The effects of food availability on the population structure of Aedes aegypti in the presence and absence of Plagiorchis elegans cercariae were studied in the laboratory. Under conditions of low food availability and in the absence of the parasite, larval population levels cycled at 40 day intervals. Cycles were initiated by the periodic build-up and decline of fourth instar larvae. These major competitors for food resources appear to be responsible for the release of a cascade of events which allowed the intermittent flow through of larvae from the first to the third instar. Under both optimal and suboptimal conditions of food availability, the introduction of high densities of P. elegans cercariae resulted in a decrease in the production of adult mosquitoes. Although the parasite reduced competition by preferentially removing fourth instar larvae and hastened the development of surviving instars, such survivors were exposed to the effects of the parasite as soon as they reached the fourth instar.

Submitted in partial fulfillment of the academic requirements for the degree of Master of Technology: Biotechnology, 2009. / Production of numerous biotechnologically-important products such as threonine is based on cultivation of bacterial cultures. Infection of these bacterial cultures by bacteriophages has a detrimental effect in the production of these bioproducts. Despite this, most people controlling these bioprocesses do not recognize the early signs of bacteriophage infection. SA Bioproducts (Ply) Ltd was no exception and has suffered tremendous loss of production time after bacteriophages infected threonine producing E. coli strain B. This study was aimed at developing assays to control and prevent bacteriophage infection at this company. These included determining the source of phages by monitoring the process plant environment, optimising the detection and enumeration methods so as to monitor the levels of bacteriophages in the environment, identification of bacteriophages in order to determine the number of bacteriophages capable of infection threonine producing E. coli strain B, treatment and of phages, and possible prevention of phage infection. Adam's DAL method was very efficient at detecting phages in the samples collected at various areas (sumps, odour scrubber, process water, and soil) around the plant for 16 weeks. High levels of phages were found in the sumps and this was identified as the source of infection. Samples collected were grouped together according to their source. The samples were enriched and purified in order to characterise them. The prevalent phage in all samples was identified as a T1-like phage. Bacterial strains that grew on the plate in the presence of phages were assumed to be resistant to phages or contained lysogenic phages which would explain the new lytic cycles that were observed whenever these resistant strains were used for production. UV light, green v indicator plates, and a mutagen (Mitomycin C) were used to detect Iysogens. Mitomycin C at 1 IJg/ml was found to be most effective in detecting lysogenic phages. This was shown by new plaque forming units that were visible on the DAL plates. Temperature (heat), chemicals, and inhibitors (vitamins) were investigated as strategies for prevention and treatment of bacteriophage infection. Bacteriophage samples were exposed to 70, 80, 100, and 120°C. At these temperatures pfu counts in the samples were reduced significantly. At 120°C there was a complete inactivation of bacteriophages within 30 minutes. Chemicals investigated such as sodium hydroxide and Albrom 100T were capable of complete deactivation of bacteriophages at a very low concentration (0.1%). Therefore, these chemicals can be used to clean the plant area and sumps. Vitamins C, K and E solutions were investigated to determine their inhibitory effect on bacteriophages. Vitamin C, K and E reduced pfu counts by 3, 2, and 4 logs, respectively. Therefore vitamin C and E solutions were mixed and to determine if mixing them would enhance their inactivation capabilities. This resulted in a reduction greater than 9 logs of phage in the sample (from 7.7 x 109 to 3 pfu/ml). The host bacterium was also exposed to this mixture to determine effect of the vitamin mixture on its growth. It was found that there was no effect exerted by this mixture on the host bacteria. This proved to be an ideal mixture for combating phages during fermentation. However, vitamin E is not cost effective for co-feeding in 200 m' fermenters, and therefore vitamin C solution was a cost-effective alternative. It was concluded that bacteriophage contaminated bioprocessing plant should be properly cleaned using a combination of heat and chemicals. Bacteriophage infection should be prevented by employing inhibitors.

The zoonotic potential of Trichinella zimbabwensis as supported by the clinical symptoms observed in experimentally infected, non-human primates (Mukaratirwa et al., 2001) necessitates research aimed at elucidating the distribution and epidemiology of this parasite. No controlled studies have been conducted to determine the predilection muscles of Trichinella zimbabwensis larvae in Nile crocodiles (Crocodylus niloticus) or the influence of infection intensity on the distribution of the larvae in crocodiles. Neither has the influence of Trichinella zimbabwensis on biochemical parameters in crocodiles been assessed previously. To determine the distribution patterns of Trichinella zimbabwensis larvae and predilection muscles and to assess the influence on selected biochemical parameters, fifteen crocodiles were randomly divided into three cohorts of five animals each to represent high infection (642 larvae/kg of body weight), medium infection (414 larvae/kg of bodyweight) and low infection (134 larvae/kg of bodyweight) cohorts. In the high infection cohort, high percentages of larvae were observed in the tricep muscles (26%) and hind limb muscles (13%). In the medium infection cohort, high percentages of larvae were found in the tricep muscles (50%), sternomastoid (18%) and hind limb muscles (13%). For the low infection cohort, larvae were mainly found in the intercostal muscles (36%), longissimus complex (27%), forelimb muscles (20%), and hind limb muscles (10%). Predilection muscles in the high and medium infection cohorts were similar to those reported in naturally infected crocodiles despite changes in infection intensity. The high infection cohort had significantly higher numbers of larvae in the intercostal, longissimus complex, external tibial flexor, longissimus caudalis and caudal femoral muscles (P < 0.05) compared to the medium infection cohort. In comparison to the low infection cohort, the high infection cohort harboured significantly higher numbers of larvae in all muscles (P < 0.05) except for the tongue and pterygoid. The high infection cohort harboured significantly higher numbers of larvae (P < 0.05) in the sternomastoid, tricep, intercostal, longissimus complex, external tibial flexor, longissimus caudalis and caudal femoral muscles compared to naturally infected crocodiles. The importance of host characteristics in determining predilection and the importance of leg musculature as a predilection site for Trichinella spp. in sylvatic carnivores were both confirmed in this study. Deviations from normal parameters of blood glucose, alanine transaminase (ALT), aspartate transaminase (AST), creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) compared to observations in uninfected reptiles were observed. Hypoglycaemia was not observed in the infected groups in this study. The humoral immune response to Trichinella zimbabwensis infection was evaluated in all three groups by way of indirect ELISA. Peak values of blood glucose, LDH and AST were observed on day 56, 49 and 42 p.i. in the high, medium and low infection cohorts respectively. CPK values peaked on day 35 p.i. in all three cohorts. Peak ALT values were reached on day 56 in the high infection cohort and on day 28 p.i. in both the medium and low infection cohorts. No correlations between the biochemical parameters and infection intensity were observed. Peak antibody titres were reached on day 49 p.i. in the medium infection cohort and on day 42 p.i. in both the high and low infection cohorts. Infection intensity could not be correlated with the magnitude of the humoral immune response or time to seroconversion. The effect of infection intensity on time to seroconversion, magnitude and persistence of the humoral immune response was assessed. No significant differences in the titre levels between the three groups were observed. Infection intensity could not be correlated with the magnitude of the humoral response or time to seroconversion. Results of this study were in agreement with results reported in mammals (wild boars and horses) infected with other Trichinella species and showed that antibody titres could not be detected indefinitely. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2013.

Protein deficiency may increase susceptibility to gastrointestinal (GI) parasitic infections, possibly as a result of impaired systemic and/or intestinal effector responses induced by downregulation of Th2 cytokines and/or upregulation of Th1 cytokines. To test this hypothesis, female BALB/c mice (n = 18/diet) were fed a control (24%), marginal (7%), or deficient (3%) protein diet and given a challenge infection with the GI nematode, Heligmosomoides polygyrus. The 3% mice had higher worm burdens at 1, 2 and 4 weeks post-challenge infection (pci), lower increases in serum IgE, reduced intestinal eosinophilia, and depressed mucosal mast cell proliferation and activation at 1 to 2 weeks pci. To determine whether these suppressed effector responses in the 3% mice were associated with altered spleen and mesenteric lymph node (MLN) cytokine profiles, cells were restimulated in vitro with parasite antigen and cytokine concentrations were measured. Deficient MLN cells secreted significantly less IL-4 and more IFN-gamma at 1--2 weeks pci than did control MLN cells. Deficient spleen cells also secreted more IFN-gamma at 2 weeks pci compared with control spleen cells. From RT-PCR analyses, the 3% mice also had lower IL-4 mRNA expression in spleen and MLN at 1--2 weeks pci. Our study supports the hypothesis that protein deficiency exacerbates the survival of a GI nematode parasite by decreasing IL-4 (Th2) and increasing IFN-gamma (Th1) early in the infection, leading to reduced gut and systemic Th2 effector responses.

Anthelmintics, antiparasitic agents, have been developed as a main weapon to control parasitic nematodes of domestic ruminants. Unfortunately, the intensive use of anthelmintics leads to the development of drug resistance in parasite populations. Anthelmintic resistance has compromised the control of nematode parasites and has become a major problem in many countries of the world. Resistance to the newest anthelmintics such as ivermectin (IVM) and related anthelmintics in Haemonchus contortus in sheep has been developing rapidly in recent years. The development of drug resistance is an evolutionary process that leads to genetic changes in parasite populations in response to drug exposure. However, the mechanism of ivermectin resistance in nematode parasites is unknown. P-glycoprotein (Pgp) has been well documented in mammalian cells as a membrane transporter by actively extruding a variety of structurally and functionally unrelated hydrophobic cytotoxic drugs out of the cell. This study was to determine whether there is an association between specific alleles at the Pgp locus and IVM or moxidectin (MOX) selection in H. contortus, by investigating the genetic variation of the Pgp homologue in unselected and IVM- and MOX-selected strains of H. contortus. (Abstract shortened by UMI.)

Association between albendazole anthelmintic resistance and a panel of life history traits in Heligmosomoides polygyrus was investigated both prior to and during drug-selection. Associations prior to anthelmintic application were studied in ten independent lines isolated without drug treatment from a susceptible stock population by random genetic drift. Variation among lines was detected in several life history traits (i.e., establishment, development and survival), and, despite lack of previous exposure to albendazole, lines also varied in their tolerance to the drug. No significant correlations were detected between drug-tolerance and any of the life history traits after 11 generations of isolation. The apparent lack of fitness differential between lesser and more drug-tolerant individuals of the susceptible population is not in accordance with the assumption that the low frequency of drug tolerant individuals in the susceptible population is explained by their lower fitness, but is consistent with the neutral theory. Associations between life history traits and drug resistance were also studied using two lines selected for albendazole resistance from the stock population, and two control lines exposed to the same monthly passage procedure but not to the drug. After 10 generations of selection, drug resistance increased from an LC50 of 0.48 $ mu$M to 2.03 $ mu$M. In a primary infection, the higher establishment and higher worm numbers one-month post-infection in the resistant parasites compared to the stock parasites occurred only in the drug-selected lines. Changes in these traits were attributed to the drug selection regime. In contrast, both drug-selected lines and passaged lines showed a faster rate of development and higher early egg production compared with the stock parasites; these changes were attributed to the passage procedure that presumably acted as a selective force on early life history traits. In immunized hosts, changes in several traits that o

An experimental study of laboratory populations of the stored-products moth, Cadra cautella (Lepidoptera: Phycitidae) and its larval parasitoid, Venturia canescens (Hymenoptera: Ichneumonidae) identified and quantified density- and age-dependent demographic characteristics of the host-parasitoid system. Host imago longevity and fecundity depended on larval weight at pupation. Observed effects of C. cautella larval competition for food on larval mortality, stage duration, and weight at pupation were successfully captured in a mathematical model. Host larval age significantly influenced inter-stage cannibalism and susceptibility to mortality resulting from parasitoid oviposition wounds. Both larval parasitoid developmental rates and adult parasitoid attack rates depended on host larval age. Long-term population experiments of host and host-parasitoid populations revealed that host populations fluctuated with a period slightly in excess of host generation time and that parasitoid populations were in synchrony with host populations.

The influence of energy restriction on the transmission dynamics of a direct life cycle nematode, Heligmosomoides polygyrus, within free-running arena Systems has to date remained unexplored. Indoor populations of CD-1 outbred mice were established for 12 weeks in arenas and fed either energy-suffi ci ent (ES) or energy-restricted (ER-20% réduction in metabolizable energy) diets. Infection was introduced to ail arenas following 3 weeks of diet treatment. Contrary to previous findings, the mice fed the ER diets compensated for the deficiency by increasing food consumption and thus, while early in the experiment energy restriction was evident, dietary effects were no longer observed after 6 weeks. Worm burdens, measured at 4 time points over the course of the experiment, were higher in mice fed the ES diets. Although mice fed the ER diets had greater contact with infected areas, the mice fed the ES diets increased the duration of behaviours that heighten ingestion of the parasite - self and allogrooming. Dietary effects on behaviour were observed only after infection was introduced and were more pronounced in the durations of individual bouts rather than in overall durations or time budgets. Nesting bouts were prolonged in mice in the ER arenas perhaps as a means of thermoregulation to counteract the combined effects of infection and energy restriction. The duration of exploratory bouts was also higher in the ER mice possibly due to an inability to receive or process information in their environment. Social interactions, predominantly involving sniffing, increased after infection was introduced, supporting the rôle of odour in communicating infection status in same-sex conspecifics. Together these results provide a more comprehensive ethogram of mice in a semi-natural setting and highlight those behaviours where adaptive plasticity allows response to dietary and infection stresses.

A study was undertaken to evaluate and compare the effectiveness of three anthelmintics, ivermectin, fenbendazole, and a combination of ivermectin and pyrantel pamoate, on fecal egg count reductions of cyathostomes and Parascaris equorum in 30 foals at the Texas A&M Horse Center. The foals were reared under standard horse center practices and were naturally infected with both cyathostomes and Parascaris. The foals were randomized into three treatment groups with individuals being rerandomized after each eight week observation period. The treatments of ivermectin and fenbendazole were given at the manufacturer's recommended doses and the pyrantel treatment was given at two times the manufacturer's recommended dose. All doses were based on weights taken prior to treatment. Fecal egg counts were performed at the time of treatment and at two week intervals after treatment for a total of eight weeks. Each foal received a total of three treatments during the course of the study along with the most effective treatment at the conclusion of the study. Fecal egg counts were performed by a modified McMaster's test with a sensitivity of 25 eggs per gram of feces and by the modified Wisconsin double centrifugal floatation with a sensitivity of 0.2 eggs per gram of feces. Fecal egg reduction percentages were calculated for each two week interval. Analysis of the results showed that ivermectin, either used alone or with pyrantel was a more effective anthelmintic for cyathostome (small strongyle) control than fenbendazole. Fenbendazole and pyrantel showed a higher initial reduction in Parascasris eggs when compared to the ivermectin only treated group, but ivermectin showed improved egg reduction over time. At the conclusion of this study, a primary treatment of ivermectin at the manufacturer's recommended dose and treatment of pyrantel at two times the manufacturer's recommended dose was recommended to control cyathostome egg production and severely reduce the initial number of Parascaris adults in the foals at this facility. Subsequent monthly does of ivermectin at the manufacturer's recommended dose was also recommended to continue to control both parasites. Follow up fecal examinations were also recommended to test the continued effectiveness of the recommended treatment protocol.

The interaction between the parasite Trichostrongylus tenuis and food quality was investigated in red grouse Lagopus lagopus scoticus, to determine the cause of variation in population cycles between different areas (Scotland and England). Analysis of long-term data, field experiments and population modelling were carried out. Food quality, in terms of nutrient content of heather, was lower on Scottish grouse moors than on English moors. Parasite burdens were also lower in Scottish grouse populations, than in English grouse populations. A three-way interaction, between food, parasites and area (ScotlandlEngland), acting on breeding production, could explain the variation in population cycle period between areas. However, body condition of grouse was not affected by a food-parasite interaction. Experimental manipulation of food quality and parasite burden did not influence the breeding production of female grouse. Modelling the effects of a food-parasite interaction on grouse populations provided evidence that such an interaction could explain variation in cycle period between areas, although other factors are likely to be important in some cases. Red grouse are not unique, as other species also have cycles driven by food and parasites. Other species do not show cyclic population fluctuations because of having shared parasites, and a strong immune response. There is a specialist predator-prey relationship between red grouse and T. tenuis.