Intraocular IgE antibody induced in guinea pigs with Ascaris suum larvae.

The systemic and local (intraocular) IgE antibody responses to infective and heat-killed Ascaris suum larvae were examined in guinea pigs. IgE antibody, demonstrated by the 6-day P-K test, was found in anterior chamber fluid following primary intravitreal injection of live second-stage A. suum larvae and in some instances occurred when no serum P-K activity was demonstrable. No intraocular IgE antibody was induced by primary intravitreal injection of heat-killed larvae. A brisk intraocular and systemic IgE antibody response followed the secondary intravitreal injection of either live or heat-killed larvae into animals systemically infected with A. suum. The guinea pig system promises to be a useful model for studying the immunopathology of human ocular parasite infections.

Immunopathology of Toxocara canis and Ascaris suum infections of the eye: the role of the eosinophil.

Intravitreal infection of guinea pigs with second-stage larvae of Toxocara canis and second- and fourth-stage larvae of Ascaris suum induced intraocular IgE antibodies and a dense eosinophil infiltration in the anterior chamber and throughout the uveal tract. The eosinophil infiltrate began within 1 day after infection and persisted for as long as 51 days. By day 12 after intravitreal infection, the injected ascarid larvae were surrounded by granulomas which consisted almost entirely of eosinophils. Firm adherence of eosinophils to the parasite cuticle, morphologic alterations and degranulation of eosinophils with the deposition of free eosinophil granules on the parasite surfaces, and ingestion of eosinophils and eosinophil granules by the parasite larvae also were observed. Intravitreal injectionof a soluble antigen derived from third-stage A. suum molting to the fourth-stage in defined media in vitro also induced intraocular IgE antibody and a diffuse ocular eosinophil infiltrate. Dense eosinophil infiltration of the choroid, not immediately adjacent to a parasite larva, was accompanied by destruction of the lverlying outer retina, with cystic changes in the retina and between the retina and the choroid. Few eosinophils were observed within the retina, and the retinal destruction may be the result of direct toxic action of constituents of the choroidal eosinophils. Evidence which indicates that the eosinophil is the principal effector cell in immunity to helminth infections and is cytotoxic for the parasites, possible mechanisms for the induction of the ocular eosinophil infiltrates, and evidence for autotoxicity by eosinophils are briefly reviewed, and the potential roles of the eosinophil in the ocular response to helminth parasites are discussed.

In vitro interaction of eosinophils from ascarid-infected eyes with Ascaris suum and Toxocara canis larvae.

The role of eosinophils in ocular ascarid infection is studied in an animal model. Primary intravitreal infection of guinea-pig eyes with ascarid (Toxocara canis, Ascaris suum) second-stage (L2) larvae resulted in an anterior chamber exudate containing 98% or more eosinophils. Anterior chamber aspirates were cultured in RPMI media 1640 with T. canis or A. suum L2 larvae at 37 degrees C for 1-96 hours. The in vitro interaction of eosinophils with L2 larvae was studied by light, and scanning and transmission electron microscopy. Eosinophil interaction with L2 larvae in vitro was dependent upon soluble factors present in the anterior chamber aspirates from the infected eyes. Eosinophils adhered firmly to the surface of the L2 larvae, to a larval sheath, or to attached eosinophils. Eosinophils interacting with larvae displayed a range of granular matrix changes, core duplication, and reversal of the relative electron densities of the core and matrix, suggestive of eosinophil activation. An eosinophil secretory granule was seen to empty its contents onto a T. canis L2 larval surface. Electron-dense material was observed in the interphase between eosinophils and the larval cuticle or sheath. Large lipid droplets within muscle cells and ballooned-out epidermal cells were seen within larvae immediately beneath adherent eosinophils. Parasites were able to partially evade interaction with eosinophils in culture by shedding their sheaths. A similar phenomenon in vivo may allow the parasite to migrate from a site of inflammation. It is possible that a discarded sheath or membrane serves as an antigenic stimulus for a local intraocular granulomatous reaction free of parasite.

The evasion of the immune response and immunological unresponsiveness: parasitic helminth infections.

A selective review is given of the mechanisms associated with the evasion of the immune response by parasitic helminths and immunological unresponsiveness as it applies to helminth infections. Immunosuppression caused by parasites leading to reduced responsiveness of lymphocytes to mitogens is discussed, and mechanisms that inhibit effector mechanisms at the parasite surface and polyclonal activation of lymphocyte populations are dealt with. Physiological immunosuppression associated with parturition and lactation and the immunological unresponsiveness of young ruminants are dealt with in detail.

Immunopathology of ascarid infection of the eye. Role of IgE antibodies and mast cells.

The roles of IgE antiascarid antibodies and mast cells were compared in passively sensitized guinea pigs and animals infected intravitreally with ascarid larvae (Toxocara canis, Ascaris suum). Intravenous IgE antibody disappeared from the serum within 48 hours, but induced a hypersensitive state that persisted for 28 days. In systemically immunized animals, the aqueous-serum IgE antibody ratio was 1:1,000 or less. Passive periocular anaphylactic reactions produced an infiltration of neutrophils and eosinophils, degranulation of mast cells, and vascular leakage in periocular and episcleral tissues. Systemic anaphylaxis also produced degranulation of uveal mast cells, and infiltration of eosinophils, and vascular leakage in the choroid. Intraocular infection produced a transient decrease of mast cells that correlated with an increased infiltration of eosinophils and plasma cells.

Ocular immunopathologic findings of experimental onchocerciasis.

Ocular immunopathologic responses of inbred guinea pigs infected with Onchocerca microfilariae from domesticated animals were studied as a laboratory model of human ocular onchocerciasis. A single intracorneal infection of normal guinea pigs with microfilariae produced only minimal ocular lesions. In contrast, intracorneal infection of guinea pigs previously immunized by systemic infection with microfilariae produced intense corneal and uveal inflammation. Transfer of splenic lymphocytes from immunized donors to syngeneic normal recipients substituted effectively for the active immunization. Cell recipients produced marked corneal inflammatory reactions when challenged by a single intracorneal infection. Fresh and cryopreserved microfilariae produced identical reactions. The corneal inflammatory infiltrates were composed primarily of eosinophils, neutrophils, and plasma cells and resembled human onchocercal keratitis. Diethylcarbamazine citrate administration after a challenge intracorneal infection increased the severity of the corneal inflammatory response in immunized animals.

Angiostrongylus cantonensis: lymphoid cell responsiveness and antibody production in rats.

Angiostrongylus cantonensis-infected rats were examined for the presence of antigen sensitive lymphocytes, as assessed by the in vitro uptake of tritiated thymidine by cells of various lymphoid organs (cervical, mediastinal and mesenteric lymph nodes, spleen and periphereal blood), following stimulation by adult worm antigen. The lymphoid cell response of rats to A. cantonensis appeared to be local in nature in that significant responses were noted only in the cervical lymph node cells during the first 4 weeks of infection. The responses of spleen cells to phytohemagglutinin gradually declined as the infection progressed and this reduced responsiveness was statistically significant during the period of 5 to 10 weeks of infection. Homocytotropic antibody, demonstrated by 72-hour homologous passive cutaneous anaphylaxis, was detected throughout 2 to 17 weeks postinfection with a peak response at the 5th week of infection. The antibody was heat labile and sensitive to reduction by 2-mercaptoethanol and alkylation. Hemagglutinating antibody was first observed 5 weeks after infection and high titers occurred throughout 6 to 17 weeks postinfection.

The homocytotropic and hemagglutinating antibody responses to Brugia pahangi infection in the multimammate rat (Mastomys natalensis).

Homocytotropic and hemagglutinating antibody responses were followed in multimammate rate (Mastomys natalensis) infected with Brugia pahangi. Homocytotropic antibodies were detected by both active and passive cutaneous anaphylaxis using an antigen prepared from Dirofilaria immitis. The homocytotropic antibody response was first evident at 3 weeks after infection and increased progressively until after patency. It then waned gradually and was absent at 33 weeks after infection (or 20 weeks after patency). During this time microfilaremia continued to increase steadily. Homocytotropic antibody induced by the infection was heat (56 degrees C) labile, sensitive to 2-mercaptoethanol reduction, and was detected in the skin of recipients following a 72-hour latent period. Hemagglutinating antibodies to the infection were detected by the D. immitis antigen. These were present by 9 days after infection and persisted throughout the course of the infection. Only 2-mercaptoethanol labile antibody was detected during the prepatent period of infection.

Advances in immunoparasitology.

A selective review of the advances in immunoparasitology is presented. It is selective simply because it is not feasible to embrace the whole field of parasitology within the compass of a single review paper, for if it were attempted, it would suffer undue abbreviation. Emphasis is placed on the advances in helminthology and especially the gastro-intestinal parasites of ruminants, an obvious selection because of the interests of the author. Reviews are always somewhat retrospective in outlook; to write a review at the present time is especially foolhardy since developments in biology are such that totally new concepts can arise almost overnight, as it were. This is a particularly healthy state, and the discipline of parasitology is caught up in the application and interpretation of molecular biological considerations. "Parasitism" is a field of increasing importance and challenge.

Fate of Litomosoides carinii adults transplanted into the pleural or peritoneal cavity of infected and naive multimammate rats (Mastomys natalensis).

In each of 4 experiments, 58 multimammate rats (Mastomys natalensis) were subdivided into 5 groups. Thirty-four rats were infected with Litomosoides carinii and infections were allowed to become patent. Ten days after patency adult worms were surgically transferred from donor rats to each of 1 group of infected rats and 1 group of naive rats. Groups of infected and naive rats served as controls. Transfers were made either intrapleurally or intraperitoneally. Samples of blood and tissues were taken from each of 2 animals necropsied from each group at intervals to 31 days. At necropsy, the transferred worms and the original population (if any) were examined and samples were fixed. Infected rats accepted new worms with a minimum of reaction while naive rats rejected worms beginning at day 10 (intrapleural) of 17 (intraperitoneal). Rejections were complete leaving a white fibrous mass by day 24 or 31, respectively. Hemagglutination antibody titers fell into 2 groups: infected and naive. IHA titers of naive recipient rats increased into the infected range by day 3 (intrapleural) or day 10 (intraperitoneal). Microfilaria counts presented a more varied pattern but a similar lag in the intraperitoneal recipient group was observed. It was concluded that a preparation period is necessary for successful residence of adult worms, and that this preparation is not restricted to the pleural cavity.

Litomosoides carinii: effect of diethylcarbamazine on microfilaremias of Mastomys natalensis harboring old infections, new infections, and transfused microfilariae.

Mastomys natalensis, matched according to age and microfilaremia, were divided into Experimental and Control groups. The former were given diethylcarbamazine (Caricide, 500 mg/kg) per os. Microfilariae counts were made at 15, 30, 60, and 120 min and at 1, 5, and 12 days. This protocol was performed on rats with: old infections (patent for 7 mo), new infections (patent for 10 days), and no infection but made microfilaremic by injection of blood or culture-derived microfilariae. In all treated groups, the microfilaremia dropped precipitously within the first 15 min. Microfilaremias of animals with old infections remained low until day 12 after treatment when they began to rise, whereas those of animals with new infections began to rise immediately, i.e., within minutes after the initial decline. Microfilaremias of animals with no adult worms present remained depressed for the duration of the experiment. Thus, the resurgence of microfilariae after treatment with diethylcarbamazine is the result of release of new microfilariae by the female worms rather than release of trapped microfilariae by the host. This investigation also demonstrates that elimination of microfilariae by a nonsensitized host is possible upon treatment with diethylcarbamazine.

The spin method for recovering tissue larvae and its use in evaluating C57BL/6 mice as a model for the study of resistance to infection with Ascaris suum.

A centrifugation method for recovering tissue larvae is described and is proven to be superior to both Baerman and tissue digest methods for recovering larvae of Ascaris suum from the liver and lungs of infected C57BL/6 mice. Using the spin method for harvesting larvae, C57BL/6 mice were evaluated for their suitability in studies on specific host immunity to infection with A. suum.

Intestinal changes in puppies infected with Toxocara canis.

Small intestinal histopathology and absorption were examined in Beagle puppies infected with either a moderate or a low burden of Toxocara canis. Infection with T. canis significantly reduced absorption of xylose, but only slightly delayed absorption of para-aminobenzoic acid. Fat assimilation was reduced and faecal proteolytic activity was increased. A significant reduction in villous height occurred and was inversely related to the extent of the infection. Villous goblet cell numbers, particularly those in the luminal third of the villus, were lowest and crypt goblet cell numbers were highest in the most heavily infected of the puppies. Villous goblet cell numbers increased rapidly after treatment of the puppies with piperazine or after the spontaneous elimination of the T. canis infection while crypt goblet cell numbers were less affected by elimination of the parasites. Intra-epithelial lymphocyte numbers were lowest in 33- to 37-day-old puppies infected with greater than 127 T. canis and highest in 44- to 46-day-old puppies losing their infection. Infection with T. canis had no apparent effect on mast cell numbers or pyroninophilic cell numbers in the lamina propria.

Lymphoid cell responses in parasitic helminth infections.

The cellular responses during experimental ascariasis provide a mechanism whereby effector systems are mobilized rapidly and locally, resulting in the prompt response which is evident on reinfection. It is proposed that the products of activated "T" lymphocytes facilitate local accumulation of lymphoid cells which, later, as specific antibody-producing cells provide the mediators (e.g. opsonizing antibody) responsible for mechanisms which destroy the parasite. While the mechanisms causing death of the parasite are still unknown, our present studies will provide an explanation of events that prepare for this event.

Survey of parasites in dairy goats.

The survey was performed to study prevalence and intensity of parasitic infection in goats. Fecal samples were examined from 336 goats in southeastern Pennsylvania and northern Maryland. On the basis of fecal egg, oocyst, and larval counts, the following results were obtained. Eimerian oocysts were found in 100% of the fecal samples and the greatest fecal oocyst counts were found in goats under 6 months of age. Strongyle eggs and Strongyloides eggs were present in 76% and 20%, respectively, of the samples. Moniezia eggs were found in 9%, Trichuris eggs in 4%, and Nematodirus eggs in 1% of the samples. Twenty of 24 flocks examined for Muellerius capillaris were infected with this parasite. In these 20 flocks, 83% of the goats examined were infected with the parasite. Skrjabinema caprae infections were found.

Survey for infection with Onchocerca cervicalis in horses in eastern United States.

This survey was performed to study the prevalence of infection with Onchocerca cervicalis in horses in the eastern United States. In the course of the survey, 121 horses, 1 mule and 1 donkey were examined. Microfilariae were recovered from 74 (61%) of the horses examined. All infected horses showed microfilariae of O cervicalis in the umbilical sample, 62 (84%) were infected in the eyelid and, in 36 (49%), microfilariae had invaded the eye. The mule was unifected and the donkey was infected with O cervicalis.

Antibiotic resistance--an evolving problem.

In 1998, an influential report on antimicrobial resistance from the House of Lords Select Committee on Science and Technology highlighted the threat posed to public health by resistance, and called for products to be used more prudently in both human and veterinary medicine. Here, Lord Soulsby, who chaired the Lords' committee on antimicrobials, and Richard Wise, who advised the committee and is now chairman of the Government's Specialist Advisory Committee on Antimicrobial Resistance, consider what has been achieved since then, along with the challenges that remain.

Use of sentinel lambs for early monitoring of the South Powys Hydatidosis Control Scheme: prevalence of Echinococcus granulosus and some other helminths.

Sentinel lambs were used to identify young Echinococcus granulosus infections in sheep, to provide an early indication of the progress of the South Powys Hydatidosis Control Scheme. Four sentinel lambs were purchased on each of 60 farms, from inside and outside the control area; they were examined when approximately six, 10 and 15 months of age. Gross examination, thin slicing of organs and histological examination of the lesions in the viscera revealed no E granulosus hydatid cysts in lambs born within the control area, whereas 25 per cent of the 15-month-old lambs from outside the area harboured E granulosus cysts (less than 1 to 2 mm in diameter). Lambs from E granulosus infected farms had significantly higher anti-E granulosus ELISA antibody titres than lambs from uninfected farms. It was concluded that within one year of beginning to treat dogs with praziquantel every six weeks the transmission of E granulosus to sheep had ceased. In contrast, this treatment did not prevent infections with Taenia hydatigena or T ovis; an examination of the 240 lambs revealed T hydatigena in 33.3 per cent of them, Tovis in 4.2 per cent, Dictyocaulus filaria in 12.1 per cent and Meullerius capillaris in 49.2 per cent.