Factors affecting the population dynamics of Theileria parva in rhipicephalid ticks

A series of experiments were carried out to investigate some of the poorly understood aspects of the life cycle of Theilefid parva in its rhipicephalid tick vectors. The first series of experiments established that nymphae infected as larvae develop lower levels of infection compared to adults infected as nymphae, while female ticks develop higher infections than males. It was shown that the period of development of sporoblasts into mature sporozoites took on average four days in the nyrnphal ticks compared to five days in the adult ticks. Infection levels developing in different tick instars or sexes appeared to be related to the number and position of type III salivary gland acini. The second series of experiments established that there were considerable differences in the vector competence of different stocks of Rhipicephalus appendiculatus and R. zambeziensis for the transmission of Muguga and Boleni stocks of Yheileria parva. Finally the study established that survival of infected R. appendiculatus and the T parva they harboured was longer under quasi-natural climatic conditions compared to all the laboratory conditions examined. Basically, infection levels in the ticks did not affect the duration of survival of the ticks, however, survival of the parasite appeared to be influenced by the intensity of infection in the tick as the parasites diminished more rapidly in ticks having high infections than in those having low infections. Nymphae and the parasites they harboured survived for shorter periods compared to the adult ticks and their infections. Data generated from these series of experiments will be used to develop quantitative models of T parva dynamics in the tick vectors. The relative importance of the factors influencing the levels of infection developing in the tick vector were analysed statistically by the logistic and Poisson regression. Factors found to play a significant role included tick instar or gender, tick stock, parasite stock, the ambient climatic conditions in which infected ticks survived and the day of tick repletion after infection of the bovine host. Individually, the bovine host or its piroplasm parasitaernia were found to be poor predictors of infection levels developing in the salivary glands of the tick vector. However, when piroplasm parasitaernia was included in a model lacking the days post-repletion variable, the bovine host factor became significant

Survival of Theileria parva in its nymphal tick vector Rhipicephalus appendiculatus under laboratory and quasi natural conditions

Groups of nymphal Rhipicephalus appendiculatus Muguga, having a mean of 1 or 9 Theileria parva Muguga-infected salivary gland acini per tick, were kept under quasi-natural conditions at an altitude of 1950 m or 20°C at a relative humidity of 85% in the laboratory and their survival and infection prevalence and abundance determined over time. Theileria parva infections for both categories of ticks survived in the nymphal ticks for 50 or 26 weeks post salivary gland infection under quasi-natural or laboratory conditions respectively. There was a distinct decline in infections in the more heavily infected nymphae under both conditions of exposure, reflecting an apparent density dependence in parasite survival. Nymphal ticks having an average infection level of 1 infected salivary gland acinus per tick, survived for up to 69 or 65 weeks post-repletion under quasi-natural or the laboratory conditions respectively. Nymphae having an average infection level of 9 infected salivary gland acini per tick survived for a similar duration under each of the 2 conditions. The infection level of 9 infected salivary gland acini per tick did not seem to significantly affect the survival of the tick vector compared to those having an average of 1 infected salivary gland acinus per tick

Phytochemical analysis of the selected five plant extracts

Herbal medicine is still the mainstay of about 75 - 80% of the whole population, and the major part of traditional therapy involves the use of plant extracts and their active constituents. Plants were collected, identified, dried then extracted using hexane, Dichloromethane/methanol and water. Identification assays to test the presence of various chemical constituents were carried out. The five plants were: Sonchus luxurians, Ocimum americanum, Bridelia micrantha, Croton megalocarpus and Aloe secundiflora. The Phytochemical screening of the compounds present in the plant extracts were; alkaloid, glycosides, Saponins, reducing sugar, Steroid, Flavones and Catecholics. The most common compound in all the plant extracts was Catecholics. Steroids are used in medicine to treat many diseases. The Plant extracts can be possible candidates for drug development. Keywords: Herbal medicine, Phytochemical compounds, Traditional therapy, Plant extract

Molluscicidal Activity of Selected Plant Extracts in Kenya

Schistosomiasis is a snail-borne infection and one approach to the control of schistosomiasis is elimination of the intermediate host. The use of synthetic molluscicides is becoming unpopular and as a result, plant molluscicides have received considerable attention in search for cheaper alternatives to synthetic molluscicides. In this study, the molluscicidal activity of aqueous and ethanol extracts of selected plants against adult and juveniles of Biomphalaria pfeifferi snails was investigated. Dried plant materials from Ocimum americanum, Sonchus luxurians, Aloe secundiflora, Bridelia micrantha and Croton megalocarpus were ground into powder and extraction done using ethanol and water. Phytochemicals were tested which include; flavonoids, saponins, tannins, alkaloids, glycosides, steroids and triterpenes. Ten adult and ten juvenile Biomphalaria pfeifferi snails were exposed to serial dilutions of 5 mg/l, 10 mg/l, 20 mg/l and 40 mg/l of the aqueous and ethanol plant extracts. The exposure period was 48 h. The LD50 value of the plant extracts was determined. The lethal dose, LD50 of B. micrantha against the adult snails was 24.98 mg/l for the aqueous extract and 19.01 mg/l for the ethanol extract. The lethal dose, LD50 of B. micrantha against the juvenile snails was 22.860 mg/l for the aqueous extract and 26.30 mg/l for the ethanol extract. The other extracts from the other plants were found to have a LD50 value of above 100 mg/l.Generally, only B. micrantha which had molluscicidal activity against adult and juvenile snails. B. micrantha extracts, that were found to have molluscicidal activity, were screened for their miracicidal and cercaricidal activity against Schistosoma mansoni miracidia and cercariae using concentrations of 5 mg/l, 10 mg/l, 20 mg/l and 40 mg/l. The exposure period was 1h. Bridelia micrantha aqueous extract had a LD50 value of 11.108 mg/l on the S. mansoni miracidia and a LD50 value of 4.465 mg/l on S. mansoni cercariae. The ethanol extract was found to have a LD50 value of above 40 mg/l for the miracidia and the cercariae. From this study, B. micrantha demonstrated molluscicidal activity against Biomphalaria pfeifferi snails and miracicidal and cercaricidal activity against Schistosoma mansoni miracidia and cercariae. Keywords: Molluscicidal, Phytochemicals, Miracicidal, Cercaricidal

Brine Shrimp Lethality Test and Characterization of Snail Soluble Proteins of Biomphalaria pfeifferi as a Candidate for Vaccine Development against Schistosoma Mansoni

Schistosomiasis infects about two hundred million people around the world. Currently, treatment for Schistosoma mansoni infection is by use of Praziquantel™. Challenges associated with Praziquantel™ use include drug resistance, rapid re-infection and high cost. A longer lasting solution would be a vaccine to enhance the use of drugs. Unfortunately, no human vaccine for schistosomiasis is available. Snails that are the intermediate host of S. mansoni have been discovered to have common proteins with the schistosome worms. A research conducted in mouse model showed that two candidate vaccines derived from Biomphalaria pfeifferi, RT (soluble proteins from the rest of snail tissue) and DG (soluble proteins from the digestive gland), were protective against S. mansoni based on increased immune responses, worm reduction and reduced pathology. Both of them met the World Health Organization criteria of over 40% protection. It is important to ensure that substances being used as vaccines are both efficacious and non-toxic and therefore are safe. There are a number of common product safety tests and the simplest being brine shrimp lethality test. This work tested for in vivo Brine Shrimp Lethality Test (BSLT) of DG and RT. For BSLT, DG and RT were processed and their concentration determined by microtitre technique. Concentrations for both DG and RT were 1.4 mg/ml. Evaluation of the cytotoxicity of DG and RT was done in in terms of Lethality concentration (LCD50) using10μg/ml, 100μg/ml and 1000μg/ml concentrations of the proteins. Ten Brine Shrimps larvae (nauplii) were placed in duplicate tubes of each concentration. After 24 hours the surviving Brine Shrimps larvae were counted and LCD50 was determined by Finney computer program at 95% confidence interval. The LCD50 for DG was 3988.73 µg/ml and RT was 4158.06 µg/ml. The average percentage mortality in all the three different concentrations for the both soluble proteins was less than 50%. DG and RT had a LCD50 of over 1000µg/ml. The toxicity results for the two soluble proteins at the three different concentrations shows that both proteins are non-toxic and are therefore safe vaccines. After a product is found safe and efficacious, it is essential to determine its structure. This study also characterized DG and RT using Gas chromatography-mass spectrometry (GC-MS) and ultraviolet (UV) spectroscopy. Chemical identification and characterization of DG and RT using the GC-MS spectrum established the presence of different chemical compounds with varied retention times. The results from the GC-MS were confirmed by UV spectrum results which confirmed the presence of proteins. Keywords: Schistosomiasis, Toxicity, vaccine, characterizatio

Worm Recovery and Pathology in the Olive baboon, Papio anubis, Immunized Against Schistosoma mansoni with Snail Soluble Proteins

Schistosomiasis is estimated to infect over 200 million people worldwide. Chemotherapy remains the major means of intervention but has the challenge of rapid re-infection, high cost and risk of drug resistance. A vaccine would have a long term effect and complement chemotherapy but none is in the market. Pilot studies in mice model showed that two proteins derived from Biomphalaria pfeifferri RT (soluble proteins from the rest of snail tissue) and DG (soluble proteins from the digestive gland) were protective against S. mansoni in terms of worm reduction and reduced pathology. Both met the World Health Organization criteria of over 40% protection. This study was done to investigate the efficacy of DG and RT in olive baboons challenged with Schistosoma mansoni. Baboons were in three groups: DG, RT and IC (infected control). DG and RT were immunized and boosted twice with their specific soluble snail antigens in Montanide at weeks 0, 3 and 6. They were challenged 2 weeks post final booster with 600 Schistosoma mansoni cercariae. DG had significant worm reduction of 11.4%. It had least gross pathology and histopathology. DG offered better protection against S. mansoni in baboon than RT, although lower than in mouse model. Keywords: Schistosoma mansoni, Biomphalaria pfeifferi, Snail soluble protein, immunizatio

Bioactivity and toxicity of Bridelia micrantha, Chenopodium ambrosoides and Ocimum americanum plant extracts

Background: Bridelia micrantha, Chenopodium ambrosoides and Ocimum americanum plant species are commonly used in traditional medicine for a number of ailments. The extracts of these plants have been shown to have anti-schistosomal activity suggesting that they could be used for the development of new chemical entities (NCEs) for the treatment of schistosomiasis. However there is limited knowledge on their toxicological profile and their use in traditional medicine may not be a satisfactory safety indication.Methods: In this study the extracts were first screened for bioactivity using brine shrimp lethality test for the determination of LC50 followed by rodent acute toxicity and 28 day subchronic studies.Results: B. micrantha water extract with a LC50 of 77µg/ml was deemed toxic while C. ambrosoides methanol and water extracts were moderately toxic with LC50 of 104.63µg/ml and 696.44µg/ml respectively. O. americanum hexane and water extracts toxicity varied from moderate to slightly toxic with LC50 of 887.59µg/ml and 2254.60µg/ml respectively. C. ambrosoides and O. americanum water extracts which were preferentially selected for subsequent studies were found to have mild to no irritation to rodent eyes and skin. Moreover, the aminotransferases AST and ALT which were used to detect liver injury suggested negligible effect.Conclusions: This therefore confirms that C. ambrosoides and O. americanum water extracts are safe for clinical use with O. americanum water extract having a slight edge

Trypanosoma

African Animal Trypanosomiasis (AAT) transmitted cyclically by tsetse fly (Glossina spp.) is a major obstacle to livestock production in the tropical parts of Africa. The objective of this study was to determine the infection rates of trypanosomes in Glossina species in Mtito Andei Division, Makueni County, Kenya. Tsetse fly species, G. longipennis and G. pallidipes, were trapped and DNA was isolated from their dissected internal organs (proboscis, salivary glands, and midguts). The DNA was then subjected to a nested PCR assay using internal transcribed spacer primers and individual trypanosome species were identified following agarose gel electrophoresis. Out of the 117 flies trapped in the area 39 (33.3%) were teneral while 78 (67%) were nonteneral. G. pallidipes constituted the largest percentage of 58% while G. longipennis were 42%. The overall trypanosomes infection rate in all nonteneral Glossina spp. was 11.53% with G. longipennis recording the highest infection rate of 23.08% while G. pallidipes had an infection rate of 5.77%. T. vivax was the most infectious (10.26%) compared to T. congolense (1.28%). Mean apparent densities were strongly positively correlated with infection rates (r=0.95) confirming the importance of this parameter as an indicator of AAT transmission risk

Experimental evaluation of inactivated and live attenuated vaccines against Mycoplasma mycoides subsp. mycoides

AbstractThe current control method for contagious bovine pleuropneumonia (CBPP) in Africa is vaccination with a live, attenuated strain of Mycoplasma mycoides subsp. mycoides (Mmm). However, this method is not very efficient and often causes serious adverse reactions. Several studies have attempted to induce protection using inactivated mycoplasma, but with widely contradictory results. Therefore, we compared the protective capacity of the live T1/44 vaccine with two inactivated preparations of Mmm strain Afadé, inoculated with an adjuvant. Protection was measured after a challenge with Afadé. The protection levels were 31%, 80.8% and 74.1% for the formalin-inactivated, heat-inactivated and live attenuated preparations, respectively. These findings indicate that low doses of heat-inactivated Mmm can offer protection to a level similar to the current live attenuated (T1/44) vaccine formulation

Frequency of Epstein - Barr Virus in Patients Presenting with Acute Febrile Illness in Kenya.

BACKGROUND:Most acute febrile illnesses (AFI) are usually not associated with a specific diagnosis because of limitations of available diagnostics. This study reports on the frequency of EBV viremia and viral load in children and adults presenting with febrile illness in hospitals in Kenya. METHODOLOGY/PRINCIPAL FINDINGS:A pathogen surveillance study was conducted on patients presenting with AFI (N = 796) at outpatient departments in 8 hospitals located in diverse regions of Kenya. Enrollment criterion to the study was fever without a readily diagnosable infection. All the patients had AFI not attributable to the common causes of fever in Kenyan hospitals, such as malaria or rickettsiae, leptospira, brucella and salmonella and they were hence categorized as having AFI of unknown etiology. EBV was detected in blood using quantitative TaqMan-based qPCR targeting a highly conserved BALF5 gene. The overall frequency of EBV viremia in this population was 29.2%, with significantly higher proportion in younger children of <5years (33.8%, p = 0.039) compared to patients aged ≥5 years (26.3% for 5-15 years or 18.8% for >15 years). With respect to geographical localities, the frequency of EBV viremia was higher in the Lake Victoria region (36.4%), compared to Kisii highland (24.6%), Coastal region (22.2%) and Semi-Arid region (25%). Furthermore, patients from the malaria endemic coastal region and the Lake Victoria region presented with significantly higher viremia than individuals from other regions of Kenya. CONCLUSIONS/SIGNIFICANCE:This study provides profiles of EBV in patients with AFI from diverse eco-regions of Kenya. Of significant interest is the high frequency of EBV viremia in younger children. The observed high frequencies of EBV viremia and elevated viral loads in residents of high malaria transmission areas are probably related to malaria induced immune activation and resultant expansion of EBV infected B-cells