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Biomedical subjects

A Spielman

Publications and source records attributed to A Spielman.

At least 181 records · Page 10Linked to original sources
PubMed1986

Comparative prevalence of Babesia microti and Borrelia burgdorferi in four populations of Ixodes dammini in eastern Massachusetts.

We determined the prevalence of Babesia microti and Borrelia burgdorferi in four populations of Ixodes dammini in eastern Massachusetts. The Feulgen's reaction was more sensitive than the Giemsa method for detecting salivarian Babesia. A combination of darkfield and direct-fluorescent-antibody examination proved more sensitive than either method alone for detecting spirochetal infection. The prevalence of spirochetes was greater than the prevalence of Babesia in each of the tick populations studied. Overall, 24% of nymphs and 47% of adults examined were infected with spirochetes; in contrast, 11% of nymphs and 14% of adults were infected with Babesia. The difference between the spirochetal and babesial prevalence was greatest in the most recently infested site. The rising incidence of Lyme disease, as compared to the stable incidence of human babesiosis, may result from the relatively greater abundance of Bo. burgdorferi infected I. dammini ticks in newly infested locations.

Animals↗
PubMed1986

Microfilarial perforation of the midgut of a mosquito.

To determine whether the midgut envelope of mosquitoes is disrupted by the passage of microfilariae, ultrastructural changes induced by microfilariae of Brugia malayi were observed in midguts of Aedes aegypti mosquitoes. Basal and apical plasma membranes were destroyed, disrupting the full depth of the midgut wall. Ingested ferritin lay against the gut wall, suggesting absence of the peritrophic membrane during penetration. Exsheathment of microfilariae appears to be enhanced by movement against the constricting midgut wall. It was concluded that particles present in the lumen of the gut may be disseminated passively to the hemocoel.

Aedes↗
PubMed1985

Antihemostatic, antiinflammatory, and immunosuppressive properties of the saliva of a tick, Ixodes dammini.

Pilocarpine-induced saliva of the tick, Ixodes dammini, inhibited platelet aggregation triggered by ADP and collagen, as well as platelet-aggregation factor. In addition, we found apyrase activity (which degrades ATP and ADP to AMP and orthophosphate) and an anticoagulant. We showed the presence of prostaglandin E2 (PGE2) by bioassay and radioimmunoassay. This saliva inhibited interleukin 2 production by T cell hybridomas, an activity consistent with that of PGE2. A kininase was demonstrated, and this may counteract the algesia- and edema-promoting properties of PGE2. Together, these salivary components produce antihemostatic, antiinflammatory, and immunosuppressive effects that may facilitate feeding, as well as transmission of tick-borne pathogens.

Animals↗
PubMed1985

Aedes aegypti: model for blood finding strategy and prediction of parasite manipulation.

Aedes aegypti mosquitoes salivate during intradermal probing of vertebrate prey before ingesting blood (Griffiths and Gordon 1952). Nonsalivating mosquitoes locate blood more slowly; this difference was ascribed to an anti-platelet activity found in the mosquito's saliva (Ribeiro et al. 1984). Mosquitoes infected with Plasmodium gallinaceum suffer pathology that specifically impairs saliva anti-hemostatic activity but without reducing volume of output (Rossignol et al. 1984). The complexity of the feeding apparatus of mosquitoes provides opportunity for a variety of strategies in which pathogens may produce specific lesions that enhance their transmission, but the variables that affect the duration of probing by mosquitoes have not been defined. We sought to resolve this complexity by identifying and quantifying relevant parameters of probing behavior. Mosquitoes thrust their mouthparts repeatedly through their host's skin while searching for blood. Female A. aegypti thrust at 7-sec intervals. If this search results in success, feeding ensues. Alternatively, the mosquito "desists," the mouthparts stylets are withdrawn, and the mosquito attempts to feed at another site. Even after previous desistance, the probability of finding blood remains undiminished. Functions for the probability of feeding success and desistance over time were derived using data from observations on 300 mosquitoes. The probability of feeding success was interpreted as being a function of the density of vessels in the skin, their geometric distribution, and the conditions locally affecting hemostasis. During each probe, the probability of desisting increased linearly with time, and after desisting once, mosquitoes tended to desist more rapidly. A model was developed incorporating Monte Carlo simulation which closely fit observed data. By changing values for the several parameters of the probability functions, we predicted modes in which parasites may manipulate their hosts to enhance transmission, both to and from the vector. In particular, parasite strategies in the vector would include induced salivary pathology; increased duration of probing thrusts; decreased desistance time; and inhibited phagoreception. Predicted parasite strategies in the reservoir host would include increased skin vascular volume and impaired host hemostasis. Our model supports the hypothesis of a mutualistic interaction of malaria and mosquitoes.

Aedes↗
PubMed1985

Enhanced mosquito blood-finding success on parasitemic hosts: evidence for vector-parasite mutualism.

The generalized hematopathology frequently found in animals infected with vector-borne pathogens may maximize transmission by enhancing the ability of vectors to locate blood in infected hosts. We tested this idea of mutualism between parasite and vector by comparing duration of probing of mosquitoes feeding on noninfected and on malaria-(Plasmodium chabaudi) or arbovirus-(Rift Valley fever virus) infected animals. We found that median duration of probing (blood location) on infected rodents was reduced by at least 1 min as compared to noninfected rodents. This enhanced ability of vectors to locate blood, possibly caused by parasite-disrupted hemostasis, may be a common feature of vector-borne diseases.

Aedes↗
PubMed1985

Mice as reservoirs of the Lyme disease spirochete.

In evaluating the white-footed mouse as a reservoir host for the Lyme disease spirochete, we compared spirochete infection in vector ticks (Ixodes dammini) having different histories of attachment to these mice, estimated their relative importance as hosts for immature I. dammini and compared the seasonality of tick activity and spirochetemia in mice. Infection in trapped white-footed mice appears to be universal. Prevalence of spirochetal infection in I. dammini correlates with frequency of attachment to mice, and in mice, with the season of vector activity. The relative abundance of this mouse makes it numerically the most important host for I. dammini. Most immature I. dammini appear to attach to white-footed mice. Taken together, these considerations demonstrate that the white-footed mouse serves as reservoir for the Lyme disease spirochete in coastal Massachusetts.

Animals↗
PubMed1984

Enhanced arboviral transmission by mosquitoes that concurrently ingested microfilariae.

Infection, dissemination, and transmission of an arbovirus in mosquitoes are enhanced by concurrent ingestion of microfilariae. Ingestion of Rift Valley fever virus alone infected only 64 percent of female Aedes taeniorhynchus. Of these, only 5 percent of refeeding mosquitoes actually transmitted virus. In contrast, ingestion of the same amount of virus from concurrently microfilaremic (Brugia malayi) gerbils resulted in 88 percent infection and 31 percent transmission. Enhanced transmission of virus may be attributed to increased transit of virus across the midgut wall. Endemic filariasis may promote arbovirus transmission in nature.

Aedes↗
PubMed1984

Salivary apyrase of Aedes aegypti: characterization and secretory fate.

Salivary gland homogenates of female adult Aedes aegypti hydrolyzed ATP and ADP thereby defining an apyrase activity. Activity is divalent cation dependent with an optimum pH of 9.0. ATPase and ADPase activities could not be dissociated thus suggesting the presence of a true apyrase enzyme. Apyrase activity is low on the day of emergence but increases to 160 mU per pair of glands on the second day. The site at which mosquitoes probed into warm polyacrylamide gels retains apyrase activity, confirming the secretory fate of this activity.

Aedes↗
PubMed1984

Role of mosquito saliva in blood vessel location.

In order to ascribe a blood feeding function to the saliva of mosquitoes, we determined whether this secretion may limit the initial probing phase of biting behaviour. The probing of hosts was indeed prolonged when the salivary ducts were severed, but this prolongation was absent when mosquitoes were fed on an artificial meal contained beneath a membrane. In vitro, turbidometric assays demonstrated that saliva inhibits the ADP- and collagen-mediated aggregation of platelets. ATP and ADP were hydrolysed by saliva, and this apyrase activity explains, in part, the observed effect upon platelets. We conclude that the saliva of mosquitoes functions by facilitating location of blood vessels.

Adenosine Diphosphate↗
PubMed1984

Paradoxical effects of simulated larviciding on production of adult mosquitoes.

We determined whether simulated mortality of larval mosquitoes in food-deprived bodies of water increases emergence of adult females as well as their size by releasing the remaining larvae from competition for food. Removal of larval Aedes aegypti from rearing containers with suboptimal amounts of food increased the number of adults that emerged. Thus, larvicidal measures do not inevitably lead to reduced numbers of mosquito vectors of disease. In food-limiting breeding sites, partially effective anti-larvae measures can be counterproductive, perhaps increasing transmission of vector-borne disease.

Aedes↗
PubMed1984

Increased intradermal probing time in sporozoite-infected mosquitoes.

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.

Aedes↗
PubMed1983

Ultrastructural studies on sporogony of Babesia microti in salivary gland cells of the tick Ixodes dammini.

Tick larvae were permitted to feed on infected hamsters and then allowed to molt. Nymphs were examined just prior to feeding on uninfected hamsters or at timed intervals thereafter. Invasion of the salivary gland by B. microti occurs before feeding of the nymph begins, and development of the parasite is further stimulated by feeding. The sporoblast forms a massive multinucleated meshwork which ramifies throughout the large host cell. No separation of the meshwork into multiple subdivisions, termed "cytomeres" by other workers, has been detected. Instead the specialized organelles characteristic of sporozoites, namely micronemes, rhoptries, and segments of double membrane appear in the meshwork itself and gradually become organized into sporozoite anlagen which protrude from its surface. At the same time the meshwork shortens and thickens giving rise to large compact undifferentiated bodies whose surface is also studded with sporozoite anlagen. Sporozoites thus originate either from the meshwork or from the undifferentiated bodies. In either case large lobate nuclei send projections into the anlagen as they protrude from the surface of the sporoblast. In a final step the mature sporozoites arise by simultaneous nuclear and cytoplasmic divisions. There is no separate stage of schizogony and the process is one of true budding.

Animals↗
PubMed1983

Sexuality in piroplasms as revealed by electron microscopy in Babesia microti.

Protozoa of the closely related genera Babesia and Theileria are intraerythrocytic parasites of vertebrates. They have a complex life cycle that includes development in an intermediate vector host, a tick. Whether sexual stages occur in the tick has been a subject of great controversy. The small size of the organism and the complexity of developmental stages in the gut of the tick have prevented a definitive solution of this problem. By means of a simple and straightforward although time-consuming method, it became possible to demonstrate gametes and their sexual fusion in Babesia microti developing in the gut of larvae of the tick Ixodes dammini. Tick larvae fed on hamsters infected with a human strain of B. microti were fixed and processed for electron microscopy. It was found that some of the parasites formed a unique structure shaped like an arrowhead. Because it was suspected that these forms might represent gametes, a search was made for pairs of parasites that were fusing and with each member of the pair emerging from a different erythrocyte. Such a fusing pair could not possibly represent a parasite undergoing division. By study of serial sections such pairs were indeed found. In every case one member of the pair of gametes had an arrowhead structure. This proves sexuality of B. microti and makes highly likely its existence in all members of the genera Babesia and Theileria.

Animals↗
PubMed1983

Invasion of Babesia microti into epithelial cells of the tick gut.

During feeding a peritrophic membrane (PM) is formed in the gut of the tick Ixodes dammini, dividing the lumen of the gut into an ecto- and endoperitrophic space. Babesia and all food particles ingested with the blood meal by the tick are retained in the endoperitrophic space, the lumen proper. Only Babesia equipped with a highly specialized organelle, the arrowhead, are able to pass the PM and enter the ectoperitrophic compartment. During the crossing of the PM the arrowhead loses its density, suggesting that enzymes released from it dissolve the polymers in the PM, making passage of the parasite through this barrier possible. In the ectoperitrophic space the arrowhead of Babesia touches the epithelial cell. At the point of contact the membrane of the host cell starts to invaginate, and simultaneously the arrowhead's fine structure loses its highly organized pattern. The growing host membrane encircles the parasite and the arrowhead diminishes progressively in size. When the piroplasm is inside the host cell, the arrowhead can no longer be found. During invasion the host membrane often touches the parasite's plasma membrane at the site of a coiled structure, and the host membrane becomes ruptured and the nearby host cytoplasm appears to be lysed. Babesia inside the host cell is covered solely by its own plasma membrane; the invaginated host membrane is missing. It is postulated that the latter disintegrates during invasion by the parasite through the action of enzymes from the coiled structure. The parasite is surrounded by a halo of homogeneous material deriving most probably from the lysed host cytoplasm.

Animals↗
PubMed1983

Predisposition to Brugia malayi microfilaremia in progeny of infected gerbils.

Patency of Brugia malayi infection in gerbils born of infected parents was compared to that in gerbils from noninfected parents. Following infection with third stage larvae, female progeny of infected parents generally became microfilaremic whereas those of noninfected parents rarely did so. Male progeny developed microfilaremia regardless of parentage, although descendants of infected parents tended to have higher parasitemia. We conclude that B. malayi infection in the mother predisposes the offspring to patent infection subsequent to inoculation with infective larvae.

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