The American Journal of Tropical Medicine and Hygiene - Volume 55, Issue 2, 1996

Severe falciparum malaria usually occurs in children, but also occurs in nonimmune migrants or partially immune adults in areas of unstable transmission. We have studied prospectively 70 adult patients with strictly defined severe malaria from the south coast of Papua New Guinea where malaria transmission is not intense. Only 19 (27.1%) were migrants from areas where malaria transmission does not occur; many other patients were periurban dwellers who had become infected after visits to their home villages. The most common clinical features were jaundice or hepatic dysfunction, impaired consciousness, renal failure, cerebral malaria, and anemia. Hypoglycemia was common following treatment with quinine. The overall case fatality rate was 18.6%; renal failure and cerebral malaria in particular were associated with a poor outcome. Reduction in mortality might be achieved by aggressive therapy of renal failure with earlier institution of dialysis; the use of preventive measures for immigrants or urban dwellers returning to high transmission areas might reduce the incidence of this dangerous disease.

Mathematical models are used to compare the effectiveness of various untested, unused, and undeveloped methods for controlling canine and human zoonotic visceral leishmaniasis (ZVL), including insecticides, vaccines, killing serologically positive and sick dogs, and drugs. For given percentage changes in control parameters, insecticides are the most effective control method. Where transmission occurs peridomestically and vectors are accessible to treatment, as in parts of tropical America, insecticides are expected to reduce the incidence of human ZVL even more effectively than they reduce the prevalence of canine leishmaniasis, a result that should encourage properly designed vector control trials. The second best strategy is to reduce susceptibility to leishmaniasis by vaccinating people or dogs, or by eliminating childhood malnutrition where it is common. Both killing vectors and reducing susceptibility (by whatever means) are more effective than killing dogs or treating them with drugs. In Europe, where vector control is less likely to be successful and canine leishmaniasis is a major veterinary problem, a dog vaccine is highly desirable. Better drugs for dogs will help case management but, with regard to bringing down the incidence in the dog population, immunization is the ultimate goal.

Following a striking increase in the severity of autumnal outbreaks of Plasmodium falciparum during the last decade in the Northwest Frontier Province (NWFP) of Pakistan, the role of climatologic variables was investigated. A multivariate analysis showed that during the transmission season of P. falciparum, the amount of rainfall in September and October, the temperature in November and December, and the humidity in December were all correlated (r2 = 0.82) with two measures of P. falciparum, the falciparum rate (percent of slides examined positive for P. falciparum) since 1981 and the annual P. falciparum proportion (percent of all malaria infections diagnosed as P. falciparum) since 1978. Climatologic records since 1876 show an increase in mean November and December temperatures by 2°C and 1.5°C, respectively, and in October rainfall. Mean humidity in December has also been increasing since 1950. These climatologic changes in the area appear to have made conditions for transmission of P. falciparum more favorable, and may account for the increase in incidence observed in the NWFP in recent years.

Bimonthly surveys were carried out for 12 months to investigate the dynamics of the acquisition of malaria parasitemia in relation to hemoglobin genotype, development of anemia, and body weight in infants during their first year of life. Thick blood smears for malaria, a capillary blood sample for measurement of packed cell volume (PCV) levels, and body weights were obtained at each survey. Generally, parasite rates (P < 0.001) and mean parasite densities (P < 0.025) increased with age. With a few exceptions, parasite rates and densities were similar in infants with hemoglobin AA and AS during the first year of life. Malaria parasitemia significantly lowered the PCV levels of the study infants only at four (P < 0.001), six (P < 0.025), eight (P < 0.001), and 10 (P < 0.01) months of age. No significant difference was observed in the mean body weight of malaria-positive and -negative infants during the first year of life except in infants two months of age (P < 0.05). The fairly rapid increase in parasite rate and density after two months of age is indicative of the decrease in protection after the first 2–3 months of life.

Repeated cross-sectional surveys among infants sleeping under insecticide-treated bed nets (ITBN) and contemporary control infants were used to estimate changes in Plasmodium falciparum exposure due to ITBN use on the Kenyan coast. Presence of P. falciparum parasites or total P. falciparum Immunoglobulin M (IgM) seropositivity were used independently and in combination in a constant risk catalytic conversion model to estimate the force of infection in ITBN and control communities. Such studies during infancy avoid problems of early saturation of prevalence due to high forces of infection and persistence of infection, minimize problems of self-treatment, and can be conducted among large populations covering a wide geographic area. These contrast previous parasitologic studies of ITBN among older children and the traditional entomologic studies of transmission that are logistically demanding. Our investigations demonstrated that parasite prevalence, IgM seropositivity, and the force of transmission were all significantly reduced by 50%. In addition, more infants under ITBN entered their second year of life without previous exposure to P. falciparum than control infants. These effects upon delayed acquisition of effective immunity require careful monitoring during future vector control programs using ITBN.

Light or moderate intensity infection with Schistosoma mansoni may contribute to growth deficits. We report on the effects of treatment for S. mansoni on growth and development in Brazilian schoolchildren. Anthropometric measurements were taken from 539 S. mansoni-infected children and their age- and sex-matched egg-negative controls between the ages of 7 and 15 years. The children as a whole exhibited chronic malnutrition, with growth retardation in height evident in 21% of the population. Infected children, however, were significantly smaller in height, weight, mid upper arm circumference (UAC), tricep skinfold (TSF), and subscapular skinfold (SSF) measurements than control children (P < 0.05). These differences were due primarily to a greater disparity between infected and egg-negative girls in height (P < 0.01), weight (P = 0.01), UAC (P = 0.02), and TSF (P < 0.01). Nevertheless, girls demonstrated a better level of development and nutrition compared with boys. While infected boys were shorter and weighed less than controls, these differences were not significant. Growth and development in girls was negatively correlated with intensity of infection. Coinfection with S. mansoni and Trichuris appeared to act synergistically in the development of malnutrition.

Although Rocky Mountain spotted fever was documented in northern Mexico during the 1940s, spotted fever group (SFG) rickettsioses have subsequently received little attention in Mexico. In this study, sera collected in 1993 from 50 patients from the Mexican states of Yucatan and Jalisco, who were suspected clinically to have dengue fever but had no antibodies to dengue virus, were examined by indirect immunofluorescence for IgM antibodies reactive with Rickettsia rickettsii, R. akari, and R. typhi. Twenty (40%) of the patients' sera contained IgM antibodies to SFG rickettsiae at a titer of 128 or greater. Among five sera reactive only against R. akari, four were from patients in Jalisco where a cluster of cases occurred in June and July. Among five sera reactive only with R. rickettsii, all were from Yucatan patients. Sera of 10 patients contained antibodies reactive with antigens shared by R. rickettsii and R. akari. The clinical signs and symptoms (fever, 100%; myalgia, 95%; headache, 85%; rash, 85%) were similar to those of dengue fever patients identified in this study. However, the incidence of rash was substantially higher than the nondengue, nonrickettsiosis patients. One or more SFG rickettsioses appear to be present in areas of Mexico not previously recognized to harbor these organisms. The etiologic agent or agents are as yet unknown.

To investigate a low rate of reported human Lyme disease adjacent to an area where the vector tick had become well established, we performed human and canine serosurveys and gathered data on environmental factors related to the risk of transmission. In March 1993, we obtained serum samples and conducted questionnaires that included information on outdoor activities, lot size, and frequency of deer sightings from 272 individuals living within a 5-km strip extending 12 km inland from a study site in south coastal Maine where collections revealed an abundant population of deer ticks. Serologic analysis was done using a flagellin-based enzyme-linked immunosorbent assay (ELISA) followed by Western immunoblot of positive and equivocal samples. Sera from 71 unvaccinated dogs within the study area were also analyzed for anti-Borrelia antibodies by ELISA. Human seropositivity was limited to two individuals living within 1.2 km of the coast. The frequency of daily deer sightings decreased sharply outside this area. Canine seropositivity, 100% within the first 0.8 km, decreased to 2% beyond 1.5 km. Canine serology appears to correlate with the entomologic indicators of the risk of Lyme disease transmission. Possible explanations for the low human seroprevalence are offered.

The risk of humans encountering vector ticks along hiking trails or in picnic grounds in a Lyme disease-endemic area was evaluated in a multipurpose recreational area (Tilden Regional Park) in the populous San Francisco Bay region of California. Four hillside hiking trials (two high-use, two low-use) were sampled by dragging and walking through low vegetation biweekly for one year; four heavily used picnic areas were sampled concurrently by dragging. Adults of three human-biting ticks were enumerated (n = 1,911) along all trails: Dermacentor occidentalis (63.6% of total), Ixodes pacificus (26.2%), and D. variabilis (0.2%). Subadults (n = 1,669) of D. occidentalis (0.06% of total) and two nonhuman-biters, D. albipictus (70.3%) and Haemaphysalis leporispalustris (29.7%), also were collected. Dragging yielded many more adult ticks than walking year-round for all trails. These methods were significantly correlated during periods of peak tick abundance, but the associations were not sufficiently strong or consistent to allow prediction of captures for either method based on the other. Adult ticks were distributed largely in clusters along the uphill sides of trails. Several adult ticks collected adjacent to trails were found to contain spirochetes identified with polyclonal antibodies as Borrelia burgdorferi (D. occidentalis, 0 of 861; D. variabilis, 2 of 126 [1.6%]; I. pacificus, 1 of 609 [0.2%]). Picnic areas produced low numbers of adult D. occidentalis and I. pacificus, which prohibited testing them for spirochetes. Two measures for evaluating risk were calculated, the encounter distance (= mean number of meters traveled before encountering a vector tick by either dragging or walking) and the mean number of spirochete-infected ticks encountered by these methods per kilometer of trail. These measures revealed that the risk of exposure to spirochete-infected adult ticks along trails was low year-round irrespective of usage, and risk was even lower in picnic areas. Future studies evaluating human exposure to vector ticks in recreational areas should incorporate, whenever possible, testing for multiple pathogens because most ixodid ticks that commonly bite people in the United States are capable of transmitting two or more microbial disease agents.

A retrospective study of 192 cases of human leptospirosis in New Caledonia (South Pacific) diagnosed between 1989 and 1993 showed that the disease was endemic throughout the territory. The annual incidence rate was 30 per 100,000 population, and the disease was more frequent in males (67.5%). Cases occurred mainly in March each year. Forty isolates were obtained (20.8%) and identified as belonging to serovars icterohaemorrhagiae (28), pomona (6), pyrogenes (3), ballum (2), and javanica (1). Most cases (54.7%) presented as influenza-like illnesses, while classical Weil's syndrome (fever, jaundice, and renal involvement) occurred in only 15.6% of the patients. Severe ocular complications were found in 3.6% of the patients. Local differences in climate, environment, and socioeconomic conditions determined the epidemiologic features. These data emphasize the potential public health importance of leptospirosis in the other insular states in the South Pacific.

Blood samples from 740 Egyptian Nationals working in the tourism industry at two sites in the South Sinai governorate were screened for markers of infection with hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), and Treponema pallidum. Study subjects included 467 individuals from a rural seashore tourist village and 273 persons at two hotels in a well-established resort town. Subjects' ages ranged from 15 to 70 years; 99.3% were male. The prevalence of serologic markers for currently asymptomatic or past HBV infection alone was 20.7% (n = 153), of markers for past or chronic HCV infection alone was 7.4% (n = 55), and of markers for both HBV and HCV was 6.9% (n = 51). Of the 204 individuals positive for anti-HBV core antibody, 12 (5.9%) were also positive for hepatitis B surface antigen. Two individuals (0.3%) had a serologic marker suggestive of an active syphilitic infection. No subject was found to be HIV-seropositive. History of prior injections and number of injections were associated with infection with HCV. Primary residence in the Nile delta and valley areas where schistosomiasis is highly endemic, was also a statistically significant risk factor for HCV, but not HBV infection.

This paper reports the first isolation of Jamestown Canyon (JC) virus from coastal California and the results of tests for antibody to JC virus in mammals living in coastal California. The virus isolation was made from a pool of 50 Aedes dorsalis females collected as adults from Morro Bay, San Luis Obispo County, California. The virus isolate was identified by two-way plaque reduction-serum dilution neutralization tests done in Vero cell cultures. Sera from the mammals were tested for antibody to JC virus by a plaque-reduction serum dilution neutralization method. A high prevalence of JC virus-specific antibody was found in horses and cattle sampled from Morro Bay. This finding is additional evidence for the presence of a virus antigenically identical or closely related to JC virus in Morro Bay and indicates that the vectors of the virus in Morro Bay feed on large mammals. A high prevalence of virus-specific antibody was also found in horses sampled from Marin and San Diego counties. This finding suggests that viruses antigenically identical or closely related to JC virus are geographically widespread in coastal California.

Viral hemorrhagic fever has re-emerged in the United Arab Emirates (UAE) since November 1993. Genomic RNA of Crimean-Congo hemorrhagic virus (C-CHFV) was detected by a newly developed, nested reverse transcriptase polymerase chain reaction (RT-PCR) in the sera of four (25.0%) of 16 suspected cases of viral hemorrhagic fever. The RT-PCR was based on oligonucleotide primers deducted from the small RNA segment encoding the nucleoprotein of the virus. By comparison with a nucleotide sequence of a C-CHFV isolate from a Chinese sheep, a divergence of 10.0–11.8% was detected in the C-CHFV variants causing the UAE outbreak. In the four positive sera, three phylogenetically distinct C-CHFV variants were amplified and confirmed by direct sequencing of the PCR fragments. These C-CHFV sequences were obtained directly from sera of infected humans without prior propagation in cell culture. The RT-PCR allows rapid detection of genomic C-CHFV RNA in clinical specimens and study of the molecular epidemiology of this infection.

The lethal effects of Africanized honey bee venom depend on the absorption of venom delivered during simultaneous sting attacks by large numbers of bees. The hypothesis that antibodies to whole bee venom and bee venom components could neutralize the lethal effect of bee venom was tested. Antibodies from beekeepers and immunized rabbits were incubated with bee venom and neutralization was studied by survival of intravenously injected mice. Beekeeper serum antibodies were found effective in protecting mice challenged with whole venom, and serum from rabbits immunized with phospholipase A2 (PLA2) was effective in protection against lethal effects of PLA2. Serum antibodies from rabbits immunized with whole venom or melittin were ineffective in neutralizing whole venom in vivo and had low titers in a venom enzyme-linked immunosorbent assay. The results suggest the need for development of more effective methods for raising antitoxic antibodies to bee venom components in other animals as a means of developing an antiserum that would be effective for treatment of human victims of multiple bee stings.

A 10-year study of blood meal identification in mosquitoes collected at numerous sites over several ecosystems in central Panama was conducted from 1977 to 1987. The hosts for 4,391 mosquito blood meals, representing 30 species, were identified to the family level of specificity in most instances. The degree that individual mosquitoes had fed on animals of different classes and families within these classes was determined. Multiple feeding among several mosquito species was documented. The relationship between reservoir hosts of endemic arboviruses and a number of known and potential mosquito vectors was demonstrated as a result of the blood meal identifications.

Plasmodium falciparum isolates from 24 Papua New Guinean patients with symptomatic malaria were tested for susceptibility to pyrimethamine and cycloguanil. Thirteen isolates were sensitive to both agents and the remainder exhibited varying degrees of resistance. No isolates were found to be resistant to one agent yet sensitive to the other and a positive correlation suggesting cross-resistance was found. Parasite DNA extracted from the patients' stained blood slides was amplified and sequenced to examine point mutations in the dihydrofolate reductase (DHFR) and dihydropteroate synthetase genes (DHPS) associated with antifolate resistance. All resistant isolates possessed mutations in the DHFR gene at codon 108, the majority changing from Ser to Asn, but one isolate from Ser to Thr, a change not previously reported in field isolates. A second mutation of the DHFR gene at Cys-59 to Arg was present in isolates with higher level resistance, but not exclusively so. Sequencing the DHPS gene, as a predictor of sulfadoxine resistance, revealed only one example that was different from DHPS alleles of sensitive isolates.

To determine if resistance/tolerance to the antischistosomal drug praziquantel (PZQ) is appearing in Egyptian villages within the Nile delta region, where it has been used extensively, we treated 1,607 infected villagers and observed that 321 required one additional treatment while 89 villagers required two additional treatments; 24 of the 89 were still not cured after a third dose of this drug. Eggs were isolated from fecal samples and serum was isolated from blood taken from seven villagers successfully treated after a single dose and from 14 villagers not successfully treated after two or three doses of PZQ. The eggs were used to establish infections in mice (isolates), which were then treated six weeks after infection with three different doses of PZQ. Serum was used to determine the concentration of PZQ in the infected humans. Three of the egg isolates from the 14 villagers that could not be treated with three doses of PZQ produced infections in mice that were statistically less responsive to PZQ when compared with isolates obtained from patients that were cured after a single dose of this drug. Pharmacokinetic parameters were the same in patients treated successfully after a single dose versus those not treated successfully following two or three doses, thus eliminating the possibility that poor cure rates among infected villagers was due to a decrease in PZQ bioavailability. From our data, approximately 1–2.4% of the villagers treated with PZQ could not be completely cured of their infection and three of every 1,000 treated villagers may harbor parasites that can tolerate high doses of PZQ. These results indicate that the extensive use of PZQ in the Nile delta region of Egypt has not resulted in a dramatic change in the efficacy of this drug. The isolation of schistosomes that are less susceptible to PZQ may be a warning signal that will require establishment of a monitoring system, similar to the one we have developed, to determine if the precentage of patients that cannot be cured by PZQ is increasing. Furthermore, if that percentage begins to increase over time, it will be critical to determine, by pharmacologic methods reported in this study, whether isolates obtained from uncured patients are becoming increasingly resistant to PZQ.

The traditional therapy for the treatment of human Babesia microti infections has been the combination of clindamycin and quinine. However, in recent years, it has become apparent that some patients have not responded to this regimen. We became involved in the treatment of several cases of babesiosis in which atovaquone was used to treat this infection. Therefore, using the hamster model, we determined the efficacy of atovaquone alone as well as atovaquone plus azithromycin for the treatment of experimental babesiosis. Atovaquone (100 mg/kg/day) and atovaquone (100 mg/kg/day) with azithromycin (150 mg/kg/day) were effective agents for the treatment of experimental babesiosis in hamsters. When atovaquone was used as monotherapy recrudescences occurred. Organisms obtained from recrudescent animals, when inoculated into uninfected animals, proved to be unresponsive to atovaquone therapy, suggesting the emergence of drug resistance. Resistant organisms did not emerge in hamsters treated with the combination of atovaquone and azithromycin. Atovaquone should be considered in the therapeutic regimen of patients with babesiosis who have either failed standard therapy or have become intolerant to such therapy.

The effects of pyronaridine on the morphology of Plasmodium falciparum were studied in an infected owl monkey (Aotus trivirgatus) that was severely ill with a parasitemia of 28%. Thirty minutes after pyronaridine administration, distinct morphologic changes were already present in late trophozoites and schizonts. Ultrastructural observations revealed that the earliest and most distinct changes induced by pyronaridine occurred in food vacuoles. The most striking change in food vacuoles was the appearance of undigested endocytic vesicles surrounded by a single membrane in the vacuolar space. These findings suggest that vacuolar degradation is inhibited by pyronaridine, and that undigested endocytic vesicles accumulate inside parasite food vacuoles impairing hemoglobin degeneration. Thus, pyronaridine appears to interfere with the parasitic digestive system.

From June until October 1993, a battalion of Dutch marines was stationed in Cambodia for a United Nations deployment. In 73 volunteers who used mefloquine as malaria chemoprophylaxis, possible mefloquine-related adverse events were monitored with special emphasis on QT prolongation. All participants started mefloquine chemoprophylaxis with a loading dose (250 mg a day for three days) one week before departure, followed by a weekly dose (250 mg) for approximately 25 weeks. One month before (t - 1) and one (t + 1) and three (t + 3) months after mefloquine prophylaxis was started, an at rest electrocardiogram was made. Frequency, PR-, and QT-intervals were measured; blood samples for liver transaminases, total white blood cell count, and mefloquine concentration were obtained after one and three months. Adverse events such as dizziness, headache, coordination problems, and nausea were spontaneously reported in one (1.4%) and three (4.1%) persons at t + 1 and t + 3, respectively, while specific questioning revealed adverse events in nine (12.3%) and five (6.9%) persons, respectively, at the same time point. Three months after starting chemoprophylaxis, the heart rate at rest and total white blood cell count were lower (P < 0.05), while the QTc-interval was longer and levels of liver transaminases increased (P < 0.05), although both were still within the normal range. There was no extreme prolongation of the QTc-interval or increased levels of liver transaminases that resulted in a need to stop the chemoprophylaxis. No accumulation of mefloquine in the serum occurred, and no relationship was observed between the incidence of adverse events and serum mefloquine concentrations. The incidence of self reported mefloquine-related adverse events was low. In conclusion, mefloquine chemoprophylaxis was safe and well-tolerated in this group.