Evaluation of PCR to detect Theileria parva in field-collected tick and bovine samples in Tanzania

The ability of PCR to detect infections of Theileria parva, the cause of East Coast Fever, in field-collected tick and bovine samples from Tanzania was evaluated. PCR-detected infection prevalence was high (15/20, 75%) in unfed adult Rhipicephalus appendiculatus ticks that fed as nymphs on an acutely-infected calf, but low (22/836, 2.6%) in unfed adult R. appendiculatus collected from field sites in Tanzania. Tick infection prevalence was comparable to that in previous studies that used salivary gland staining to detect T parva infection in field-collected host-seeking ticks. Of 282 naturally-exposed zebu calves, seven had PCR-positive buffy coat samples prior to detection of Theileria spp. parasites in stained huffy coat cells or lymph node biopsies. Evidence of Theileria spp. infections was detected in stained smears of lymph node biopsies from 109 calves (38.6%) and huffy coat samples from 81 (28.7%), while huffy coat samples from 66 (23.4%) were PCR-positive for T parva. Implications of these findings for the sensitivity and specificity of the PCR are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.

Facultative scavenging as a survival strategy of entomopathogenic nematodes

Entomopathogenic nematodes cannot be considered only as parasitic organisms. With dead Galleria mellonella larvae, we demonstrated that these nematodes use scavenging as an alternative survival strategy. We consider scavenging as the ability of entomopathogenic nematodes to penetrate, develop and produce offspring in insects which have been killed by causes other than the nematode-bacteria complex. Six Steinernema and two Heterorhabditis species scavenged but there were differences among them in terms of frequency of colonisation and in the time after death of G. mellonella larvae that cadavers were penetrated. The extremes of this behaviour were represented by Steinernema glaseri which was able to colonise cadavers which had been freeze-killed 240 h earlier and Heterorhabditis indica which only colonised cadavers which had been killed up to 72 h earlier. Also, using an olfactometer, we demonstrated that entomopathogenic nematodes were attracted to G. mellonella cadavers. (c) 2007 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

Steinernema feltiae: ammonia triggers the emergence of their infective juveniles

Entomopathogenic nematodes complete their life cycles inside dead insects. The emergence of new infective juveniles from the cadaver has been attributed (but never demonstrated) to food depletion or to the accumulation of metabolites from the breakdown of the host's tissues. Here we give evidence that emergence is triggered by ammonia, a product of nematode defecation. We found that the emergence of Steinernema feltiae infective juveniles from Galleria mellonella cadavers was stimulated by a particular level of ammonia. Emergence was delayed when ammonia in the cadaver was decreased and was prompted when increased. These findings will further improve the understanding of the nematode life cycle. Here we speculate that production of infective juveniles can be mediated by ammonia and work in a manner analogous to that of the clatter recovery inhibiting factor (DRIF) in Caenorhabditis elegans. (C) 2008 Elsevier Inc. All rights reserved.

A longitudinal study of sero-conversion to tick-borne pathogens in smallholder dairy youngstock in Tanzania

A longitudinal study of sero-conversion of youngstock to the tick-borne pathogens Theileria parva, T mutans, Anaplasma marginale, Babesia bigemina and B. bovis was conducted over two years on smallholder dairy farms in Tanga region, Tanzania. There was evidence of maternal antibodies to all tick-borne pathogens in animals less than 18 weeks of age. Seroprevalence increased as expected with age in animals older than this but seroprevalence profiles underestimated the force of infection due to waning antibody levels between samplings. By the end of the 2-year study, less than 50% of study animals had seroconverted to each of the tick-borne pathogens investigated, consistent with the low levels of tick attachment observed on the study animals. Some associations between seroconversion to tick-borne pathogens, and counts of their known tick vectors on the animals, were identified as expected. However, some were not, suggesting that counts of some tick species may act as an index of rates of attachment of other vector species. Variation in acaricide treatment frequencies was not associated with variations in tick-borne pathogen seroprevalence suggesting that acaricides may be used more frequently than necessary on many farms. Most animals were zero-grazed, a management system associated with a significantly lower likelihood that animals seroconverted to any tick-borne pathogen exceptA. marginale. Seroprevalence varied locally with farm location (particularly for Babesia spp.) but was not well predicted by indices of ecological conditions. Our findings suggest that attempts to achieve a state of 'endemic stability' for tick-bome pathogens may be unreasonable on the smallholder dairy farms studied but reductions in the frequency of use of acaricides may be possible following prospective studies of effects on mortality and morbidity due to tick-bome pathogens. (c) 2005 Elsevier B.V. All rights reserved.

Spatial and management factors associated with exposure of smallholder dairy cattle in Tanzania to tick-borne pathogens

A cross-sectional study of serum antibody responses of cattle to tick-borne pathogens (Theileria parva, Theileria mutans, Anaplasma marginale, Babesia bigemina and Babesia bovis) was conducted on smallholder dairy farms in Tanga and Iringa Regions of Tanzania. Seroprevalence was highest for T. parva (48% in Iringa and 23% in Tanga) and B. bigemina (43% in Iringa and 27% in Tanga) and lowest for B. bovis (12% in Iringa and 6% in Tanga). We use spatial and non-spatial models, fitted using classical and Bayesian methods, to explore risk factors associated with seroprevalence. These include both fixed effects (age, grazing history and breeding status) and random effects (farm and local spatial effects). In both regions, seroprevalence for all tick-borne pathogens increased significantly with age. Animals pasture grazed in the 3 months prior to the start of the sampling period were significantly more likely to be seropositive for Theileria spp. and Babesia spp. Pasture grazed animals were more likely to be seropositive than zero-grazed animals for A. marginale, but the relationship was weaker than that observed for the other four pathogens. This study did not detect any significant differences in seroprevalence associated with other management-related variables, including the method or frequency of acaricide application. After adjusting for age, there was weak evidence of localised (< 5 km) spatial correlation in exposure to some of the tick borne diseases. However, this was small compared with the 'farm-effect', suggesting that risk factors specific to the farm were more important than those common to the local neighbourhood. Many animals were seropositive for more than one pathogen and the correlation between exposure to the different pathogens remained after adjusting for the identified risk factors. Identifying the determinants of exposure to multiple tick-borne pathogens and characterizing local variation in risk will assist in the development of more effective control strategies for smallholder dairy farms. (c) 2005 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

The effects of infection by Tetracapsuloides bryosalmonae (Myxozoa) and temperature on Fredericella sultana (Bryozoa)

The myxozoan, Tetracapsuloides bryosalmonae, exploits freshwater bryozoans as definitive hosts, occurring as cryptic stages in bryozoan colonies during covert infections and as spore-forming sacs during overt infections. Spores released from sacs are infective to salmonid fish, causing the devastating Proliferative Kidney Disease (PKD). We undertook laboratory studies using mesocosm systems running at 10, 14 and 20 degrees C to determine how infection by T bryosalmonae and water temperature influence fitness of one of its most important bryozoan hosts, Fredericella sultana, over a period of 4 weeks. The effects of infection were context-dependent and often undetectable. Covert infections appear to pose very low energetic costs. Thus, we found that growth of covertly infected F. sultana colonies was similar to that of uninfected colonies regardless of temperature, as was the propensity to produce dormant resting stages (statoblasts). Production of statoblasts, however, was associated with decreased growth. Overt infections imposed greater effects on correlates of host fitness by: (i) reducing growth rates at the two higher temperatures: (ii) increasing mortality rates at the highest temperature: (iii) inhibiting statoblast production. Our results indicate that parasitism should have a relatively small effect on host fitness in the field as the negative effects of infection were mainly expressed in environmentally extreme conditions (20 degrees C for 4 weeks). The generally low virulence of T. bryosalmonae is similar to that recently demonstrated for another myxozoan endoparasite of freshwater bryozoans. The unique opportunity for extensive vertical transmission in these colonial invertebrate hosts couples the reproductive interests of host and parasite and may well give rise to the low virulence that characterises these systems. Our study implies that climate change can be expected to exacerbate PKD outbreaks and increase the geographic range of PKD as a result of the combined responses of T. bryosalmonae and its bryozoan hosts to higher temperatures. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

Optimality analysis of Th1/Th2 immune responses during microparasite-macroparasite co-infection, with epidemiological feedbacks

Individuals are typically co-infected by a diverse community of microparasites (e.g. viruses or protozoa) and macroparasites (e.g. helminths). Vertebrates respond to these parasites differently, typically mounting T helper type 1 (Th1) responses against microparasites and Th2 responses against macroparasites. These two responses may be antagonistic such that hosts face a 'decision' of how to allocate potentially limiting resources. Such decisions at the individual host level will influence parasite abundance at the population level which, in turn, will feed back upon the individual level. We take a first step towards a complete theoretical framework by placing an analysis of optimal immune responses under microparasite-macroparasite co-infection within an epidemiological framework. We show that the optimal immune allocation is quantitatively sensitive to the shape of the trade-off curve and qualitatively sensitive to life-history traits of the host, microparasite and macroparasite. This model represents an important first step in placing optimality models of the immune response to co-infection into an epidemiological framework. Ultimately, however, a more complete framework is needed to bring together the optimal strategy at the individual level and the population-level consequences of those responses, before we can truly understand the evolution of host immune responses under parasite co-infection.

Litomosoides sigmodontis: vaccine-induced immune responses against Wolbachia surface protein can enhance the survival of filarial nematodes during primary infection

Wolbachia are bacteria present within the tissues of most filarial nematodes. Filarial nematode survival is known to be affected by immune responses generated during filarial nematode infection and immune responses to Wolbachia can be found in different species harbouring filarial nematode infections, including humans. Using the rodent filarial model Litomosoides sigmodontis, we show that pre-exposure to wolbachia surface protein in a Th1 context (but not in a Th2-context) enhances worm survival on subsequent challenge. This study suggests that despite abundant evidence that pro-inflammatory reactions to the endosymbiont have detrimental effects on the both the nematode and mammalian host, they may under some circumstances be beneficial to the nematode.

Endoparasitism in colonial hosts: patterns and processes

This study begins to redress our lack of knowledge of the interactions between colonial hosts and their parasites by focusing on a novel host-parasite system. Investigations of freshwater bryozoan populations revealed that infection by myxozoan parasites is widespread. Covert infections were detected in all 5 populations studied and were often at high prevalence while overt infections were observed in only 1. Infections were persistent in populations subject to temporal sampling. Negative effects of infection were identified but virulence was low. Infection did not induce mortality in the environmental conditions studied. However, the production of statoblasts (dormant propagules) was greatly reduced in bryozoans with overt infections in comparison to uninfected bryozoans. Overtly-infected bryozoans also grew more slowly and had low fission rates relative to colonies lacking overt infection. Bryozoans with covert infections were smaller than uninfected bryozoans. High levels of vertical transmission were achieved through colony fission and the infection of statoblasts. Increased fission rates may be a strategy for hosts to escape from parasites but the parasite can also exploit the fragmentation of colonial hosts to gain vertical transmission and dispersal. Our study provides evidence that opportunities and constraints for host-parasite co-evolution can be highly dependent on organismal body plans and that low virulence may be associated with exploitation of colonial hosts by endoparasites.

Malacosporean-like spores in urine of rainbow trout react with antibody and DNA probes to Tetracapsuloides bryosalmonae

Tetracapsuloides bryosalmonae is the myxozoan parasite causing proliferative kidney disease (PKD) of salmonid fishes in Europe and North America. The complete life cycle of the parasite remains unknown despite recent discoveries that the stages infectious for fish develop in freshwater bryozoans. During the course of examinations of the urine of rainbow trout (Oncorhynchus mykiss) with or recovering from PKD we identified spores with features similar to those of T. bryosalmonae found in the bryozoan host. Spores found in the urine were subspherical, with a width of 16 mum and height of 14 mum, and possessed two soft valves surrounding two spherical polar capsules (2 mum in diameter) and a single sporoplasm. The absence of hardened valves is a distinguishing characteristic of the newly established class Malacosporea that includes T. bryosalmonae as found in the bryozoan host. The parasite in the urine of rainbow trout possessed only two polar capsules and two valve cells compared to the four polar capsules and four valves observed in the spherical spores of 19 mum in diameter from T. bryosalmonae from the bryozoan host. Despite morphological differences, a relationship between the spores in the urine of rainbow trout and T. bryosalmonae was demonstrated by binding of monoclonal and polyclonal antibodies and DNA probes specific to T. bryosalmonae.

Hepatozoon griseisciuri in grey squirrels (Sciurus carolinensis): changes of blood leucocyte numbers resulting from infection

Numbers of leucocytes in squirrels with gametocytes of Hepatozoon in their blood (infected) were compared with animals without gametocytes (uninfected). Typical values for leucocytes/mm(3) blood in uninfected squirrels were: leucocytes 5-7 x 10(3), granulocytes 3-4 x 10(3), lymphocytes 2-0 x 10(3) and monocytes 0-3 x 10(3) cells. Infection caused an increase in monocytes, lymphocytes and granulocytes, and there was a significant positive association between parasitaemia level and numbers of both total leucocytes and monocytes. Infected animals had more uninfected monocytes/mm(3) blood than did uninfected animals. The proportions of monocytes were more variable over time in infected animals, but no shift between infected and uninfected status was detected. Transfer of serum from infected squirrels to mice resulted in elevated counts of total blood leucocytes, monocytes and granulocytes, but not of lymphocytes, as compared with controls. Serum from squirrels with high parasitaemias had a more marked effect than serum from squirrels with low parasitaemias. Results indicate an infection - related monocytosis, possibly controlled by cytokines, that increases the number of cells available for invasion by gametocytes, thus enhancing the chances of parasite transmission.

Condensed tannins act against cattle nematodes

The use of natural plant anthelmintics was suggested as a possible alternative control of gastrointestinal nematodes (GIN) in ruminants. Direct anthelmintic effects of tannin-containing plants have already been shown in sheep and goat GIN. These anthelmintic properties are mainly associated with condensed tannins. In the present study, we evaluated possible in vitro effects of three tannin-containing plants against bovine GIN. Effects of Onobrychis viciifolia, Lotus pedunculatus and Lotus corniculatus condensed tannin (CT) extracts on Cooperia oncophora and Ostertagia ostertagi were determined by a larval feeding inhibition assay (LFIA) and a larval exsheathment assay (LEA). In the LFIA, all three plant extracts significantly inhibited larval feeding behaviour of both C. oncophora and O. ostertagi first stage larvae in a dose-dependent manner. The L. pedunculatus extract, based on EC50 (effective concentration for 50% inhibition), was the most effective against both nematodes, followed by O. viciifolia and L. corniculatus. The effect of CT extracts upon larval feeding behaviour correlates with CT content and procyanidin/prodelphidin ratio. Larval exsheathment of C. oncophora and O. ostertagi L3 larvae (third stage larvae) was also affected by CT extracts from all three plants. In both in vitro assays, extracts with added polyvinylpolypyrrolidone, an inhibitor of tannins, generated almost the same values as the negative control; this confirms the role of CT in the anthelmintic effect of these plant extracts. Our results, therefore, indicated that tannin-containing plants could act against cattle nematodes.

In vitro effects of extracts and purified tannins of sainfoin (Onobrychis viciifolia) against two cattle nematodes

Sainfoin (Onobrychis viciifolia) is a condensed tannin (CT)-containing legume and has anthelmintic potential against gastrointestinal nematodes of ruminants. This study investigated in vitro effects of acetone/water extracts and derived CT fractions from different types of sainfoin (i.e. accessions) against larvae of Cooperia oncophora and Ostertagia ostertagi by applying the larval feeding inhibition assay (LFIA). Seven sainfoin accessions were extracted and tested with L1 larvae at 10 and 40 μg extract/ml. In addition, CT in extracts from 4 accessions were fractionated according to polymer size and tested by LFIA at two concentrations (2 and 10 μg CT fraction/ml). All sainfoin extracts caused significant inhibition of L1-feeding of both C. oncophora and O. ostertagi with varying intensity compared to the control (phosphate buffered saline). For both nematode species the in vitro effect was positively correlated with CT content in the extracts, but not with any of the structural CT parameters. In contrast, the 16 CT fractions revealed significant correlations between in vitro effect and CT content, polymer size (mean degree of polymerisation, mDP) and monomeric composition (prodelphinidin percentage, % PD). These differences between crude extracts and purified fractions may stem from the fact that extracts contain complex CT mixtures, which may mask and thus suppress CT structural effects. This study provides the first indication that, apart from CT and % PD content, polymer size also contributes to anthelmintic activity of CTs. The results, therefore, suggest that the inter-accession variability in CT content and composition needs to be taken into account in future plant breeding programmes which seek to enhance the anthelmintic properties of sainfoin

Use of pelleted sericea lespedeza (Lespedeza cuneata) for natural control of coccidia and gastrointestinal nematodes in weaned goats

Infection with Eimeria spp. (coccidia) can be devastating in goats, particularly for young, recently-weaned kids, resulting in diarrhea, dehydration, and even death. Feeding dried sericea lespedeza [SL; Lespedeza cuneata (Dum.-Cours.) G. Don.] to young goats has been reported to reduce the effects of internal parasites, including gastrointestinal nematodes (GIN) but there have been no reports of the effects of feeding this forage on Eimeria spp. in goats. Two confinement feeding experiments were completed on recently-weaned intact bucks (24 Kiko-cross, Exp. 1; 20 Spanish, Exp. 2) to determine effects of SL pellets on an established infection of GIN and coccidia. The bucks were assigned to 1 of 2 (Exp. 1) or 3 (Exp. 2) treatment groups based upon the number of Eimeria spp. oocysts per gram (OPG) of feces. In Exp. 1, the kids were fed 1 of 2 pelleted rations ad libitum; 90% SL leaf meal + 10% of a liquid molasses/lignin binder mix and a commercial pellet with 12% crude protein (CP) and 24% acid detergent fiber (n = 12/treatment group, 2 animals/pen). For Exp. 2, treatment groups were fed 1) 90% SL leaf meal pellets from leaves stored 3 years (n = 7), 2) 90% SL pellets from leaf meal stored less than 6 months, (n = 7), and the commercial pellets (n = 6) ad libitum. For both trials, fecal and blood samples were taken from individual animals every 7 days for 28 days to determine OPG and GIN eggs per gram (EPG) and packed cell volume (PCV), respectively. In Exp. 2, feces were scored for consistency (1 = solid pellets, 5 = slurry) as an indicator of coccidiosis. In Exp. 1, EPG (P < 0.001) and OPG (P < 0.01) were reduced by 78.7 and 96.9%, respectively, 7 days after initiation of feeding in goats on the SL pellet diet compared with animals fed the control pellets. The OPG and EPG remained lower in treatment than control animals until the end of the trial. In Exp. 2, goats fed new and old SL leaf meal pellets had 66.2 and 79.2% lower (P < 0.05) EPG and 92.2 and 91.2% lower (P < 0.05) OPG, respectively, than control animals within 7 days, and these differences were maintained or increased throughout the trial. After 4 weeks of pellet feeding in Exp. 2, fecal scores were lower (P < 0.01) in both SL-fed groups compared with control animals, indicating fewer signs of coccidiosis. There was no effect of diet on PCV values throughout either experiment. Dried, pelleted SL has excellent potential as a natural anti-coccidial feed for weaned goats.