-stained cells or mouse protection assays are slow, labor-intensive, and expensive. We explored the use of flow cytometry to measure rickettsial infection in vitro in L-929 cells treated with and without doxycycline, ciprofloxacin, erythromycin, and chloramphenicol. It was possible to detect the rickettsiae down to a level of 83% of the cells infected, mean of 37 rickettsiae per cell, and 40% of cells with too many rickettsiae to count. This level of sensitivity was sufficient to determine the inhibitory effect of all four drugs at standard screening concentrations. At lower concentrations of doxycycline, flow cytometry detected inhibition of rickettsial growth at a concentration of 6.25 × 10-2 µg/ml but not at 6.25 × 10-3 µg/ml, suggesting that the minimum inhibitory concentration is somewhere between these two values. The data from this study show that flow cytometry permits the rapid screening of numerous rickettsial isolates for their susceptibility to a variety of antibiotics, but that visual counts of infected cells provide a more precise indication of rickettsial growth.

Plasmodium falciparum parasites develop in the liver before being released into the bloodstream, where they exert the potentially lethal effects characteristic of malaria. Our understanding of the hepatic phase of the life cycle is limited by the parasite's requirement for fresh human liver cells in which to mature. In this work, liver parasites completed their development within a Thai human hepatoma cell line (HHS-102), and the presence of ring-form parasites in erythrocytes overlying the liver cell culture confirmed that an entire liver cycle was completed, culminating in the production of viable blood-stage parasites. The HHS-102 cell line allows investigation of the undefined liver stage of falciparum malaria previously unavailable in the laboratory.

To investigate the mechanisms underlying the increased susceptibility to malaria in pregnant women, we determined the level of malaria-specific immunity in primigravidae. Humoral and cellular in vitro responses to unpurified (a crude schizont extract and a gametocyte preparation) and purified (affinity-purified Pf155/ring-infected erythrocyte surface antigen [RESA]) Plasmodium falciparum proteins, an immunodominant 45/47-kilodalton antigen from Mycobacterium bovis, and leucoagglutinin were compared between 52 primigravidae and 52 nonpregnant women from a semirural area of Cameroon. In vitro cellular responses were investigated in terms of lymphocyte proliferation, as well as production of interleukin-2 (IL-2), interferon-gamma (IFN-γ), and IL-4. Cells from primigravidae exhibited a reduced proliferative response to schizont and gametocyte antigens, as well as to the M. bovis antigen. Conversely, the IL-2 response to Pf155/RESA was reduced. Interleukin-4 and IFN-γ production did not appear to be affected in primigravidae. Antibody levels were also similar between pregnant and nonpregnant women. Our results underline the importance of examining several parameters of T cell activation with different types of antigens for a correct evaluation of the ability of lymphocytes to respond to malaria.

An antigen, designated here as the parasitized erythrocyte membrane antigen (PEMA), is present in the erythrocyte membrane surrounding all intraerythrocytic stages of Plasmodium brasilianum. An antibody specific for PEMA appeared in 21 (50%) of 42 antisera from Saimiri sciureus monkeys naturally infected with P. brasilianum. Of these 42 sera, nine (21.4%) contained antibody to the ring-infected erythrocyte membrane antigen (RESA); of these nine sera, six did not react with PEMA. Sera of humans infected with P. malariae reacted with PEMA and RESA in a similar pattern; i.e., of 83 antisera, 71 (85.5%) reacted with PEMA and 30 (36%) reacted with RESA. Only one of these latter 30 sera were not reactive with PEMA. Of 167 sera from humans infected with P. falciparum but not P. malariae, 133 (79.6%) reacted with RESA; of these, 43 (25.7% of the total) reacted with PEMA but not RESA. Although PEMA was demonstrated with P. brasilianum and RESA with P. falciparum, neither PEMA or RESA could be demonstrated with P. malariae. Interactions of PEMA and RESA and the corresponding antibodies offer a method whereby the two morphologically similar quartan species, P. malariae and P. brasilianum, can be readily distinguished from each other and may furnish clues to genetic separation of the two and the mechanisms of interaction of quartan malaria and P. falciparum where they are coendemic.

Cattle experimentally infected with Onchocerca lienalis were examined by enzyme-linked immunosorbent assay and immunoblotting to determine the degree of stage- and species-specificity in the immune response to infection. Levels of serum antibodies to antigens derived from third-stage larvae increased little after the first three weeks of infection, and the range of antibody specificities remained limited following the appearance of microfilariae (mf) in the skin. In contrast, antibodies to antigens from adult worms of either sex exhibited a vigorous response, characterized by a series of peaks arising 15–30, 79, and > 266 days after infection that were coincident with the timings of larval molts and the onset of a patent infection. Antibody specificities to the adult worms included many directed to molecules that were shared with other life-cycle stages, but some were stage-specific and others were confined to one sex. A response cross-reactive with antigens from mf was initiated during the prepatent period, but antibody levels increased steeply after the infection became patent. This was followed by a major expansion of antibody specificities to products exclusively directed to mf, most notably in the range of 12–18 kilodaltons. Sera from O. lienalis-infected cattle cross-reacted extensively with antigens derived from O. volvulus adult worms and the profiles of antibody levels over time were indistinguishable from those obtained with O. lienalis extracts. The dominant response was of IgG1, although limited IgG2 and IgM reactivities were found, while no Onchocerca-specific IgA was detected. These results demonstrate that parasite development has a profound influence on the level and repertoire of antibodies produced during Onchocerca infections, and that extensive cross-reactivity exists between O. lienalis and O. volvulus, lending support to the role of cattle models in the study of human onchocerciasis.

The clinical efficacy of oral and intravenous (iv) artesunate was compared in an open randomized trial in 50 male adult patients with uncomplicated Plasmodium falciparum malaria in Kibaha, Tanzania. Oral artesunate treatment was started with 2 × 50 mg initially followed by 50 mg 12 hr later and then 50 mg twice a day for four days (total dose = 550 mg or 9.6 mg/kg). Intravenous artesunate administration began with 2 × 0.8 mg/kg initially followed by 0.8 mg/kg 12 hr later and then 0.8 mg/kg twice a day for four days (total dose = 8.8 mg/kg). The mean ± SD parasite clearance times (PCTs) were nearly identical at 23.4 ± 5.9 hr and 24.2 ± 7.2 hr after oral and iv administration, respectively. Mean ± SD fever subsidence times (FSTs) were also similar at 18.7 ± 8.3 hr and 21.0 ± 4.8 hr, respectively. All patients remained negative for P. falciparum for at least 14 days. Recrudescence/reinfection occurred between days 21 and 28 in five of 25 patients (20%) after oral treatment and in four of 25 patients (16%) after iv treatment. The mean erythrocyte count and hemoglobin concentration were slightly reduced after iv treatment but remained in the normal range. Otherwise, there was no change in blood biochemistry, hematology, and electrocardiograms monitored prior to and during the last dose. It is concluded that treatment with oral and iv artesunate was equally efficacious and well tolerated. A 24-hr in vitro susceptibility test of P. falciparum to artemisinin, chloroquine, and mefloquine was performed in samples from all patients. The three compounds exhibited 100% inhibition with the exception of three isolates, which showed chloroquine resistance. Parameter estimates of a sigmoid Emax model (drug concentration at which 50% of the growth inhibition occurs [EC50]), the sigmoidicity factor s and EC95 fitted to the growth inhibition data differed between compounds and isolates, indicating different sensitivity of P. falciparum isolates. There was no correlation between artemisinin and mefloquine EC50 values, while artemisinin and chloroquine EC50 values showed weak correlation (r2 = 0.223, P = 0.006). There was no correlation between parameters describing clinical outcome (the PCT, the time needed for reduction of the parasite density to 50% and 95% of the initial parasitemia, and the FST) and those describing in vitro susceptibility.

Twenty-four patients presenting with severe Plasmodium falciparum infection at the Kamenge Hospital in Burundi were enrolled in a double-blind study comparing the efficacy of a seven-day regimen of intravenous quinine alone or in combination with pefloxacin. The aim of this study was to assess whether pefloxacin modified chloroquine efficacy or its uptake by infected erythrocytes as shown with other antimalarials. Pefloxacin did not modify the antimalarial activity of quinine, in terms of speed of parasite or fever clearance. Moreover, pefloxacin does not appear to interact with quinine uptake by erythrocytes in humans.

The effect of a two-week regimen of topical aminosidine was investigated in a randomized, double-blind, placebo-controlled trial of 251 selected Iranian patients with zoonotic cutaneous leishmaniasis. Patients underwent clinical and parasitologic assessment before and 15 (end of therapy), 45, and 105 days after starting the treatment. Aminosidine ointment was safe and well-tolerated, and produced significant reductions in the prevalence of parasitologically positive smears on days 15 and 105 (but not day 45) after treatment compared with placebo. However, there was no clear clinical benefit at any stage after treatment. We conclude that this twice a day two-week regimen of aminosidine was inadequate to accelerate the recovery of most cases of cutaneous leishmaniasis. However, the ointment did show some clear evidence of parasitologic efficacy and should now be studied in longer or more frequent regimes in an effort to prevent parasitologic relapse and thus promote clinical improvement.

Ivermectin is used in veterinary practice against many ectoparasites and endoparasites and is the drug of choice for treatment of human onchocerciasis. This study was carried out to investigate the effect of topical application of this drug against human ectoparasites (Sarcoptes scabiei and Pediculus humanus capitis). Ivermectin was found to have a curative effect on head lice after a single topical application. In patients with scabies, the drug was also found to be effective after a single application. However, in 50% of the cases, another application was needed five days later.

The prevalence of hepatitis C antibodies (anti-HCV) was investigated in 1,378 central Brazilian children, students, and street youths (homeless adolescents without family links or adolescents working in poorly paid activities). Sera were tested with a second generation enzyme-linked immunosorbent assay, and positive samples were retested by a confirmatory assay (line immunoassay). All children attending day care centers were anti-HCV negative. Only one (0.2%) adolescent was positive in the student group. However, higher positivity was found in street youths; four (1.0%) living at home and three (3.0%) living in the streets had anti-HCV antibodies. Among these, the prevalence of anti-HCV increased significantly with age from 0% in the 9–12-year-old group to 6.9% in the 17–20-year-old group. Risk factors including blood transfusion, tattooing, intravenous drug use, and sexual intercourse with multiple partners were significantly associated with the presence of anti-HCV in street youths. These results indicate that apparently healthy children and adolescents attending day care centers or primary schools in central Brazil have a low exposure to HCV infection, but street youths in the same area are at risk for infection with this virus.

To determine factors associated with isosporiasis in persons with acquired immunodeficiency syndrome (AIDS) in Los Angeles County, data from the AIDS surveillance registry were analyzed for the eight-year period 1985–1992. Isosporiasis was reported in 127 (1.0%) of 16,351 persons with AIDS during the study period. Prevalence of infection was highest among foreign-born patients (3.2%), especially those from El Salvador (7.4%) and Mexico (5.4%), and in all persons of Hispanic ethnicity (2.9%). Persons with a history of Pneumocystis carinii pneumonia (PCP) were less likely than PCP-negative patients to have isosporiasis (0.2% and 1.4%, respectively, P < 0.01). A decrease in the prevalence of isosporiasis in patients negative for PCP was observed beginning in 1989 (P = 0.02). Prevalence decreased with age (P < 0.01, by chi-square test for trend). After controlling for multiple factors by logistic regression, isosporiasis was more likely to occur in foreign-born patients than in those born in the United States (adjusted odds ratio [OR] = 5.8, 95% confidence interval [CI] 3.4, 9.9, P < 0.001) and in Hispanics than in whites (non-Hispanics) (adjusted OR = 3.5, 95% CI 1.7, 7.2, P < 0.001). A prior history of PCP continued to be negatively associated with isosporiasis (adjusted OR = 0.2, 95% CI 0.1, 0.3, P < 0.001). Age and time remained independently associated with infection. These data suggest that isosporiasis among persons with AIDS in Los Angeles County may be related to travel exposure and/or recent immigration and that the use of trimethoprim-sulfamethoxazole (TMP-SMX) for PCP may effectively prevent primary infection or expression of latent isosporiasis. Physicians should have an increased index of suspicion for Isospora in AIDS patients with diarrhea who have immigrated from or traveled to Latin America, among Hispanics born in the United States, in young adults, and in those not receiving PCP prophylaxis. Food and water precautions should be advised and TMP-SMX prophylaxis considered for the prevention of Isospora infection for patients with human immunodeficiency virus infection who travel to Latin America and other developing countries.

Assessment of the public health importance of schistosomiasis mansoni is hampered by the nonspecificity of many of its disease symptoms. Parasitologic, clinical, and anamnestic data from two areas in Burundi were used to obtain estimates of the attributable fractions for different disease symptoms at both the population level and within different age strata. A large proportion of individuals had symptoms commonly associated with Schistosoma mansoni infection that were not attributable to this parasite. The clinical indicator with the best test efficiency was shown to be bloody diarrhea. At the population level, 35% of bloody diarrhea cases were attributable to S. mansoni, compared with only 9% of diarrhea cases without blood. The attributable fractions were age-dependent, and in the case of diarrhea (with and without blood), children had a higher proportion of cases attributable to S. mansoni infection than adults. The association between infection and disease symptoms also increased with the intensity of infection. The prevalence of morbidity attributable to S. mansoni was similar for all symptoms, and higher in children than adults. The estimation of attributable fractions provides a simple approach to quantify S. mansoni-related morbidity, which could also be extended to both S. haematobium and S. japonicum. Attributable fraction estimates for these three schistosome species in different endemic areas would greatly aid in the assessment of the health burden of this parasite and the effectiveness of control programs.

A retrospective chart review conducted at two teaching hospitals in Los Angeles County identified 28 patients with infection due to Echinococcus granulosus diagnosed by positive echinococcal serology and/or tissue biopsy between January 1981 and December 1990. Of these patients, 25 (89%) were foreign born and 19 (68%) were immigrants from the Middle East or central Asia. Only 12 of 22 immigrants questioned about epidemiologic risk factors described a history of rural residence or direct exposure to dogs in their native country. Single cysts of liver, lung, and soft tissue were present in six of 28 patients; multiple cysts in the 22 remaining patients were exclusively hepatic in 13 patients, exclusively pulmonary in two patients, and involved mixed sites including liver, lung, abdomen, central nervous system, and bone in seven patients. Natives of middle eastern countries currently constitute a major risk group for imported infection due to E. granulosus in the United States. Since their epidemiologic risk factors may be absent and clinical presentations varied, a high index of suspicion for echinococcosis is warranted in this population based solely on the presence of a cystic mass in liver, lung, or another organ site.