Effects of the trematode Microphallus turgidus on locomotion and prey capture in the grass shrimp Palaemonetes pugio.

The grass shrimp, Palaemonetes pugio, is common in estuaries and marshes along the east coast of the USA and is frequently infected with metacercariae of the trematode, Microphallus turgidus. To test whether or not M. turgidus has an effect on intermediate host behaviour, the length of time spent swimming and walking over 1 min and 3 min intervals and prey (Artemia) capture rates of uninfected grass shrimp and those infected with 1-10, 11-20 or 21-30 metacercarial cysts were compared. Uninfected shrimps spent significantly more time swimming than infected shrimps during the first minute of observation. There were no differences between the control and infected groups in terms of swimming at 3 min, walking at 1 and 3 min, or in numbers of prey captured. These results indicate that M. turgidus may induce little or no change in grass shrimp locomotion nor in prey capture behaviour. This is in contrast to other parasites that modify intermediate host behaviour to enhance their transmission to definitive hosts. Furthermore, these data support earlier studies indicating that M. turgidus does not affect the growth and survival of P. pugio.

Comparison of serological methods and blood culture for detection of Trypanosoma cruzi infection in raccoons (Procyon lotor).

The indirect immunofluorescent antibody test (IFAT) and enzyme-linked immunosorbent assay (ELISA) were compared with blood culture for the detection of Trypanosoma cruzi infection in 83 raccoons (Procyon lotor) trapped in 4 counties of southeast Georgia. Both IFAT and ELISA detected 24 of 25 culture-positive samples (96% sensitivity). Cultures from 25 raccoons (30%) were positive for epimastigotes, whereas a total of 50 raccoons (60%) was seropositive by either the IFAT or ELISA. Forty-five of 83 serum samples (54%) were positive for anti-T. cruzi antibodies with the ELISA, and 47 were IFAT positive (57%). Forty-two of the 50 seropositive raccoons (84%) were seropositive by both tests. Endpoint titers of IFAT-positive samples were determined by testing doubling dilutions from 1:40 to 1:1280. High titers of 640 and 320 were observed for 4 raccoons trapped in 1 county (St. Catherines Island, Liberty County) and titers of 160 for 1-2 raccoons from each of the 4 counties sampled. IFAT titers and ELISA optical density values were positively correlated. Both serological tests have a high sensitivity and should be excellent tools for studying the prevalence of T. cruzi in wildlife populations.

Ectoparasites and gastrointestinal helminths of southern flying squirrels in southeast Georgia.

Southern flying squirrels (Glaucomys volans) from southeastern Georgia were examined for ectoparasites and gastrointestinal helminths. Ten species of ectoparasites were recovered, including 3 species of sucking lice (Hoplopleura trispinosa, Microphthirus uncinatus, and Neohaematopinus sciuropteri), 1 species of flea (Orchopeas howardi), 2 species of ticks (Amblyomma maculatum and Ixodes scapularis), 3 species of mesostigmatid mites (Androlaelaps casalis, A. fahrenholzi, and Haemogamasus ambulans), and 1 species of chigger (Leptotrombidium peromysci). Only the sucking lice and fleas were common on this host. M. uncinatus is reported for the first time from eastern North America. The 2 most commonly collected ectoparasites, N. sciuropteri (prevalence = 63%) and O. howardi (prevalence = 47%), have previously been shown to be vectors of the rickettsial zoonotic agent that causes sporadic epidemic typhus. Also, 3 nematodes (Citellinema bifurcatum, Strongyloides robusius, and Syphacia thompsoni), 1 unidentified cestode, and 1 acanthocephalan (Moniliformis clarki) were found in flying squirrel gastrointestinal tracts. With the exception of S. thompsoni, which was common and relatively abundant in the cecum (prevalence = 94%, intensity = 51+/-12), both the prevalence and intensity of helminth parasites were low. The nematode S. thompsoni and the acanthocephalan M. clarki are new state records for tree squirrels in Georgia.

Survey and host fitness effects of red-cockaded woodpecker blood parasites and nest cavity arthropods.

Blood parasites and nest cavity arthropods associated with the red-cockaded woodpecker (Picoides borealis) were surveyed and the impact of blood-feeding arthropods on woodpecker fitness traits was assessed. Five woodpeckers (8%) were infected with unidentified microfilariae, and 1 woodpecker (2%) was infected with 2 species of haemoproteid (Haemoproteus velans and Haemoproteus borgesi). This is the first record of haemoproteids in this species and the first observation of H. borgesi in North America. We collected representatives of at least 6 families of mites and 12 families of primarily commensal insects from woodpecker cavities. Only a few specimens of blood-feeding insects were recovered. The mite Androlaelaps casalis was the most common hematophagous arthropod (prevalence = 76%, mean density = 51+/-7 mites/cavity). The number of A. casalis mites increased with cavity age but there was no association between the number of mites and the number of woodpecker eggs laid or the number of hatchlings or fledglings. In conclusion, the prevalence of blood parasites in the red-cockaded woodpecker is low, woodpecker cavities are not heavily infested with blood-feeding insects, and there is no evidence that A. casalis mites affect woodpecker fitness.

Site selection by intestinal helminths of the Virginia opossum (Didelphis virginiana).

Digestive tract helminths of the Virginia opossum (Didelphis virginiana) were examined for site specificity and interspecific interactions. Thirty opossums were live-trapped at 2 localities in Georgia, killed, and their digestive tracts removed and divided into the following sections; esophagus, stomach, small intestine (20 equal sections), cecum, and large intestine (5 equal sections). Helminths present in each section were identified and counted. Three trematode, 1 cestode, 2 acanthocephala, and 6 nematode species were found. Two parasites (the acanthocephalan Centrorhynchus spinosus and the nematode Viannaia hamata) are new state records for Georgia and this is the first report of C. spinosus from an opossum. There was considerable overlap between the spatial distributions of many of the helminth species found in the small intestine though most species had different modal locations. Helminth species locations were unaffected by host sex or trapping locality. There was no evidence that the presence, absence, or intensity of any helminth species affected the location or intensity of other helminth species in the digestive tract.

Trypanosoma cruzi infection of free-ranging lion-tailed macaques (Macaca silenus) and ring-tailed lemurs (Lemur catta) on St. Catherine's Island, Georgia, USA.

Free-ranging Old World primates released on St. Catherine's Island, Georgia (USA), were tested for infection with Trypanosoma cruzi as part of a study of the epizootiology of sylvatic T. cruzi in the southeastern USA. The parasite was observed in liver infusion tryptose medium cultures of blood from seven of 11 lion-tailed macaques (Macaca silenus) and one of 19 ring-tailed lemurs (Lemur catta). Cultures of blood from 10 black and white ruffed lemurs (Varecia variegata) were all negative. Analysis of small subunit ribosomal RNA gene polymorphisms detected using polymerase chain reaction techniques indicates that the parasites isolated from both the lion-tailed macaques and the ring-tailed lemur are probably the same as T. cruzi parasites isolated from raccoons (Procyon lotor) trapped on St. Catherine's Island and other locations in the southeastern USA. Foraging lion-tailed macaques were observed to handle and partially consume specimens of Triatoma sanguisuga, the triatomine bug thought to be a vector of T. cruzi in the southeastern USA. Oral transmission of the parasite may have occurred as a result of this behavior.

Trypanosomiasis in raccoons from Georgia.

Trypanosoma cruzi frequently infects wild mammals in the southern United States but little is known about the effect of the parasite on reservoir hosts such as the raccoon (Procyon lotor). To investigate this issue, 30 raccoons trapped on St. Catherine's Island (Georgia, USA) during September, 1994 were tested for T. cruzi infection by examination of wet mounts of fresh blood and by culturing blood in liver infusion tryptose medium. Thirteen animals (43%) were found to be infected with T. cruzi. Heart tissues from 10 of the infected raccoons and 4 uninfected raccoons were fixed, sectioned, stained and examined for the presence of parasites and evidence of tissue damage. One T. cruzi pseudocyst was found in cardiac tissue from the left ventricle of a female raccoon. In addition, Sarcocystis sp. sarcocysts and schizonts of Hepatozoon sp. were observed in heart tissue from seven of the T. cruzi-infected raccoons. Mild, multifocal and interstitial inflammation was observed in the heart tissues of all 10 of the infected animals. No evidence of T. cruzi pseudocysts or tissue damage was observed in heart tissue from C3H/HeJ mice infected with culture forms of the parasites isolated from raccoons. Our findings suggest that the T. cruzi parasites isolated from raccoons in Georgia are not pathogenic to this host or C3H/HeJ mice and may be of low virulence.

Haemoproteus greineri in wood ducks from the Atlantic flyway.

Thin smears of blood were examined from 157 wood ducks (Aix sponsa) trapped at Savannah National Wildlife Refuge (South Carolina, USA) and Harris Neck National Wildlife Refuge (Georgia, USA) during spring and summer, 1994 and 1995. Thirteen wood ducks (8%) were infected with blood parasites. Eleven of these birds were infected with Haemoproteus nettionis, seven with Leucocytozoon simondi, and five with unidentified microfilariae. Additionally, eight wood ducks (5%) were infected with Haemoproteus greineri. This is the first record of H. greineri in anatids trapped along the Atlantic Flyway south of Labrador and the first record of this species in wood ducks. To further characterize the distribution of H. greineri in the wood duck, blood smears were examined from hatching year ducks trapped at 10 different Atlantic flyway locations during spring and summer, 1980 to 1983. Haemoproteus greineri was found in wood ducks trapped in all 10 locations which extend from 46 degrees N latitude in New Brunswick to 37 degrees N latitude in Virginia. These findings indicate that H. greineri is not exclusively boreal in distribution, but also is found, at least in wood ducks, along much of the Atlantic Flyway.

Filariae of raccoons from southeast Georgia.

The prevalence of filariae in wild raccoons trapped in southeast Georgia was determined. Examination of blood samples revealed that 74 of 113 raccoons (66%) trapped in 6 southeastern Georgia counties were infected. Seventy-three of these raccoons (65%) were infected with Mansonella llewellyni and this parasite was observed in raccoons from every location examined. Dirofilaria tenuis was found in 22 raccoons (20%) and was observed in only 3 of the 6 counties surveyed. An adult specimen of Acanthocheilonema procyonis was found in the subcutaneous tissues of 1 of 5 necropsied raccoons. This is the first record of filariae in raccoons from Georgia. In addition, Dirofilaria-like larvae were found in Aedes taeniorhyncus mosquitoes collected in Liberty County.

Trypanosoma cruzi in wild raccoons, opossums, and triatomine bugs in southeast Georgia, U.S.A.

The prevalence of Trypanosoma cruzi infection among wild opossums and raccoons live-trapped in 6 southeast Georgia counties was determined. Epimastigotes typical of T. cruzi were observed in liver infusion tryptose medium cultures of blood from 6 of 39 opossums (15.4%) and 12 of 54 raccoons (22.2%). Trypomastigotes (6,000/ml) were observed in a wet mount of blood from 1 of the animals, a raccoon trapped on St. Catherines Island in Liberty County. In addition, T. cruzi parasites were observed in the gut contents of 3 of 5 specimens of the triatomine bug Triatoma sanguisuga (Leconte) collected near human dwellings in Bulloch County. This is the first report of T. cruzi-infected triatomine bugs in Georgia.

Ectoparasites of opossums and raccoons in southeastern Georgia.

Twelve species of ectoparasites (four fleas, three ticks, three chiggers, one macronyssid mite, and one atopomelid mite) were recovered from 42 opossums, Didelphis virginiana Kerr, live-trapped from September 1992 through April 1994 in southeastern Georgia. The fleas, Ctenocephalides felis (Bouché) (prevalence = 19%) and Polygenis gwyni (C. Fox) (36%); the ticks, Dermacentor variabilis (Say) (40%) and Ixodes scapularis Say (19%); and the macronyssid mite, Ornithonyssus wernecki (Fonseca) (21%), exhibited the highest infestation prevalences on opossums. The atopomelid mite, Didelphilichus serrifer Fain, and the chigger mite Leptotrombidium peromysci Vercammen-Grandjean & Langston, both ectoparasites of opossums, are reported from Georgia for the first time. Six species of ectoparasites (one chewing louse, four ticks, and one macronyssid mite) were collected from 58 raccoons, Procyon lotor (L.), examined between October 1992 and September 1993 in the same region. The chewing louse, Trichodectes octomaculatus Paine (prevalence = 24%); and the ticks, Amblyomma americanum (L.) (69%), D. variabilis (55%), and Ixodes texanus Banks (24%), exhibited the highest infestation prevalences on raccoons. Three species of ticks, A. americanum, D. variabilis, and I. scapularis, were the only ectoparasites recovered from both host species. Several of the ectoparasites collected are proven vectors of pathogenic agents that affect humans and animals.

Experimental American leishmaniasis and Chagas' disease in the Brazilian squirrel monkey: effect of dual infection on antibodies to parasite antigens.

Adult, laboratory-bred squirrel monkeys (Saimiri sciureus) were infected with either Leishmania braziliensis braziliensis or L. b. panamensis and, 42 weeks later, they were challenge-infected with Trypanosoma cruzi. Another group of monkeys was infected with T. cruzi and challenged with L. b. braziliensis after 42 weeks. Immunoblotting was used to examine parasite antigens bound by antibodies in plasma obtained from the monkeys during the course of primary and challenge infections. During primary infections Leishmania-infected monkeys produced antibodies which bound to a number of Leishmania antigens, most notably a Leishmania antigen of 72 kDa, which were not recognized by antibodies produced by the monkeys given a primary infection of T. cruzi. These Leishmania-induced antibodies were no longer detectable 42 weeks after primary infections. However, when the Leishmania-infected monkeys were challenged with T. cruzi they once again produced antibodies capable of binding numerous Leishmania antigens, including the antigen of 72 kDa, which had not been recognized by antibodies produced by the monkeys with primary T. cruzi infections. A similar phenomenon was observed in T. cruzi-infected animals following Leishmania challenge.

Experimental American leishmaniasis in the Brazilian squirrel monkey (Saimiri sciureus): lesions, hematology, cellular, and humoral immune responses.

Unulcerated cutaneous lesions appeared and persisted in squirrel monkeys experimentally infected with Leishmania braziliensis braziliensis or L. b. panamensis. Peripheral blood mononuclear cell (PBMC) numbers increased following infection, and cultured PBMCs from infected monkeys proliferated in response to parasite antigens. The responses of PBMCs to mitogens were not suppressed in infected monkeys. Elevated levels of leishmania-specific immunoglobulins M and G were also observed. Thus, the squirrel monkey is susceptible to American leishmaniasis and is capable of responding to the infection with measurable cellular and humoral immunity.

Toxoplasma gondii: decreased resistance to infection in mice due to estrogen.

Exposure to pharmacological concentrations of potent estrogenic compounds, including 17 beta-estradiol, diethylstilbestrol, and alpha-dienestrol, increased the susceptibility of mice to Toxoplasma gondii as measured by brain cyst formation. Compounds with weak estrogenic activity or other hormonal activity, including 5 alpha-dihydrotestosterone, progesterone, and zearalanol, did not alter host resistance to infection. The ability of estrogens to alter susceptibility was inhibited by the estrogen antagonist, tamoxifen. The restoration of ovariectomized mice with normal physiological concentrations of estrogen had no effect on subsequent infection with T. gondii. These results indicate that pharmacological, but not physiological, levels of estrogen selectively alter host resistance to T. gondii, possibly through hormonal events.

Influence of estrogen on host resistance: increased susceptibility of mice to Listeria monocytogenes correlates with depressed production of interleukin 2.

Mice given pharmacological levels of the synthetic estrogen diethylstilbestrol demonstrated a marked increase in susceptibility to infection with Listeria monocytogenes. Experiments were performed in an effort to determine the mechanism(s) by which estrogen treatment increases the susceptibility of mice to L. monocytogenes infection. Estrogen exposure depressed the in vivo proliferative response of splenic lymphocytes to L. monocytogenes, which correlated with the decreased in vitro response of these cells to phytohemagglutinin. Interleukin 2 (IL 2) production by splenic lymphocytes from estrogen-treated mice was decreased, although these cells were capable of proliferating normally in response to exogenous IL 2. Interleukin 1 production by peritoneal macrophages was not depressed by estrogen exposure. The number of bacteria observed in the spleens of estrogen-exposed mice challenged with L. monocytogenes was reduced by IL 2 administration. Thus, estrogens may decrease host resistance to L. monocytogenes by inhibiting IL 2 production and the subsequent proliferation of antigen-sensitized T lymphocytes required for recovery.

Immunosuppressive effects of benzidine in mice: evidence of alterations in arachidonic acid metabolism.

Benzidine (4,4'-diaminobiphenyl), a known human bladder carcinogen used in the synthesis of dyes, was immunosuppressive in mice after subchronic exposure. Suppression, particularly of cell-mediated immunity, occurred at dose levels previously found to be subtumorigenic in mice, as evidenced by suppressed lymphoproliferative and delayed hypersensitivity responses. In addition, benzidine exposure was found to decrease host resistance, including resistance to the growth of transplantable tumor cells and infection with Listeria. These data suggest that the development of neoplastic disease may be facilitated by the ability of benzidine to alter the immune response. The mechanism(s) responsible for immunosuppression by benzidine, however, is probably not the same as that responsible for its direct carcinogenicity. The addition of benzidine in vitro to mitogen-activated lymphocytes mimicked the suppression of lymphocyte responsiveness in vivo. In vitro studies suggested that alterations in metabolites of the arachidonic acid/lipoxygenase pathway were responsible for the immune alterations. Benzidine and the lipoxygenase inhibitor NDGA inhibited arachidonic acid metabolism and the mitogen response in lymphocytes, whereas the cyclooxygenase inhibitor indomethacin was ineffective. Addition of 8brcGMP partially restored benzidine-suppressed responses, whereas arachidonic acid potentiated the suppression. These data are consistent with the hypothesis that alterations in lymphocyte functions may occur as a result of quantitative changes or depletion of conversion products in the arachidonate/lipoxygenase pathway induced by the addition of compounds that serve as co-oxidative substrates for hydroperoxidases, the prototype being benzidine.

Influence of steroidal and nonsteroidal sex hormones on host resistance in mice: increased susceptibility to Listeria monocytogenes after exposure to estrogenic hormones.

Subchronic exposure to pharmacological levels of estrogenic compounds, including 17 beta-estradiol, diethylstilbestrol, and alpha-dienestrol, significantly increased the mortality of B6C3F1 female mice after Listeria infection. Compounds with little estrogenic activity, including 5 alpha-dihydrotestosterone, progesterone, zearalenol, and corticosterone, did not alter Listeria-related mortality. Estrogen-induced alterations in resistance were inhibited by both adult thymectomy and the estrogen antagonist tamoxifen. Estrogen exposure depressed the accumulation of monocytes and lymphocytes at infective foci. Significantly elevated numbers of bacteria were observed in infective foci of estrogen-treated mice later in the infection when bacteria were nearly eliminated from untreated animals. These results indicate that estrogen-induced suppression of Listeria immunity is partially mediated by the thymus, probably through receptor events which may ultimately suppress the activation of T cell-dependent defense mechanisms. This may be partially reflected by the inability of estrogen-exposed mice to eliminate Listeria cells or to accumulate mononuclear effector cells at infective foci at the same rate as controls.