The use of Anticoccidial Sensitivity Tests (ASTs) by the Poultry Industry.

Anticoccidial drug resistance in coccidia has been known since the 1960s, and experimental selection for resistance in the laboratory has been done for most available products. However, routine testing for sensitivity in field isolates has only begun in recent years. Poultry producers are faced with greater challenges because of consumer preferences for 'antibiotic-free' products and a lack of new products for disease control. The classification of some of our most effective anticoccidials as 'antibiotics' has severely limited their use, causing us to rely on older products that are prone to resistance development. The interaction between coccidiosis and other diseases such as necrotic enteritis places more importance on routine testing for drug sensitivity. In this review, we have summarized the use of the anticoccidial sensitivity test (AST) as it is conducted and interpreted by poultry health specialists.

Estudio recapitulativo- El uso de pruebas de susceptibilidad para anticoccidianos (ASTs) en la industria avícola. La resistencia a los fármacos anticoccidianos se ha reconocido desde los años 1960s y la selección experimental para resistencia en el laboratorio se ha demostrado para la mayoría de los productos disponibles. Sin embargo, las pruebas rutinarias de susceptibilidad a los agentes anticoccidianos con aislamientos de campo solo se han generalizado en los últimos años. Los productores avícolas enfrentan desafíos mayores debido a la preferencia de los consumidores por productos "libres de antibióticos" y la falta de nuevos productos para el control de enfermedades. La clasificación como "antibióticos" de algunos de los anticoccidianos más efectivos ha limitado su uso enormemente, causando la dependencia de anticoccidianos más antiguos que en general tienen una mayor predisposición al desarrollo de resistencia. La interacción entre la coccidiosis y otras enfermedades como la enteritis necrótica dan mayor relevancia a las pruebas rutinarias de susceptibilidad a los fármacos anticoccidianos. En esta revisión, hemos resumido el uso de la prueba de susceptibilidad a los anticoccidianos (AST) tal y como es realizada e interpretada por los especialistas en la salud aviar.

Oviduct Fluke (Prosthogonimus macrorchis) Found Inside a Chicken Egg in North Carolina.

A video received by faculty at North Carolina State University's Prestage Department of Poultry Science revealed a live parasite inside a chicken egg. The parasite was identified as an oviduct fluke (Prosthogonimus macrorchis), a trematode with a three-host life cycle: the primary host, a galliform bird, then an aquatic snail, and finally a dragonfly larva or adult consumed by the infected bird. The egg was from a "backyard flock" with access to a watercourse. No other instances of this parasite were seen in eggs from the flock. The presence of this parasite inside an egg suggests that the worms had migrated above the shell gland in the oviduct to be incorporated inside the egg. Currently, the occurrence of an oviduct fluke inside an egg in the United States is rare. Such parasites are not found in eggs from caged layers because those birds do not have access to watercourses. This case reinforces the view that parasites requiring intermediate hosts may become more common in birds reared under free-range conditions.

Coccidiosis in the Chukar Partridge ( Alectoris chukar ): A Survey of Coccidiosis Outbreaks and a Test of Anticoccidial Drugs Against Eimeria kofoidi.

Field isolates of coccidia from 20 natural outbreaks in the chukar partridge ( Alectoris chukar ) were received from gamebird farms in 10 U.S. states. These were propagated in the laboratory and identified by microscopy and PCR. Of 20 samples, 18 were Eimeria kofoidi, two were Eimeria legionensis only, and one was a mixture of the two species. One isolate of E. kofoidi also contained an unidentified species detected only by PCR, nucleotide sequencing, and phylogenetic analysis. The efficacy of anticoccidial drugs against chukar coccidia was tested with experimental infections in battery cages. Isolates of E. kofoidi were used to infect 2-wk-old chukars. Anticoccidial products were given in the feed at levels approved for other poultry or for chukars. Tests were terminated at 6 days postinoculation with measurement of weight gains, fecal diarrhea scores, and necropsy to observe for lesion severity. Lasalocid (120 ppm) was moderately effective in one test. When tested against four field isolates, other ionophores (monensin, salinomycin, semduramicin) showed moderate effectiveness in reducing lesions and improving weight gains. Rofenaid (a potentiated sulfa mixture), robenidine (30 ppm), diclazuril (2 ppm), and decoquinate (80 ppm) were highly effective. In a test of nine products against a highly virulent field isolate, only diclazuril (2 ppm) and clopidol (125 ppm) reduced the severity of lesions and improved weight gain relative to infected controls, suggesting the extent to which previous drug usage had selected for drug resistance.

A novel, simplified technique to amplify Eimeria (Coccidia: Apicomplexa) DNA from oocysts.

A new method to amplify coccidia DNA by polymerase chain reaction (PCR) was developed by placing freeze-thawed oocysts in Ready-to-Go PCR bead tubes and using a 5-min initial heat denaturation step. Positive PCR reactions were found in 3 of 3 samples containing 20 or 50 oocysts; when ≤5 oocysts were used, 1 of 3 samples was positive. This technique shows potential for effectively and efficiently detecting and identifying oocysts from soil, feces, and other matter.

Blackhead disease: reduced sensitivity of Histomonas meleagridis to nitarsone in vitro and in vivo.

Histomonas meleagridis, a flagellated protozoan parasite, is the causative agent of blackhead disease or histomoniasis in gallinaceous birds. Currently nitarsone (4-nitrophenylarsonic acid) is the only approved preventative drug available in the United States against blackhead disease. Initially we tested the sensitivity of three different isolates of H. meleagridis collected from outbreaks in North Carolina (strain MNC), Michigan (strain ZM), and Georgia (strain BG) to nitarsone using in vitro culture conditions. Strain ZM and strain BG at 100 and 400 ppm showed reduced growth in comparison to their respective control groups. However, there was no inhibition of growth in strain MNC treated with nitarsone at 100 ppm, while reduced growth was seen at 400 ppm. To test the resistance of strain MNC to nitarsone in vivo, turkey poults fed a nitarsone or a control diet were inoculated cloacally with H. meleagridis. The nitarsone-treated group of birds did not show any significant difference compared to that of infected control group when measuring weight gain and liver and cecal lesions scores. Histomonas meleagridis were reisolated from the nitarsone-fed turkeys and subjected to the in vitro assay. Regenerated H. meleagridis maintain their resistance to nitarsone at 100 ppm. This study demonstrates that strain MNC has acquired partial resistance to nitarsone.

A genomic analysis of Histomonas meleagridis through sequencing of a cDNA library.

Histomonas meleagridis, a flagellated protozoan of the Order Trichomonadida, is the causative agent of blackhead disease in gallinaceous birds. Few genes have been identified in this organism; thus, little is known regarding the molecular basis for its metabolism, virulence, and antigenicity. To identify new genes, a cDNA library derived from a lab strain of H. meleagridis was sequenced and annotated. Data obtained from these experiments identified 3,425 H. meleagridis genes. Analysis of the data allowed the identification of 81 genes coding for putative hydrogenosomal proteins and was used to determine the codon usage frequency. Sequence information also identified bacteria that are cultured with H. meleagridis. Future analysis of these data should provide valuable molecular insights into H. meleagridis and provide the platform for molecular studies aimed at understanding the pathogenesis of blackhead disease.

An outbreak of blackhead disease (Histomonas meleagridis) in farm-reared bobwhite quail (Colinus virginianus).

An outbreak of blackhead disease (Histomonas meleagridis) in farm-reared flock of 13,500 bobwhite quail (Colinus virginianus) resulted in mortality totaling approximately 1500 in 4 wk. Necropsy of 56 dead birds at midoutbreak (from a total that day of 131) revealed that 55 had severe cecal lesions typical of blackhead, and only 3 had visible lesions in the liver. Necropsy of apparently healthy birds failed to detect any signs of infection. Presence of H. meleagridis in affected ceca was proved by culture in vitro and PCR tests.

Immunization of chukar partridges against coccidia (Eimeria kofoidi and Eimeria legionensis) with low doses of live oocysts.

Experiments were conducted to determine whether chukar partridge (Alectoris chukar) chicks would develop protective immunity after inoculation with coccidia. Young chukar chicks in battery cages inoculated with 100 or more oocysts of Eimeria kofoidi or Eimeria legionensis had significant protection at challenge 4 wk later, as measured by greatly reduced oocyst shedding and improved weight gain as compared with unvaccinated, challenged controls. However, when birds were housed in litter pens and vaccinated by various regimens (including two species of chukar coccidia at 100/dose), coccidiosis rapidly spread through all treatments and caused significant mortality. Vaccination with Coccivac-T or with 100 oocysts of Eimeria dispersa did not prevent mortality resulting from accidental contamination, and feed treatment with a Lactobacillus competitive-exclusion product had no benefit. Most if not all of the mortality was from E. kofoidi. This study illustrated the natural fecundity of chukar coccidia in a floor-pen environment where multiplication rate and reinfection combine to produce clinical disease from a small original exposure. Further, these results cast doubt on the potential use of low doses of live oocysts as a vaccine in the chukar partridge.

The infection of turkey poults with Histomonas meleagridis by contact with infected birds or contaminated cages.

The conditions under which infection with Histomonas meleagridis could spread from directly inoculated turkey poults to uninoculated poults without the aid of invertebrate hosts or vectors was investigated in several experiments. In three experiments in battery cages, uninoculated poults were commingled with directly infected birds on pine-shaving litter. Directly exposed birds were inoculated per cloaca with H. meleagridis by means of a plastic pipette tip attached to a 10-ml syringe or orally gavaged with fresh cecal droppings from donor turkeys 4 days postinoculation (PI). Of the cloacally inoculated controls in these experiments, 31 of 44 (70.5%) birds had severe lesions ofhistomoniasis at 14 days PI, whereas none of the orally gavaged birds became infected. Histomoniasis developed in 11 of 36 (30.5%) birds allowed to commingle with inoculated birds. In other treatments, poults were allowed only contact with droppings from directly inoculated birds after the infected birds were removed from the cages. This was done for a single period of 1 hr or repeated five times. Four of 32 birds (12.5%) became infected in this way after the single exposure, whereas only four of 44 birds (9.1%) exposed five times developed lesions. In a comparison of floor materials, 35 of 35 control birds inoculated per cloaca developed severe liver and cecal lesions, irrespective of litter. Uninoculated birds allowed to commingle with infected birds on paper or pine shavings became severely infected in all cases (12/12 and 12/12 birds, respectively), whereas only 33% of those on wire-floored cages became infected (4/12). These results suggest that transmission of infection is more likely to occur as a result of direct contact between birds than from contact with litter or fecal material.

The efficacy of anticoccidial products against Eimeria spp. in northern bobwhites.

To determine whether chemotherapeutic compounds available for use in domestic poultry are effective at controlling coccidiosis in northern bobwhites (Colinus virginianus), we tested 13 chemotherapeutic anticoccidials including amprolium (250 parts per million [ppm]), clopidol (125 ppm), diclazuril (1 ppm and 2 ppm), decoquinate (30 ppm), lasalocid (120 ppm), monensin (90 ppm), narasin/nicarbazin (36/36 ppm), robenidine (33 ppm), roxarsone (50 ppm), sulfadimethoxine/ ormetoprin (125/75 ppm), salinomycin (60 ppm), semduramicin (25 ppm), and zoalene (125 ppm and 150 ppm). Three tests were conducted using two replicates of 10 birds each: Infected, unmedicated controls and medicated birds were challenged with 1 x 10(6) oocysts of a field isolate consisting primarily of Eimeria lettyae. Subsequently, we tested clopidol, lasalocid, salinomycin, diclazuril (1 ppm), and monensin against mixed-species field isolates containing E. lettyae, E. dispersa, E. colini, or all. Weight gain, gross intestinal lesions, severity of diarrhea, and feed conversion ratio (FCR) 6 days postinfection were recorded. Lesion score, as previously reported, was unreliable as a measure of severity of infection in comparison with weight gain, fecal scores, and FCR. Excellent to good efficacy was found in clopidol, decoquinate, diclazuril (1 ppm and 2 ppm), and in lasalocid, narasin and nicarbazin, robenidine, sulfadimethoxine/ormetoprin, and zoalene (150 ppm). Marginal protection was found using monensin, salinomycin, semduramicin, or a roxarsone/semduramicin combination. Amprolium, roxarsone, and zoalene (125 ppm) were ineffective at controlling coccidia. Two of the six isolates tested against diclazuril 1 ppm and clopidol demonstrated a high degree of resistance, but none of the six isolates was resistant to lasalocid. Four of the eight isolates showed mild to moderate, and moderate to high, resistance against monensin and salinomycin, respectively. These findings indicate that several available compounds are effective at controlling coccidiosis in bobwhites.

An unusual case of coccidiosis in laboratory-reared pheasants resulting from a breach in biosecurity.

An outbreak of coccidiosis in laboratory-reared Chinese ring-necked pheasants (Phasianus colchicus) resulted in high morbidity and moderate mortality. The outbreak was associated with a breach in biosecurity caused by the cleaning of a sewer line with a mechanical device, resulting in extensive splattering of fecal material throughout the "clean room" where birds were held prior to use in coccidiosis experiments. Mortality and morbidity in the affected birds were seen exactly 5 days after the incident, after birds had been moved to another room for experimental use, corresponding closely with the known prepatent or preclinical period of Eimeria phasiani and Eimeria colchici. Gross lesions in the affected birds varied from dehydration to intestinal and ventricular hemorrhage. Microscopic examination confirmed a diagnosis of severe intestinal coccidiosis. This report underscores the ease of contamination of experimental birds leading to coccidiosis outbreaks during breaches of management and biosecurity.

Establishment of culture conditions for survival of Histomonas meleagridis in transit.

Fresh ceca samples from turkeys in North Carolina infected with Histomonas meleagridis were collected at necropsy, inoculated into warmed Dwyers medium, and sent by overnight courier to our laboratory at The University of Georgia. Further incubation at 40 C yielded positive cultures from all four samples. PCR and DNA sequencing confirmed the presence of H. meleagridis. To further establish conditions for survival in transit, we infected turkeys with H. meleagridis, euthanatized the birds 10 days postinfection, and allowed carcasses to incubate at room temperature for either 2 or 24 hr. After incubation, samples of cecal contents (0.5 g) were placed in Dwyers medium and held at 4, 25, or 30 C for 6, 18, 24, 48, 72, 96, or 120 hr, simulating holding conditions during transit. Samples were placed in a 40 C incubator at the specified times and examined daily for histomonad growth by light microscopy. Positive histomonad growth was detected from cecal samples obtained from the 2-hr incubated carcass and from cultures held at 30 C for 6, 18, 24, 48, and 72 hr. No growth was seen from cultures held at 25 or 4 C or at any temperature from the carcass allowed to incubate for 24 hr at room temperature. These results suggest that positive isolation can be made from field samples, provided that material is collected at warm temperatures and transported rapidly to the laboratory.

Evaluation of nifurtimox for potential use in control of histomoniasis in turkeys.

Nifurtimox (NFX), a compound with known antiprotozoal activity, was evaluated for potential use in the prevention or treatment of histomoniasis in turkeys. A test of NFX in vitro showed that the compound was progressively active at concentrations of 12.5-200 ppm. Lower concentrations appeared only to delay growth of histomonads, while a concentration of 200 ppm was completely inhibitory. A series of tests in turkey poults showed that NFX had significant (P < 0.05) efficacy at 300-400 ppm when given in the feed throughout a 14-day experimental infection period. The beneficial effect was most prominent in the reduction of mortality and the suppression of liver lesions. Cecal lesions appeared less affected. Treatment with 400 ppm for a 3-day period after inoculation of turkeys was partially effective. In all tests, liver lesions were suppressed more effectively than cecal lesions, indicating that the concentration of the compound in the liver during metabolic excretion was important in the observed efficacy of this compound. Lack of any effect on growth or feed consumption in uninfected turkeys during a medication period of 16 days indicated that this compound was well tolerated by turkeys at 400 ppm in the feed and might be of benefit in the prevention or treatment of histomoniasis in turkeys.

Low-dose immunization of northern bobwhites (Colinus virginianus) with Eimeria lettyae provides protection against a high-dose challenge.

To determine whether northern bobwhite quail (Colinus virginianus) could be immunized against Eimeria lettyae by a low-dose inoculation of oocysts, we inoculated 30 birds each with either 100 or 1000 oocysts at 2 days of age (given orally by pipette). Four weeks after immunization, the immunized birds and unimmunized controls were challenged with 1 x 10(6) E. lettyae oocysts. Eight days after challenge, birds were killed and weighed, and their intestines examined for gross lesions. Effectiveness of the immunization was measured by analyzing weight gain, intestinal lesions, severity of diarrhea, feed conversion ratio, and oocyst production. After challenge, birds immunized with 100 or 1000 oocysts gained an average of 33.3 g and 28.9 g, respectively, whereas unimmunized challenged birds gained an average of 11.5 g. Immunized quail produced approximately 99.7% fewer oocysts, had minimal gross intestinal and cecal lesions, had minimal diarrhea, and had a 50% lower feed conversion ratio compared to unimmunized challenged controls. These findings indicate that vaccination is a viable option for controlling coccidiosis in quail and that further research into vaccination is warranted.

Histomonas meleagridis (Protozoa: Trichomonadidae): analysis of growth requirements in vitro.

Histomonads grew rapidly in Dwyer's medium, consisting of medium 199, chick embryo extract, serum, and rice powder, reaching a population size of about 5 x 10(5) in 3-4 days, followed by a rapid decline. Substitution of other cell culture media (L-15, MEM, or RPMI) for M199 was also satisfactory, except for Waymouth's medium, which produced a lower and later peak of growth. Omission of serum or rice rendered media unsuitable for growth. Bacteriological culture media did not support growth of histomonads. Media that included glucose were unsuitable because the pH of the cultures dropped to about 4. The effect of glucose on pH was due to the action of bacteria. Oxygen inhibited growth of histomonads. There was no growth when culture tubes were not capped tightly, regardless of the medium used. Histomonads grew well with rice flour, cornstarch, oat flour, rye flour, and buckwheat flour. Barley and blue corn meal were less satisfactory. It appeared that the requirements for growth of the lumen phase Histomonas meleagridis included a suitable physiological saline, serum (of any source), and a starch source (grain flour). Anaerobic conditions and a pH near neutral were best. Histomonads separated into pure cultures by flow cytometry would not grow without the inclusion of an unspecified species of bacteria.

Efficacy of lasalocid against coccidiosis in Chinese ring-necked pheasants.

Two battery efficacy studies were conducted with field isolates of Eimeria spp. from outbreaks of coccidiosis on pheasant-rearing farms in Georgia (GA) and Illinois (IL), United States. The coccidian isolates were mixed species containing E. phasiani, E duodenalis, and E colchici. Lasalocid (LAS) was tested prophylactically at 120 parts per million (ppm) in the feed. Anticoccidial activity was assessed, in comparisons between infected and uninfected control birds, by the effects on weight gain and oocyst passage. The GA isolate reduced weight gain of infected controls by 64% (P < 0.05) during the week after inoculation. LAS-treated birds also suffered some depressed gain, but average gains were significantly improved (P < 0.05) in comparison with that of the infected controls. Fecal oocyst counts of infected controls averaged 10-24 x 10(6)/day for days 5-11 postinoculation (PI), after which oocyst passage declined. Birds given LAS passed 10-20 x 10(6) oocysts on days 5-6 PI, after which counts dropped to much lower levels. Oocyst passage was significantly reduced (P < 0.05) by LAS treatment on all but days 5 and 6 PI. The IL isolate reduced weight gain by 36% in infected controls, relative to uninfected controls (P < 0.05). LAS-treated birds also suffered reduced gain, but the gain was significantly improved in comparison with the infected controls. Oocyst counts averaged 3-9 x 10(6)/day on days 6-14 PI, but were significantly reduced by LAS treatment on all but day 6 PI. Thus, LAS was effective in pheasants against the tested field isolates of Eimeria spp. and was well tolerated at 120 ppm in the feed. However, the level of control was not as high as previously observed. Possible explanations for this difference include an emergence of drug resistance from prior use of LAS and a differential efficacy of LAS against different species of Eimeria used in the studies.

Enhancement of resistance to coccidiosis and necrotic enteritis in broiler chickens by dietary muscadine pomace.

Muscadine pomace (MP), a by-product of the production of wine and juice from Vitis rotundifolia, was dried and tested in chickens for effects on primary resistance to coccidiosis, development of protective immunity after vaccination with live coccidia, and resistance to necrotic enteritis (NE) caused by the joint action of Clostridium perfringens and coccidia. To test primary resistance to coccidiosis, 2-wk-old chicks were given 2% or 5% MP in the diet and inoculated with Eimeria acervulina and E. maxima. Birds given MP at either level had significantly (P < 0.05) lower lesion scores at 7 days postinoculation, in comparison with control birds, although weight gains were statistically similar. Broiler chickens were given 2% or 5% MP and grown to 42 days to test the palatability of MP. Birds given 2% MP in feed grew similarly to untreated controls, but birds given 5% had poorer average live weight. This suggested a negative effect on feed intake at the higher level. The effects of dietary 0.5% or 2.0% MP on immune protection were tested after live coccidiosis vaccination in the hatchery. Chicks were removed from each pen at 21 days of age and challenged with E acervulina, E. maxima, and E. tenella. Resistance to infection was improved by MP as suggested by significantly (P < 0.05) lower lesion scores 7 days postchallenge, and improved weight gains in comparison with immunized control birds that did not receive MP. At 42 days of age, birds given MP had higher average live weights than controls, although feed efficiency was not affected. An established model was used to study the effect of MP on NE in broiler chickens. Chicks were inoculated with live coccidia at 14 days of age and dosed orally with live cultures of C perfringens on day 19, day 20, and day 21. Enteritis caused 48% mortality in the first study and 67% mortality in the second study. Dietary MP at 0.5-2.0% significantly (P < 0.05) reduced mortality in both experiments; improved weight gain relative to the unmedicated, infected control; and reduced lesion scores at necropsy. Overall, the results of six experiments suggested that MP given in the diet at 0.5% or higher had a positive effect on primary resistance and development of acquired resistance to two severe intestinal diseases in chickens.

Histomonas meleagridis (Parabasala, Trichomonadea, Monocercomonadidae): presence of natural agglutinins in horse serum.

Cultured Histomonas meleagridis cells were readily agglutinated in vitro by horse serum at concentrations as low as 5%, although clumping was more rapid and prominent at 15% or higher. For observation of clumping, the cultured organisms were washed twice in Hanks balanced solution (HBSS) by centrifugation (1,000 x g for 15 min) and filtered through glass wool. The test sera were added and the mixture incubated in a Petri plate or 24-well culture plates at r.t. for 15-30 min. Formation of clumps was time- and concentration-dependent. Gentle agitation hindered agglutination at low serum concentration and accelerated agglutination at higher concentrations. The agglutinating factor (AF) was detected in several batches of serum from different sources, regardless of whether sera were heat-treated to inactivate complement. Histomonads were not clumped by either fetal horse or bovine serum (5-30%). Neither chicken nor turkey serum agglutinated histomonads to the extent seen with horse serum. Immune turkey serum lysed histomonads, hindering observation of clumping. Complement inactivation of immune serum slightly reduced lysis. AF in horse serum was precipitated with 25-40% ammonium sulfate and was active when cleaned by dialysis and reconstituted in HBSS. Clumping by serum facilitated the cleaning of histomonads for other studies where pure suspensions were needed.

Histomonas meleagridis in chickens: attempted transmission in the absence of vectors.

The progress and transmission of blackhead disease in chickens was studied in battery cages and floor pens in the absence of vectors. Two-week-old chicks were inoculated intracloacally with Histomonas meleagridis and allowed to commingle with others in floor pens. There was no confirmed transmission of blackhead to other birds in the pen, whether stocked at 10% or 25% with infected birds. A second experiment evaluated the effects of feed restriction of chickens on spread of blackhead within floor pens. Inoculated seeder birds had severe cecal lesions of blackhead at necropsy, regardless of feed restriction. Uninoculated birds did not develop lesions by the time of necropsy at 42 days of age, regardless of whether full-fed or limited by skip-day feeding. Chickens inoculated intracloacally with H. meleagridis and placed in battery cages became infected and had cecal lesions of blackhead, but few liver lesions. Chickens allowed to commingle with the inoculated birds in batteries had no lesions of histomoniasis at necropsy 2 wk postinoculation. Coccidial oocysts from turkeys (Eimeria adenoeides) were inoculated along with H. meleagridis from cultures to test the effects of sporozoite penetration in the ceca on progress of blackhead disease. Histomoniasis was not worsened by the interaction with sporozoites, as shown by unchanged severity of cecal lesions, the number of birds showing liver lesions, or the overall number of positive birds. Overall, blackhead infections showed no inclination to spread from bird to bird under conditions of these studies, in contrast to what has been reported for turkeys. These results suggest that the dynamics of blackhead transmission in chickens differs significantly from that of turkeys, where transmission from bird to bird is rapid and effective in the absence of vectors.

Blackhead disease in turkeys: direct transmission of Histomonas meleagridis from bird to bird in a laboratory model.

The spread of Histomonas meleagridis infections through groups of turkeys in the absence of the cecal worm vector (Heterakis gallinarum) was studied in a battery cage model. Battery-reared poults were exposed at 2 wk of age by commingling with infected birds into cages that had the floor lined with paper. One treatment received no exposure, whereas other birds were commingled with two, three, or four birds/cage (25%, 37.5%, or 50%) inoculated per cloaca with cultured H. meleagridis (200,000/bird). Inoculated birds died at 7-13 days postinoculation (DPI) showing typical liver and cecal lesions of histomoniasis. By 14 DPI, 87.5% of the directly inoculated birds died or had severe lesions of histomoniasis. Turkeys commingled with two, three, or four infected birds became infected at the rate of 72%, 80%, or 75%, respectively. In another experiment, two birds/cage (25%) were inoculated with Histomonas from culture and allowed to commingle with other birds for 1, 2, 3, or 4 days. Two of 12 (16.7%) birds had minor cecal lesions after contact with inoculated birds for 1 day, but 87.5%-100% became infected if inoculated birds remained in the cage for 2-4 days. Contemporaneous inoculation with cecal coccidia (Eimeria adenoeides) as a predisposing factor in blackhead infections was studied using the model. Turkey poults directly inoculated with Histomonas were allowed to commingle for 5 days with uninoculated birds that had received inoculation with 0, 10(3), or 10(4) sporulated oocysts. The coccidian infection appeared to interfere with transmission of blackhead infection by 7 DPI, as suggested by lessened severity of cecal lesions and a lower percentage of infected birds. These studies confirm that histomoniasis is transmitted readily from directly exposed young turkeys to others in the absence of the cecal worm vector, and that this phenomenon can be reproduced in battery cages as an experimental model.