Mapping the poultry insectome in and around broiler breeder pullet farms identifies new potential Dipteran vectors of Histomonas meleagridis.

BACKGROUND: Histomonas meleagridis can infect chickens and turkeys. It uses the eggs of the cecal worm Heterakis gallinarum as a vector and reservoir. Litter beetles (Alphitobius diaperinus) and other arthropod species have been implicated as potential vectors, but little information about other arthropod species as potential vectors is known. METHODS: Four broiler breeder pullet farms were sampled every 4 months. On each farm, three types of traps were set inside and outside two houses. Trapped arthropod specimens were morphologically identified at order level and grouped into families/types when possible. Selected specimens from abundant types found both inside and outside barns were screened for H. meleagridis and H. gallinarum by qPCR. RESULTS: A total of 4743 arthropod specimens were trapped. The three most frequently encountered orders were Diptera (38%), Coleoptera (17%), and Hymenoptera (7%). Three hundred seventeen discrete types were differentiated. More arthropods were trapped outside than inside. Alpha diversity was greater outside than inside but not significantly influenced by season. The composition of the arthropod populations, including the insectome, varied significantly between trap location and seasons. Up to 50% of litter beetles tested positive for H. meleagridis DNA 4 months after an observed histomonosis outbreak. Sporadically litter beetles were positive for H. gallinarum DNA. Thirteen further arthropod types were tested, and specimens of four Dipteran families tested positive for either one or both parasites. CONCLUSIONS: This study describes the insectome in and around broiler breeder pullet farms and identifies new potential vectors of H. meleagridis through qPCR. The results show a limited but present potential of arthropods, especially flies, to transmit histomonosis between farms.

Effects of prolonged lung inflation or deflation on pulmonary stretch receptor discharge in the alligator (Alligator mississippiensis).

The American alligator (Alligator mississippiensis) is a semi-aquatic diving reptile that has a periodic breathing pattern. Previous work identified pulmonary stretch receptors, that are rapidly and slowly adapting, as well as intrapulmonary chemoreceptors (IPC), sensitive to CO2, that modulate breathing patterns in alligators. The purpose of the present study was to quantify the effects of prolonged lung inflation and deflation (simulated dives) on pulmonary stretch receptors (PSR) and/or IPC discharge characteristics. The effects of airway pressure (0-20 cm H2O), hypercapnia (7% CO2), and hypoxia (5% O2) on dynamic and static responses of PSR were studied in juvenile alligators (mean mass=246 g) at 24°C. Alligators were initially anesthetized with isoflurane, cranially pithed, tracheotomized and artificially ventilated. Vagal afferent tonic and phasic activity was recorded with platinum hook electrodes. Receptor activity was a mixture of slowly adapting PSR (SAR) and rapidly adapting PSR (RAR) with varying thresholds and degrees of adaptation, without CO2 sensitivity. Receptor activity before, during and after 1 min periods of lung inflation and deflation was quantified to examine the effect of simulated breath-hold dives. Some PSR showed a change in dynamic response, exhibiting inhibition for several breaths after prolonged lung inflation. Following 1 min deflation, RAR, but not SAR, exhibited a significant potentiation of burst frequency relative to control. For SAR, the post-inflation receptor inhibition was blocked by CO2 and hypoxia; for RAR, the post-inflation inhibition was potentiated by CO2 and blocked by hypoxia. These results suggest that changes in PSR firing following prolonged inflation and deflation may promote post-dive ventilation in alligators. We hypothesize that PSR in alligators may be involved in recovery of breathing patterns and lung volume during pre- and post-diving behavior and apneic periods in diving reptiles.

Involvement of ß(3)-adrenergic receptors in in vivo cardiovascular regulation in rainbow trout (Oncorhynchus mykiss).

Currently, we have little information concerning the involvement of ß(3)-adrenergic receptors (AR) in cardiovascular regulation in fishes. The goal of this study was to investigate the effect of ß(3)-AR ligands on in vivo cardiovascular function in larval and adult rainbow trout (Oncorhynchus mykiss). In adult fish, injection of BRL(37344) (ß(3)-AR agonist) resulted in an increase in heart rate (f(H)) (~31%) while stroke volume (Sv) was reduced (-25.9%). Injection of SR(59230A) (ß(3)-AR antagonist) and propranolol (ß(1)/ß(2)-AR antagonist) resulted in increases in dorsal aorta blood pressure (P(DA)) with differing effect on cardiac variables (f(H) and Sv). To confirm specificity of the results, BRL(37344) was injected following sequential injections of phentolamine (α(1)-AR antagonist), atropine (muscarinic antagonist), propranolol and SR(59230A). While phentolamine had no effect on BRL(37344), atropine completely abolished the influence of BRL(37344) on f(H), Sv and cardiac output (Q). In larval trout, BRL(37344) (10 and 100 µM) induced a significant concentration-dependent increase in f(H) while SR(59230A) (1 and 10 µM) and propranolol (1 and 10 µM) separately caused a significant concentration-dependent decrease. These data suggest that ß(3)-ARs have an important role in regulation of cardiovascular function, and provide evidence for a potential interaction between muscarinic and adrenergic receptors in rainbow trout.

Cross Tolerance to Environmental Stressors: Effects of Hypoxic Acclimation on Cardiovascular Responses of Channel Catfish (Ictalurus punctatus) to a Thermal Challenge.

Hypoxia and temperature are two major, interactive environmental variables that affect cardiovascular function in fishes. The purpose of this study was to determine if acclimation to hypoxia increases thermal tolerance by measuring cardiovascular responses to increasing temperature in two groups of channel catfish. The hypoxic group was acclimatized to moderate hypoxia (50% air saturation, a P(O2) of approximately 75 torr) at a temperature of 22° C for seven days. The normoxic (i.e. control) group was maintained the same, but under normoxic conditions (a P(O2) of approximately 150 torr). After acclimation, fish were decerebrated, fitted with dorsal aorta cannulae, and then exposed to increasing temperature while cardiovascular variables were recorded. The end point (critical thermal maximum, CTMax) was defined as a temperature at which heart rate and blood pressure sharply decreased indicating cardiovascular collapse. Fish acclimatized to moderate hypoxia had higher resting heart rate than controls. Hypoxic acclimatized fish had a significantly higher CTMax. Acclimation to hypoxia increases the cardiovascular ability of channel catfish to withstand an acute temperature increase.

Epidemiology and effect on production parameters of an outbreak of inclusion body hepatitis in broilers.

In 2007, an inclusion body hepatitis (IBH) outbreak affected several broiler farms in Mississippi. Results of logistic regression analyses showed significant associations between IBH occurrence and high enzyme-linked immunosorbent assay geometric mean titers for infectious bursal disease virus. However, there was no association between IBH occurrence and chicken infectious anemia virus status. Results of linear regression model analyses showed significant associations between IBH occurrence with average weight and with cost deviation. Broiler meat production cost was $0.0058/kg more expensive to produce when IBH occurred. Although feed conversion was higher with IBH occurrence, the association was not significant. IBH onset in the first farms affected occurred between 19 and 30 days of age, whereas in the last farms affected, IBH onset occurred as early as 10 days.

Sensory innervation of the Gills: O2-sensitive chemoreceptors and mechanoreceptors.

Physical characteristics of water (O(2) solubility and capacitance) dictate that cardiovascular and ventilatory performance be controlled primarily by the need for oxygen uptake rather than carbon dioxide excretion, making O(2) receptors more important in fish than in terrestrial vertebrates. An understanding of the anatomy and physiology of mechanoreception and O(2) chemoreception in fishes is important, because water breathing is the primitive template upon which the forces of evolution have modified into the various cardioventilatory modalities we see in extant terrestrial species. Key to these changes are the O(2)-sensitive chemoreceptors and mechanoreceptors, their mechanisms and central pathways.

Peripheral arterial chemoreceptors and the evolution of the carotid body.

There has been a reduction in the distribution of peripheral respiratory O(2) chemoreceptors from multiple, dispersed sites in fish and amphibia to a single dominant receptor site in birds and mammals. In the process, the cells in the fish gill associated with O(2) chemosensing (5-HT containing neuroepithelial cells often found in association with ACh/catecholamine (CA) containing cells) are replaced by the glomus cells of the mammalian carotid body (which contain multiple putative neurotransmitter substances, including 5-HT, CA and ACh, all within the same cells), although this difference may be more superficial than first appears. While still highly speculative, these trends would appear to be correlated with the transition from aquatic respiration and bimodal breathing, and from animals with intra-cardiac shunts (two situations where the ability to sense O(2) at multiple sites would be an advantage), to strictly air breathing in animals with no intra-cardiac shunts. It is also tempting to speculate that while the basic O(2)-sensing mechanism is the same for all receptor cells, the receptor groups in fish have evolved in such a way to make the responses of some more sensitive to changes in O(2) delivery than others. The net result is that those receptors associated with the first gill arch of fish (the third branchial arch) become the carotid body in higher vertebrates associated with the regulation of ventilation and ensuring oxygen supply to the gas exchange surface. Those receptors associated with the second gill arch (fourth branchial arch) become the aortic bodies capable of sensing changes in oxygen content of the blood and primarily involved in regulating oxygen transport capacity through erythropoiesis and changes in blood volume.

Respiratory chemoreceptor function in vertebrates comparative and evolutionary aspects.

The sensing of blood gas tensions and/or pH is an evolutionarily conserved, homeostatic mechanism, observable in almost all species studied from invertebrates to man. In vertebrates, a shift from the peripheral O(2)-oriented sensing in fish, to the central CO(2)/pH sensing in most tetrapods reflects the specific behavioral requirements of these two groups whereby, in teleost fish, a highly O(2)-oriented control of breathing matches the ever-changing and low oxygen levels in water, whilst the transition to air-breathing increased the importance of acid-base regulation and O(2)-related drive, although retained, became relatively less important. The South American lungfish and tetrapods are probably sister groups, a conclusion backed up by many similar features of respiratory control. For example, the relative roles of peripheral and central chemoreceptors are present both in the lungfish and in land vertebrates. In both groups, the central CO(2)/pH receptors dominate the ventilatory response to hypercarbia (60-80%), while the peripheral CO(2)/pH receptors account for 20-30%. Some basic components of respiratory control have changed little during evolution. This review presents studies that reflect the current trends in the field of chemoreceptor function, and several laboratories are involved. An exhaustive review on the previous literature, however, is beyond the intended scope of the article. Rather, we present examples of current trends in respiratory function in vertebrates, ranging from fish to humans, and focus on both O(2) sensing and CO(2) sensing. As well, we consider the impact of chronic levels of hypoxia-a physiological condition in fish and in land vertebrates resident at high elevations or suffering from one of the many cardiorespiratory disease states that predispose an animal to impaired ventilation or cardiac output. This provides a basis for a comparative physiology that is informative about the evolution of respiratory functions in vertebrates and about human disease. Currently, most detail is known for mammals, for which molecular biology and respiratory physiology have combined in the discovery of the mechanisms underlying the responses of respiratory chemoreceptors. Our review includes new data on nonmammalian vertebrates, which stresses that some chemoreceptor sites are of ancient origin.

Isolation and characterization of putative O2 chemoreceptor cells from the gills of channel catfish (Ictalurus punctatus).

Little is known about the cells or mechanisms of O2 chemoreception in vertebrates other than mammals. The purpose of this study, therefore, was to identify O2-sensitive chemoreceptors in a fish. Putative O2-sensitive chemoreceptors were dissociated from the gills of channel catfish, Ictalurus punctatus, and cultured. A population of cells was identified with morphology and a histochemical profile similar to mammalian carotid body Type I (glomus) cells and pulmonary neuroepithelial cells. These cells stain with neutral red and appear to be the branchial neuroepithelial cells. Immunocytochemical staining showed that these cells contain neuron-specific enolase (NSE), tyrosine hydroxylase (TH) and 5-hydroxytryptamine (5HT). Patch-clamp experiments showed that these cells have a O2-sensitive, voltage-dependent outward K+ current like mammalian O2 sensors. Two kinds of electrophysiological responses to hypoxia (P(O2) < 10 Torr) were observed. Some cells showed inhibition of outward current in response to hypoxia, whereas other cells showed potentiation. Neurochemical content and electrophysiological responses to hypoxia indicate that these cells are piscine O2-sensitive chemoreceptors.

An evaluation of cobalt chloride as an O2-sensitive chemoreceptor stimulant in channel catfish.

The effects of cobalt chloride on heart rate, blood pressure, ventilatory frequency and opercular pressure amplitude in channel catfish, Ictalurus punctatus were measured to evaluate the potential of cobalt as a histochemical probe to study mechanisms of oxygen chemoreception, as well as assess the general effects of cobalt on the cardioventilatory physiology of fishes. Cobalt, like cyanide, has been previously used to stimulate oxygen chemoreceptors and hypoxic reflexes in mammals but there is little information on the cardioventilatory effects of cobalt on fish. Catfish were exposed to increasing concentrations (1-20 mg/kg) of cobalt in the water (external) or injections into the dorsal aorta (internal) and the cardioventilatory effects recorded. Mean arterial pressure showed a significant, dose-dependent increase in response to cobalt injections. Heart rate increased slowly, but significantly after cobalt injections but the magnitude of change was not dose-dependent. There was a small increase in ventilatory rate but no effect on amplitude. External cobalt had similar effects but the responses were weaker. Although cobalt stimulated some cardioventilatory reflexes the pattern and magnitude of the responses were noticeably different from those of cyanide and hypoxia. The results suggest that the cardioventilatory reflexes stimulated by cobalt were not mediated by O(2)-sensitive chemoreceptors and that cobalt is not an effective O(2) receptor stimulant in fishes.

Cardioventilatory effects of acclimatization to aquatic hypoxia in channel catfish.

The mechanisms responsible for altering cardioventilatory control in vertebrates in response to chronic hypoxia are not well understood but appear to be mediated through the oxygen-sensitive chemoreceptor pathway. Little is known about the effects of chronic hypoxia on cardioventilatory control in vertebrates other than mammals. The purpose of this study was to determine how cardioventilatory control and the pattern of response is altered in channel catfish (Ictalurus punctatus) by 1 week of moderate hypoxia. Fish were acclimatized for 7 days in either normoxia (P(O(2)) approximately 150 Torr) or hypoxia (P(O(2)) approximately 75 Torr). After acclimatization, cardioventilatory, blood-gas and acid/base variables were measured during normoxia (P(O(2)) 148+/-1 Torr) then at two levels of acute (5 min) hypoxia, (P(O(2)) 72.6+/-1 and 50.4+/-0.4 Torr). Ventilation was significantly greater in hypoxic acclimatized fish as was the ventilatory sensitivity to hypoxia (Delta ventilation/Delta P(O(2))). The increase in ventilation and hypoxic sensitivity was due to increases in opercular pressure amplitude, gill ventilation frequency did not change. Heart rate was greater in hypoxic acclimatized fish but decreased in both acclimatization groups in response to acute hypoxia. Heart rate sensitivity to hypoxia (Delta heart rate/Delta P(O(2))) was not affected by hypoxic acclimatization. The ventilatory effects of hypoxic acclimatization can be explained by increased sensitivity to oxygen but the effects on heart rate cannot.