Strongyloides stercoralis: an initial autoinfective burst amplifies primary infection.

Compartmental analysis of Strongloides stercoralis burdens in experimentally infected, serially necropsied dogs was used to test an autoinfective burst hypothesis. The hypothesis states that in well-established, active infections and in chronic infections as well, the rate of larval development is down-regulated so that most larvae do not attain infectivity internally. The majority pass in the feces as preinfective, rhabditiform larvae, but a few (those with the most rapid developmental rate) attain infectivity internally, and therefore are positioned for autoinfectivity. In contrast, in immunologically naive hosts, larval development proceeds without host hindrance and many larvae, proceeding at the most rapid rate of a spectrum of normal intrinsic developmental rates, attain infectivity internally. For a brief period, hyperinfection occurs, during which the adult worm population increases sharply. Gut-level resistance soon occurs, larval development is retarded, and an increasing proportion of larvae are discharged as preinfective rhabditiform larvae. With fewer larvae developing to infectivity internally, recruitment into the adult population decreases, with an attendant increase in the mean age and a gradual decrease in the size of the adult population. The data and the attendant model strongly support this autoinfective burst hypothesis.

Cryopreservation of human hookworms.

First-stage larvae (L1) of the human hookworms Ancylostoma duodenale and Necator americanus were frozen over liquid nitrogen after a 1-hr incubation in a cryoprotectant (10% DMSO and 10% dextran). Thawed larvae developed to the infective third stage (L3) on agar plates. In the case of A. duodenale, the larvae were infective to dogs. The infectivity of N. americanus L3 was not tested.

Immune reactions and immunopathologic changes induced in ovine fetuses and lambs by maedi-visna virus.

Seventy- to 80-day fetuses of Merino ewes were inoculated intramuscularly in utero and 2-week-old lambs of the same breed intratracheally with 10(6.3) TCID50/0.1 ml of maedi-visna virus strain K1512 isolated in Iceland. While no precipitins appeared in the serum of fetuses, such antibodies were demonstrable in the lambs from postinoculation (PI) day 30. Indirect immunofluorescence (IIF) revealed the presence of antibodies in samples from both fetuses and lambs; the detectability of these antibodies, however, varied even within a given animal during the experiment. The serologic results were inversely proportional to the kinetics of circulating immune complex (cIC) production. By the lymphocyte stimulation test (LST), the blastogenic transformation of lymphocytes as measured by 3H-TdR incorporation was 6-8% and 6-14% in the fetuses and lambs, respectively. By antibody-dependent cell-mediated cytotoxicity (ADCC) test, cytotoxic capacity (10-14%) was only demonstrable in lambs inoculated at 2 weeks of age, in the 2nd month of life. Histologic examination showed that in the lungs of both fetuses and lambs lympho-histiocytic infiltration developed from PI week 4. This was later joined by lymphoid hyperplasia in the peribronchial lymph nodes. T lymphocyte proliferation was dominant in these lesions as shown by a histochemical procedure (alpha-naphthyl-acetate-esterase, ANAE). By immunofluorescence (IF), deposited immune complexes (IC) were demonstrable in various organs (wall of cerebral ventricles, endothelium of blood vessels of the brain stem, cerebellum, lungs, kidneys). These IC may play an important role in the pathogenesis of maedi-visna.

Intestinal absorption of colostral lymphocytes in newborn lambs and their role in the development of immune status.

Two model experiments were conducted to study the intestinal absorption of colostral lymphoid cells and the role of these cells in the development of immune status in newborn lambs. In experiment I, 17 lambs of 14 Merino ewes were used. Suspensions of lymphoid cells separated from the colostrum (cell density: 5 x 10(6)/ml) and blood (3 x 10(6)/ml) were labelled with technetium (Na99mTcO4) of 37 MBq/ml radioactive concentration. In three groups of lambs, 10-ml volumes of the cell suspensions were injected directly into the duodenum after laparotomy, while in a fourth group (group Ia) the same volume was administered to the animals through an oesophageal tube. The labelled cells revealed that colostral cells of the lamb's own dam are absorbed from the gastrointestinal tract and get into the newborn lamb's lymph circulation irrespective of the route of application. In experiment II, involving 40 lambs of 40 ewes, we studied the effect of absorbed colostral lymphocytes on the development of the newborn lamb's immune status. Twenty ewes (group A) each were treated with 3 ml tetanus anatoxin twice, while the remaining animals (group B) were left uninoculated. Lambs of group A (designated A2) were separated from their dams immediately after birth, then were administered, through an oesophageal tube, 10 ml of a suspension of lymphoid cells (cell density: 5 x 10(6)/ml) separated from the maternal colostrum. Subsequently, the lambs were interchanged with lambs of nonimmunized ewes of group B (designated lambs B1), i.e. were mutually put out to nursing. At three days of age, lambs of groups A1, A2, B1 and B2 were inoculated with 3 ml tetanus anatoxin, then blood samples were taken from them 5 times in a period of 27 days for comparative examination of the humoral and cellular immune reactions. The results demonstrate that lymphoid cells from the colostrum of the lambs' own dam become absorbed into the newborn lambs' lymph circulation, remain immunologically active and may transfer, besides immunological memory, also cellular activity.

T-cell deficiency in Suffolk lambs.

In a flock of Suffolk sheep respiratory diseases were regularly observed, while a flock of Booroola sheep kept under similar feeding and management conditions remained healthy. Experiments were conducted to compare the immunological and haematological parameters of Suffolk and Booroola sheep of different age groups. The percentage of T and B cells in the lymphocyte population and the capacity for blastogenesis induced by nonspecific mitogens were analyzed. Suffolk sucking lambs had significantly (P < 0.001) lower Concanavalin A (Con-A) induced blastogenesis and significantly lower T cell percentage at 6 months of age than Booroola lambs of the same age. B cell percentage and the rate of blastogenesis induced by Phaseolus vulgaris lectin (PHA) were lower in Suffolk lambs, though the differences were not significant. Sucking and growing Suffolk lambs had significantly (P < 0.01) lower red blood cell count and packed cell volume than Booroola lambs of the same age. Blood haemoglobin concentration was also lower in Suffolk lambs. No consistent differences were seen between the two breeds in total leucocyte count. T-cell deficiency and anaemia could be corrected by treatment with the immunomodulator levamisole (administered at a dose of 3 mg/kg body mass intramuscularly, twice with an interval of 10 days) and with vitamin B12 (1,000 micrograms/animal i.m.), respectively. On day 16 after the first treatment, the T-cell percentage, Con-A induced blastogenesis, red blood cell count, and packed cell volume of growing Suffolk lambs increased. T-cell deficiency and anaemia, either separately or together, may explain the lower resistance of Suffolk lambs to opportunistic pathogens. The relative contribution of genetic and environmental factors requires further studies.

Strongyloides stercoralis: the first rodent model for uncomplicated and hyperinfective strongyloidiasis, the Mongolian gerbil (Meriones unguiculatus).

Strongyloidiasis is the most common endemic helminthiasis in several of the world's industrialized nations, yet relatively little is known about its basic biology and immunobiology because a practical rodent model for the investigation of this clinically important parasitism is lacking. This study reports such a model for use in the investigation of Strongyloides stercoralis infection. Normal male gerbils infected subcutaneously with 1000 infective filariform larvae harbored moderate numbers (83.6 +/- 27.6) of adult worms at 35 days after infection, and a low-grade infection persisted for at least 131 days mimicking the chronicity of human infections. Gerbils treated weekly with 2 mg of methylprednisolone acetate developed hyperinfective strongyloidiasis with up to 8000 autoinfective larvae occurring in these animals at postinfection day 21. Autoinfection never occurred in normal (untreated) gerbils.