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Journal of Wildlife Diseases, 41(1), 2005, pp. 149-162
© Wildlife Disease Association  2005
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HELMINTHS OF SAIGA ANTELOPE IN KAZAKHSTAN: IMPLICATIONS FOR CONSERVATION AND LIVESTOCK PRODUCTION

Eric R. Morgan1,2,6, Blok Shaikenov3, Paul R. Torgerson2,4, Graham F. Medley1 and E. J. Milner-Gulland5

1 Ecology and Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
2 Department of Veterinary Microbiology and Parasitology, University College Dublin, Belfield, Dublin 4, Ireland
3 Institute of Zoology, Ministry of the Environment, Akademgorodok, Almaty, Kazakhstan
4 Institute of Parasitology, University of Zürich, Winterthurerstrasse 266a, CH-8057, Zürich, Switzerland
5 Renewable Resources Assessment Group, Department of Environmental Science and Technology, Imperial College London, SW7 2AZ, UK
6 Current address and corresponding author: School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK (email: eric.morgan{at}bristol.ac.uk)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Saiga antelope (Saiga tatarica) graze extensively on livestock pasture, potentially enabling transmission of a wide range of parasitic helminths between saigas and domestic ruminants. Thirty-six of the 38 species of helminth that have been found in saigas in Kazakhstan in the past have been found also in domestic livestock. We examined 133 saigas culled for meat in autumn 1997, and found three species of cestode and 12 nematodes (nine in the abomasum), but no trematodes or lungworms. The most abundant species were Marshallagia marshalli, Marshallagia mongolica, and Nematodirus gazellae in the abomasum, Nematodirus gazellae in the small intestine, and Skrjabinema ovis in the large intestine. There was no clear relationship between intensities of abomasal nematodes and body condition. Age-intensity patterns differed between species: N. gazellae intensities were highest in saigas around 2–3 yr old, and declined in older animals, whereas the intensity of Marshallagia spp. rose asymptotically with age. Fecal egg density was directly proportional to adult worm intensity across ages for Marshallagia spp., but only in young animals for N. gazellae. There was no evidence that helminths, at the intensities observed, adversely affect saiga populations. The host range of many of the parasites found is broad, and transmission between saigas and livestock in both directions might become important to agriculture and conservation as livestock numbers recover. Simplified sampling techniques used in this study, and statistical analysis based on bootstrapping, could prove useful in other parasitologic surveys of wildlife in remote areas.

  Key words:  Gastrointestinal nematodes, host specificity, Marshallagia spp., Nematodirus gazellae, Saiga tatarica, wildlife-livestock boundary.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
The saiga antelope (Saiga tatarica) is a nomadic herding antelope of Central Asia, which shares its range with several species of domestic livestock (Bekenov et al., 1998; Robinson and Milner-Gulland, 2003). The majority of saigas live in Kazakhstan, with an additional population in Russia and a separate subspecies in Mongolia (Bekenov et al., 1998). In Kazakhstan, there are three separate populations, each of which undergoes long seasonal migrations and ranges over a wide area (Fig. 1Go). Climatic conditions in the area are extremely harsh, with cold winters and hot dry summers, confining free-living parasite stages and transmission to limited periods. Before 1998, annual legal saiga culls provided an opportunity to sample relatively large numbers of saigas at the same time and place. Since 1998, saiga populations have declined precipitously due to illegal hunting (Milner-Gulland et al., 2001), leading to the species being listed as critically endangered on the World Conservation Union red list (IUCN, 2004) and halting of all legal take. Because of this, further sampling will be extremely limited in the foreseeable future, and the data presented in this study will remain the most recent substantial survey of parasites in saigas for some time. These data also provide a baseline for possible future assessments of the distribution of parasites among Eurasian ungulates, and ecologic perturbations linked to global climate change or anthropogenic disturbance (Brooks and Hoberg, 2000; Hoberg et al., 2003).



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  		FIGURE 1. Approximate distribution of populations of saiga antelope in Kazakhstan, adepted from Bekenov et al. (1998). Latitude and longitude, and distance marker, are approximate.

 
Parasites of saigas were first studied in the 1920s, and suspicion that transmission of gastrointestinal helminths from saigas to domestic sheep could damage livestock production led to intense investigation in the 1970s and 1980s (Petrov, 1985). Transmission of parasites from livestock to saigas is also possible, and could have a negative impact on remaining saiga populations (Priyadko et al., 1995). Despite a long history of study, which addresses questions pertinent to wildlife parasitology in general, only the most basic list of parasites infecting the saiga has been published in the international scientific literature (Bekenov et al., 1998), and even this is inconsistent with current taxonomy. Cattle, sheep, and goats graze many parts of the saiga range, and camels are found in the western areas. Sheep are by far the most numerous livestock species in Kazakhstan, and along with goats have the greatest opportunity for livestock-wildlife transmission by grazing remote land frequented by saigas. Although horses are also widely reared across Kazakhstan, they have few parasites in common with saigas, and will not be considered further. Numbers of livestock throughout Kazakhstan decreased following agricultural restructuring in the early 1990s (Robinson and Milner-Gulland, 2003) and veterinary services and drugs (including anthelmintics) became less available (Lundervold, 2001). These changes might affect patterns of parasite transmission between saigas and livestock in future.

In this study we document the helminths reported in saigas in Kazakhstan and their other known hosts in the saiga range. Patterns of infection reported in the Russian language literature, and those observed in saigas culled in this study, are used to identify helminth species that might cause disease in saigas. We focus particularly on species that can be transmitted between saigas and livestock, because these have the potential for impact on both the critically endangered saiga and on the depressed livestock sector. Based on our results we identify species that should be targeted in future parasite control programs in saigas and livestock.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
Collection and analysis of parasites

Parasites were collected from saigas in Betpak–Dala, Central Kazakhstan (Fig. 1Go) in November 1997 during the official annual cull. Groups of saigas were identified at night using vehicle-mounted searchlights, and as many as possible shot, in compliance with licence restrictions. Body condition was graded by daylight according to the amount of abdominal and retroperitoneal fat, and each carcass allocated a score of 1 (poor: almost no fat); 2 (average: fair amount of fat present, but kidneys clearly visible); or 3 (good: plentiful fat, completely obscuring kidneys). A similar index was used in white-tailed deer (Odocoileus virginianus) by Waid et al. (1985) and in peccaries (Tayassu pecari) by Corn et al. (1985). Age was determined in the first instance by an experienced observer from the Institute of Zoology in Almaty (Kazakhstan), on the basis of body size and head shape: animals were categorized as juveniles in their first yr of age or adults. The central incisor teeth were taken from each animal, and the complete mandibles from some, in order to age animals more accurately. In the tooth sectioning technique, age was estimated from annuli in the cementum of a transverse section of the tooth root (Gruzdev and Pronyaev, 1994; Pronyaev et al., 1998). In the tooth eruption and wear technique, measurements of the mandible and assessment of tooth eruption and wear provided a guide to age (Pronyaev et al., 1998). Both techniques were carried out at the Norwegian Institute for Nature Research in Trondheim, Norway, and detailed test methods and reliability are discussed in Lundervold (2001) and Lundervold et al. (2003).

The first 50 saigas killed were subjected to a general parasitologic examination the day after slaughter, consisting of visual inspection and digital palpation of the integument, liver, trachea, lungs, diaphragm, mesentery and, in 22 animals, the nasal chambers and heart. The liver and lungs were inspected for metacestodes, and incised for detailed examination. In 20 animals, the liver was sectioned into small (0.5 cm square) cubes, which were washed in water and examined with the naked eye against a pale background for trematodes. All animals killed were eviscerated and the abomasum and small and large intestines processed separately. Helminths were collected using methods adapted from the Ministry for Agriculture, Fisheries and Food (MAFF, 1986). Visceral contents were emptied into a bucket and mucosa washed thoroughly in water with firm digital pressure. Washings were combined with contents, passed through a sieve of 220 µm aperture, and a 15 ml aliquot taken from the measured residue. This was preserved in formalin to a final concentration of 5–10% for later examination. When there was insufficient time to examine abomasa immediately, they were allowed to freeze outdoors, and thawed for processing some days later. The contents of 50 cm lengths of small intestine were extruded by digital pressure and sieved to recover nematodes.

The study area was remote and resources scarce. Retrieval of aliquots from the gastrointestinal washings was designed to economize water, formalin, and sample containers, and facilitate transport to the laboratory. Provided that the material was well mixed, the worms in the aliquot should be a good reflection of the actual worm numbers (Reinecke, 1984). To check for parasites not extracted by extrusion, a subset of small intestines was further opened longitudinally, the mucosa washed and scrubbed, and the whole residue examined. Adult cestodes found in the gut were extracted and preserved in formalin separately from the washings.

In the laboratory, nematodes were picked out from digesta under the dissecting microscope, and mounted in lactophenol for identification (Mahoney, 1966). In samples with large numbers of worms, at least 40 specimens were retained and total worm intensity calculated from the proportion of gut contents examined (Reinecke, 1984). Female nematodes were identified to the level of genus, and males to species, using keys and illustrations in Skrjabin et al. (1954), Andreeva (1957), and Boev et al. (1962). Where taxonomy in the Russian texts differed from that generally accepted in the current international literature, the latter was adopted, although it is recognized that species diversity within several taxa remains unresolved (Hoberg and Lichtenfels, 1994). Total nematode intensities were assigned to species on the basis of the proportion of males of each species counted. Adult and larval cestodes were identified under the dissecting microscope using Dunn (1978) and Boev et al. (1962). Representative samples of abomasal nematodes recovered from saigas during this expedition have been deposited at the U.S. National Parasite Collection, accession numbers 95427–95438.

Analysis of fecal samples

Fecal samples were analyzed using a standard McMaster technique (MAFF, 1986), modified to increase sensitivity and decrease reliance on specialized equipment. Approximately 3 g of feces were added to 12 ml of tap water. After crushing and suspending feces, coarse debris was removed using a tea strainer, and 9 ml of the well-mixed suspension transferred to a glass test tube. The contents were allowed to sediment for 1 hr, and the supernatant decanted off and replaced with saturated saline solution. The fecal material was re-suspended and used to fill four standard Mc-Master slides. Slides were examined between 10 and 40 min after loading, to maximize the proportion of eggs floating (Dunn and Keymer, 1986). Medium power magnification (100x) was used. The total amount of feces examined in eight McMaster chambers was 0.24 g, and the number of eggs therein, multiplied by a factor of four, gave the approximate number of eggs per g (epg). Nematode eggs were identified morphologically as Nematodirus, Marshallagia, or "other" (Thienpont et al., 1979). Forty samples were also examined for trematode eggs using either coverslip flotation in zinc sulphate (Thienpont et al., 1979) or sedimentation in water (MAFF, 1986).

Analytical methods

The effect of abomasal parasitism on individual saigas was investigated by measuring the correlation between body condition score and total abomasal nematode intensity, and for M. marshalli, M. mongolica, and N. gazellae separately, in juvenile saigas of each sex, and adult females. Fecal egg counts (FEC) as a reflection of nematode intensity were assessed by measuring the correlation between total numbers of adult Marshallagia spp. and Nematodirus spp., and fecal density of the corresponding egg type (epg). A causative link between these variables was assumed, and linear regression analysis was conducted using maximum likelihood (Williams and Dye, 1994), using the PopTools software (www.csiro.au). Models using negative binomial and Poisson error structures, and those using common or separate parameter estimates for juvenile and adult saigas were compared using the likelihood ratio test (Hilborn and Mangel, 1997; Torgerson et al., 2003a, b). Regression was attempted in spite of the limited data, as there are no published estimates of egg production by nematodes in saigas.

Parasites are usually highly aggregated among wildlife hosts (Shaw et al., 1998), and parametric statistical tests are therefore inappropriate (Rózsa et al., 2000). The degree of overdispersion of each parasite species among juvenile and adult saigas was estimated using the corrected moment estimate of k (Hudson and Dobson, 1995). Parasite counts in different groups of saigas were compared using the Mann-Whitney U-test (SPSS software, SPSS Inc., Chicago, Illinois, USA). We used bootstrapping to estimate confidence intervals around mean parasite counts (Efron and Tibshirani, 1993; Rózsa et al., 2000). One count was replaced with another from the same data set, and the mean recalculated. Repeated replacement and resampling resulted in a frequency distribution of simulated means from which confidence bounds were drawn empirically. Bootstrapping was extended to a comparison of parasite abundance between samples. The mean abundance in each sample was first estimated by bootstrapping with replacement, and the two means compared. The process was then repeated many times. In general, if the mean of sample 1 nearly always exceeds that of sample 2, this is unlikely to be due to chance, and sample 1 can be said to contain more parasites per host than sample 2. In this case, the proportion of comparisons in which mean abundance in the more lightly infected sample exceeded that in the samples of high intensity was taken to indicate the probability of the observed difference being spurious, and is here called the bootstrap p-value. We used the Crystal Ball (Decisioneering Inc., Denver, CO, USA) add-in to Microsoft Excel (Microsoft Inc., Redmond, Washington, USA) for bootstrapping.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
Helminth host range and abundance

All helminth species recorded in saigas have also been found in other sympatric artiodactylids (Table 1Go). Fifteen helminth species were recorded in saigas in the present survey, including nine abomasal nematodes, but no trematodes or lungworms (Table 2Go). The most abundant gastrointestinal nematodes were M. marshalli, M. mongolica, N. gazellae, and Skrjabinema ovis.


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  		TABLE 1. Host ranges of parasitic helminths of saiga antelope in Kazakhstan. All these species have been recorded in saigas (Berkinbaev et al., 1994). Sources: Boev et al. (1962), Lavrov (1970), Radionov (1973), Kuznetsov and Dikov (1979), Scholl et al. (1979), Berkinbaev et al. (1994). Several other parasite species have also been recorded in other wild ruminants in Kazakhstan, which rarely or never co-occur with saigas, notably forest and mountain cervids and bovids (Boev et al., 1962).
 

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  		TABLE 2. Prevalence (P), mean intensity (I), and inverse degree of aggregation (k) of parasitic helminths found in saiga antelope in Kazakhstan during November 1997.
 
Sampling and parasitologic methods

Shooting individual saigas opportunistically on encounter is not an ideal sampling method, and can be prone to biases; for example, towards animals with parasites of high intensity. However, there was no significant relationship between group size and either body condition or nematode intensity. Because all saigas in smaller groups were often shot, and although some animals from larger groups escaped, we assumed that shooting did not result in the selection of thinner saigas or those with high intensities of parasites, assuming that group size itself is independent of parasite intensity.

The number of nematode species found in saiga abomasa did not appear to be related to the total proportion of digesta examined, either on visual inspection of the data or on calculation of correlation (n=108, Spearman rs=0, NS), which might mean that incomplete examination of gut contents did not underestimate nematode diversity. The observed prevalence of infection was also unaffected by the proportion of digesta examined. One adult and four juvenile saigas were inadvertently shot through the abomasum. The volume of the contents of breached abomasa was significantly reduced relative to undamaged abomasa (median volume 10 ml, and 30 ml respectively, Mann-Whitney U=13.5, n=4 and 63, P=0.01). However, the calculated intensity of abomasal nematodes was not lower in damaged abomasa (U=158, NS), and both Marshallagia spp. and Nematodirus spp. were found in washings from them. Samples from damaged abomasa were therefore included in subsequent analysis. There was no significant difference in either the medians of total nematode counts, or those of the separate counts of Marshallagia spp. and Nematodirus spp., in frozen and unfrozen abomasa (n=26 and 107, Mann-Whitney U=1,237, 1,291, 1,315 respectively, NS). Nematode specimens from frozen abomasa were apparently undamaged and as easy to identify as those collected from fresh abomasa. Failure to ligate the pylorus did not appear to allow significant movement of nematodes between the abomasum and small intestine, as Marshallagia spp. were recovered from the small intestine only very occasionally and in small numbers.

Recovery of nematodes from the small intestine by extrusion, without subsequent washing, might lead to underestimation of small intestinal intensities if some nematodes remain attached to the mucosa. Adult nematodes were found in all five sets of intestines opened and washed after extrusion. Assuming that washing recovered all remaining adult nematodes, extrusion was successful in recovering on average 98.9%, and in no case fewer than 98%, of adult nematodes. No species were recovered by washing that were not already present in the extruded samples. Nematode intensities calculated from aliquots of extruded small intestinal contents were used without adjustment in subsequent analysis.

Effect of parasitism on body condition

The proportion of juvenile saigas in poor body condition did not vary with sex ({chi}2=0.918, 1df, NS), but for females, a higher proportion of juveniles than adults was in poor condition ({chi}2=4.956, 1df, P=0.03). Adult males were not sampled due to licensing restrictions. The abundance of all three parasite species was higher in juvenile females than juvenile males (Table 3Go). The prevalence of both Marshallagia species, but not Nematodirus gazellae, was higher in female juveniles than male juveniles (M. marshalli {chi}2=37.60, 1df, P<0.001; M. mongolica {chi}2=4.576, 1df, P=0.03; N. gazellae {chi}2=3.670, 1df, NS). The only significant correlation between parasite intensity and body condition was found for M. marshalli in female juvenile saigas (n=44, rs=–0.492, P=0.001), with higher intensities found in animals in poor condition. No such correlation was found in other age-sex classes.


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  		TABLE 3. Mean abundance of nematodes (=average number of adult parasites in all animals sampled) in male and female saiga antelope 6–7 mo of age, culled in Betpak-Dala, Kazakhstan in autumn, 1997. The mean difference and P-values were calculated by bootstrapping: 1,000 comparisons were made between samples of 100 drawn from the data, with replacement.
 
Age-infection patterns

The relationship between saiga age and abomasal nematode prevalence and intensity is summarized in Figure 2Go. Nematodirus gazellae and Marshallagia spp. had contrasting patterns. The prevalence of abomasal N. gazellae infection is fairly constant across age groups, whereas the proportion of animals carrying Marshallagia spp. increases progressively with age. The mean intensity of N. gazellae infection reaches a peak around age 3, and declines in older animals. Marshallagia spp., on the other hand, are present in low numbers in saigas less than a year old, and increase to an asymptote in older animals.



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  		FIGURE 2. The prevalence and mean intensity of abomasal nematodes in saiga antelope of different ages. Bars represent 95% confidence intervals: for prevalence, these were calculated by the exact binomial method, and for mean intensity, by bootstrapping directly from the data (1,000 samples, with replacement). Sample sizes = 87, 17, 10, and 9 for consecutive age classes.

 
Convexity in age-prevalence and age-intensity curves can be an artifact of aggregation in parasite populations, such that typically small sample sizes from older hosts are more likely to underestimate the mean than large sample sizes from younger hosts. This possibility was tested by combining counts from saigas older than 2 yr, and comparing them with those from younger animals using bootstrapping (Table 4Go). Where comparisons between age classes revealed the larger sample size to contain significantly more parasites per animal, the analysis was repeated with an equal sample size. This was achieved by selecting a random sequence of counts at each bootstrap iteration, equal in length to that of the smaller sample. According to this analysis, N. gazellae intensities declined significantly in animals older than 2 yr, but Marshallagia spp. intensities do not.


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  		TABLE 4. Bootstrap comparisons of mean intensity of infection in saiga antelope from Kazakhstan of different ages. P-values are the proportion of comparisons in which intensity in the younger age class exceeded that in the older age class. In each test, 1,000 comparison were made between samples of 1,000 values drawn from the observed counts, with replacement.
 
Fecal egg counts

There was a significant correlation between abomasal Marshallagia spp. intensity and the density of Marshallagia type eggs in saiga feces, irrespective of host age. Using maximum likelihood linear regression with a negative binomial error structure, separate estimates for the overdispersion parameter k in juvenile and adult saigas significantly improved the model fit, but no advantage was gained by adding age-specific slope parameters (Table 5Go). Confidence intervals for the intercept included zero for both adult and juvenile saigas, and the intercept term was consequently removed from the regression equation. Changing the error structure for FEC about intensity to Poisson significantly decreased the maximum likelihood fit of this optimal model (likelihood ratio {chi}2=145, 2df, P<0.001). For Nematodirus, total counts from the abomasum and small intestine were considered, giving a smaller sample size. Just five of the FEC from adult saigas were positive, and none exceeded four Nematodirus eggs per g. Correlation between intensity and FEC was not significant (rs=0.42, P=0.31). Among juvenile saigas, total Nematodirus spp. intensity and FEC were significantly correlated. Using the same approach as for Marshallagia, separate juvenile and adult terms for slope and k significantly improved model fit, but neither intercept terms nor the slope for adult saigas were significantly different from zero. Regression was therefore repeated for juvenile saigas only. A negative binomial error did not significantly improve model fit compared with a Poisson error ({chi}2=0.999, 1df, P=0.32). Regressions are shown in Figure 3Go.


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  		TABLE 5. Effect on linear regression model fit for Marshallagia fecal egg density on adult intensity of including separate slope (m) and error (negative binomial distribution parameter k) terms for juvenile and adult saiga antelope in Kazakhstan. Model fit was assessed using maximum likelihood: figures given are the minimum possible sum of the negative log of the likelihoods of individual data points, given model assumptions. {chi}2 values refer to the likelihood ratio test statistic.
 


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  		FIGURE 3. The relationship between grastrointestinal nematode intensity and fecal egg count (FEC) in saiga antelope in Kazakhstan. Coefficients are given for maximum likelihood linear regression, with 95% confidence intervals in parentheses. (a) Marshallagia in 48 saiga antelope of all ages, assuming a negative binomial error structure. Pearson r=0.82, P<0.001. Slope=0.022 (0.013–0.039), intercept=0, k=0.05 (0.01–0.15) for juveniles, and 1.2 (0.4–3.3) for adults. (b) Nematodirus (abomasum and small intestine) in six saiga antelope less than 1 yr of age, assuming a Poisson error structure. Pearson r=0.87, P=0.024. Slope=0.017 (0.014–0.021).

 
Interaction between nematodes

The observed proportion of males in Marshallagia spp. infections was 49% (n=1,718), and in Nematodirus spp. infection 52% (n=962): in both cases the sex ratio is approximately 1:1 ({chi}2=0.34 and 0.83 respectively, 1df, NS). The proportion of female nematodes observed to contain eggs was high in both genera (84%, n=140 for Marshallagia spp., and 75%, n=163 for Nematodirus spp.). The proportion of gravid female Nematodirus spp. was not related to the number of Nematodirus spp. adults in the intestine (rs=–0.25, n=9, NS). This might mean that mating probability is not limiting to reproduction in the populations considered.

There were no negative correlations in the abundance of any Marshallagia or Nematodirus species in individual saigas, which might mean that competition and cross-immunity do not significantly constrain the infrapopulations sampled.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
In terms of overall numbers found, the dominant helminth genera in saigas were Marshallagia, Nematodirus, and Skrjabinema. The helminth intensities found in saigas were lower than those associated with clinical signs in domestic animals (Reinecke, 1984). However, subclinical gastrointestinal nematode infections are known to reduce growth rates in domestic ruminants (Forbes et al., 2000), and decreased body mass and condition have been reported in parasitized animals in a range of wildlife species, including ruminants (Gulland, 1992; Stien et al., 2002). In the present study we found that 6-mo-old saigas in poor body condition carried higher intensities of M. marshalli. This was true only of females, and was not due to sample size bias, because the higher intensities of infection were not in the larger samples. This observation is at odds with the tendency of male animals to carry higher parasite intensities; however, theories of immune handicap in male mammals stem mostly from experiments that subject hosts to relatively high intensities of infection, and the vagaries of parasite acquisition in nature might reduce the importance of this effect (Wilson et al., 2002). Furthermore, the sex bias in this study was in pre-reproductive saigas, and could reflect differences in maternal investment (Clutton-Brock et al., 1982).

Effects of parasitism on host survival and fecundity are difficult to detect in free-ranging ruminants (Hudson and Dobson, 1995). Albon et al. (2002) found that anthelmintic treatment of free-living Sval-bard reindeer (Rangifer tarandus) increased their fecundity, but had no effect on overwinter survival. Hence the observed poor body condition and higher parasite intensities in female saigas in their first yr of breeding might reduce their ability to carry a pregnancy to term. Coulson et al. (2000) found decreased fecundity in adult saigas during periods of high population density and after cold winters (which could affect both nutritional status and parasite acquisition), but no such patterns were detected in first year breeders. A similar analysis found a stronger negative association between population density and fecundity in young Soay sheep than mature adults, and the failure to detect an effect in first year saigas could be due to high variance and low sample size in this group (Coulson et al., 2000). Both parasitism and immunity impose energy costs, confounding relationships between parasite intensity and body condition. Thus, individuals that divert resources to an immune response might have fewer parasites and poorer body condition than those that "allow" a higher intensity of infection (Medley, 2002). Longitudinal data on the acquisition of parasites, resources, and resistance to infection are needed to disentangle these processes. Even then, lags between maximum parasite intensity, peak body condition, and effects on host vital rates mean that the timing of observations can be crucial to detecting these effects (Stien et al., 2002). In the present study, sampling was restricted to the hunting season in November, when saigas are most likely to be in good body condition. If parasite intensities earlier in the year are more important determinants of body condition, or if there is a lag between intensities in November and effects on body condition and vital rates, a single cross-sectional sample is unlikely to provide a sensitive test of the biologically important relationships. Furthermore, different nematode species might vary in abundance asynchronously within and between years (Irvine et al., 2000), and affect their hosts unequally or in combination, confounding relationships between total nematode intensities and body condition.

Despite the potential significance of high M. marshalli intensities in young female saigas, Marshallagia intensities were much higher in adults than in juveniles, and any effects of infection might therefore be more pronounced later in life. However, intensities did not decline in older saigas, as we might expect if heavily infected hosts were lost from the population. Trichostrongyloid nematodes of domestic ruminants are characteristically more abundant in subadult than adult animals (Armour, 1989), and the asymptotic rise in Marshallagia intensities with age observed in this study could be indicative of the relative unimportance of immunity in free-living populations, due perhaps to lower nutritional status or less intense antigenic stimulation. Nematodirus gazellae intensities were lower in older saigas, but this could be due to acquired immunity rather than parasite-induced host mortality. Nematodirus spp. tend to penetrate deeper into the mucosa than other tri-chostrongyloid nematodes (Anderson, 2000) and might be more immunogenic as a result (Vercruysse and Claerebout, 1997). This could also account for the apparent reduction in egg output from Nematodirus spp., but not from Marshallagia spp., in older saigas. The presence of N. gazellae in the intestine could also help to elicit a stronger immune response to this species in the abomasum. It should be noted that in cross-sectional surveys such as this one, differences in infection intensity with age could also be caused by variation in infection pressure between years.

Inference of density dependence from age-intensity curves is complicated by aggregation in parasite populations (Pacala and Dobson, 1988; Hudson and Dobson, 1995; Wilson et al., 2002). Large sample sizes are needed for adequate statistical comparison of intensities between host groups, yet opportunities to sample large numbers of free-living hosts are rare. The methods used in this study could help to address this problem in other parasitological surveys of wildlife. Firstly, the simplified parasite extraction methods described allow larger numbers of hosts to be sampled where time, water, equipment and transport are limited. Secondly, bootstrap comparisons of parasite intensities avoid reliance on flawed statistical assumptions, and, by adjusting for sample size, can eliminate artifactual inflation of mean intensity in larger host groups without wasting data. Indirect measures of parasitism, such as FEC, can also enable more hosts to be sampled, especially where post mortem examination of wildlife is difficult or undesirable. At the intensities of infection observed in this study, FEC appear to provide a useful indication of the intensity of Marshallagia infections in saigas of all ages, and of Nematodirus infections in saigas below 1 yr of age.

Saigas share many helminth species with domestic livestock, especially sheep. Several common helminths of saigas (species of Marshallagia, Nematodirus, and Moniezia) are considered to be significant pathogens of sheep in Central Asia (Irgashev, 1973; Denisova, 1976), and in Kazakhstan saigas have been thought to infect sheep with Marshallagia spp. (Mustafin, 1987), Avitellina centripunctata (Petrov, 1985), Nematodirus archari, N. gazellae, N. mauritanicus (Karabaev, 1953), and Skrjabinodera saiga (Radionov, 1973). Our understanding of host specificity among these parasites, however, remains confused. Radionov (1973), for instance, considers M. marshalli to be primarily a parasite of sheep that occasionally spills over into saigas, and M. mongolica a parasite of saigas that can infect sheep. Scholl et al. (1979), however, found both species in saigas that were isolated from livestock on Barsa-Kel’mes island. Both species were also common in saigas in the present study, and age-intensity patterns were similar, providing no evidence for pronounced host specificity in this genus. More generally, the trichostrongylid nematodes appear to have a relatively wide host range in Kazakhstan, whereas the moleinids (Nematodirus and Nematodirella spp.) are more specific. This is similar to the typical distribution of gastrointestinal nematodes among wild ruminant species in North America (Hoberg et al., 2001).

Actual transmission of helminths between saigas and livestock is likely to depend on host abundance and patterns of contact, and not just on host specificity (Morgan et al., 2004). Recent declines in saiga and livestock populations in Kazakhstan might have led to decreased opportunities for contact (Robinson and Milner-Gulland, 2003). However, concurrent impoverishment of the livestock sector has also decreased the availability of drugs and eroded the effectiveness of centrally planned animal health initiatives (Lundervold, 2001). Livestock movements planned in part to evade parasitic infection have in many cases ceased (Robinson and Milner-Gulland, 2003). It is unlikely that helminth infections at the intensities observed in this study contribute significantly to the ongoing population decline in saigas. However, helminths are likely to cause problems to recovering livestock populations in Kazakhstan, and saigas could suffer both by acquiring these parasites and by being blamed for their spread. Low rates of parasite transmission from saigas to livestock are not necessarily harmful, and could boost immunity or supply anthelmintic susceptible parasite genotypes (Van Wyk et al., 2002). However, given the considerable overlap in helminth fauna between saigas and livestock demonstrated in this study, parasite control should be considered in future livestock health and wildlife conservation initiatives in the saiga range.


   ACKNOWLEDGMENTS
 
This work was funded by INTAS project 95–29, "The interaction between saiga and domestic livestock in the Aral Sea area (through contact, competition, parasites and disease)," and E. R. M. gratefully acknowledges support from a University College Dublin Graduate Award, and from BBSRC (UK) through a Veterinary Research Fellowship Studentship. A. B. Bekenov and Y. A. Grachev of the Institute of Zoology in Almaty and M. Lundervold provided invaluable assistance in organizing the expedition. The ageing of saigas from teeth was organized by M. Lundervold and carried out by R. Langvatn at the Norwegian Institute for Nature Research in Trondheim. Thanks also go to P. J. Quinn, S. Hogan, and D. Maguire (Department of Veterinary Microbiology and Parasitology) for laboratory space, R. Lomakin (A. N. Severtsov Institute for Ecology and Evolution) and A. Khrustalev (K. I. Skrjabin Institute for Helminthology) who assisted with the identification of difficult specimens, M. Kholodova for helping to organize this expert assistance, and A. Nemet and others for their practical help in the field.


   LITERATURE CITED
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
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Received for publication 26 March 2004.




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