Elizabeth D. Kokwaro

Prevalence of enlarged salivary glands in wild populations of Glossina pallidipes in Kenya, with a note on the ultrastructure of the affected organ.

Abstract Enlarged salivary gland was found to be widespread among wild populations of Glossina pallidipes in Kenya. The incidence of this abnormality varied from 0.9% in Meru National Park in Central Kenya to 5.4% in the Shimba hills area on the Kenya coast. Ultrastructurally, the enlarged glands were multinucleated with lumen reduced substantially in size. A large number of viruses filled both the lumen and the broken pieces of epithelial cytoplasm. In some cases Trypanosoma brucei trypanosomes were seen in the lumen of the enlarged glands. The epithelial cytoplasm was heavily vacuolated. Comment is made on the suitability of the diseased flies as transmitters of T. brucei .

Ultrastructural changes in salivary glands of tsetse, Glossina morsitans morsitans, infected with virus and rickettsia-like organisms.

Electron microscope observations on enlarged hypertrophied salivary glands dissected from adult laboratory-reared male Glossina morsitans morsitans show a concurrent infection of the salivary gland tissue with rod-shaped virus particles and intracellular rickettsia-like organisms. The latter are found intracellular in the epithelium and in the gland lumen enclosed within lytic zones. The virus particles are found within the degenerating cytoplasm, nuclei, and lumen of the cell where they are especially numerous. Stratified epithelium and gland enlargement are a prominent feature of the infection. These observations suggest that biological associations between salivary gland tissue and diverse microbes may be more common than formerly recognized. The microbes appear to cause damage to salivary gland cells, causing hyperplasia which assumes pathologic proportions.

Isolation of Trypanosoma brucei from the monitor lizard (Varanus niloticus) in an endemic focus of Rhodesian sleeping sickness in Kenya.

Monitor lizards were sampled along the shores of Lake Victoria to detect natural infections of potentially human-infective trypanosomes. In an area with endemic rhodesian sleeping sickness, one of 19 lizards was infected (Busia, Kenya). Six of ten lizards also showed indirect evidence of infection with Trypanosoma brucei (antibody ELISA). In an area with no recent history of human disease (Rusinga Island), no parasites were found and no antibodies to T. brucei were detected. The isolate was identified as T. brucei through xenodiagnosis (completion of the life cycle in the salivary glands of tsetse), and through molecular techniques (positive reactions with a PCR primer and a microsatellite DNA probe characteristic of the subgenus Trypanozoon). Experimental infections of monitor lizards were also attempted with a variety of parasites and tsetse species. It was possible to infect monitor lizards with T. brucei but not with forest or savannah genotypes of Trypanosoma congolense. Parasites reached low levels of parasitaemia for a short period without generating any pathology; they also remained infective to tsetse and laboratory rats. The implications of these findings are discussed in relation to the endemicity of sleeping sickness.

Monitoring Malaria Vector Control Interventions: Effectiveness of Five Different Adult Mosquito Sampling Methods

ABSTRACT Long-term success of ongoing malaria control efforts based on mosquito bed nets (long-lasting insecticidal net) and indoor residual spraying is dependent on continuous monitoring of mosquito vectors, and thus on effective mosquito sampling tools. The objective of our study was to identify the most efficient mosquito sampling tool(s) for routine vector surveillance for malaria and lymphatic filariasis transmission in coastal Kenya. We evaluated relative efficacy of five collection methods—light traps associated with a person sleeping under a net, pyrethrum spray catches, Prokopack aspirator, clay pots, and urine-baited traps—in four villages representing three ecological settings along the south coast of Kenya. Of the five methods, light traps were the most efficient for collecting female Anopheles gambiae s.l. (Giles) (Diptera: Culicidae) and Anopheles funestus (Giles) (Diptera: Culicidae) mosquitoes, whereas the Prokopack aspirator was most efficient in collecting Culex quinquefasciatus (Say) (Diptera: Culicidae) and other culicines. With the low vector densities here, and across much of sub-Saharan Africa, wherever malaria interventions, long-lasting insecticidal nets, and/or indoor residual spraying are in place, the use of a single mosquito collection method will not be sufficient to achieve a representative sample of mosquito population structure. Light traps will remain a relevant tool for host-seeking mosquitoes, especially in the absence of human landing catches. For a fair representation of the indoor mosquito population, light traps will have to be supplemented with aspirator use, which has potential for routine monitoring of indoor resting mosquitoes, and can substitute the more labor-intensive and intrusive pyrethrum spray catches. There are still no sufficiently efficient mosquito collection methods for sampling outdoor mosquitoes, particularly those that are bloodfed.

Comparative studies on the infectivity of Theileria parva in ticks fed in vitro and those fed on cattle

Nymphs of the brown ear tick, Rhipicephalus appendiculatus, were fed on heparinised bovine blood infected with Theileria parva parasites in an in vitro feeding system consisting of rabbit skin membranes. The main feeding and development parameters such as the mean attachment rate, feeding duration and engorgement weights of membrane-fed ticks were not significantly different from nymphs fed on cattle. The moulting rate was also comparable although a slight significant difference was observed. Assessment of infection prevalence and abundance with T. parva in adults indicated that the membrane-fed ticks acquired infection to the same level as those fed on cattle. Stabilates prepared from both the membrane- and cattle-fed adult ticks were found to be infective and caused severe reactions in susceptible cattle. When the immunised cattle were challenged with a lethal homologous dose of T. parva (Marikebuni), they were found to be immune.

Morphological variation and incidence of cuticular lesions in the tsetse Glossina pallidipes Austen, G. brevipalpis Newstead and G. austeni Newstead (Diptera:Glossinidae) on the Kenyan coast

The incidence of cuticular lesions on the ventral abdominal integument of the tsetse Glossina pallidipes, G. brevipalpis and G. austeni was monitored by trapping over 12 months in four localities along the Kenyan coast. Four types of lesions were observed: necrotic pits, necrotic warts, necrotic striations and necrotic discs. Necrotic discs were most prevalent, and up to 30.5% of female tsetse had this type of lesion. The differences in cuticular lesion levels on flies trapped in the dry and wet seasons were not significant. There were no significant differences in the proportions of tsetse with lesions sampled at different sites. Females had a significantly higher proportion of necrotic pits, necrotic warts and necrotic striations than males but the level of necrotic discs on males and females were the same. Histological examination of tissues did not demonstrate any causal association between lesions and infectious microorganisms. There was no correlation between the presence of cuticular lesions and hypertrophy of the salivary glands, a pathology associated with virus-like particles in G. pallidipes.

Salivary glands of the tsetse Glossina pallidipes Austen infected with Trypanosoma brucei and virus particles: ultrastructural study

The effects of infection by Trypanosoma brucei and DNA virus on the ultrastructure of the salivary gland cells in Glossina pallidipes Austen were investigated. Cytoplasm of uninfected cells contains a dense ribosomal population and rough endoplasmic reticulum, scattered Golgi areas and mitochondria. In Infected cells of salivary glands the ultrastructural integrity of the cytoplasm is profoundly changed due to cellular proliferation giving rise to a stratified epithelium and gland enlargement; cell degeneration characterized by formation of cytoplasmic vacuoles, chromatin margination, disorganization and elimination of cell organelles and gland hypertrophy. The virus particles are found in the nucleoplasm as well as the cytoplasm of cells. The ultrastructural evidence indicates that the virus are largely assembled in nucleiof cells and virions pass through the nuclear membrane. The trypanosomes are found within the degenerating cytoplasm and lumen of the cell.The implications of the features observed in the infected cells are discussed, and possible suggestions are made regarding alteration of the metabolic functions due to infection.RésuméLes effets de l’infection due aux Trypanosoma brucei et au DNA-virus sur l’ultrastructure des cellules de glandes salivaires des Glossina pallidipes Austen furent analysée. Le cytoplasme des cellules non-infecté contient une population dense de ribosomes et un reticulum endoplasmique rugeux, des surfaces de Golgi et de mitochondries eparpilles. Chez les cellules infectées l’integral de l’ultrastructure du cytoplasme est profondement changée grâce à une prolifération cellulaire donnant naissance à un epithelium stratifié et à une hypertrophie de la glande; dégéneration cellulaire characterisée par la formation des vacoules cytoplasmiques, marginalisation de la chromatine, désorganisation et élimination de la substance cellulaire et hypertrophie de la glande. Les particules virales se trouvaient dans le nucleoplasme ainsi que dans le cytoplasme des cellules. L’évidence ultrastructurale indique que les virus sont asemblées dans le noyeau cellulaire et que le virion passe à travers la membrane nucleaire. Les trypanosomes ont été trouvé dans le cytoplasme en dégéneration. p ]Les implications de ces observations dans les cellules infectées ont été discuté et des suggestions ont été faites en ce que regarde l’alteratlons des fonction metaboliques due à l’infection.

A cold receptor on the tick, Rhipicephalus appendiculatus : Electrophysiological and ultrastructural observations

A sensillum trichodeum on tarsus I of Rhipicephalus appendiculatus displays a tonic impulse frequency at constant temperature but shows a phasic-tonic increased activity when temperature is lowered. Rising temperature has an inhibitory effect. Ultrastructural details show that it bears resemblance to a double-walled sensillum with spoke canals, and has dendrites of seven receptor cells. One of the cells responds to temperature changes. The function of the others is unknown.

Responses of Chilo partellus to material obtained from susceptible and resistant maize cultivars: Electrophysiology and behaviour

Electrophysiological tests were done on larval and adult stages of Chilo partellus. The first tarsomere on the forelegs of the moths has three pairs of sensilla; two of them have similar ultrastructural details and they are innervated by gustatory cells which respond equally well to maize leaf exudate but differ in their sensitivity to sucrose. Although the third pair has morphological features resembling those of contact chemoreceptor, it responds to mechanical stimulation only. Taste sensilla on the ovipositor are more sensitive to NaCl than sucrose and they respond to the unknown components in the maize leaf exudate. On the larval maxillae the lateral styloconica sensilla are very sensitive to sucrose and the aqueous extracts from susceptible and resistant maize cultivars; the medial styloconica sensilla are mainly sensitive to NaCl and the aqueous exudate from maize stems. Preliminary tests showed that treated maize piths can provide a suitable medium for the bioassay of larval feeding behaviour.RésuméDes tests électrophysiologiques ont été faits sur le Chilo partellus au stade larvaire et adulte. Le premier tarsomère sur les avant pattes des insectes a trois pairs de sensilla; deux desquelles ont des détails structurels similaires et elles sont innervées par de cellules du goût qui réagissent aussi bien à l’exudat de la feuille de mais maïs diffèrent quant à leur sensibilité au sucrose. Quoique la troisième paire a des aspects morphologiques ayant une ressemblance avec ceux du chemorecepteur de contact, elle ne réagit qu’à la stimulation mécanique. Les sensilla gastotoires sur l’ovipositeur sont plus sensibles au NaCl qu’au sucrose et elles réagissent aux composés inconnus dans l’exudat de la feuille de maïs. Les sensilla stylonica latéraux sur les maxillae larvaires sont très sensibles au sucrose ainsi que aux extraits aqueux provenant des cultivars de maïs susceptibles et resistants; les sensilla styloconica mediales sont surtout sensibles au NaCl et l’exudat acqueux provenant des tiges de maïs. Des tests préliminaires ont montré que des plants de maïs traité peuvent constituer un milieu adéquat pour l’essai biologique sur le comportement alimentaire larvaire.

Tibial campaniform sensilla of Glossina morsitans

Abstract On the basis of behavioural tests and light microscopy, a pair of dome shaped sensilla occuring on the outer and inner surfaces of Glossina morsitans morsitans tibiae were considered to be sex pheromone receptors. Recent observations using electrophysiological tests and ultrastructural methods have revealed that those receptors have no olfactory function; they are ampaniform sensilla sensitive to mechanical stimulation.