Higher Parasite Intensity Research Articles

Intestinal helminthiasis, anaemia and associated risk factors in a cross-section of the population of Melong, Littorial Region of Cameroon

Assessment of risk factors of intestinal helminths and anaemia in various geographical regions is important for the development of appropriate control strategies. This study aimed at determining the risk factors associated with intestinal helminths and anaemia in Melong, Cameroon. A total of 325 participants were recruited in this study between September–December 2021. Faecal samples were examined using the formol-ether sedimentation technique while haemoglobin level was measured using a HemoCue spectrometer. Data on demographic and behavioural factors was collected and used to determine the risk factors using a pretested structured questionnaire and analysed using SPSS. The overall prevalence of intestinal helminths was 24.6% (80/325). Helminths recovered from the study included hookworm (16%; 52/325), Schistosoma mansoni (10.8% 35/325) Ascaris lumbricoides (1.9%; 6/325), and Trichuris trichiura (0.6%; 2/325) with 15 participants having multiple infections (4.6%). The geometric mean egg density was 77epg and ranged from 20 to 560 epg of faeces. Males and age group ≤ 5 years had the highest parasite intensity (248epg). The overall prevalence of anaemia was 33.5% (109/325). Anaemia was significantly (p = 0.001) high at 48.8% (39/80) in those infected with intestinal parasites compared to non-infected individuals. Age group of 31–45 years; [3.42(1.05–11.21)] and > 65 years [6.21(1.75–12.47)], poor knowledge [0.41(0.67–6.07)], no regular deworming [0.70(1.76–21.96)], mud floors toilet [6.18(1.61–23.79)], toilets made of sticks [16.5(4.24–64.31)], and participants who did not have stomach/abdominal pains [0.22(0.07–0.67)] were significant predictors of helminth infections. Age group < 15 years [2.58(1.09–6.11)], geophagia [3.69(1.91–9.33)], hookworm infection [3.26(1.49–7.11)], S. mansoni [1.72 (1.16–3.41)] and those with multiple infections [1.76(1.04–2.88)] were identified as risk factors for anaemia. Risk factors identified in this study can be used to improve the control mechanism put in place by the government.

Pro- and anti-inflammatory cytokine profiles in Plasmodium Falciparum-infected individuals from Baiyeku, Ikorodu, Lagos, Nigeria

Available evidence indicates that the various stages of the malaria parasite life cycle elicit specific immune responses of which the relative levels of pro-inflammatory cytokines are key to disease progression, killing the parasite and mediating disease outcomes. This study investigated T-cell response in malaria. Four hundred and sixty-two participants were screened in a community survey of Plasmodium falciparum malaria in Baiyeku, Lagos, Nigeria. P. falciparum parasitaemia was determined by microscopy while the serum levels of IL-10, IFNγ and TNFα were determined by Enzyme-linked immunosorbent assay (ELISA). A total of 70 (15.2 %) participants were microscopically positive for P. falciparum of which 70% were females, 30% were males while children aged 1-17 years were 65.7%. The geometric mean parasite density (GMPD) was significantly (p=0.001) higher among females than males. The GMPD of participants &lt;5 years of age was also significantly (p=0.001) higher than other age groups. About 46.8% of the participants were underweight (Body Mass Index, BMI &lt; 18.5) and also had the highest parasite intensity. The TNFα, IFNγ and IL-10 levels were significantly (p&lt; 0.05) higher in the infected than the uninfected participants. IFN-γ values were significantly (p=0.014) elevated among the symptomatic than the asymptomatic participants while there was no significant difference (P&gt;0.053) in the levels of TNF-α and IL-10 (P&gt;0.093) between the symptomatic and asymptomatic participants. The prevalence of P. falciparum obtained in this study area which is endemic to malaria is 15.2% suggesting a significant reduction of the disease over time due to awareness of the disease in the community. The levels of pro-inflammatory cytokines (IFN-γ and TNF-α) in this study were lower due to the down-regulatory action of the anti-inflammatory cytokines (IL-10). These findings suggest that higher levels of anti-inflammatory cytokines, especially IL-10 levels may contribute to the pathogenesis of uncomplicated malaria.

METALLOTHIONEIN EXPRESSION IN A PARASITIC CRUSTACEAN, LAMPROGLENA CLARIAE (CRUSTACEA: COPEPODA), ON CLARIAS GARIEPINUS (TELOESTEI: CLARIIDAE) CORRESPONDS TO WATER QUALITY.

Globally, parasites are sensitive toward environmental changes, and, in some cases, they are even more sensitive than their hosts. However, there is limited knowledge on the physiological responses of parasites and their effects on their hosts in relation to environmental degradation. In this study, metallothioneins (MTs) were isolated and compared between the ectoparasite Lamproglena clariae and its host fish Clarias gariepinus. Differences in the levels of MTs in the parasite and host were compared to physicochemical water quality variables and metals to determine if MT expression was linked with changes in water quality. Clarias gariepinus individuals were sampled from 2 sites of differing water quality along the Vaal River using gill nets and assessed for L. clariae. Gill, muscle, and liver tissue of the host and L. clariae were collected and stored in liquid nitrogen for analysis of MT. Water and sediment samples were collected for metal analysis by inductively coupled plasma-optical emission spectrometry and inductively coupled plasma-mass spectrometry. Nutrient levels and water hardness in water samples were assessed using spectrophotometry. MTs were quantified using spectrophotometry and size exclusion chromatography in the host and parasite, respectively. Infections by L. clariae differed between sites, with higher parasite intensity at the unpolluted Vaal Dam site. Concentrations of MT in host tissues and L. clariae were significantly higher at the polluted site, below the Vaal River Barrage, compared to the Vaal Dam site. Parasite MT concentrations were significantly lower compared to concentrations in the liver and gill tissue of C. gariepinus individuals. In conclusion, differences in the concentrations of MT and infection biology of L. clariae reflected the state of the environment and support the usefulness of this parasite and other Lamproglena spp. as bioindicators.

Temporal and Geographical Variation of Intestinal Ulcers in Grey Seals (Halichoerus grypus) and Environmental Contaminants in Baltic Biota during Four Decades.

Simple SummaryIn the 1970s it was discovered that seal populations in the Baltic Sea had decreased severely due to hunting and high levels of contaminants. Lesions were found in several organs and many of the females became sterile. Since then, most of the organ lesions have decreased and so have the levels of some pollutants. However, ulcers in the large intestines of the grey seals increased in the early 1980s and decreased after the mid-1990s. The aims of this study were to: (1) describe the ulcers and investigate if there is a trend over time that coincides with concentrations of some pollutants in Baltic biota; (2) evaluate the significance of different sea areas in the Baltic, grade of parasite intensity, as well as the sex and age of the seals. The results show that seals with ulcers had, in general, higher parasite intensity. Ulcers were more common in older seals and in the Bothnian Sea. The time trend of ulcers coincides with the trend of certain contaminant levels (BDE-47, PFOS and cadmium). The high prevalence of intestinal ulcers and the high intensity of acanthocephalan parasites appear to be unique to the Baltic population of grey seals.The prevalence of intestinal ulcers and parasites was investigated in 2172 grey seals (Halichoerus grypus) collected in the Baltic Sea and 49 grey seals collected outside the Baltic Sea (i.e., the Atlantic). An increase in frequency of ileocaeco-colonic ulcers was observed in the early 1980s, followed by a decrease in the mid-1990s. At the same time, there was an increase followed by a decrease in brominated flame retardants, Perfluorooctanesulfonic acid (PFOS) and cadmium levels in herring (Clupea harengus), the most common prey item in Baltic grey seal diet, as well as in another top predator in the Baltic, the common guillemot (Uria aalge). The frequency of intestinal ulcers was significantly related to the intensity of acanthocephalan parasites, the age of the seal and the region of the Baltic Sea. Perforation of the intestinal wall was the cause of death in 26 of the investigated Baltic grey seals. In contrast, none of the investigated Atlantic grey seals had intestinal ulcers. They showed a thin colonic wall and very few acanthocephalan parasites. The high prevalence of intestinal ulcers and the high parasite intensity appear to be unique to the Baltic population of grey seals.

Distribution, prevalence and intensity of moose nose bot fly (Cephenemyia ulrichii) larvae in moose (Alces alces) from Norway.

High host density combined with climate change may lead to invasion of harmful parasites in cervid (host) populations. Bot flies (Diptera: Oestridae) are a group of ectoparasites that may have strong impact on their hosts, but data on the current distribution, prevalence and intensity of the moose nose bot fly (Cephenemyia ulrichii) in Scandinavia are lacking. We estimated prevalence and intensity of nose bot fly larvae in 30 moose from southern and 79 moose from central Norway. All larvae detected were identified as the moose nose bot fly. We found surprisingly high prevalence in these areas, which are up to 1300 km south-southwest of the first published location in Norway and west of the distribution in Sweden. Prevalence (0.44–1.00) was higher in areas with higher moose density. Parasite intensity in hunter killed moose was higher in central Norway (mean 5.7) than southern Norway (mean 2.9), and in both regions higher in calves and yearlings than adults. Fallen moose had higher parasite intensity (mean 9.8) compared to hunter killed moose in the subsample from central Norway, suggesting a link to host condition or behavior. Our study provides evidence of parasite range expansion, and establishing monitoring appears urgent to better understand impact on host populations.

Reviewing Fasciola hepatica transmission in the West Indies and novel perceptions from experimental infections of sympatric vs. allopatric snail/fluke combinations

Fasciolosis is an important food-borne parasitic disease affecting over two million people worldwide with economic losses related to cattle production of up to US$ 3 billion annually. Despite the long known presence of Fasciola hepatica in the Caribbean islands its transmission is not well known. This study reviews historical and recent data on fasciolosis in the West Indies, revealing for the first time the outcomes of sympatric and allopatric fluke/snail interactions in the area by exploring the susceptibility of four lymnaeid species after exposure to F. hepatica isolates from Cuba, the Dominican Republic and France. Overall, Galba cubensis showed a mean prevalence of 71.8% and appears to be the most suitable intermediate host species irrespective of the isolate used. Sympatric combinations (snail and parasite from the same country) were generally more compatible (higher susceptibility, parasite intensity and snail survival post-exposure) and only the allopatric interaction of French G. truncatula/Cuban F. hepatica attained 100% prevalence and mean intensity over 33 rediae/snail. However, certain Dominican populations of Pseudosuccinea columella showed high parasite intensities (>30 rediae/snail) when infected with Cuban flukes, highlighting the potential risks of biological introductions. Overall, high compatibility in most sympatric combinations compared to low or moderate compatibility in allopatric ones, suggests the existence of local adaptation from a long sustained interaction that has led to high rates of transmission. Interestingly, attempts to infect G. schirazensis with sympatric and allopatric flukes failed and coupled with the lowest survival rates which supposes a low risk of fasciolosis transmission in areas where this is the only snail species. Although there are significant gaps in the actual status of fasciolosis transmission from several islands in the West Indies these results show a permanent risk. We conclude that fasciolosis transmission is high in areas where the local snail, G. cubensis, occurs, and will be even higher in the presence of the invasive P. columella.

Estimating prevalence of avian haemosporidians in natural populations: a comparative study on screening protocols

BackgroundBirds harbour an astonishing diversity of haemosporidian parasites. Renewed interest in avian haemosporidians as a model system has placed a greater emphasis on the development of screening protocols to estimate parasite prevalence and diversity. Prevalence estimates are often based on the molecular or blood-smear microscopy techniques. However, variation in diagnostic sensitivity among screening methodologies represents a potential source of bias that may lead to erroneous inference in comparisons of prevalence across studies. Here, we analyzed a suite of blood samples for the presence of parasites using four diagnostic tools and compared method-specific estimates of detection probability to assess the relative performance of screening strategies.MethodsWe screened a total of 394 bird blood samples collected in India (n = 203) and Sweden (n = 191) for the combined presence of Plasmodium, Haemoproteus and Leucocytozoon with three PCR assays: (i) qPCR; (ii) restriction enzyme-based assay; and (iii) nested protocol. In addition, we examined blood smears for estimates of parasite intensity which was further screened using qPCR method to evaluate if parasite intensity shows a relationship with qPCR (Ct values). Furthermore, we used single infected samples from parasite intensities: low, medium, high, very high to establish the reproducibility in qPCR.ResultsFor the combined data sets from India and Sweden, detection probability for submicroscopic and low intensity infections was highest for the qPCR method, followed by the nested protocol and the restriction enzyme-based assay. For high parasite intensities, the qPCR had high PCR reproducibility, with three out of three PCR replicates being positive and with consistent Ct values across all tenfold dilution series. For parasite intensities at very low and submicroscopic samples, the qPCR was reproducible in one out of the three replicates. The intensity of parasitemia estimated from smears showed inverse relationship with Ct values in both the Indian and Swedish data sets.ConclusionsOur study highlights the importance of accounting for methodological issues to better estimate infection in parasitological studies and illustrates how a wider deployment of diagnostic tools combined with statistical approaches is needed for each study, in order to provide adequate insight into the most appropriate approach to avoid erroneous inferences.

The effect of foraging and ontogeny on the prevalence and intensity of the invasive parasite Anguillicola crassus in the European eel Anguilla anguilla.

Infection patterns of the invasive Anguillicola crassus nematode were investigated in a population of the European eel Anguilla anguilla where parasite invasion is very recent, Loch Lomond, Scotland. Intensity levels of the parasite were associated with differences in fish ontogeny and trophic ecology. Although eels foraged on both fish and invertebrates, individuals which were smaller and fed on invertebrates (>70% contribution to diet) were found to contain a greater number of swim bladder parasites compared to larger eel with a predominance of fish (>60% contribution) in their diet. Within affected fish, a significant negative relationship was found between fish length and parasite intensity, with smaller individuals having higher parasite intensity than larger individuals. This study indicates that food intake and infection risk are linked in this recently infected host-parasite system. From a management perspective increasing our understanding of how infection intensity and repeated exposure is linked to resource use in an ecosystem is important for the future management of this endangered species in Europe.

The Relationships between Parasite Intensity, Locomotor Performance, and Body Condition in Adult Toads (Rhinella icterica) from the Wild

Abstract Most of the evidence for the deleterious effects of parasites on performance and body condition in their hosts results from experimental infection using one species of parasite. However, hosts in the field are normally infected by multiple parasite species present in different organs. We investigated the relationship between intensity of different parasites and several phenotypic characters of adult males of Rhinella icterica (Cururu Toad) captured in the field. We predicted that toads with higher parasite intensity would show lower locomotor performance, higher standard rates of oxygen consumption, poorer body-condition indices, and larger kidney, intestine, heart, lung, and liver masses. We found that these hosts were infected by six different species of parasites, with a dominance of monoxenous nematodes and no correlation between intensities of different parasites. Rhabdias fuelleborni was the only parasite associated with variation in a host's phenotype. Individuals of R. icterica with highe...

Darwin's Finch Begging Intensity Does Not Honestly Signal Need in Parasitised Nests

AbstractParental care should be selected to respond to honest cues that increase offspring survival. When offspring are parasitised, the parental food compensation hypothesis predicts that parents can provision extra food to compensate for energy loss due to parasitism. Chick begging behaviour is a possible mechanism to solicit increased feeding from attending parents. We experimentally manipulated parasite intensity from Philornis downsi in nests of Darwin's small ground finch (Geospiza fuliginosa) to test its effects on chick begging intensity and parental food provisioning. We used in‐nest video recordings of individually marked chicks to quantify nocturnal parasite feeding on chicks, subsequent diurnal chick begging intensity and parental feeding care. Our video analysis showed that one chick per brood had the highest parasite intensity during the night (supporting the tasty chick hypothesis) and weakest begging intensity during the day, which correlated with low parental care and rapid death. We observed sequential chick death on different days rather than total brood loss on a given day. Our within‐nest video images showed that (1) high nocturnal larval feeding correlated with low diurnal begging intensity and (2) parent birds ignored weakly begging chicks and provisioned strongly begging chicks. Excluding predation, all parasite‐free chicks survived (100% survival) and all parasitised chicks died in the nest (100% mortality). Weak begging intensity in parasitised chicks, which honestly signalled recent parasite attack, was not used as a cue for parental provisioning. Parents consistently responded to the strongest chick in both parasitised and parasite‐free nests.

Positive co-occurrence of flea infestation at a low biological cost in two rodent hosts in the Canary archipelago

Non-random assemblages have been described as a common pattern of flea co-occurrence across mainland host species. However, to date, patterns of flea co-occurrence on islands are unknown. The present work investigates, on one hand, whether the decrease in the number of species on islands affects the pattern of flea co-occurrence, and on the other hand, how the cost of higher flea burdens affects host body mass. The study was carried out in the Canary Islands (Spain) using null models to analyse flea co-occurrence on Rattus rattus and Mus musculus. Results supported aggregation of flea species in Mus but not in Rattus, probably due to the relationship between abundance and both prevalence and intensity of infection of the main flea species parasitizing Mus. In addition, heavy individuals of both rodent species showed the highest flea burdens as well as higher species richness, probably due to the continued accumulation of fleas throughout life and/or immunological resistance mechanisms. Whatever the mechanisms involved, it is clear that co-occurrence and high parasite intensities do not imply a detrimental biological cost for the rodents of the Canary Islands.

Synergistic effects of seasonal rainfall, parasites and demography on fluctuations in springbok body condition

1. Seasonality of rainfall can exert a strong influence on animal condition and on host-parasite interactions. The body condition of ruminants fluctuates seasonally in response to changes in energy requirements, foraging patterns and resource availability, and seasonal variation in parasite infections may further alter ruminant body condition. 2. This study disentangles the effects of rainfall and gastrointestinal parasite infections on springbok (Antidorcas marsupialis) body condition and determines how these factors vary among demographic groups. 3. Using data from four years and three study areas, we investigated (i) the influence of rainfall variation, demographic factors and parasite interactions on parasite prevalence or infection intensity, (ii) whether parasitism or rainfall is a more important predictor of springbok body condition and (iii) how parasitism and condition vary among study areas along a rainfall gradient. 4. We found that increased parasite intensity is associated with reduced body condition only for adult females. For all other demographic groups, body condition was significantly related to prior rainfall and not to parasitism. Rainfall lagged by two months had a positive effect on body condition. 5. Adult females showed evidence of a 'periparturient rise' in parasite intensity and had higher parasite intensity and lower body condition than adult males after parturition and during early lactation. After juveniles were weaned, adult females had lower parasite intensity than adult males. Sex differences in parasitism and condition may be due to differences between adult females and males in the seasonal timing of reproductive effort and its effects on host immunity, as well as documented sex differences in vulnerability to predation. 6. Our results highlight that parasites and the environment can synergistically affect host populations, but that these interactions might be masked by their interwoven relationships, their differential impacts on demographic groups, and the different time-scales at which they operate.

Philornis downsi parasitism is the primary cause of nestling mortality in the critically endangered Darwin’s medium tree finch (Camarhynchus pauper)

Darwin’s medium tree finch (Camarhynchus pauper) meets the 2009 International Union for Conservation of Nature Red List criteria for a critically endangered species because it has “a very small range on a single island” and is “declining rapidly owing to the effects of the parasite Philornis downsi”, habitat degradation, and introduced predators. The medium tree finch is only found in patches of remnant highland forest on Floreana Island, where it co-exists with breeding populations of small and large tree finches (C. parvulus and C. psittacula). Here, we examine the intensity of P. downsi in nests of small, medium, and large tree finches on Floreana. We expected that parasite intensity would increase with finch body size, and with greater rainfall, and would also correlate with increased nestling mortality. We found a trend in the expected direction for parasite intensity and rainfall. Combined meta-analytically with data from a previous study, the overall trend for the two studies was significant. We also found a significant linear trend in parasite intensity with finch body size. In addition, the medium tree finch exhibited a somewhat higher parasite intensity than would be expected based on body mass alone. Of 63 active medium tree finch nests, 17 nests had nestlings: all of which were infested with P. downsi. Only 25% of medium tree finch nestlings fledged, 28% were depredated, 41% died due to P. downsi parasitism, and 6% died for other reasons.

Effects of host characteristics and parasite intensity on growth and fecundity ofTrichostrongylus retortaeformisinfections in rabbits

Host-mediated responses and parasite density-dependent processes can have a major influence on the growth and fecundity of parasitic nematodes. However, host characteristics and parasite intensity consistently change during the course of an infection and these could affect worm length and number of eggs in a non-constant way. We used a free-living population of rabbits naturally infected with Trichostronglyus retortateformis and examined how adult nematode length and the number of eggs in utero were affected by host characteristics (i.e. age, sex, breeding status) and parasite intensity, in a seasonal environment, between 2004 and 2007. Nematode length and number of eggs in utero decreased exponentially with host age; in contrast, parasite intensity increased, peaked in juveniles and decreased in older hosts. These patterns were consistent between rabbit cohorts. A negative relationship was observed between parasite intensity and nematode length, as well as number of eggs. Nematode length was strongly affected by nematode sex and host age, while the number of eggs was mainly influenced by nematode length. The direct influence of host-mediated effects appeared quantitatively more important than parasite density dependence in controlling length and egg production in naturally infected wild rabbits. However, their relative contribution changed during the course of the infection such that, while host immunity still influenced worm numbers, the direct effect of density-dependent interactions contributed the most at high parasite intensities.

Maximum Host Survival at Intermediate Parasite Infection Intensities

BackgroundAlthough parasitism has been acknowledged as an important selective force in the evolution of host life histories, studies of fitness effects of parasites in wild populations have yielded mixed results. One reason for this may be that most studies only test for a linear relationship between infection intensity and host fitness. If resistance to parasites is costly, however, fitness may be reduced both for hosts with low infection intensities (cost of resistance) and high infection intensities (cost of parasitism), such that individuals with intermediate infection intensities have highest fitness. Under this scenario one would expect a non-linear relationship between infection intensity and fitness.Methodology/Principal FindingsUsing data from blue tits (Cyanistes caeruleus) in southern Sweden, we investigated the relationship between the intensity of infection of its blood parasite (Haemoproteus majoris) and host survival to the following winter. Presence and intensity of parasite infections were determined by microscopy and confirmed using PCR of a 480bp section of the cytochrome-b-gene. While a linear model suggested no relationship between parasite intensity and survival (F = 0.01, p = 0.94), a non-linear model showed a significant negative quadratic effect (quadratic parasite intensity: F = 4.65, p = 0.032; linear parasite intensity F = 4.47, p = 0.035). Visualization using the cubic spline technique showed maximum survival at intermediate parasite intensities.Conclusions/SignificanceOur results indicate that failing to recognize the potential for a non-linear relationship between parasite infection intensity and host fitness may lead to the potentially erroneous conclusion that the parasite is harmless to its host. Here we show that high parasite intensities indeed reduced survival, but this effect was masked by reduced survival for birds heavily suppressing their parasite intensities. Reduced survival among hosts with low parasite intensities suggests costs of controlling parasite infections; however, the nature of such costs remains to be elucidated.

Observations on the intestinal helminth parasites of cichlids in the upper reaches of River Orogodo, a freshwater body in Delta State, Southern Nigeria

The prevalence and intensity of intestinal helminth parasites of five predominant cichlids; Hemichromis fasciatus, Chromidotilapia guentheri, Tilapia mariae, Tilapia zilli and Tilapia aurea of the upper reaches of River Orogodo in Delta State, Southern Nigeria were examined. The water body was randomly sampled using a variety of fishing gear which included funnel entrance traps, cast nets of varying mesh sizes and baited hook long lines. Of a total of 183 fishes investigated, 111 (60.66%) were infected. The increasing order of relative prevalence was Chromidotilapia quentheri (21.62%), Tilapia mariae (63.64%), Tilapia aurea (70.97%), Tilapia zilli (71.79%) and Hemichromis faciatus (74.42%). The intestinal helminth parasites recovered were Acanthophalans (Acanthogyrus sp and Octospiniferoides sp), Nematodes (Camallanus sp and Cucullanus sp) and Cestodes (Wenyonia sp). Tilapia mariae had the highest parasite intensity (425) while Chromidotilapia quentheri had the least (65). Although, the sex predilection skewed towards females (64.77%) as against males (56.84%) significant difference was not observed (P>0.05). Viable preventive measures against fish parasitism in Nigerian freshwater bodies are highly recommended.Keywords: helminth, cichlids, freshwater, Nigeria Tropical Freshwater Biology 2003/2004 Vol. 12/13: 131-136

Faecal egg counts provide a reliable measure of Trichostrongylus tenuis intensities in free-living red grouse Lagopus lagopus scoticus.

The reliability of different egg counting methods for estimating the intensity of Trichostrongylus tenuis infections in red grouse, Lagopus lagopus scoticus, was investigated in the autumn, when grouse may harbour high parasite intensities. Possible limitations to the use of these methods were also examined. Faecal egg counts were found to accurately estimate T. tenuis worm intensities, at least up to an observed maximum of c. 8000 worms. Two egg counting methods (smear and McMaster) gave consistent results, although the exact relationship with worm intensity differed according to the method used. Faecal egg counts significantly decreased with increasing length of sample storage time, but egg counts were reliable for estimating worm intensity for three weeks. The concentration of eggs in the caecum was also found to reliably estimate worm intensity. However, egg counts from frozen gut samples cannot be used to estimate worm intensities. These results conclude that, despite some limitations, faecal and caecum egg counts provide useful and reliable ways of measuring T. tenuis intensities in red grouse.

Chicks resist high parasite intensities in an Algerian population of blue tits

The impact of nest ectoparasites on chicks was studied for the first time in a free-living North African cavity nesting bird, an Algerian population of blue tits, Parus caeruleus ultramarinus. The proportion of nests (prevalences) with acarids (mite Dermanyssus, tick Ixodes) and insects (blow fly Protocalliphora, flea Ceratophyllus) varied between 80-100%. Compared to most European studies of cavity nesters, parasite intensities were high for blow flies and low for mites or fleas. Experiments to diminish the high parasite pressures in this population had little or no effect on different morphological measures of chicks that could reflect post-fledging survival, such as mass gain and body size (tarsus length, mass at fledging). Nestling mortality was only weakly affected by the experiments. Our results suggest that hosts can resist high parasite pressures. We conclude that understanding the mechanisms involved in host-parasite interactions requires both experimental and long-term multi-factor analyses.