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PubMed2005

Mosquito (Diptera: Culicidae) development within microhabitats of an Iowa wetland.

Although they provide a number of valuable ecological services, wetlands also may harbor mosquitoes that are vectors of human pathogens. During 2002 and 2003, we measured biological (i.e., abundances of mosquitoes, other insects, and total heterotrophic bacteria, vegetational cover, and dead organic material), chemical (i.e., pH, dissolved nitrate, dissolved nitrite, dissolved phosphate, total alkalinity, and electrical conductivity), and physical (i.e., water temperature, dissolved oxygen, depth, and turbidity) attributes at fixed survey sites in Beaver Valley Wetlands, a small reconstructed palustrine wetland in Black Hawk County, Iowa. The number of immature mosquitoes was significantly correlated with dissolved nitrate and dissolved phosphate concentrations in both years. During the second year of the study, the number of immature mosquitoes was significantly correlated with nonpredators and water turbidity, but not with other measured variables. Independent variables explained 87 and 70% of the variability in mosquito numbers per survey site for the 2 yr of the study, respectively. The most common species of mosquitoes developing in Beaver Valley Wetlands were Aedes vexans (Meigen) Culex territans Walker, Uranotaenia sapphirina (Osten Sacken), and Culex tarsalis Coquillet. We compared relative risks of disease transmission by the mosquitoes developing in wetland microhabitats based upon published species-specific infection rates and propensities to bite humans. The majority of mosquitoes and the greatest potential disease risks were associated with temporary pools, which represented a small proportion of the wetlands. Although relatively few mosquitoes developed in Beaver Valley Wetlands, targeted control efforts could dramatically reduce the numbers of mosquitoes produced with minimal impacts upon nontarget species.

Animals↗
PubMed1977

Experimental infection of birds with epidemic Venezuelan encephalitis virus.

Sixty-three birds representing 13 species were inoculated with a strain of epidemic Venezuelan encephalitis (VE) virus from the 1971 Texas outbreak. More than 95% of the birds became infected. Mortality which could be attributed to infection with VE virus was very low. Viremia persisted 2-6 days. Peak viremia levels ranged from 10(3.2) to 10(8.2) suckling mouse intracranial 50% lethal doses per milliliter (SMICLD50/ml). Blood virus levels were highest in juvenile Louisiana Herones, adult Robins and adult Mockingbirds and were lowest in juvenile Common Egrets. Most bird species had blood virus levels about 10(5) SMICLD50/ml (high vector infection potential) for 2-3 days. Neutralizing antibody response was more uniform and frequent in herons (95%) than in passerines (56%). The role of birds in the epidemiology of Venezuelan is discussed.

Aedes↗
PubMed2001

Evaluation of a Triatoma infestans elimination program by the decrease of Trypanosoma cruzi infection frequency in children younger than 10 years, Chile, 1991-1998.

Chagas disease is widespread in Chile, distributed in rural and periurban areas in the 7 most northern regions of the country. The principal vector of Trypanosoma cruzi is Triatoma infestans. The interruption of the domestic cycle of transmission of T. cruzi has been attempted by health education, human housing improving, and elimination of the vector by means of systematic insecticide spraying of human dwellings. Spraying with insecticides has been supported by Chile's health authorities and has been carried out for the last 12 years. A total of 13,280 children (aged up to 10 years) were randomly selected from 47 counties in the area of Chile endemic for Chagas disease, and blood samples were collected to determine the levels of antibodies to T. cruzi by indirect hemagglutination and enzyme-linked immunosorbent assay tests. The results of the tests were analyzed to determine the changes that occurred after 12 years of insecticide spraying of dwellings to eliminate T. infestans infestation. A total of 142 (1.1%) samples of children showed antibodies to T. cruzi. This rate is significantly lower than the data generated in similar studies conducted in 1982-1985. The following reduction in prevalence rates were observed in each of the 7 endemic regions of the country: region I, 5.5-0.3%; region II, 6.6-0.3%; region III, 9.8-1.0%; region IV, 7.2-2.0%; region V, 5.2-1.9%, Metropolitan region, 1.4-0.6%; and region VI, 1.4-0.4%. Serovigilance of T. cruzi antibodies level represents a novel approach that may allow the evaluation of the impact of the vector elimination program. The results identify regions that need to strengthen the efforts to reduce the insect infestation of dwellings.

Animals↗
PubMed1999

[Diversity of flea vectors as a function of plague foci].

The Indian model of plague transmission by Xenopsylla cheopis, discovered by P.L. Simond, has been largely adopted even though it is flawed. X. cheopis cannot be the primitive vector, for neither its nor the rats' cradle is the same as for plague. Furthermore, the insect's vital cycle is impaired by proventriculus blocking. The combination of three factors--the synathropic rat, X. cheopis and Yersinia pestis--coupled with man's seafaring was what led to the multiplication of plague foci. This in turn "created" the third pandemic only because the disease was thus spread to very diverse biogeographical zones. The perennial establishment of the cycle happened through the bacillus' adaptation to many endemic fleas and parasites of numerous endemic animals. Indeed, in many countries, X cheopis is not involved in the persistence of selvatic plague.

Animals↗
PubMed2000

[The state of vector-borne diseases in Indonesia].

From epidemiological point of view, Indonesia is an extremely interesting area owing its insular structure and ecological, anthropological, cultural and economical diversity. As everywhere, vector-borne diseases are the result of complex and variable epidemiological systems, subject both to biogeographical rules and human activity. Two main arboviroses are present in Indonesia: dengue and Japanese encephalitis. Dengue appears as an endemoepidemic disease and is mostly circumscribed to urban areas. Haemorrhagic cases were first observed in 1968; since then, the incidence has been constantly increasing and the disease is now one of the principal causes of child lethality. Japanese encephalitis is a rural endemic disease transmitted by rice-field mosquitoes; its incidence remains relatively low since pigs, which are usual link-hosts for the virus, are uncommon in this mainly Muslem country. Human clinical cases are recorded from non-Muslem islands such as Bali or Irian Jaya which raises the question of immunisation for travellers. Recently, Japanese encephalitis was observed on east of the Wallace line which had been considered as the eastern cut-off line. Malaria is common throughout the country, Plasmodium vivax being the most frequent species. Some of the Anopheline vectors are related to brackish water as are coastal species; others have been favoured by rice growing. Several species bite and rest outdoors, rendering control measures complex. Moreover, chloroquine resistance is increasing in both P. falciparum and P. vivax. All three filaria species responsible for human lymphatic filariasis exist in Indonesia. Bancroft filariasis is present in rather limited foci on most of the islands; malayan filariasis is very prevalent on many islands, mostly in coastal areas, and Timor filariasis exist only on a few small islands. These parasitic diseases are cumulative and do not practically endanger the health of travellers. In the past, plague was common on Java island, but today, human cases are very rare. Scrub typhus is prevalent everywhere, as is murine typhus, being very frequent in harbour cities and one of the main causes of hospitalisation for febrile syndromes.. On the whole, the situation of several of these diseases has been worsening in Indonesia for about thirty years. Although epidemiological situations constantly evolve, two recent occurrences should be paid particular attention: -transmigration which is now a national priority and greatly facilitates the spread of many pathogens, arboviroses or chloroquine-resistant plasmodia, but also of rats, mosquitoes, etc. -deforestation due either to land-farming by Javanese transmigrants or to sudden climatic changes such as El Niño in 1997. Such deep ecological transformations may have considerable and unforeseeable consequences on the epidemiology of vector-borne diseases in Indonesia.

Animals↗
PubMed2001

Bloodsucking arthropods: the danger for travellers and hazard of vector travelling.

The newly obtained data supplemented our knowledge about risk for travellers, tourists and natives of Europe connected with malaria, leishmaniasis and other tropical diseases. It was discovered that healthy carriers of Epstein-Barr virus (nearly 90% of human population) have a great risk to get chronic Burkitt lymphoma disease as a result of Plasmodium falciparum (tropical malaria agent) infection. HIV carriers being occasionally in contact with visceral leishmaniasis vectors (sand-flies infected on dogs in the Mediterranean area) not only got a heavy form of disease but became a source of infection for healthy people. Airport malaria and outbreaks of dengue fever sometimes were (and are) connected with an import of infective Anopheles or Aedes mosquitoes. The high risk of borreliosis and ehrlichiosis infection exists in the forested European areas along the highways, where picnics and other types of recreation of travellers and tourists are typical and where the anthropogenically changed Ixodes ticks subpopulations are distributed. Such physiologically changed part of tick population is more aggressive and "changed ticks" more often are vectors of one, two or even more agent species simultaneously.

AIDS-Related Opportunistic Infections↗
PubMed1985

[New data on the transmission of filariae].

This paper summarizes research of the past several years on two phases of filarial transmission: the ingestion of microfilariae by the vector and the regulation of the percentage of successful parasites by the vector. Experiments involved several different models for study: injection of inert particles into the bloodstream of a rodent and their subsequent ingestion by a vector; ingestion of gametocytes of different ages by vectors of a rodent malaria; and a monkey simultaneously infected with four different species of filariae. This has led to the idea that there exist two categories of microfilariae: those blood-borne microfilariae which cannot enter capillaries and those microfilariae which are said to be "dermic" but in fact live trapped in capillaries and are only taken up through the suction applied by vectors during their feeding. Thus, the lesions of onchocerciasis are caused by microfilariae accidentally leaving the capillaries and entering the surrounding tissues. Passage through the stomach wall of a vector by microfilariae is the essential stage in regulating the percentage of successful parasites: the phenomena of facilitation or limitation. Two examples of limitation are given. In the model--Onchocerca volvulus-Simulium sirbanum--the thickness of the peritrophic membrane which traps microfilariae is determined by the number of microfilariae ingested; the greater the number ingested the thicker is the membrane. In the model--Molinema dessetae-Aedes aegypti--the lytic reactions of individual digestive cells which are provoked by attacking microfilariae occur only in heavily infected mosquitoes. The "immunity" of the arthropod vector seems to take a number of forms which are distinctly different from those of vertebrates.

Animals↗
PubMed1997

Characterization of a novel gut-specific chitinase gene from the human malaria vector Anopheles gambiae.

Chitinases that function in the molting of the larval exoskeleton have been characterized previously. However, chitinase expression in an adult insect gut has not been described. Here we report on the initial characterization and cloning of a novel chitinase gene that is expressed specifically in the midgut of adult Anopheles gambiae females. Upon feeding, chitinase is secreted into the gut lumen as an inactive pro-enzyme that is later activated by trypsin. Thus, temporal regulation of chitinase activity is tightly coupled to the temporal pattern of trypsin secretion. The enzyme may play a role in structuring the chitin-containing extracellular peritrophic matrix, whose formation is also induced by feeding. A chitinase cDNA was cloned from a library enriched for gut-specific sequences. The open reading frame encodes a 525-amino acid protein comprised of a putative catalytic domain at the N terminus, a putative chitin-binding domain at the C terminus, and a threonine/serine/proline-rich amino acid stretch in between them. Northern analysis indicates that this chitinase is expressed exclusively in the guts of adult females and not in adult carcasses or in any larval or pupal tissues. The present findings suggest the possibility of using this chitinase as an antigen for a malaria transmission-blocking vaccine.

Amino Acid Sequence↗
PubMed1983

Production of human beta interferon in insect cells infected with a baculovirus expression vector.

Autographa californica nuclear polyhedrosis virus (AcNPV) was used as an expression vector for human beta interferon. By using specially constructed plasmids, the protein-coding sequences for interferon were linked to the AcNPV promoter for the gene encoding for polyhedrin, the major occlusion protein. The interferon gene was inserted at various locations relative to the AcNPV polyhedrin transcriptional and translational signals, and the interferon-polyhedrin hybrid genes were transferred to infectious AcNPV expression vectors. Biologically active interferon was produced, and greater than 95% was secreted from infected insect cells. A maximum of ca. 5 X 10(6) U of interferon activity was produced by 10(6) infected cells. These results demonstrate that AcNPV should be suitable for use as a eucaryotic expression vector for the production of products from cloned genes.

Amino Acid Sequence↗