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Biomedical subjects

B M Christensen

Publications and source records attributed to B M Christensen.

At least 109 records · Page 6Linked to original sources
PubMed1986

Hemocyte-mediated melanization of microfilariae in Aedes aegypti.

The melanization response of adult female Aedes aegypti (black-eyed Liverpool strain) against intrathoracically inoculated Dirofilaria immitis microfilariae (mff) was assessed with transmission electron microscopy. The initial reaction involved the lysis of hemocytes at or near the surface of the parasite prior to the deposition of pigment. Subsequently, melanin formation was noted in the area of lysed cells and appeared to cascade onto the parasite surface. Observations suggest that melanin may be synthesized within certain hemocytes and released by exocytosis or upon cell lysis. Intact and disrupted nuclei and cytoplasmic elements from lysed hemocytes became numerous as mff became completely coated with melanin. A double membrane-like structure formed around the melanized mff and cellular debris during the later stages of the reaction, which eventually isolated the melanin capsule from hemolymph components. Results obtained are discussed in relation to the melanization response previously described for Aedes trivittatus.

Aedes↗
PubMed1986

Hemocyte cell surface changes in Aedes aegypti in response to microfilariae of Dirofilaria immitis.

This study involved the assessment of surface changes on hemocytes of Aedes aegypti black-eyed Liverpool strain in association with the melanization response against intrathoracically inoculated Dirofilaria immitis microfilariae (mff). Surface changes on hemocytes were identified using fluorescein-labeled wheat germ agglutinin (WGA). In mosquitoes eliciting a melanization response against inoculated mff, there was a 5-fold increase in the percentages of hemocytes exhibiting WGA binding compared with saline inoculated controls. Relationships of this hemocyte activation in relation to cell-mediated melanization responses of adult mosquitoes against mff are discussed.

Aedes↗
PubMed1985

Ultrastructure of the melanization response of Aedes trivittatus against inoculated Dirofilaria immitis microfilariae.

Scanning and transmission electron microscopy revealed that intrathoracically-inoculated microfilariae (mff) of Dirofilaria immitis elicited a rapid and effective immune response in the hemocoel of Aedes trivittatus mosquitoes. Hemocyte lysis and melanization of inoculated mff began immediately following exposure to the hemolymph environment. Initial melanin accumulation occurred at any site along the surface of mff and rapidly increased in thickness. Hemocyte encapsulation generally described for insects did not occur, but hemocytes might be necessary for activation of the melanization response. Although intact hemocytes were never abundant, those that were present seemed to show an active secretion of membrane-bound vacuoles directed toward mff. Activated hemocytes were in close association, but never in direct contact with the parasite, and were most commonly seen in various stages of lysis. Numerous cell remnants were noted throughout the developing melanin capsule. Parasites were completely melanized by 24 hr postinoculation (PI). By about 3 days PI, a membrane began to form around deposited melanin and hemocyte remnants. This developed into a double membrane-like structure of 25-30 nm thickness and resulted in the enclosure and isolation of the mff, melanin deposits, and cellular remnants from hemolymph components. It is suggested that this membrane functions as a boundary to isolate the melanized parasite and prevents additional hemocyte involvement.

Aedes↗
PubMed1984

Blood and gastrointestinal parasites of eastern wild turkeys from Kentucky and Tennessee.

Fifty-nine gastrointestinal tracts and 52 blood samples were collected from eastern wild turkeys (Meleagris gallopavo silvestris Vieillot) during the spring turkey hunts of 1979-1980 from two areas in western Kentucky and Tennessee. Eight species of parasites were recovered, and included (combined prevalence): Haemoproteus meleagridis Levine, 1961 (25%), Hymenolepis carioca (Magalhaes, 1898) (44%), Metroliasthes lucida Ransom, 1900 (25%), Raillietina georgiensis (Reid and Nugara, 1961) (15%), R. williamsi Fuhrmann, 1932 (64%), Ascaridia dissimilis Perez Vigueras, 1931 (83%), Capillaria caudinflata (Molin, 1858) (2%), and Heterakis gallinarum (Schrank, 1788) (27%). A significant difference existed between the intensities of A. dissimilis from the two states. Twenty-two subinoculations of collected blood were made in 1979, but no Plasmodium infections were recovered. Helminths of wild turkeys from 11 southeastern states were compared using similarity and diversity indices. High similarities were observed in helminth populations of two groups of states: 1) Alabama, Mississippi, Arkansas, Virginia, and Tennessee; and 2) Tennessee, Kentucky, and Illinois. Simpson's diversity index indicated helminth populations of wild turkeys in Florida were the most diverse (0.10), while those in Louisiana turkeys were the least diverse (0.33).

Animals↗
PubMed1983

Metazoan parasites of the eastern cottontail rabbit in western Kentucky.

Forty-five eastern cottontail rabbits (Sylvilagus floridanus Allen), collected over a 15 mo period from two areas of western Kentucky, were examined for disease conditions, helminth and arthropod parasites. A single lymphosarcoma, two cutaneous papillomas and the following parasites were identified: Hasstilesia tricolor, Taenia pisiformis, Cittotaenia variabilis, Raillietina stilesiella, Obeliscoides cuniculi, Trichuris leporis, Longistriata noviberiae, Trichostrongylus calcaratus, Dermatoxys veligera, Odontopsyllus multispinosus, Cediopsylla simplex, Haemaphysalis leporispalustris, Ixodes dentatus, Amblyomma americanum, and Dermacentor variabilis. Simpson's Indices indicated that parasite communities were fairly diverse, with some degree of dominance exhibited by O. cuniculi, T. pisiformis and H. leporispalustris. The parasite faunas of rabbits from the two areas were similar. Hasstilesia tricolor was associated with the absence of kidney fat.

Animals↗
PubMed1983

Vertebrate host specificity and experimental vectors of Plasmodium (Novyella) kempi sp. n. from the eastern wild turkey in Iowa.

Vertebrate host specificity, experimental laboratory vectors, and a description of Plasmodium (Novyella) kempi sp. n. from eastern wild turkeys (Meleagris gallopavo silvestris Vieillot) in Iowa are presented. Plasmodium kempi is infective for domestic turkeys, bobwhites (Colinus virginianus), chukars (Alectoris graeca), guinea fowl (Numida meleagris), peacocks (Pavo cristatus), and canaries (Serinus canaria), produces a transient infection in mallards (Anas platyrhynchos) and domestic geese (Anser anser), but will not infect ring-necked pheasants (Phasianus colchicus), pigeons (Columba livia), Japanese quail (Coturnix coturnix), leghorn white chickens (Gallus gallus), or starlings (Sturnus vulgaris). Oocysts and (or) sporozoites were recovered from 68% (84/124) and 98% (60/61) of the Culex pipiens pipiens and C. tarsalis examined, respectively. Oocysts developed faster and sporozoites invaded the salivary glands sooner in C. tarsalis (6 days) than in C. p. pipiens (7 days). Culex tarsalis transmitted P. kempi more effectively than C. p. pipiens, although both species were capable of transmitting the parasite by natural feeding. Oocysts developed and sporozoites also were produced in C. restuans, but its ability to transmit the parasite was not determined. Aedes aegypti (Rockefeller strain) and A. triseriatus were refractive to P. kempi. Plasmodium kempi produces trophozoites with large refractile globules and fine cytoplasmic extensions, mature schizonts in the form of a condensed fan containing four to eight nuclei (usually 5), and elongate gametocytes with irregular borders. All stages are confined almost exclusively to mature erythrocytes, with no effect on host cell size or position of host cell nucleus. Plasmodium kempi is most similar morphologically to P. (Novyella) hexamerium and P. (Novyella) vaughani. It differs from P. hexamerium in having large refractile globules in trophozoites and immature schizonts, an inability to infect starlings, an absence of phanerozoites in capillary endothelium of the brain, and the ability to develop in C. pipiens mosquitoes. Plasmodium kempi is more like P. vaughani morphologically, but differs by infecting turkeys and ducks (transient), by its inability to infect starlings, its lack of morphological variation even when in different hosts, and its ability to develop in C. pipiens and C. tarsalis.

Aedes↗
PubMed1981

Observations on the immune response of Aedes trivittatus against Dirofilaria immitis.

Laboratory studies on the immune response of Aedes trivittatus to Dirofilaria immitis revealed an active immune response to developing larvae. A response was noted in 41 of 268 (15.3%) mosquitoes that fed on an infected dog. Mosquitoes exhibiting an immune response contained a significantly greater number of parasites (21.9 larvae/mosquito) than mosquitoes in which no response was evident (14.7 larvae/mosquito). The microfilarial stage was melanized more frequently than later developmental stages, although all developmental stages were affected. Melanized microfilariae appeared to be voided from the Malpighian tubules through the hindgut and anus. Early melanization was directed at the area of the excretory pore of the parasites, suggesting at least an indirect response to excretory products. Microfilariae that accidentally migrated through the Malpighian tubules into the haemocoele were completely encapsulated and melanized. All microfilariae that were intrathoracically inoculated into the haemocoele were completely encapsulated and melanized by four days after inoculation. The role the immune system might play in limiting parasite burdens of D. immitis in A. trivittatus is discussed.

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PubMed1978

Epidemiologic findings on canine and feline intestinal nematode infections from records of the Iowa state University Veterinary Clinic.

A wealth of data was available on intestinal nematode infections of dogs and cats in the Ames, Iowa, practice area served by the Iowa State University Veterinary Clinic. From July 1966 through June 1974, 8.5% of 33,594 dogs and 4.5% of 11,995 cats hospitalized for 1 or more days were recorded as infected with at least 1 type of intestinal nematode. For both dogs and cats, infection rates were generally higher in males than in females and in those that were sexually intact, compared with those that were neutered. The highest prevalence of hookworm infections in both dogs and cats was recorded in June and July, and the highest prevalence of ascarid infections in cats, but not in dogs, was in December. Seasonal patterns were not demonstrated for other nematode infections. Ascarid infections in dogs and cats and hookworms infections in dogs were most prevalent in 2-week-old to 2-month-old animals. Whipworm infections in dogs and hookworm infections in cats generally appeared at greater ages, reaching their highest prevalence in hosts 1 to 2 years old.

Animals↗
PubMed1978

Laboratory studies of transovarial transmission of trivittatus virus by Aedes trivittatus.

Aedes trivittatus were experimentally exposed through a membrane to a concentration of trivittatus (TVT) virus in dog defibrinated blood of 10(3.4)-10(3.5) SMICLD 50/0.025 ml. Transovarial and transstadial transmission was demonstrated. Fifty-five percent of the infected mosquitoes tested transovarially transmitted TVT virus. TVT virus was isolated from 16% of the F1 generation progeny examined, including 19% of the larvae, 23% of adult females, and 10% of adult males.

Aedes↗
PubMed1978

Laboratory observations on the insusceptibility of raccoons to Dirofilaria immitis.

Two raccoons, Procyon lotor, were exposed to Dirofilaria immitis by subcutaneous injection of infective third stage larvae obtained from experimentally-infected Aedes trivittatus. Nematodes were not recovered from either raccoon when examined at necropsy 223 and 254 days postexposure. Large numbers of adult D. immitis were found in six dogs used as controls. These data indicate that raccoons cannot support the development of D. immitis.

Animals↗
PubMed1976

Natural infection of Aedes trivittatus (COQ) with Dirofilaria immitis in central Iowa.

Juveniles identified as Dirofilaria immitis were recovered from Aedes trivittatus and Anopheles punctipennis collected CO2-baited CDC light traps in Ames, Iowa, during 10 days in July and August 1975. Ae. trivittatus composed 58.7% of the mosquitoes collected, and D. immitis was recovered from 18 of 393 (4.6%) dissected and from 7 of 31 pools (911 mosquitoes; 0.77%). Approximately 1.0% of the Ae. trivittatus collected harbored infective-stage juveniles, and as many as 27 were recovered from a single mosquito. This is the first report of Ae. trivittatus supporting the development of D. immitis. An. punctipennis was the only other species infected, with 2 of 468 harboring first-stage juveniles. The data suggest that Ae. trivittatus probably is the principal vector of D. immitis in central Iowa.

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