World association for the advancement of veterinary parasitology (WAAVP): Second edition of guidelines for evaluating the efficacy of anthelmintics in poultry.

This revision of the original poultry guidelines has been prepared to assist in the planning, conduct and interpretation of studies designed to assess the anthelmintic efficacy of drugs (newly discovered or currently used) against helminth parasites of chickens and turkeys. The original set of poultry guidelines was published in 2003. The current version provides an update on procedures to study and quantify the most important helminth parasites of chickens and turkeys, and to integrate these poultry guidelines with a new series of general, reflective and host-specific guidelines relative to assessing anthelmintic efficacy in production and companion animals. General considerations required for the conduct of studies designed to evaluate anthelmintics regardless of animal host such as the selection of study animals, animal housing, feeding, study design, record keeping and statistical analysis are for the most part provided in the newly published general guidelines. Taken together, the general and poultry guidelines should help investigators and others design and conduct studies and evaluate data concerned with determining the efficacy and safety of anthelmintics in chickens and turkeys. Additionally, this revision draws attention to several timely considerations inherent to anthelmintic evaluations such as the need to properly collect helminth specimens for subsequent determinations (e.g. species and stage verification, helminth genotyping). The investigations addressed herein, will most likely provide the very first public record of a new product's abilities to effectively reduce targeted, helminth infections in animals, and particular attention should be focused on study excellence and accuracy. Due to changes in consumer preferences, and new regulatory requirements, poultry husbandry, especially regarding laying hens, has changed immensely in many countries since the publication of the first poultry guidelines. These changes have generally allowed for a much greater exposure of birds to the source of helminth challenge (litter and fields as opposed to cages). Parasitic helminthiosis of poultry has therefore greatly increased in incidence and magnitude; changes that accentuate the need for more effective anthelmintic intervention and an update on the means of determining anthelmintic efficacy.

Test and validation of methods to sample and detect human virus from environmental surfaces using norovirus as a model virus.

BACKGROUND: Viruses cause a major proportion of human infections, especially gastroenteritis and respiratory infections in children and adults. Indirect transmission between humans via environmental surfaces may play a role in infections, but methods to investigate this have been sparse. AIM: To validate and test efficient and reliable procedures to detect multiple human pathogenic viruses on surfaces. METHODS: The study was divided into two parts. In Part A, six combinations of three different swabs (consisting of cotton, foamed cotton, or polyester head) and two different elution methods (direct lysis or immersion in alkaline glycine buffer before lysis) were tested for efficient recovery of human norovirus GII.7 and mengovirus from artificially contaminated surfaces. In Part B we determined the detection limit for norovirus GI.1 and GII.3 using the best procedure found in Part A linked with a commercial multiplex real-time quantitative polymerase chain reaction detection assay. FINDINGS: Combining the polyester swab with direct lysis allowed recovery down to 100 and 10 genome copies/cm(2) of norovirus GI.1 and GII.3, respectively. This procedure resulted in the significant highest recovery of both norovirus and mengovirus, whereas no differences in amplification efficiencies were observed between the different procedures. CONCLUSION: The results indicate that it is possible to detect low concentrations of virus on environmental surfaces. We therefore suggest that a polyester swab, followed by direct lysis, combined with a multiplex qPCR detection assay is an efficient screening tool that merits study of different respiratory and gastrointestinal viruses on environment surfaces.

Acquisition of resistance after continuous infection with Ascaridia galli in chickens.

SUMMARY Acquired resistance against Ascaridia galli infection was studied in seventy-two 18-week-old white Leghorn chickens allocated to six groups (G1-G6). In order to understand the population dynamics following trickle-infection (100 eggs per chicken twice weekly), chickens of subgroups of G1 were necropsied 3 days after 1, 6 or 12 inoculations (G1A, G1B and G1C respectively), while G2-G4 were inoculated for 6 weeks. G2 was necropsied 4 weeks after the last inoculation. The number of established larvae increased initially (between G1A and G1B) but decreased after repeated inoculations (G1C, G2). G3, G4 and G5 were used to measure the efficacy of anthelminthic treatment and to monitor the acquisition of resistance following a challenge infection. At week 7 G3, G4 and G5 were treated with flubendazole for 7 days in the feed. Two weeks after treatment the chickens in G4 and G5 were challenged with 500 eggs. G6 was left as uninfected control. Necropsy at week 10 after first inoculation revealed a lower establishment rate, an impaired development and a more posterior localization of the larvae in G4 (trickle-infected-treated-challenged) compared with G5 (treated-challenged). IgY level in serum reached noticeable level at 14 dpi in G2 and G4 chickens, and in G4 chickens IgY level further increased after challenge infection. The study provides evidence that acquired resistance against A. galli in chickens leads to a significant yet incomplete protection against re-infection.

In vitro inhibition of Clostridium difficile and Clostridium perfringens by commercial probiotic strains.

Probiotics have gained importance in human and veterinary medicine to prevent and control clostridial enteric disease. Limited information is available on the ability of different probiotic bacteria used in food products to inhibit Clostridium difficile and Clostridium perfringens. The objective of this study was to examine the in vitro inhibitory effects of selected commercial bacterial strains on pathogenic clostridia and their growth characteristics under simulated gastrointestinal conditions. The inhibitory effects of 17 commercial strains of Lactobacillus (n = 16) and Bifidobacterium (n = 1) on the reference strains of C. difficile and C. perfringens were assessed by an agar well diffusion assay and by a broth culture inhibition assay using cell-free supernatant harvested at different growth phases, with and without pH neutralization. To study growth characteristics, probiotic strains were cultivated in different acid and bile environments, and growth in the modified media was compared to growth in standard medium. In the agar well diffusion assay, supernatant obtained from two probiotic strains inhibited the growth of both reference and clinical strains of C. perfringens. This effect as seen when supernatant was assessed with and without pH neutralization. Supernatants obtained from 10 probiotic strains inhibited C. difficile only when supernatant was added without pH neutralization. In the broth culture inhibition assay, growth of C. perfringens and C. difficile was inhibited by supernatant without pH neutralization from 5 and 10 probiotic strains, respectively. All potential probiotic strains were able to grow at pH 4.0 and in the presence of 0.15% and 0.3% bile but none were able to grow or survive at pH 2.0. Altogether five probiotic strains [Lactobacillus plantarum (n = 2), Lactobacillus rhamnosus (n = 2), Bifidobacterium animalis lactis (n = 1)] were shown to inhibit all strains of C. difficile and C. perfringens. The inhibitory effect was probiotic strain-specific. Two strains showed a pH-independent inhibitory effect likely due to production of either antibiotics or bacteriocins inhibiting C. perfringens only. These strains have favourable growth characteristics for use as probiotics and their efficacy as prophylactic or therapeutic measures against clostridial enteric disease should be further evaluated by clinical trials in animals.

Multi-locus sequence typing and plasmid profile characterization of avian pathogenic Escherichia coli associated with increased mortality in free-range layer flocks.

Avian pathogenic Escherichia coli strains originating from 10 free-range layer flocks were characterized by multi-locus sequence typing and plasmid profile analysis to investigate their phylogenetic relationship and diversity, respectively. In addition to colibacillosis, all flocks tested positive for antibodies against avian metapneumovirus (aMPV) during production, and six of the flocks were concurrently affected by histomonosis. Accumulated average mortality for flocks concurrently affected by colibacillosis and histomonosis made up 17.4%, while the average mortality for E. coli-infected flocks was 16.5%. A total of eight different sequence types (STs) and 47 different plasmid profiles were demonstrated among the E. coli isolates. Within each flock between one and four different STs and between three and 13 different plasmid profiles were demonstrated. A statistical significant difference in STs and plasmid profile diversity of the population of E. coli was not demonstrated between flocks affected by histomonosis compared with histomonosis-free flocks. Only minor clonal diversity was demonstrated for each flock, and in all but one flock colibacillosis started before antibodies against aMPV were detected. All isolates, except two, carried plasmids greater than 100 kb, but only a single plasmid replicon type, IncFIB, was demonstrated, suggesting plasmids representing this type might represent a common pathogenicity factor for the different STs of E. coli. Within each flock a clonal tendency was observed, indicating that only certain clones of E. coli possess a significant pathogenic potential. These clones act as primary rather than secondary pathogens, resulting in colibacillosis without predisposing factors, including histomonosis and aMPV.

Causes of mortality in commercial organic layers in Denmark.

A longitudinal study investigated the courses of mortality in commercial free-range organic layer flocks in Denmark. In total, 15 organic egg-producing flocks from 11 farms were randomly selected among 80 farms registered in Denmark. Four farms with confined egg production on deep litter were included for comparison. Flock sizes ranged from 2260 to 5940 layers. The flocks were monitored from introduction to the layer farm until slaughter. Flock mortalities ranged from approximately 2% to 91%, with a mean of 20.8% for organic flocks compared with 7% for confined flocks on deep litter. In total, 4608 layers were submitted for postmortem examination, representing > 40% of all the dead layers in the investigated flocks. Outbreaks of erysipelas (Erysipelothrix rhusiopathiae) and fowl cholera (Pasteurella multocida) were observed in two and three organic flocks, respectively. The mortality rate reached 91% in one organic flock dually affected by erysipelas and fowl cholera. In six organic flocks, outbreaks of blackhead were diagnosed. Concurrent infections of erysipelas and blackhead were diagnosed in one organic flock. Escherichia coli infections in the form of septicemia were identified in all organic flocks. In addition, cannibalism and constipation contributed significantly to the mortality in some organic flocks. In the confined deep litter flocks, E. coli infection, constipation, and cannibalism represented the most common causes of mortality.

MHC haplotype and susceptibility to experimental infections (Salmonella Enteritidis, Pasteurella multocida or Ascaridia galli) in a commercial and an indigenous chicken breed.

In three independent experimental infection studies, the susceptibility and course of infection of three pathogens considered of importance in most poultry production systems, Ascaridia galli, Salmonella Enteritidis and Pasteurella multocida were compared in two chicken breeds, the indigenous Vietnamese Ri and the commercial Luong Phuong. Furthermore, the association of the Major Histocompatibility Complex (MHC) with disease-related parameters was evaluated, using alleles of the LEI0258 microsatellite as markers for MHC haplotypes. The Ri chickens were found to be more resistant to A. galli and S. Enteritidis than commercial Luong Phuong chickens. In contrast, the Ri chickens were more susceptible to P. multocida, although production parameters were more affected in the Luong Phuong chickens. Furthermore, it was shown that the individual variations observed in response to the infections were influenced by the MHC. Using marker alleles of the microsatellite LEI0258, which is located within the MHC region, several MHC haplotypes were identified as being associated with infection intensity of A. galli. An association of the MHC with the specific antibody response to S. Enteritidis was also found where four MHC haplotypes were shown to be associated with high specific antibody response. Finally, one MHC haplotype was identified as being associated with pathological lesions and mortality in the P. multocida experiment. Although not statistically significant, our analysis suggested that this haplotype might be associated with resistance. These results demonstrate the presence of local genetic resources in Vietnamese chickens, which could be utilized in breeding programmes aiming at improving disease resistance.

Mannan-binding lectin (MBL) in two chicken breeds and the correlation with experimental Pasteurella multocida infection.

The present study is the first demonstration of an association of the genetic serum Mannan-binding lectin (MBL) concentration with bacterial infections in chickens. The genetic serum MBL concentration was determined in two chicken breeds, and the association with the specific Pasteurella multocida humoral immune response during an experimental infection was examined. Furthermore, we examined the association of the genetic serum MBL concentration with systemic infection. The chickens with systemic infection had a statistically significant lower mean serum MBL concentration than the rest of the chickens, suggesting that MBL plays an important role against P. multocida. A statistically significant negative correlation was found between the specific antibody response and the genetic serum MBL concentration for both breeds. This indicates that MBL in chickens is capable of acting as the first line of defence against P. multocida by diminishing the infection before the adaptive immune response takes over.

Gastrointestinal helminths in indigenous and exotic chickens in Vietnam: association of the intensity of infection with the Major Histocompatibility Complex.

This study compared the prevalence and intensity of infections of helminths in 2 chicken breeds in Vietnam, the indigenous Ri and the exotic Luong Phuong. Also, possible correlations with the Major Histocompatibility Complex (MHC) were tested. The most prevalent helminths were Ascaridia galli, Heterakis beramporia, Tetrameres mothedai, Capillaria obsignata, Raillietina echinobothrida and Raillietina tetragona. Differences in prevalence and intensity of infection were found between the 2 breeds. Comparing the 2 groups of adult birds, Ri chickens were observed to have higher prevalence and infection intensities of several species of helminths, as well as a higher mean number of helminth species. In contrast, A. galli and C. obsignata were shown to be more prevalent in Luong Phuong chickens. Furthermore, an age-dependent difference was indicated in the group of Ri chickens in which the prevalence and the intensity of infection was higher for the adult than the young chickens for most helminths. The most notable exception was the significantly lower prevalence and intensities of A. galli in the group of adult chickens. In contrast, the prevalence and intensity were very similar in both age groups of Luong Phuong chickens. Using a genetic marker located in the MHC, a statistically significant correlation between several MHC haplotypes and the infection intensity of different helminth species was inferred. This is the first report of an association of MHC haplotype with the intensity of parasite infections in chickens.

Infection and excretion of Salmonella Enteritidis in two different chicken lines with concurrent Ascaridia galli infection.

Studies on the impact of interaction of Salmonella enterica serovar Enteritidis and the parasitic nematode Ascaridia galli with the avian host were undertaken with particular emphasis on infection and excretion of these pathogens in two different layer lines. A total of 148 salmonella-free 1-day-old chickens (73 Hellevad and 75 Lohmann Brown) were randomly divided into five groups for each line. Group 1 served as an uninoculated control group. Groups 2 and 3 were infected with A. galli and S. Enteritidis, respectively. Group 4 was first infected with S. Enteritidis and subsequently with A. galli, and vice versa for group 5. The number of chickens excreting S. Enteritidis was significantly higher (P < 0.001) in the groups infected with both S. Enteritidis and A. galli compared with those only infected with S. Enteritidis over time. Furthermore, excretion of S. Enteritidis over time was significantly higher (P < 0.001) in the group first infected with S. Enteritidis and subsequently with A. galli compared with the group infected in the reverse order. No significant differences were observed between the two lines concerning excretion of S. Enteritidis over time in any group (P = 0.61 (group 3), P = 0.73 (group 4), P = 0.31 (group 5)). A. galli established itself significantly better (P = 0.02) in the group first infected with A. galli and subsequently with S. Enteritidis compared with the group infected in the reverse order. Furthermore, the A. galli infection rate was significantly higher (P = 0.02) in Hellevad chickens compared with Lohmann Brown chickens at the end of the experiment.

Consequences of concurrent Ascaridia galli and Escherichia coli infections in chickens.

Three experiments were carried out to examine the consequences of concurrent infections with Ascaridia galli and Escherichia coli in chickens raised for table egg production. Characteristic pathological lesions including airsacculitis, peritonitis and/or polyserositis were seen in all groups infected with E. coli. Furthermore, a trend for increased mortality rates was observed in groups infected with both organisms which, however, could not be confirmed statistically. The mean worm burden was significantly lower in combined infection groups compared to groups infected only with A. galli. It was also shown that combined infections of E. coli and A. galli had an added significant negative impact on weight gain.

Clonal stability of Pasteurella multocida in free-range layers affected by fowl cholera.

Detailed longitudinal studies of the genetic stability of Pasteurella multocida ssp. multocida, the cause of fowl cholera, have not previously been carried out. Consequently, the aim of the present study was to provide detailed information on the genetic stability and diversity of P. multocida ssp. multocida in poultry flocks over time, enabling new insights into the molecular epidemiology of this important poultry pathogen. Longitudinal investigations of the rate and causes of mortality were carried out on two free-range layer farms (A and B) over a period of 11 months. The total mortality of two flocks, A1 and A2, on farm A were 62 and 91%, respectively, while the total mortality of a single flock B1 on farm B was 6%. Postmortem examinations were performed on 708 layers from flocks A1 and A2 and in 159 from flock B1. Fowl cholera was the main cause of mortality on both farms. Pasteurella multocida isolates recovered from layers on both farms were characterized phenotypically and genotypically, and 322 isolates were identified as P. multocida ssp. multocida. The genetic diversity of 99 isolates from farm A and 31 from farm B was characterized by restriction endonuclease analysis and amplified fragment length polymorphism analysis. The isolates on each farm had a unique restriction endonuclease analysis and amplified fragment length polymorphism analysis type, suggesting a single introduction of a successful clone. Furthermore the clone on farm A was identical to clones previously isolated from outbreaks in the avifauna of Denmark in 1996 and 2001 and in Sweden in 1998. This study provides convincing evidence for the clonal stability of outbreak clones of P. multocida.

Influence of Dermanyssus gallinae and Ascaridia galli infections on behaviour and health of laying hens (Gallus gallus domesticus).

(1) The effect of infections with Dermanyssus gallinae (poultry red mite or chicken mite) and Ascaridia galli (roundworm) on the behaviour and health of laying hens was investigated. (2) Six groups of 15 pullets (Isa Brown) were kept in indoor pens from 18 weeks of age. Two groups were artificially infected with D. gallinae, two groups with A. galli and two groups were kept as uninfected controls. The hens were observed for behavioural reactions and physiological changes (weight gain and various blood variables) to the parasitic infections. (3) Infections with D. gallinae resulted in reduced weight gain, anaemia and even death of some of the hens. Behavioural changes were also observed, as the mite-infected hens showed higher self-grooming and head scratching both during the day and night. (4) A. galli resulted in a lower weight gain but no significant changes were seen in blood variables or behavioural activities.

An experimental infection model for Tetrameres americana (Cram 1927).

An experimental infection model for the heteroecious spiruid nematode Tetrameres americana (Cram 1927) was developed. The cockroach Blattella germanica (L.) and the locust Locusta migratoria (L.) were found to serve as intermediate hosts for the parasite. T. americana larvae developed to full maturity in these intermediate hosts and were infective to young Lohman Brown chickens after 32 days in the cockroach and 28 days in the locust. The maximum length of the larvae was reached in the insects at 28-30 degrees C after 10-15 days, at which time the larvae measured up to 2.2 mm. The parasite did not develop in the cockroach Periplaneta americana (L.), the woodlouse Oniscus asellus (L.), or the pupal stage of the giant mealworm Zophobas morio (Fabricius). Trials in which chickens were infected directly without an intermediate host failed. Infection of 24 chickens with a dosage of 100 larvae was followed by weekly post-mortems until day 48 post-infection (p.i.) and used to describe the development of T. americana. The average establishment rate (%) and the average worm burden varied from 16.5 to 30.8. The total numbers of parasites recovered ranged from 9 to 40. During mating, in the first 2 weeks p.i. females and males were equally abundant, whereas from day 20 p.i. twice as many females were recovered. From day 13 p.i. the females average length fluctuated between 2.6 and 3.7 mm, whereas they reached their maximum width of 2.4 mm on day 48 p.i. Males reached their full length after 27 days p.i. and measured up to 6.7 mm.

Tetrameres americana Cram (1927) populations in chickens infected with different dose levels.

Three groups of 20-45 Lohman brown chickens aged 3 weeks were orally infected with doses of 25, 100 and 400 Tetrameres americana, respectively. Fifteen chickens were kept as uninfected controls. Every third week in a period of 12 weeks, 5-15 chickens were slaughtered and the proventriculi were examined for the presence of adult stages of T. americana. From day 21 post-infection, pooled feacal samples were examined for parasite eggs, whereas the weight gain of the chickens was monitored weekly. The parasite established the infection in similar rates in all the three groups, 9.5-15.2%, except on day 84 post-infection, when the establishment rate of the high-dose group was significantly lower (P < 0.005). The average worm burden increased with increasing dosages, though displaying the worm burden of the high-dose group as being roughly halved on day 84 post-infection, thus suggesting an expulsion of worms. Females were more abundant than males. The mean lengths of male and female specimens showed no significant differences between the groups. The egg output was also increased with increasing dosages with the earliest prepatent period of 38 days post-infection found in the high-dose group. Infected chickens exhibited no difference in weight gain in comparison with the controls. This study demonstrated that single infections with varying doses influenced the establishment rate and the worm burden but not the parasites egg excretion, worm size nor the weight gain and mortality of the final host.

Host age only partially affects resistance to primary and secondary infections with Ascaridia galli (Schrank, 1788) in chickens.

Two experiments were conducted to compare the effect of chickens' age on resistance to primary and secondary infections with Ascaridia galli. In Experiment I, three groups, each of 80 female Lohman Brown chickens, aged one day, one month, or four months were compared. Within each group, 54 chickens were infected orally with 500 embryonated eggs and 26 were kept as non-infected controls. Weights were recorded weekly and five chickens in each group were slaughtered every 2 weeks for worm counts. At week 10 post-infection, 17 of the infected chickens and 18 of the controls were challenged with 500 eggs. In a replicate experiment (Experiment II), 35 one-day-old and 53 one-month-old female Lohman Brown chickens were infected orally with 500 A. galli eggs. Weights and fecal egg counts were recorded every week and infected chickens were necropsied every two weeks for determination of the worm burden. Chickens infected at one month of age excreted significantly fewer A. galli eggs when measured at 14 weeks of inoculation. The worms recovered from the one-month-old age group were significantly shorter than those from the chickens infected at one day of age in the first experiment. Worm burden and female fecundity values, however, were not significantly different between age groups in both Experiments I and II. Weight gains of infected chickens were not significantly different from the controls' and only a few chickens exhibited occasional slight diarrhea in both experiments. The results from these experiments demonstrate that the chickens' age only partially influences resistance to A. galli infection.

Zoonotic risk of Toxocara canis infection through consumption of pig or poultry viscera.

The potential zoonotic risk of Toxocara canis infections from consumption of swine or poultry viscera containing larvae was assessed using a pig model. Two groups of six pigs were fed either fresh swine viscera (group FS) or poultry viscera (FP) containing around 3500 Toxocara larvae. Another two groups of six pigs were fed swine viscera (PS) or poultry viscera (PP) preserved at 4 degrees C for 1 week. All pigs were necropsied 14 days after the exposure. Liver white spots were counted and T. canis specific IgG antibodies were measured by ELISA. Larval burdens were assessed in the mesenteric lymph nodes, liver, lungs, brain, tongue, and eyes. All recipient pigs exhibited several white spots on the liver surface and detectable antibody levels. Larvae were recovered predominantly from the lungs, but also from the mesenteric lymph nodes and the liver, a few larvae were found in the brain and tongue of the pigs. Two larvae were found in the eyes of two pigs in group FS. Mean percentages of total larval recoveries in groups FS, FP, PS, and PP were 75.3, 63.6, 42.6, and 18.8%, respectively. Significantly higher numbers of larvae were recovered from pigs given swine viscera than pigs given poultry viscera. The preservation at 4 degrees C for 1 week caused a significant reduction in the larval infectivity overall, nevertheless, the recoveries remained substantial. The fact that larvae migrating in swine or poultry organs and tissues have high infectivity in pigs even after preservation at 4 degrees C for 1 week, suggests that human infection with T. canis might easily occur following consumption of raw or undercooked dishes, either fresh or refrigerated, prepared from swine or poultry organs and tissues harbouring T. canis larvae.

Investigations on the influence of helminth parasites on vaccination of chickens against Newcastle disease virus under village conditions.

Prevalence studies have shown that almost 100% of free-range chickens are infected with a wide range of parasites. The infections are mostly subclinical in nature, resulting in production losses and occasionally mortality. Newcastle disease (ND) on the other hand, results in high mortality rates during epidemics. ND is a limiting factor for increasing poultry production in many tropical countries, where frequent reports indicate vaccination failures. The aim of our study was to investigate the influence of helminths on the antibody response after vaccination against Newcastle disease of free-range chickens naturally infected with parasites. Sixty chickens were divided into six groups, of which three were vaccinated against ND with a live De Soto vaccine, while the other three remained non-vaccinated. One group within the vaccinated groups and the one within the non-vaccinated group was kept naturally infected with helminth parasites, while the other two groups in each set were dewormed with fenbendazole and niclosamide, and one of each of these groups was subsequently infected with Ascaridia galli. After vaccination, all the groups were followed for 5 weeks and their antibody titres were determined weekly using a HI test. All the birds were finally challenged 4 weeks after vaccination with a virulent velogenic ND virus obtained from a field outbreak. All the vaccinated chickens seroconverted and had high antibody levels after 3 weeks, but these dropped to low levels at 4 weeks after vaccination. After challenge, the antibody titres rose in the dewormed groups but not in the parasite-infected groups. After 5 weeks, all the parasite-infected animals had significantly lower antibody titres than the dewormed animals. All the vaccinated chickens survived the challenge infection, emphasizing the importance of the cellular immune response. Further studies are needed to examine the effects of the parasitic infection on protection against ND over a longer period.

Comparative genetic resistance to Ascaridia galli infections of 4 different commercial layer-lines.

1. The objective of the study was to compare the establishment and effect of Asaridia galli infections in 4 different layer-lines. 2. A total of 160 birds comprising 4 different commercial layer-lines, ISA Brown, New Hampshire, Skalborg and a cross of New Hampshire(NH) and Skalborg (Sk), were infected with A. galli eggs. The birds were examined for the presence of parasite eggs and parasites at weeks 3, 6 and 9 post infection (pi). 3. At week 6 pi the chickens of the NH line harboured more larvae compared with the three otherlines. The Sk line chickens excreted more A. galli eggs throughout the study compared with the other lines. Female worms in the Sk line were more fecund than the worms in the other lines. Male and female worms recovered from the Sk line at week 9 pi were longer. Male worms recovered from the NH line 6 weeks pi were shorter than male worms from the other lines. Female worms recovered from the NH line were shorter than the female worms from the ISA line and the Sk line. No differences were seen in weight gain among the 4 lines. 4. The results suggest that genetic factors are involved in the establishment and survival of A. galli in the intestine of layers. Further studies are needed to elucidate the genetic mechanisms behind the observed parasitological findings.