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Summary: Evidence for the presence of simian T-lymphotropic viruses (STLV-I) was identified in live-caught pig-tailed macaques from two locations in southern Sumatra, Indonesia. Of 60 animals tested, 13.3% of the animals showed seroreactivity to HTLV-I/II enzyme-linked immunosorbent assay (ELISA) antigens. Of these, 75% showed indeterminate reactivity and 25% showed positive reactivity to HTLV-I/II Western blot antigens. Polymerase chain reaction (PCR) analysis of 6 of 8 seroreactive monkeys' peripheral blood mononuclear cell (PBMC) DNA showed production of proper size molecular weight product that hybridized specifically to an STLV-I tax genespecific probe. Phylogenic analyses of tax gene fragment sequences from the PCR products of two samples, 930287 and 930306, indicated that these animals were infected with retroviruses related to those of the Asian STLV-I clade.

Initially, strain CUAS-1T (T = type strain), which was isolated from a frozen triturate of Culex annulus mosquitoes collected in Taiwan, was thought to be a member of spiroplasma group VII. This placement was based on the spiroplasma deformation test titer observed when strain CUAS-1T spiroplasmas were tested with Spiroplasma monobiae MQ-1T antiserum. The results of subsequent reciprocal spiroplasma deformation, metabolism inhibition, and growth inhibition tests clearly revealed that strain CUAS-1T is not serologically related to previously described spiroplasma groups (groups I to XXIV) and thus is a representative of a new group, group XXV. Strain CUAS-1T was characterized by using the minimal standards for mollicute species descriptions. During logarithmic-phase growth, strain CUAS-1T cells are characteristically very short helices with 1.5 to 2 helical turns (1 to 2 microns), highly motile, and bounded by a single trilaminar membrane and form granular colonies with satellites when the organism is grown aerobically on MID medium containing 1.6% agar. Growth in MID broth occurs at temperatures ranging from 10 to 37 degrees C, and the optimum temperature is 30 degrees C. Substrate utilization tests revealed that cholesterol is required for growth, that glucose is hydrolyzed, and that arginine is not hydrolyzed both in the presence and in the absence of glucose. The genome of strain CUAS-1T is 1,080 kbp long, and the guanine-plus-cytosine content is 26 +/- 1 mol%. On the basis of the results of our studies we propose that strain CUAS-1T (group XXV) should be placed in a new species, Spiroplasma diminutum. Strain CUAS-1 (= ATCC 49235) is the type strain of S. diminutum.

International audience; Dengue hemorrhagic fever has been a major health problem in Asia since the 1950s. During this period, the former principal vector of dengue viruses in Asia, Aedes albopictus, was replaced by Aedes aegypti in most major cities of the area. Ae. aegypti is now considered the main vector of dengue viruses in Asia. Surprisingly, however, this mosquito has been described as having a relatively low oral receptivity for dengue viruses compared with Ae. albopictus. In the present study, we compared the relative oral receptivities of Ae. aegypti and Ae. albopictus collected in southeast Asia from both sympatric and allopatric breeding sites. In all instances, the oral receptivity of Ae. aegypti to the dengue type 2 virus used was significantly higher than that of Ae. albopictus. We also compared the relative oral receptivity of Ae. aegypti and Ae. albopictus for two other low-passage strains of dengue 2. In all instances, Ae. aegypti was significantly more receptive than Ae. albopictus. It should be noted, however, that the difference was found only for Ae. albopictus recently collected from the field (Ta Promh strain, Cambodia, 2001) and not for an Ae. albopictus strain that had been colonized for many years (Oahu strain, Hawaii, 1971). We also observed a significant increase in the infection rate of Ae. albopictus of the Ta Promh strain with increasing generations in the laboratory. These observations demonstrate the importance of considering the colonization history of mosquitoes when assessing their susceptibility to infection with dengue viruses and, perhaps, other arboviruses.

Autopsy tissues from 18 children believed to have died of dengue hemorrhagic fever were tested for the presence of dengue virus RNA by reverse transcription-polymerase chain reaction (RT-PCR). Such RNA was found in 14 of 18 liver specimens, 13 of 18 spleen specimens and 7 of 16 mesenteric lymph node specimens. No dengue virus RNA was detected in 44 samples of brain tissue from 15 individuals, 1 or more of whose other tissues yielded such RNA. All tissues had been tested previously for dengue virus by mosquito inoculation. In those tests, virus was recovered from 5 of 18 liver and 2 of 18 spleen specimens. Thus, the RT-PCR is more sensitive than the most sensitive virus isolation technique for detecting dengue virus or its components in human tissue. Failure to isolate virus from most of spleen and all mesenteric lymph node specimens may indicate that those tissues contained primarily degraded virus undergoing inactivation.

Evolutionary associations of human and simian T-cell leukemia/lymphotropic viruses I and II (HTLV-I/II and STLV-I/II) are inferred from phylogenetic analysis of tax gene sequences. Samples studied consisted of a geographically diverse assemblage of viral strains obtained from 10 human subjects and 20 individuals representing 12 species of nonhuman primates. Sequence analyses identified distinct substitutions, which distinguished between viral types I and II, irrespective of host species. Phylogenetic reconstruction of nucleotide sequences strongly supported two major evolutionary groups corresponding to viral types I and II. With the type I lineage, clusters were composed of strains from multiple host species. A genetically diverse, monophyletic lineage consisting of eight new viral strains from several species of Asian macaques was identified. The second lineage consisted of a monophyletic assemblage of HTLV-II/STLV-II strains from Africa and the New World, including an isolate from a pygmy chimp ( Pan paniscus ) as an early divergence within the lineage. High levels of genetic variation among strains from Asian STLV-I macaque suggest the virus arose in Asia. Evidence of the origin of the type II virus is less clear, but diversity among HTLV-II variants from a single isolated population of Mbati villagers is suggestive but not proof of an African origin.

The dengue type 4 virus (DEN4) RNA genome contains a 101-nt 5′ noncoding (NC) sequence which is predicted to form a stable secondary structure DEN4 cDNA from which infectious RNA can be transcribed was used to engineer deletions in the 5′ NC region for functional analysis of RNA structure and for isolation of DEN4 mutants that could be evaluated as candidates for use in a live attenuated vaccine. Eleven distinct deletions in the region of the DEN4 genome between nts 18 and 98 were constructed; each mutation was predicted to alter or disrupt the local base-parings in the 5′ NC RNA structure. An infectious virus was not recovered from the RNA transcripts of five of these deletion mutants. Significantly, four of the five apparently lethal deletions were located in a 5- to 6-nt base-paired region of a predicted long stem or adjacent to it. In contrast, with one exception, mutants which yielded infectious virus had deletions which were located in a loop or short stem region. The effect of the deletions on the efficiency of translation of viral RNA transcripts was examined in vitro . The RNA transcripts of deletion constructs which did not yield viable virus were translated at an efficiency ranging from 40 to 160% that of wild-type virus transcripts. The translation efficiency of infectious RNA transcripts also varied. Deletion mutants recovered from RNA transcripts that exhibited low to moderate efficiency of translation had a small plaque morphology and exhibited reduced growth in simian LLC-MK 2 and mosquito C6/36 cells compared to the wild-type virus. Among the 11 mutant constructs, deletion of nts 82-87 caused the greatest reduction in translation efficiency. Nevertheless, an infectious virus was recovered from LLC-MK 2 cells transfected with the RNA transcripts of mutant d(82-87). The progeny of this mutant produced small plaques on LLC-MK 2 cells and grew to low titer in these cells. Unlike wild-type DEN4 or other DEN4 deletion mutants tested, mutant d(82-87) failed to produce plaques on C6/36 cells and was also replication-defective in Aedes aegypti and Aedes albopictus following intrathoracic inoculation.

Japan is one of the highest endemic areas of the world for human T cell leukemia-lymphoma virus type I (HTLV-I). To gain new insight as to the origin of this virus in Japan and especially in the southern islands of the archipelago, we investigated the long terminal repeat (LTR) of 67 newly isolated HTLV-I proviral DNAs from peripheral blood mononuclear cells of HTLV-I-infected individuals for their restriction fragment length polymorphism (RFLP). The specimens were from Japanese living in different geographical areas (Hokkaido, Honshu, Kyushu, or the Ryukyu Islands) of Japan (59 cases) or Americans of Japanese ancestry living in Hawaii (8 cases). The analysis of the results, together with data for the 19 previously published LTR sequences, demonstrated the existence of 2 subtypes of HTLV-I in Japan. The first, which we propose to name Japanese subtype (previously named subtype III), is more frequent (67 of 86: 78%) than the second, the cosmopolitan subtype (previously named subtype II) (19 of 86: 22%). In parallel, a fragment of 413 base pairs of the U3/R region (nucleotide 22 to 434) was cloned and sequenced from 10 of the new Japanese samples. The alignment of these sequences and their comparison and phylogenetic analysis with previously published LTR HTLV-I sequences, demonstrated clearly the existence of the two distinct molecular subtypes of HTLV-I in Japan, diverging in this LTR region by about 1.6%. Furthermore, the study of the geographical distribution of the 2 subtypes among the 80 samples from patients whose place of residence in Japan was known showed an uneven distribution. While the Japanese subtype was present in all parts of Japan, the cosmopolitan subtype seemed to cluster in the southern islands of the archipelago (i.e., Kyushu and the Ryukyu Islands) as well as in immigrants from those areas who had lived in Hawaii for decades. These new molecular data raise questions and suggest hypotheses, discussed here, concerning the origin and means of dissemination of these human retrovirus subtypes in Japan.

A virus, named Matsu, presumed to be the etiologic agent of hereditary sensitivity to carbon dioxide in Culex quinquefasciatus mosquitoes, was adapted to growth in the C6/36 line of Aedes albopictus cells. Though it was expected that the mosquito virus would be a rhabdovirus like sigma, the etiologic agent of hereditary carbon dioxide sensitivity in Drosophila melanogaster flies, that was not the case. The virion of Matsu was found to be unlike any previously described virus. It was pleomorphic, enveloped, from 200 to 550 nm in maximum diameter, and contained from three to several dozen virus-like polyhedral structures approximately 30 nm in diameter.

As previously observed for dengue viruses, vertical (i.e., transgenerational) transmission of Japanese and St. Louis encephalitis viruses by Aedes albopictus takes place when the fully formed egg, enclosed in the chorion, is oviposited. The demonstration of such a mechanism for three flaviviruses suggests that vertical transmission of all mosquito-borne flaviviruses may occur in the same manner.

Dengue virus isolates have been grown in the Igarashi clone C6/36 Aedes albopictus cells in amounts suitable for biochemical studies. Oligonucleotide fingerprint analyses have been used to characterize the virion 40 S RNA species of the four prototype dengue (DEN) serotype viruses: DEN 1, Hawaiian strain; DEN 2, New Guinea C strain (both insect and mouse brain passaged derivatives); DEN 3, H-87 strain; and DEN 4, H-241 strain. Comparisons of the largest oligonucleotides derived by ribonuclease T1 digestion of these 40 S DEN virion RNA species indicate that ther are few, if any, large oligonucleotides that are homologous between any two fo the four dengue prototype strains. Preliminary analyses of the 40 S RNA 5' terminal sequence of DEN 3 virion RNA indicate that it has the composition of m7GpppAmpXp.

An outbreak of dengue type 2 infection occurred in the Pacific island Kingdom of Tonga in 1974 and an outbreak of dengue type 1 occurred there in 1975. The 1974 outbreak was characterized by relatively mild clinical disease with few hemorrhagic manifestations, a low attack rate, and relatively low viremia levels. The 1975 outbreak was characterized by relatively severe disease with frequent hemorrhagic manifestations and a high attack rate. The differences between the outbreaks could not be attributed to differences in abundance of, or susceptibility to infection of, mosquito vectors or to the prior immune status or other characteristics of the human population. It appeared that a difference in viral virulence was the most likely explanation.

Five species of colonized Toxorhynchites mosquitoes were compared for relative susceptibility to parenteral infection with the four dengue serotypes and St. Louis and Japanese encephalitis viruses. Tx. amboinensis, Tx. brevipalpis, Tx. rutilus, and Tx. splendens were equally susceptible to infection with the dengue viruses, while Tx. theobaldi was relatively resistant to infection with those viruses. All five mosquito species were equally susceptible to infection with the encephalitis viruses. The intensity of immunofluorescence in head squashes was slightly less in Tx. brevipalpis infected with the dengue viruses as compared to the other three mosquito species susceptible to those viruses. Immunofluorescence was also less in Tx. theobaldi infected with the encephalitis viruses as compared with all the other mosquito species.

It can be concluded from the data cited that transovarial transmission is a plausible explanation for the overwintering of mosquito-borne bunyaviruses of the California serogroup. Vertical transmission of mosquito-borne flaviviruses could explain the overwintering of this group of viruses, but this is far from having been established. At present, the mechanism by which mosquito-borne alphaviruses pass the winter is obscure.

Single strains of dengue (DEN) virus types 1–4 at low passage levels after isolation in Thailand, New Caledonia or the Philippine Islands produced no overt, febrile or hematologically detectable subclinical disease in chimpanzees inoculated subcutaneously and intradermally. After primary inoculation, viremias occurred usually from days 2 or 3 through days 5–7. Virus was detected in serum with about equal frequencies by either mosquito inoculation or LLCMK2 monkey kidney cell cultural technics, although mosquito inoculations usually yielded higher titers of virus. After secondary challenge with DEN 2 virus 26 mo after primary infection with DEN 1, 2, 3 or 4, viremias lasting 2–4 days occurred during days 3–6 in one or two chimpanzees originally infected with DEN 1 or DEN 4, but not with DEN 2 or DEN 3. Primary homologous DEN hemagglutination-inhibition (HI) antibody responses were greater than heterologous in pairs of young chimpanzees born in the U.S.A. and inoculated with DEN 3 or DEN 4. However, primary homologous DEN HI antibody responses were similar to heterologous responses in five adult chimpanzees from Africa inoculated with DEN 1, 2, 3 or 4 viruses and in three young chimpanzees born in the U.S.A. and inoculated with DEN 2 virus. Homologous and heterologous neutralizing (N) antibodies were found in serum 4–6 wk after primary infection of adult chimpanzees, but only homologous DEN 2 N antibodies were detected in three young chimpanzees. Preexisting antibodies to other flaviviruses were found in sera of some chimpanzees from Africa, and broad flavivirus anamnestic HI antibody responses occurred after primary inoculations of DEN viruses. Broad flavivirus HI antibody responses were also observed after primary DEN inoculations in three young chimpanzees born and housed near New York City and without preexisting flavivirus antibodies. Following secondary challenge with DEN 2 virus, HI and complement fixation antibody responses occurred to all DEN types and to related flaviviruses.

Replication of the 4 prototype strains of dengue viruses was studied in male and female Ae. albopictus mosquitoes following intrathoracic infection, and in females following oral infection. Replication was rapid in both sexes and virus titers reached levels of 107 or more mosquito infectious doses50 per insect in females. Titers attained in males were about 5-fold less than in females. Maximum titers occurred several days later in females infected orally as compared with those infected intrathoracically. Virus titers in both sexes declined slowly after reaching their maxima. Replication of 3 nonprototype strains of dengue type 3 also was studied in male and female Ae. albopictus mosquitoes following intrathoracic infection. Replication of each strain appeared to be significantly different than the prototype.

Aedes japonicus (Theobald) was evaluated for competence as a vector of Japanese encephalitis virus and for its ability to transmit the virus vertically to its F1 larvae. Ae. japonicus supported the growth of the virus at 20 and 28 degrees C after feeding on a virus-blood mixture of 10(6.2) plaque forming unit (PFU)/ml. This species was able to transmit the virus to suckling mice after feeding on a virus-blood meal (10(6.2) PFU/ml) or a viremic chick (10(3.7) PFU/ml). Vertical transmission of the virus in Ae. japonicus was demonstrated with a minimum infection rate of 0.7%.

Male Aedes albopictus experimentally infected with dengue virus types 1, 2, 3, or 4 transmitted their infection sexually to female Ae. albopictus. Such transmission was enhanced if the females had taken a bloodmeal 2 to 7 days prior to mating. Male Ae. albopictus also transmitted dengue virus vertically to their F1 progeny. Infected progeny were found among those derived from eggs laid greater than or equal to 73 hr after mating but not among those derived from eggs laid prior to that time. This suggests that virus probably was not transmitted directly to ova but, rather, underwent prior replication in the female genital tract. Female Ae. albopictus experimentally infected with dengue type 1 virus did not transmit their infection sexually to males. This finding supports the hypothesis that male mosquitoes naturally infected with dengue virus acquired their infection vertically.

An epidemic of Ross River virus infection occurred in the Cook Islands early in 1980 and affected the majority of the inhabitants of Rarotonga, the most populated island in the group. This represents the easternmost extension of the virus which, until 1979, was believed limited to Australia, New Guinea, and the Solomon Islands. The clinical manifestations of Ross River disease, predominantly polyarthritis, did not differ significantly from those observed previously in Australia. However, unlike the experience in Australia, where Ross River virus has never been isolated from a patient with polyarthritis, the agent was recovered from the serum of one-half of approximately 100 such patients with serologically proven infections. It is not known if this latter observation is the result of a change in the virus, the different virus isolation technique employed, or other factors. It was found that the incubation period of the disease could be as short as 3 days--much less than previously suspected. Ross River virus was isolated from six pools of Aedes polynesiensis mosquitoes collected in nature and it appeared that this species was the most probable vector on Rarotonga. In view of the widespread distribution of Ae. polynesiensis on islands, in the eastern Pacific it would not be surprising if Ross River virus occurs in other previously unaffected areas in the future.

Mosquitoes from a laboratory colony of Culex quinquefasciatus from Matsu Island, China, develop irreversible paralytic symptoms after exposure to carbon dioxide at 1°. This CO2 sensitivity is caused by an inherited infectious agent, probably a virus. Crossing studies between CO2-sensitive and -resistant mosquitoes showed that the sensitivity trait is inherited extrachromosomally in a fashion strictly analogous to the hereditary transmission of sigma virus in Drosophila melanogaster. Sensitivity could be maintained through maternal transmission alone, despite nine generations of backcrossing of "stabilized" CO2-sensitive females to males from a resistant strain. CO2-sensitive males crossed to resistant females transmitted sensitivity to a portion of their F1 progeny, and only the female F1 sensitives were capable of further hereditary transmission.—Matsu, or a very similar hereditary infectious agent, is common in natural populations of Cx. quinquefasciatus on Oahu, Hawaii. Fifty-nine percent of the families reared from field-collected egg rafts contained CO2-sensitive mosquitoes, and some families contained only sensitive mosquitoes.

Prior laboratory studies and field observations suggested that it might be possible to reduce the size of the population of, or eliminate, Aedes polynesiensis by the introduction of Aedes albopictus. The former mosquito is the principal vector of nonperiodic filariasis caused by Wuchereria bancrofti and the latter is a closely related species refractory to the development of human filariae. The practicability of such competitive displacement was studied by a field trial on a remote coral atoll where there was an established population of A. polynesiensis. Three strains of A. albopictus were liberated at separate localities on the atoll and their fate was followed for 4 years. One strain disappeared within 12 months after release and the other two disappeared within 48 months. It was not clear whether A. albopictus failed to become established because the strains were unsuitable, the general environment was inappropriate, or A. polynesiensis was present in such numbers that A. albopictus rarely succeeded in mating with its own species.

Female Aedes albopictus and Aedes epactius infected by inoculation with St. Louis encephalitis (SLE) virus transmitted virus transovarially to their F1 progeny. With Ae. epactius, minimal infection rates (MIR) in F1 larvae were similar for progeny reared at 18 (+/- 1) degree C or 27 (+/- 1) degree C, whereas, MIR's were significantly higher in F1 adults reared at 18 degrees C, than they were in F1 adults reared at 27 degrees C. Use of different strains of SLE virus appeared to influence transovarial transmission of virus by Ae. albopictus, but not by Ae. epacticus. Transovarial transmission of SLE virus was not demonstrated with colonized strains of Aedes dorsalis, Ades sierrensis, Ades triseriatus, Ades vexans, Culex pipiens, Culex quinquefasciatus and Culex tarsalis, and field strains of Ae. vexans.

Transovarial transmission of all four dengue serotypes was demonstrated in Aedes albopictus mosquitoes. The rates of such transmission varied with the serotype and strain of virus. In general, the highest rates were observed with strains of dengue type 1 and the lowest with dengue type 3. Surprisingly, despite the use of viral strains of the four dengue serotypes which gave the highest rates with Ae. albopictus, transovarial transmission was observed in Aedes aegypti only with dengue type 1, and then only at a relatively low rate. Five different strains of Ae. aegypti were employed, including one that was known to be relatively susceptible to oral infection with dengue viruses. The findings support the view that Ae. aegypti, while of major importance from the point of view of transmission of dengue to man, may be relatively unimportant in the overall natural history of dengue viruses.

The characteristics of a hemagglutinating enterovirus, Toluca-1, are described. The virus appears to be sufficiently distinct from all previously described enteroviruses to be considered a new serotype.

SummaryA study of heterologous CF antibody responses in persons naturally or experimentally infected with ECHO virus types 10, 16, and 20, Coxsackie B virus type 3, or poliovirus type 1, indicated an antigenic relationship between the following viruses: ECHO types 2, 4, 5, 6, 7, 8, 11, 14, 16, and 20, Coxsackie B virus types 1, 3, 4, and 5. No antigenic relationship was noted between ECHO virus type 10 and any of the other enteroviruses.

Mollusks from the volcanic islands of Oahu, Hawaii; Tahiti, Society Islands; and Rarotonga, Cook Islands; and from the coral atoll of Majuro, Marshall Islands, were studied in an attempt to determine which species might serve as intermediate hosts of the rat lung worm, Angiostrongylus cantonensis. Mollusks found infected with A. cantonensis on the volcanic islands were all common, introduced species that have been referred to as “tropical tramps.” They included the veronicellid slugs, Laevicaulus alte (only on Oahu) and Vaginulus plebeius (only on Rarotonga and Tahiti); the subulinid snails, Subulina octona and Prosopeas javanicum; the helicid snail, Bradybaena similaris; and the limacid slug Deroceras laeve. A. cantonensis was also found in the giant African snail, Achatina fulica, which is common on Oahu, but not present on Rarotonga or Tahiti. A large proportion of the veronicellid slugs and A. fulica contained A. cantonensis larvae, often more than 1,000 per infected mollusk. The other mollusks were much less commonly and less heavily infected. Although no marked seasonal fluctuations in the prevalence of infection was noted, a smaller percentage of mollusks was found infected, and mollusks generally contained smaller numbers of larvae, in drier areas. At least five species of aquatic and amphibious snails, of five families, were examined from the island of Oahu, but only one species, the pilid snail, Pomacea paludosa, was found infected with A. cantonensis. Ten species of snail, of six families, were examined from Majuro, but none was infected.

ECHO virus, type I was isolated from the cerebrospinal fluid and feces of an infant with aseptic meningitis. A fourfold rise in neutralizing antibody to the prototype virus occurred. This virus has been recovered from sick and well individuals but its isolation from cerebrospinal fluid has not been reported previously in the English literature. The patient subsequently appeared retarded but other possible responsible factors were present. Our findings contribute to the evidence that ECHO Type I may be etiologically related to aseptic meningitis.

An identification of the virus called U-virus has been presented and the results have shown this virus to be antigenically related to ECHO-11-virus. This was ascertained by conventional neutralization tests in tissue cultures and by the plaque reduction test as well as by haemagglutination-inhibition and complement-fixation tests.

Terrestrial, aquatic, and amphibious mollusks from Pacific islands were tested for susceptibility to infection with Angiostrongylus cantonensis. The terrestrial mollusks included five introduced species that occur commonly on high islands and 11 species typical of coral atolls. The aquatic and amphibious mollusks included species of five families of fresh-water snails, and one species of oyster. The veronicellid slug, Laevicaulus alte, was found to be a highly susceptible intermediate host of A. cantonensis, whereas two small subulinid snails, Subulina octona and Prosopeas javanicum, and a helicid snail, Bradybaena similaris, were relatively resistant. The limacid slug, Deroceras laeve, was of intermediate susceptibility when compared with the veronicellid and the snails. As a group, the atoll species were relatively resistant to A. cantonensis. With the exception of Biomphalaria glabrata, a laboratory-cultured aquatic snail not indigenous to the Pacific, the fresh-water snails were either completely or partially resistant. Attempts to infect one species of oyster were unsuccessful.

Summary In a study to determine the natural vectors of avian Plasmodium infection in Kern County, California 3,364 mosquitoes were examined for parasites during the summers of 1946, 1947, 1949 and 1950. The following average infection rates were demonstrated: Culex tarsalis, 199 of 2,074 (9.6 per cent); Culex stigmatosoma, 28 of 180 (15.6 per cent); and Culex quinquefasciatus, 14 of 746 (1.9 per cent). These differences are believed to reflect variation in vector efficiency. Of 364 Anopheles and Aedes examined, only 2 Anopheles franciscanus were infected with what appeared to be young oocysts of unidentified parasites. The intensity of infection in the principal vector, Culex tarsalis, varied considerably in different years and in different areas. These variations are believed to be due to changeable factors such as climate, the effect of mosquito control on the vector population, and ecological differences between areas. Plasmodium relictum was isolated from naturally infected Culex tarsalis and Culex stigmatosoma.

Summary Thirty monkeys of six genera which occur in the New World were inoculated with strains of type 1 and type 2 dengue virus which had never been passaged in laboratory animals. Although none of the monkeys showed overt signs of illness, almost all developed hemagglutination-inhibition (HI) or neutralizing antibodies. Viremia was demonstrated in four species of monkeys of three different genera 4 to 6 days after inoculation. The dengue and yellow fever HI antibody responses of these monkeys and others inoculated with yellow fever virus were similar to those which have been observed in persons naturally infected with these viruses.