Showing papers in "American Journal of Tropical Medicine and Hygiene in 1984"

Epidemiology, malaria and pregnancy.

Abstract: It is a great honor for me to be invited to give this Soper Lecture. I met Fred Soper only once—at the 6th International Congresses of Tropical Medicine and Malaria at Lisbon in 1958. I had, of course, known of him for a number of years beforehand, and had read with the greatest interest his account of how Anopheles gambiae was halted in its invasion of Brazil and finally expelled from an area of some 18,000 square miles. In his lifetime, Soper was associated with many significant achievements in diverse fields of public health, but to me as a malariologist none compares with his eradication of Anopheles gambiae from Brazil. More than 40 years later, this episode still stands as one of the most significant victories that man has scored over malaria and epitomizes Soper's administrative genius and technological competence.

Mosquito cell cultures and specific monoclonal antibodies in surveillance for dengue viruses.

Abstract: During the fall of 1981, a new method for the routine isolation and identification of dengue viruses in Puerto Rico was implemented utilizing C6/36 cell cultures and serotype specific antidengue monoclonal antibodies. A blind comparison of the monoclonal antibody indirect fluorescent antibody test (IFAT) and the complement fixation (CF) test for identification of 89 newly isolated dengue viruses of all four serotypes from the Caribbean, Asia and Africa showed 100% agreement. Although virus isolation rates were slightly lower than with the mosquito inoculation technique, use of the C6/36 cell culture system was much less time-consuming and allowed the processing of larger numbers of sera. Beginning in November 1981, a new virologic surveillance system was begun in Puerto Rico. Acute sera from persons with suspected dengue were selected for virus isolation attempts on the basis of geographic area of residence on the island, day after onset the blood was taken and clinical signs and symptoms. These sera were processed for virus isolation in C6/36 cell cultures, and virus isolates were identified by the IFAT using the monoclonal antibodies. Using this system, 2,702 sera were tested from November 1981 through August 1982. Dengue virus was isolated from 518, for an isolation rate of 19.2%. Dengue 1 was the predominant virus until December 1981, when dengue 4 became dominant. The changing patterns of dengue 1 and 4 distribution by time and geographic location on Puerto Rico were followed. This system allows the dengue viruses being transmitted in an area to be monitored with a minimal amount of effort and provides the early warning capability necessary to predict epidemic dengue.

Identification of Plasmodium falciparum-infected mosquitoes by a double antibody enzyme-linked immunosorbent assay

Abstract: A double antibody micro enzyme-linked immunosorbent assay (ELISA) for identifying Plasmodium falciparum sporozoites in mosquitoes is described. Using monoclonal antibodies made against South American P. falciparum sporozoites, the ELISA was able to detect and identify sporozoite antigens of South American and Asian origins in extracts of dried infected mosquitoes.

Increased intradermal probing time in sporozoite-infected mosquitoes.

Abstract: Because malaria sporozoites destroy segments of the salivary glands of vector mosquitoes, we determined whether salivary function is impaired. Such pathology would result in a prolonged intradermal probing phase of feeding behavior, because the role of saliva is to help locate blood vessels. Indeed, non-infected Aedes aegypti mosquitoes probed for a shorter period than did either sporozoite-infected or saliva-deprived mosquitoes. Salivary apyrase activity is reduced to a third following maturation of sporozoites. Apyrase activity, normally, is confined to those regions invaded by sporozoites. Sporozoite-infected and non-infected mosquitoes produced equal volumes of saliva. We conclude that sporozoite infection impairs the vector's ability to locate blood vessels by affecting the quality of salivary product, thereby increasing potentially infective host contacts.

Replication and Dissemination of Rift Valley Fever Virus in Culex Pipiens

Abstract: Following ingestion of 10(4.2) to 10(7.2) plaque-forming units (PFU) of Rift Valley fever (RVF) virus, 662 of 850 female Culex pipiens (78%) became infected. Those mosquitoes that became infected separated into two distinct groups: 1) those with a nondisseminated infection limited to the gut, and 2) those with a disseminated infection. The former group contained a median of 10(3.2) PFU, while those females with a disseminated infection contained a median of 10(5.5) PFU. Only those females with a disseminated infection were capable of transmitting virus by bite to a susceptible hamster. This is consistent with a mesenteronal escape barrier to viral dissemination. Following intrathoracic inoculation of RVF virus, all females developed a disseminated infection (26/26) and successfully transmitted virus by bite (49/49) if allowed to feed on a susceptible hamster or suckling mouse. Examination of legs and bodies separately provided a rapid and efficient method of determining dissemination status.

Cryptosporidiosis in children from some highland Costa Rican rural and urban areas.

Abstract: This report summarizes both a prospective study of diarrhea in cohorts of rural children in their natural ecosystem, and a vertical study of diarrheic urban children attending a hospital emergency service. Cryptosporidium oocysts were found in feces of 4.3% of the cases, while all controls were negative. No infection occurred in the first year of life among rural infants, contrasting with a 3% infection rate in children under 1 year of age in the metropolitan area. This could be attributed to intense and exclusive breast-feeding for several months in the rural area while in the urban area many infants are not breast-fed at all, or are weaned prematurely. No infection was found in wholly breast-fed infants. Diarrhea associated with Cryptosporidium was watery and without inflammatory cells. Dehydration was common in urban children, but was rapidly corrected by oral rehydration therapy, or by intravenous fluid therapy in some cases. Infections clustered in the warmer, rainy and humid months of the year.

Gametocyte-forming and non-gametocyte-forming clones of Plasmodium falciparum.

Abstract: Three clones have been prepared from the Honduras I/CDC strain of Plasmodium falciparum by a method of microscopic selection. One of these (HB-2) does not form gametocytes whereas the others (HB-1 and HB-3) do. All three are as resistant to pyrimethamine as the original line, and all three form knobs on the erythrocyte surface.

Synergistic antimalarial activity of pyrimethamine and sulfadoxine against Plasmodium falciparum in vitro.

Abstract: Two strains of Plasmodium falciparum were tested in vitro for sensitivity to the dihydrofolate reductase inhibitor pyrimethamine, the p-aminobenzoic acid (PABA) analogue sulfadoxine, and combinations of both drugs. One strain was sensitive and one resistant to pyrimethamine in vitro. Parasites cultured in medium containing neither folic acid nor PABA were inhibited by 10-6 M sulfadoxine, a concentration well below that achievable after therapeutic dosage. Folic acid added to this medium at a physiological concentration of 0.01 mg/liter caused a 1,000-fold reduction in sulfadoxine activity; a 100-fold higher concentration of folic acid caused a 10-fold reduction in pyrimethamine activity. Sulfadoxine in a concentration of 10-7 M was able to potentiate pyrimethymine activity in PABA-free medium with no added folic acid or with 0.01 mg folic acid/liter. These data indicate that P. falciparum can utilize exogenous folic acid, and suggest that sulfadoxine may potentiate pyrimethamine activity by simultaneous inhibition of dihydrofolate reductase.

Chronic strongyloidiasis in World War II Far East ex-prisoners of war.

Abstract: Fifty-two of 142 (37%) American ex-prisoners of war that worked on the Burma-Thailand Railroad during World War II were found to have previously unrecognized symptomatic Strongyloides stercoralis infections. A characteristic urticarial creeping skin eruption on the abdomen, buttocks and thighs occurred in 92%. Infection was also associated with pruritus ani, abdominal pain, indigestion, heartburn, and diarrhea. Demonstration of larvae in ether-formalin stool concentrates in these chronic low density infections required 5 hours of microscopy per case to detect 90% of positive cases. Therapy with thiabendazole resulted in a clinical cure in 93% and a microscopic cure in 100%; but was associated with frequent side effects. Chronic strongyloidiasis should be considered in veterans of Far East conflicts and in others with intimate soil contact in rural Strongyloides stercoralis-endemic areas who present with recurrent creeping skin eruption, abdominal pain, and eosinophilia.

Nitazoxanide in the Treatment of Taenia Saginata and Hymenolepis nana Infections

Abstract: Nitazoxanide, a nitrothiazole derivative, was tested in 22 patients infected with Taenia saginata and 18 infected with Hymenolepis nana. A single 25 mg/kg body weight dose was effective against T. saginata, while twice this dose level (50 mg/kg), also as a single dose, was required for treating H. nana infection. Tolerance of the drug was good at both dose levels used.

Penicilliosis marneffei in Thailand: report of five human cases.

Abstract: The first two cases of Penicillium marneffei infection in humans were reported in 1959 and 1973. There had been no additional clinical reports of penicilliosis marneffei, until the five new cases of human infection described in this paper, the first from Thailand. The patients, three of whom died, came from various parts of the country. Their common clinical manifestations were fever and generalized lymphadenopathy, with multiple soft tissue, bone, joint and pulmonary involvement. Pericarditis with effusion was also seen. The diagnosis was established by isolating and identifying a dimorphic Penicillium species that produced a soluble red pigment in its mycelial form. The histopathologic features of the lymph nodes and bone marrow were similar to those of histoplasmosis capsulati. However, the yeast-like tissue form of P. marneffei divides by fission; that of Histoplasma capsulatum by budding. Treatment with amphotericin B was effective when this antifungal antibiotic was administered early in the course of the disease.

Gametocyte production in cloned lines of Plasmodium falciparum.

Abstract: Gametocyte production by cloned lines of Plasmodium falciparum and their parental isolates has been studied in culture over periods of several months. Many isolates differed significantly from each other in their capacity for gametocyte production. Clones derived from an individual isolate were also widely different in capacity for gametocyte production. Consistent differences in gametocyte production were observed between clones which had always been grown concurrently and thus had identical culture histories. Levels of gametocytogenesis characteristic of individual clones, although subject to transient fluctuations under environmental influence, were stable over several months.

Comparison of Schistosoma mansoni migration patterns in normal and irradiated cercaria-immunized mice by means of autoradiographic analysis. Evidence that worm elimination occurs after the skin phase in immunized mice.

Abstract: Migration and elimination of radiolabeled Schistosoma mansoni were compared in naive and irradiated cercaria-immunized mice by autoradiography of compressed host tissues. The results indicated that 1) most of the normal elimination of schistosomula in unimmunized mice and the additional elimination in immunized mice occur at some point(s) after arrival of schistosomula in the lungs and before their development into adult worms, 2) migration of schistosomula from skin to lungs is delayed for several days but not reduced in immunized mice, 3) migration of schistosomula from lungs to liver is delayed for several days in immunized mice, and 4) schistosomula reach the liver in reduced numbers or are killed and cleared in the liver in greater numbers in immunized mice. The lung chop procedure was shown to recover schistosomula from control and irradiated cercaria-immunized mice with equal efficiency. Autoradiography of all tissues of the body demonstrated that, in both control and immunized mice, at least 20–25% of the schistosomula detectable 2 and 3 weeks after infection were present in tissues other than the skin, lungs and liver.

In vitro antimalarial activity of tetrahydrofolate dehydrogenase inhibitors.

Abstract: Three tetrahydrofolate dehydrogenase (dihydrofolate reductase = EC 1.5.1.3) inhibitors were tested for antimalarial activity against Plasmodium falciparum, using an in vitro radioisotopic technique. Activity of each drug was tested in both normal RPMI medium 1640 and in modified medium (containing no p-aminobenzoic acid and 2.27 × 10-8 M folic acid) after a 24- or 48-hour exposure. Activity was increased 20- to 85-fold using the modified medium and the longer exposure time. Under all conditions, pyrimethamine and cycloguanil were of equal or greater potency than an experimental pyrimethamine analogue, M&B 35769, against pyrimethamine-sensitive strains, but M&B 35769 was more active than either pyrimethamine or cycloguanil against pyrimethamine-resistant strains.

Hantaan-Like Viruses from Domestic Rats Captured in the United States*

Abstract: Recent observations that Rattus rodents in Asia harbor Hantaan (HTN)-like viruses associated with hemorrhagic fever with renal syndrome led us to investigate the possibility that similar viruses might be present in the United States. Wharf rats were captured at major port cities, their sera were examined for HTN antibody by immunofluorescent antibody (IFA) assay and tissues from selected antibody-positive rats were examined for HTN antigen. Rats positive for both antibody and antigen to HTN virus were found in Philadelphia, PA and Houston, TX. Infected rats were found clustered in discrete foci where a significant proportion was antibody and antigen positive. Viruses isolated from lung tissues of Rattus norvegicus captured at Philadelphia and Houston were grown in cell culture and shown to be closely related to each other and to the 76–118 strain of HTN virus by IFA, but clearly distinct from HTN by plaque reduction neutralization tests. The isolates appear to be variants of the same new virus, for which the name Girard Point virus is proposed.

The Prevalence of Human Melioidosis in Northern Queensland

Abstract: Sera from 9,047 individuals from Northern Queensland were examined for the presence of hemagglutinating antibodies to Pseudomonas pseudomallei, the causative agent of melioidosis, and 512 (5.7%) were found to have titers of 1:40 or greater. The distribution of positive reactors in various groups was uneven, and significantly higher prevalences of positive antibody titers were found in the sera from Aborigines (7.9-10.6%), Torres Strait Islanders (7.8%), Vietnamese refugees (29%) and from persons with certain medical conditions including chronic alcoholism (15%), chronic infections (14.8%), diabetes mellitus (8.6%) and liver disease (12.9%). There were significantly fewer positive reactors (1.4%) amongst the armed forces stationed in Northern Queensland. At present, the boundaries of the major endemic region of Australia extend north from Rockhampton along the coast to Darwin and inland, west from Rockhampton to Tennant Creek in central Australia. Townsville was found to have the highest prevalence (5.2%) of positive reactors of all urban populations of Northern Queensland. The extent of the disease is such that it can no longer be considered a rare infection in Northern Queensland.

Febrile illness in Malaysia--an analysis of 1,629 hospitalized patients.

Abstract: We studied 1,629 febrile patients from a rural area of Malaysia, and made a laboratory diagnosis in 1,025 (62.9%) cases. Scrub typhus was the most frequent diagnosis (19.3% of all illnesses) followed by typhoid and paratyphoid (7.4%); flavivirus infection (7.0%); leptospirosis (6.8%); and malaria (6.2%). The hospital mortality was very low (0.5% of all febrile patients). The high prevalence of scrub typhus in oil palm laborers (46.8% of all febrile illnesses in that group) was confirmed. In rural Malaysia, therapy with chlor-amphenicol or a tetracycline would be appropriate for undiagnosed patients in whom malaria has been excluded. Failure to respond to tetracycline within 48 hours would usually suggest a diagnosis of typhoid, and indicate the need for a change in therapy.

Identification of malaria-infected mosquitoes by a two-site enzyme-linked immunosorbent assay.

Abstract: A micro enzyme-linked immunosorbent assay (ELISA) for identifying malaria sporozoites in mosquitoes is described. Using an extract of dried infected mosquitoes as antigen, a two-site ELISA was sensitive enough to detect one infected mosquito in a pool of 20. The species specificity, sensitivity and ease of performance of this assay, as well as the stability of the reagent, should make it a useful epidemiological tool.

Intestinal Protozoa in Homosexual Men of the San Francisco Bay Area: Prevalence and Correlates of Infection*

Abstract: To compare the prevalence of intestinal parasitic infection in male homosexuals selected from other sources with the levels previously reported from clinic-derived populations, various homosexual groups of the San Francisco Bay Area were checked by means of stool examination and questionnaires for prevalence of intestinal parasites and for related sexual behavioral patterns during a 3-year period. The prevalence of Entamoeba histolytica (28.6%) was similar to that reported in other studies, whereas that of Giardia lamblia was lower. Infection with E. histolytica was correlated significantly with a prior history of syphilis or gonorrhea (P < 0.0001), with the number of sexual partners in the preceding 12-month period (P < 0.0001), and with the reported frequency of oral-anal sexual contact (P < 0.001). Giardial infection was also significantly related to oral-anal sex (P < 0.001). No relation was seen between the presence or absence of gastrointestinal symptoms and infection with pathogenic protozoa. Factors associated with parasitic infection differed little from those found in previous studies, although significance levels were considerably higher because of the larger size of our study group.

Plasmodium falciparum strain-specific human antibody inhibits merozoite invasion of erythrocytes.

Abstract: The extent to which human antibodies involved in functional immunity react with antigenic determinants varying between different isolates or strains of the human malaria parasite Plasmodium falciparum will influence the design of vaccines against malaria. We identified nine immune sera from Cambodian refugees which blocked in vitro invasion of erythrocytes by merozoites of the Camp strain of P. falciparum and agglutinated Camp strain merozoites. However, none of these sera blocked invasion of erythrocytes by merozoites of the FCR-3 strain. We conclude that antibodies in these human sera recognized antigenic determinants present on the surface of viable merozoites of the Camp strain but not the FCR-3 strain. These parasite strains and in vitro assays can be used to analyze strain-specific functional immunity in humans.

Monoclonal antibody characterization of Plasmodium falciparum antigens.

Abstract: We characterized a set of eight monoclonal antibodies produced against Plasmodium falciparum. In an indirect fluorescent antibody assay the antibodies produced small dots of fluorescence in schizonts and individual merozoites. This merozoite-associated dot reactivity occurred with 21 different strains of P. falciparum, but there was no reactivity with other human, nonhuman primate, or rodent Plasmodium species. Three of the monoclonal antibodies precipitated proteins of Mr 145,000, 135,000, and 104,000. Five of the monoclonal antibodies precipitated proteins of Mr 78,000, 63,000, 42,000, and 40,000.

An immunoassay for the detection of circulating antigens in human echinococcosis.

Abstract: An immunoassay (double-antibody-sandwich-ELISA) was developed to detect circulating antigens (CAg) in patients with cystic (Echinococcus granulosus) echinococcosis. Echinococcus antigens derived from heterologous intermediate hosts were used to immunize rabbits and to purify the rabbit-IgG-fraction obtained by affinity-chromatography, thus avoiding major interference with host components. The purified rabbit anti-hydatid IgG was immunosorbed with bovine and human sera. One part of the resulting IgG served as coating agent in a double antibody sandwich-ELISA; the other part, coupled to alkaline phosphatase, as detecting conjugate. The specificity of the antibody reaction was demonstrated by immunoelectrophoresis. Sera of 21 patients with cystic echinococcosis were examined with this test system. In seven of the patients' sera CAg were detected in concentrations ranging between 310 ng and 680 ng protein per ml serum. Comparing pre- and postoperative serum samples obtained from nine patients operated on for cystic echinococcosis, four sera were found to be CAg-positive before and three after operation.

Enteric coccidiosis among patients with the acquired immunodeficiency syndrome.

Abstract: Ten patients were identified at Jackson Memorial hospital/University of Miami Hospitals and Clinics with enteric coccidial infection due to Cryptosporidium spp. or Isospora belli. All had the acquired immunodeficiency syndrome as manifested by Kaposi's sarcoma or multiple opportunistic infections, or both. They presented with profuse diarrhea associated with weakness, anorexia, and weight loss. Routine examinations of stools for eggs and parasites as performed by the hospital laboratory were negative in all patients. Sugar flotation and modified acid fast techniques were used in the Tropical Disease Laboratory to identify oocysts of Cryptosporidium spp. in stools of seven patients. Malabsorption, characterized by a low 5-hour D-xylose and positive fecal fat, was observed in 6/6 of these patients. In three other patients Isospora belli oocysts were identified in stool specimens or via a duodenal string test. Spiramycin was the only drug found to be effective in treating patients with cryptosporidiosis. Patients with Isospora belli responded to a prolonged course of trimethoprim-sulfamethoxazole.

Melioidosis in Far North Queensland. A clinical and epidemiological review of twenty cases.

Abstract: During the last 4 years, 20 cases of clinical melioidosis were diagnosed in the geographical area between Tully and Thursday Island. Sixteen were diagnosed by culture of Pseudomonas pseudomallei, and four by positive serology with appropriate clinical features. Most cases occurred during or after a heavy wet season. All patients were adult, and males predominated. Farmers and stockmen represented predisposed populations due to their prolonged soil contact. Ten patients were white Australians, six were Aborigines and four were Torres Strait Islanders. Twelve cases were first diagnosed by positive blood culture and four by sputum culture. The primary site of infection was pulmonary in 14 cases, genitourinary tract in one case, subcutaneous tissues in one case, and joints in two cases. In cases of fulminating infection metastatic abscesses were commonly found in many organs; typically lungs, liver, kidneys and spleen. Six patients had acute fulminating disease and died. Fourteen patients successfully responded to appropriate therapy, but relapse occurred in three, all of whom had an alcohol problem and showed poor drug compliance. The presence of diabetes mellitus in six patients confirmed the important known association of these two diseases. In three fulminating and four subacute infections the serology was negative at the time of diagnosis by culture. Antibiotic therapy for the different forms of this disease is reviewed, and a laboratory protocol for the rapid reporting of positive culture results is included.

The effect of colonization upon aedes aegypti susceptibility to oral infection with yellow fever virus.

Abstract: Two colonies of Aedes aegypti were established from two independent col lections from Vero Beach, Florida. Eleven sequential generations of the first colony were tested for variation in oral susceptibility to infection with yellow fever virus (YFV). Each generation was also assayed for genetic variability at seven enzyme loci using elec- trophoretic techniques. Significant differences in infection rates were detected between some generations. These differences were significantly correlated with genetic variation at the malate dehydrogenase locus. Seven generations from the second colony were examined simultaneously for variation in susceptibility to YFV. Significant differences were also detected between some of these generations. The results suggest that colonization may have an effect on the genetic and phenotypic variation in a mosquito strain, and that genetically based variation for susceptibility to infection with YFV occurs in populations of Ae. aegypti.

The effectiveness of permethrin and deet, alone or in combination, for protection against Aedes taeniorhynchus.

Abstract: Field tests were conducted to compare the degree of protection from bites by the mosquito Aedes taeniorhynchus (Wiedemann) provided by wearing clothing treated with permethrin [(3-phenoxyphenyl)methyl (+/-) cis/trans 3-(2-dichloroethenyl)2, 2-dimethylcyclopropanecarboxylate] with that provided by applying deet (N,N-diethyl-m-toluamide) to exposed skin or by applying deet and wearing the treated clothing. Human test subjects were exposed to natural populations of mosquitoes for a 9-hour daytime period (total of 8 days/treatment) while using one or both protection methods. Unprotected test subjects were also exposed for short periods each day as a check to determine the overall biting rate of mosquitoes. The combined use of both protection methods was the most effective treatment in preventing bites, resulting in an average of 1.5 bites/9-hour day, compared with 53.5 and 98.5 bites on subjects protected only with treated clothing or deet, respectively, and 2,287 bites (extrapolated) on subjects who wore untreated clothing during the same time period. Measurements also indicated that the toxic effect of permethrin reduced biting rates by greater than 90% within the immediate area where subjects wore permethrin-treated uniforms for 9 hours.

First field trial of an immunoradiometric assay for the detection of malaria sporozoites in mosquitoes

Abstract: An immunoradiometric assay (IRMA) using a monoclonal antibody to the major surface protein of Plasmodium falciparum sporozoites was used to assess the P. falciparum sporozoite rate in a West African population of Anopheles gambiae (s.1.). Unlike current dissection techniques, the IRMA could detect sporozoite antigen in dried as well as fresh mosquitoes. In a controlled comparison, the sensitivity of the IRMA was comparable that of the dissection technique. Additionally, the IRMA was species specific and quantitative. Sensitivity of the assay was sufficient to detect sporozoite infections resulting from the development of a single oocyst.

Proteins responsible for a punctate fluorescence pattern in Plasmodium falciparum merozoites.

Abstract: Mouse monoclonal antibodies (McAbs) have been used to characterize the proteins of the asexual erythrocytic cycle of Plasmodium falciparum. Three different McAbs react with antigens of the schizont and extracellular merozoite to give a punctate fluorescence pattern. In many cases, such areas of fluorescence were composed of two adjacent, fluorescent bodies; these were distinct from the nuclei. In contrast, McAbs which bound to the ring-stage parasite were not localized, but were diffusely distributed within or around the ring-stage parasite. These McAbs immunoprecipitated five prominent, 35S-methionine-labeled schizont proteins (p) of Mr 82K, 70K, 67K, 39K, and 37K. Only p82, p39, and p37 were immunoprecipitated from schizont-labeled ring-stage parasites; thus, it appears that p70 and p67 are modified, degraded, or secreted some time between intracellular merozoite maturation and erythrocyte invasion.

Natural transovarial transmission of dengue 4 virus in Aedes aegypti in Trinidad.

Abstract: The isolation of dengue 4 virus from adult Aedes aegypti, reared from eggs collected in nature, is reported for the first time. From the locality where the isolate was made, 25 pools consisting of 1,848 Ae. aegypti reared from eggs were processed. In this study, 10 different localities were sampled and a total of 10,957 Ae. aegypti adults, collected as eggs or larvae in nature, were processed for virus isolation. From a total of 158 mosquito pools tested, one recovery of dengue 4 virus was made. The isolation of dengue 4 virus from this field-collected material gives further evidence that transovarial transmission of dengue viruses occurs in nature.

Association of a Sindbis-like virus with Ockelbo disease in Sweden.

Abstract: An alphavirus isolated from Culiseta mosquitoes has been associated with Ockelbo disease, an exanthema arthralgia syndrome occurring in Sweden. The isolate was made from mosquitoes collected in Edsbyn (central Sweden), an area with considerable Ockelbo disease morbidity. This isolate proved to be indistinguishable from Sindbis virus by complement-fixation and hemagglutination-inhibition tests, and was antigenically related to Sindbis in plaque reduction neutralization tests. Patients with Ockelbo disease developed neutralizing antibodies to the virus in their convalescent sera, suggesting that it is the etiologic agent of the disease.