JOHN MAINA - Academia.edu (original) (raw)

Papers by JOHN MAINA

BackgroundThe Nairobi dairy food system is highly complex and involves informal and formal dairy ... more BackgroundThe Nairobi dairy food system is highly complex and involves informal and formal dairy production and marketing channels. The sector comprises numerous small-scale interlinked actors characterized by diverse food handling practices that may affect product safety. This cross-sectional study sought to analyze the diversity of Escherichia coli, which contaminates cow milk, in material obtained from the supply chain serving Nairobi's rapidly urbanizing city in Kenya. The GTG5 fingerprinting method was used to determine the diversity of 107 E. coli isolates obtained from milk. Dendrograms were used to display E. coli genetic diversity patterns within and between farms from different types of samples. These included raw, pasteurized, processed fermented, and home-made fermented milk sourced from various nodes, including farms, milk bars, milk vending machines, roadside milk vendors and shops. ResultsAnalysis of the first dendrogram with 46 E. coli isolates recovered from var...

Acta Zoologica, 2018

Available studies that have examined O 2 sensing in fish have indicated that oxygensensitive neur... more Available studies that have examined O 2 sensing in fish have indicated that oxygensensitive neuroepithelial cells (NECs) are O 2 sensors in the gills and initiate cardiorespiratory reflexes in aquatic vertebrates. This is the first study describing the occurrence of NECs in accessory respiratory organs in the air-breathing catfish Clarias gariepinus. Immunocytochemical stainings with specific neuronal markers such as nNOS, VAchT, 5-HT and TH have been shown to be very useful for location and distribution of these cells in the gill fans and suprabranchial chamber that take origin from the transformation of the gill tissue. But the response of these putative O 2 chemoreceptors, their role in the respiratory reflexes and their innervation await investigation. K E Y W O R D S accessory respiratory organ, Clarias gariepinus, neuroepithelial cells, neurotransmitter substances, nitric oxide How to cite this article: Zaccone G, Maina J, Germanà A, et al. First demonstration of the neuroepithelial cells and their chemical code in the accessory respiratory organ and the gill of the sharptooth catfish, Clarias gariepinus: A preliminary study.

Journal of clinical medicine, Jan 26, 2018

Children with autism spectrum disorder (ASD) are at risk for obesity, commonly have sleep disorde... more Children with autism spectrum disorder (ASD) are at risk for obesity, commonly have sleep disorders, and exhibit stereotypic behaviors that disrupt their learning. Vigorous levels of exercise have been shown to ameliorate these issues in children with ASD, but little research exists to provide techniques for motivating children with ASD to engage in exercise. The present study examined the effect of music on exercise intensity in a group of 13 elementary school students with ASD. Data were collected across six days during structured (e.g., verbal and physical prompts) and unstructured (e.g., minimal prompting) exercise periods. During these exercise periods, three music conditions were randomized: no music, slow-tempo music, and fast-tempo music. Exercise intensity, measured in Metabolic Equivalent of Tasks by triaxial accelerometers, was greatest during the structured exercise periods and during the slow music condition. Student characteristics moderated the impact of music conditi...

African Zoology, 2017

Studies on metal pollution (cadmium, cobalt, chromium, copper, manganese and nickel) in South Afr... more Studies on metal pollution (cadmium, cobalt, chromium, copper, manganese and nickel) in South African terrestrial environments are severely lacking. Due to being relatively unaffected by industrialisation, the Thohoyandou region may provide data on natural levels of metals for use as baseline data. The House Sparrow (Passer domesticus) was chosen as a bio-indicator of metal pollution due to its abundance, non-migratory lifestyle and close association with humans. The aims were to determine the viability of using feathers as a non-lethal bio-indicator tissue compared with muscle. Plume feathers, flight feathers and muscle tissue were analysed using ICP-OES techniques. Analyses of tissue metal concentrations identified the following trend: plume feather > flight feather > muscle tissue. Within the Thohoyandou region, Magondi, which was affected by anthropogenic activities at the time of sampling, had significantly higher concentrations (p ≤ 0.05) for each of the metals, indicating potential metal contamination from various sources. Alternatively, Makonde had the lowest metal concentrations and may be an important reference site for future comparative studies. The results showed that the House Sparrow can be used as a bio-indicator organism in South African terrestrial environments. The plume feathers indicate that they are a good non-lethal tissue for determining metal pollution levels on a temporal scale, indicating recent metal exposure.

Biology open, Jan 28, 2016

Insect larvae are reported to be a major component of the simple but highly productive trophic we... more Insect larvae are reported to be a major component of the simple but highly productive trophic web found in Lake Magadi (Kenya, Africa), which is considered to be one of the most extreme aquatic environments on Earth. Previous studies show that fish must display biochemical and physiological adjustments to thrive under the extreme conditions of the lake. However, information for invertebrates is lacking. In the present study, the occurrence of the larval chironomid Tanytarsus minutipalpus is reported in Lake Magadi for the first time. Additionally, changes in larval metabolism and antioxidant defense correlated with diel variations in the extremely hostile environmental conditions of the lake are described. Wide variations in water temperature (20.2-29.3(o)C) and dissolved oxygen content (3.2-18.6 mg O2 L(-1)) were observed at different times of day, without significant change in water pH (10.0±0.03). Temperature and dissolved oxygen were higher at 1:00 pm (29.3±0.4(o)C and 18.6±1.0...

4th Annual International Conference on Advances in Veterinary Science Research (VETSCI 2016), 2016

Scientific reports, Jun 3, 2016

The Magadi tilapia, Alcolapia grahami, a small cichlid fish of Lake Magadi, Kenya lives in one of... more The Magadi tilapia, Alcolapia grahami, a small cichlid fish of Lake Magadi, Kenya lives in one of the most challenging aquatic environments on earth, characterized by very high alkalinity, unusual water chemistry, and extreme O2, ROS, and temperature regimes. In contrast to most fishes which live at temperatures substantially lower than the 36-40 °C of mammals and birds, an isolated population (South West Hot Springs, SWHS) of Magadi tilapia thrives in fast-flowing hotsprings with daytime highs of 43 °C and night-time lows of 32 °C. Another population (Fish Springs Lagoon, FSL) lives in a lagoon with fairly stable daily temperatures (33-36 °C). The upper critical temperatures (Ctmax) of both populations are very high; moreover the SWHS tilapia exhibit the highest Ctmax (45.6 °C) ever recorded for a fish. Routine rates of O2 consumption (MO2) measured on site, together with MO2 and swimming performance at 25, 32, and 39 °C in the laboratory, showed that the SWHS tilapia exhibited the...

Anatomical record (Hoboken, N.J. : 2007), Jan 9, 2015

The blood capillaries (BC) and the air capillaries (ACs) are the terminal gas exchange units of t... more The blood capillaries (BC) and the air capillaries (ACs) are the terminal gas exchange units of the avian lung. The minuscule structures are astonishingly strong. It is only recently that the morphologies and the biomechanical properties of the BCs and the ACs were investigated. Regarding size and shape, the BCs and the ACs differ remarkably. While they were previously claimed to be tubular (cylindrical) in shape, the ACs are rather rotund structures which interconnect across short, narrow passageways. Atypical of those in other tissues, the BCs in the exchange tissue of the avian lung comprise of distinct segments which are about as long as they are wide and which are coupled in three-dimensions. The thin blood-gas barrier (BGB) which separates the ACs from the BCs is peculiarly strong. The causes of the strengths of the ACs and the BCs in general and the BGB in particular are varied and controversial. Here, the recent morphological and physiological findings on the structure, biom...

International Journal of Salt Lake Research, 1996

A morphometric analysis of the gills of Oreochromis alcalicus grahami has been carried out on spe... more A morphometric analysis of the gills of Oreochromis alcalicus grahami has been carried out on specimens from ecologically distinct lagoons and a water-holding tank of Lake Magadi, a highly alkaline salt lake situated in a volcanically active region of the southern part of the Great Rift Valley in Kenya. The data were compared with those from Oreochromis niloticus, a close relative that lives in fresh water and with data from other fresh water and marine fish. Our primary goal was to identify the possible adaptive features which enable the fish to survive in an environment characterized by severely fluctuating levels of oxygen, a condition exacerbated by factors such as high temperature, alkalinity and osmolarity. The specimens of O. a. grahami from the southwestern lagoons of the lake had gills better adapted for gas exchange with a body mass specific diffusing capacity for oxygen which was about 2 times greater than that of the gills of the specimens from the fish spring lagoons and 2.5 times that of those from the water-holding tanks. Some parameters of the gills of O. a. grahami, e.g. the gill filament length and number of gill filaments are significantly greater than those of O. niloticus but the number of secondary lameUae, area of secondary lamellae and the diffusing capacity of the gills are similar in the two species. Compared with most other fish, the gills of O. a. grahami appear to be particularly well adapted for gas exchange especially by having a thin water-blood barrier. Perhaps in no other extant fish have the gills had to be so exquisitely designed to meet environmental extremes and regulate complex and at times conflicting functions such as gas exchange, iono-regulation, acid-base balance and nitrogenous waste excretion as in 0. a. grahami

Biomedical engineering and computational biology, 2013

Complete blood-gas barrier breaks (BGBBs) and epithelial-epithelial cells connections breaks (E-E... more Complete blood-gas barrier breaks (BGBBs) and epithelial-epithelial cells connections breaks (E-ECCBs) were enumerated in the lungs of free range chickens, Gallus gallus variant domesticus after vascular perfusion at different pressures. The E-ECCBs surpassed the BGBBs by a factor of ~2. This showed that the former parts of the gas exchange tissue were structurally weaker or more vulnerable to failure than the latter. The differences in the numbers of BGBBs and E-ECCBs in the different regions of the lung supplied with blood by the 4 main branches of the pulmonary artery (PA) corresponded with the diameters of the blood vessels, the angles at which they bifurcated from the PA, and the positions along the PA where they branched off. Most of the BGBBs and the E-ECCBs occurred in the regions supplied by the accessory- and the caudomedial branches: the former is the narrowest branch and the first blood vessel to separate from the PA while the latter is the most direct extension of the P...

Biology open, Jan 15, 2013

Structural failure of blood-gas barrier (BGB) and epithelial-epithelial cell connections (EECCs) ... more Structural failure of blood-gas barrier (BGB) and epithelial-epithelial cell connections (EECCs) in different vascular regions of the exchange tissue of the lung was studied in rested and exercised chickens. The number of red blood cells (nRBCs) was counted and protein concentration (PC) measured after lavaging the respiratory system, and blood was sampled to determine the blood lactate levels (BLLs). The numbers of complete BGB breaks (nBGBBs) and those of the EECCs (nEECCBs) were counted in the different vascular territories of the lung. The nRBCs and the PCs increased with increasing exercise intensities but the rate of increase decreased at higher workloads. From rest to the fastest experimental treadmill speed of 2.95 m.sec(-1), BLLs increased 4-fold. In all cases, the nEECCBs exceeded those of the BGB, showing that structurally the BGB is relatively weaker than the EECC. The increase in the number of breaks with increasing exercise can be attributed to increase in the pulmonar...

Very high pressures are required to cause stress failure of pulmonary capillaries in Thoroughbred... more Very high pressures are required to cause stress failure of pulmonary capillaries in Thoroughbred racehorses.

Zoomorphology, 1992

The lungs of two fossorial rodents, the mole rat Tachyoryctes splendens and the naked mole rat He... more The lungs of two fossorial rodents, the mole rat Tachyoryctes splendens and the naked mole rat Heterocephalus glaber were investigated by transmission and scanning electron microscopy and a comparative morphometric analysis of the lungs carried out in an attempt to find out whether there are any possible structural adaptational features which may be associated with fossoriality. The data from these two ecologically disparate fossorial rodents were compared with those of surface dwelling rodents on which equivalent data are available. Morphologically, the lung of T. splendens is essentially similar to that of terrestrial mammals while that of H. gIaber shows features of underdevelopment. In H. glaber, a cuboidal epithelium extends down the respiratory tree to line what appear to be alveolar spaces, the blood capillaries constitute a double capillary system and the type I pneumocytes have microvilli on their free surface. Morphometrically, H. glaber has notably lower values indicative of rather unspecialized lungs. While the volume density of the parenchyma is 88 % in T. splendens, that in H. glaber is only 76%. The blood-gas (tissue) barrier in H. glaber is notably thicker than in T. splendens. When normalized with body weight, the surface area of the blood-gas (tissue) barrier, the pulmonary capillary blood volume, the diffusing capacities of the tissue barrier and of the whole lung are consistently appreciably lower in H. glaber. When compared with Mus musculus, Rattus rattus and Cavia porcellus, T. splendens has somewhat comparable values with the surface dwelling rodents but the values of H. glaber are the lowest in the group. It is suggested that T. splendens has not undergone full adaptation to fossoriality as is supported by its behavioural activities, particularly those of occasionally surfacing to feed and making overland excursions. The low values of H. glaber may be commensurate with its extreme physiological adaptations for fossoriality, features which culminate in low basal metabolism and may in part explain paedomorphic traits of its respiratory system.

Transportation Research Record: Journal of the Transportation Research Board, 1999

The causes of premature failures in asphalt surfacings in Kenya have been identified. Two heavily... more The causes of premature failures in asphalt surfacings in Kenya have been identified. Two heavily trafficked sites had suffered top-down cracking, associated with severe hardening of the asphalt in the surface of the wearing course, whereas others had deformed plastically. Tests confirmed that reduction of voids in the mix (VIM) to less than 3 percent resulted in a high risk of plastic deformation under heavy traffic. Difficulties arise in designing asphalt mixes for heavily trafficked roads in countries where laboratory equipment is limited. These difficulties include selection of appropriate levels of compaction in the Marshall test and predicting the combined effect of asphalt hardening and secondary compaction. Use of a refusal density test is recommended to determine a reference density to ensure that 3 percent VIM will be retained. The importance of preconstruction field trials to establish the workability of such a mix is emphasized. Acceptable results were most easily obtain...

Physiological Reviews, 2005

In gas exchangers, the tissue barrier, the partition that separates the respiratory media (water/... more In gas exchangers, the tissue barrier, the partition that separates the respiratory media (water/air and hemolymph/blood), is exceptional for its remarkable thinness, striking strength, and vast surface area. These properties formed to meet conflicting roles: thinness was essential for efficient flux of oxygen by passive diffusion, and strength was crucial for maintaining structural integrity. What we have designated as “three-ply” or “laminated tripartite” architecture of the barrier appeared very early in the evolution of the vertebrate gas exchanger. The design is conspicuous in the water-blood barrier of the fish gills through the lungs of air-breathing vertebrates, where the plan first appeared in lungfishes (Dipnoi) some 400 million years ago. The similarity of the structural design of the barrier in respiratory organs of animals that remarkably differ phylogenetically, behaviorally, and ecologically shows that the construction has been highly conserved both vertically and hor...

Journal of Microscopy, 2008

We have previously reconstructed the gas exchange tissue of the adult muscovy duck, Cairina mosch... more We have previously reconstructed the gas exchange tissue of the adult muscovy duck, Cairina moschata using a method of manually aligning sections and tracing the contours of the components of the gas exchange tissue. This reconstruction method demonstrated that the air capillaries are comprised of an expanded globular part interconnected by narrow air channels. The blood capillaries completely surround the air capillaries forming an anastomosing meshwork of short segments. However, the resulting reconstruction was limited in scope because of the laborious process of tracing the profiles of each component through the sequence of micrographs. We have now reconstructed a larger proportion of the exchange tissue by using a cross-correlation based alignment strategy and have demonstrated that the staining intensity of each of the exchange tissue components is sufficiently different to allow them to be identified by simple filtering and thresholding. The resulting reconstructions sample a much larger proportion of the exchange tissue and demonstrate the heterogeneity of structures from different locations in the parabronchus. We have shown that a sheet-flow-type arrangement of blood capillaries surrounds the infundibulum; this represents an unexpected functional convergence with the arrangement of blood capillaries surrounding the mammalian alveoli. It is feasible, using this reconstruction strategy, to analyse the exchange tissue of a large number of avian species in order to determine structural correlates of function. The resulting reconstructions could be analysed in order to determine the basis of the functional efficiency and rigidity of the avian lung.

Journal of Fish Biology, 2000

The control region of the mitochondrial DNA haplotype frequencies were significantly different am... more The control region of the mitochondrial DNA haplotype frequencies were significantly different among the two separate lagoon populations of Oreochromis alcalicus grahami in Lake Magadi and of O. a. alcalicus from lake Natron, and DNA fingerprint similarity indices were significantly higher for intra-population comparisons of the two Magadi lagoon populations and the Lake Natron population than the inter-population similarity indices among these populations. A modified F st measure indicated population subdivision and the phylogeographic partitioning of the VNTR fragments observed were unique to specific populations further indicating substantial genetic differentiation. The lagoon populations within Lake Magadi demonstrated the same degree of genetic differentiation as either of these populations did to the outgroup (the Lake Natron population). There appears to be limited gene flow between Lake Magadi tilapia populations and this population structure has important implications for protecting locally adapted populations within this unique ecosystem.

Journal of Comparative Physiology B, 2011

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. Th... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author's version for posting to your own website or your institution's repository. You may further deposit the accepted author's version on a funder's repository at a funder's request, provided it is not made publicly available until 12 months after publication.

Journal of Anatomy, 2008

In mammals, surface macrophages (SMs) play a foremost role in protecting the respiratory system b... more In mammals, surface macrophages (SMs) play a foremost role in protecting the respiratory system by engulfing and destroying inhaled pathogens and harmful particulates. However, in birds, the direct defense role(s) that SMs perform remains ambiguous. Paucity and even lack of SMs have been reported in the avian respiratory system. It has been speculated that the pulmonary defenses in birds are inadequate and that birds are exceptionally susceptible to pulmonary diseases. In an endeavour to resolve the existing controversy, the phagocytic capacities of the respiratory SMs of the domestic fowl and the rat were compared under similar experimental conditions by exposure to polystyrene particles. In cells of equivalent diameters (8.5 μ m in the chicken and 9.0 μ m in the rat) and hence volumes, with the volume density of the engulfed polystyrene particles, i.e. the volume of the particles per unit volume of the cell (SM) of 23% in the chicken and 5% in the rat cells, the avian cells engulfed substantially more particles. Furthermore, the avian SMs phagocytized the particles more efficiently, i.e. at a faster rate. The chicken erythrocytes and the epithelial cells of the airways showed noteworthy phagocytic activity. In contrast to the rat cells that did not, 22% of the chicken erythrocytes phagocytized one to six particles. In birds, the phagocytic efficiencies of the SMs, erythrocytes, and epithelial cells may consolidate pulmonary defense. The assorted cellular defenses may explain how and why scarcity of SMs may not directly lead to a weak pulmonary defense. The perceived susceptibility of birds to respiratory diseases may stem from the human interventions that have included extreme genetic manipulation and intensive management for maximum productivity. The stress involved and the structural-functional disequilibria that have occurred from a 'directed evolutionary process', rather than weak immunological and cellular immunity, may explain the alleged vulnerability of the avian gas exchanger to diseases.

Canadian Journal of Zoology, 1995

The morphology and morphometry of the gills of Oreochromis alcalicus grahami, a unique ureogenic ... more The morphology and morphometry of the gills of Oreochromis alcalicus grahami, a unique ureogenic teleost that lives in the alkaline environment of Lake Magadi, Kenya (pH 10, [Formula: see text], temperature 30 – 40 °C) were examined by transmission electron, scanning electron and light microscopy. Fish were examined in normal Lake Magadi water and 2 – 3 or 24 h after transfer to Lake Magadi water neutralized to pH 7 with HCl (i.e., [Formula: see text] replaced with Cl−), a treatment that caused severe reductions in urea excretion and O2uptake, internal acidosis, and ionoregulatory disturbance. In Lake Magadi water, the organization of the filament epithelium of the gill was similar to that of sea water teleosts. Indeed, chloride cells were located at the bottom of pits bordered by overlying pavement cells and flanked by typical accessory cells. Total numbers of chloride cells remained unchanged after transfer to pH 7, but after 2 – 3 h, many were covered by pavement cells, restricti...