Trypanosomiasis and the conservation of black rhinoceros (Diceros bicornis) at the Ngulia Rhino Sanctuary, Tsavo West National Park, Kenya

Assessing Disease Risks in Wildlife Translocation Projects: A Comprehensive Review of Disease Incidents

Although translocation projects have been instrumental in the supplementation or restoration of some wild populations, they also carry a large risk of disease transmission to native and translocated animals. This study systematically reviewed conservation translocation projects to identify projects that met the criteria for a translocation significant disease incursion (TSDI), whereby the translocation resulted in negative population growth rates or the failure of populations to grow due to an infectious disease-either in the native or translocated species. In doing so, risk factors for these incidents could be identified. Analysis of the resulting 30 TSDIs demonstrated that there was equal representation of TSDIs using wild-caught and captive-bred animals. Additionally, the type of pathogen predisposed in a TSDI was more likely a result of the animal group translocated (e.g., fungal pathogens were more likely to be detected in amphibian translocations) and it was nearly five times more likely for a disease to be encountered by a translocated species than for a disease to be introduced to a native population. However, there are numerous project-specific predisposing factors for TSDIs, and therefore it is essential that future translocation projects conduct thorough disease risk analysis as well as report their outcomes for the benefit of their own and future translocations.

Parasitological investigation of bovine Trypanosomosis, vector distribution and tsetse flies infection rate study, Dabo Hana District, Buno Bedelle Zone, Southwest Ethiopia

A cross-sectional study was conducted to explore the prevalence of Trypanosome infections in cattle and within the tsetse flies from December 2020 to May 2021 in Dabo Hana district, Buno Bedelle Zone, Southwest Ethiopia. A total of 415 blood samples were examined utilizing Buffy coat and Giemsa-stained thin blood smear techniques. Vector distribution and tsetse fly infection rate were studied by deploying 60 traps in four purposively chosen villages of the district. The prevalence of Trypanosomes was 10.6% and 6.5% in cattle and in tsetse flies, respectively. Trypanosoma congolense (59.1%) in cattle and T. vivax (62.5%) in tsetse flies, were the foremost common species distinguished in the area. A significant difference (P ≤ 0.05) was observed in the prevalence of bovine Trypanosomosis between body condition scores of cattle. However, differences were not significant between coat color, sex, and age categories (P > 0.05). The mean PCV values of Trypanosome-infected cattle (22.6 ± 0.6) were significantly (P < 0.05) lower than those of non-infected cattle (25.6 ± 0.3). Out of 1441 flies caught, 1242 (86.2%) were Glossina, 113 (7.84%) were Stomoxys, and 86 (5.97%) were Tabanus. Of 1242 Glossina, 85% were G. tachinoides and the remaining 15% were G. m. sub-morsitans. This finding revealed that, three Trypanosoma species are circulating in cattle as well as in tsetse flies. It is recommended that, sustainable and integrated tsetse and Trypanosomosis control practices should be implemented to foster live stock health and agricultural development in the district. Other sensitive methods should be employed to determine the true picture of infection in the area.

Apparent density, trypanosome infection rates and host preference of tsetse flies in the sleeping sickness endemic focus of northwestern Uganda

Background

African trypanosomiasis, caused by protozoa of the genus Trypanosoma and transmitted by the tsetse fly, is a serious parasitic disease of humans and animals. Reliable data on the vector distribution, feeding preference and the trypanosome species they carry is pertinent to planning sustainable control strategies.

Methodology

We deployed 109 biconical traps in 10 villages in two districts of northwestern Uganda to obtain information on the apparent density, trypanosome infection status and blood meal sources of tsetse flies. A subset (272) of the collected samples was analyzed for detection of trypanosomes species and sub-species using a nested PCR protocol based on primers amplifying the Internal Transcribed Spacer (ITS) region of ribosomal DNA. 34 blood-engorged adult tsetse midguts were analyzed for blood meal sources by sequencing of the mitochondrial cytochrome c oxidase 1 (COI) and cytochrome b (cytb) genes.

Results

We captured a total of 622 Glossina fuscipes fuscipes tsetse flies (269 males and 353 females) in the two districts with apparent density (AD) ranging from 0.6 to 3.7 flies/trap/day (FTD). 10.7% (29/272) of the flies were infected with one or more trypanosome species. Infection rate was not significantly associated with district of origin (Generalized linear model (GLM), χ² = 0.018, P = 0.895, df = 1, n = 272) and sex of the fly (χ2 = 1.723, P = 0.189, df = 1, n = 272). However, trypanosome infection was highly significantly associated with the fly’s age based on wing fray category (χ² = 22.374, P < 0.001, df = 1, n = 272), being higher among the very old than the young tsetse. Nested PCR revealed several species of trypanosomes: T. vivax (6.62%), T. congolense (2.57%), T. brucei and T. simiae each at 0.73%. Blood meal analyses revealed five principal vertebrate hosts, namely, cattle (Bos taurus), humans (Homo sapiens), Nile monitor lizard (Varanus niloticus), African mud turtle (Pelusios chapini) and the African Savanna elephant (Loxodonta africana).

Conclusion

We found an infection rate of 10.8% in the tsetse sampled, with all infections attributed to trypanosome species that are causative agents for AAT. However, more verification of this finding using large-scale passive and active screening of human and tsetse samples should be done. Cattle and humans appear to be the most important tsetse hosts in the region and should be considered in the design of control interventions.

Global distribution, host range and prevalence of Trypanosoma vivax: a systematic review and meta-analysis

BACKGROUND

Trypanosomosis caused by Trypanosoma vivax is one of the diseases threatening the health and productivity of livestock in Africa and Latin America. Trypanosoma vivax is mainly transmitted by tsetse flies; however, the parasite has also acquired the ability to be transmitted mechanically by hematophagous dipterans. Understanding its distribution, host range and prevalence is a key step in local and global efforts to control the disease.

METHODS

The study was conducted according to the methodological recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist. A systematic literature search was conducted on three search engines, namely PubMed, Scopus and CAB Direct, to identify all publications reporting natural infection of T. vivax across the world. All the three search engines were screened using the search term Trypanosoma vivax without time and language restrictions. Publications on T. vivax that met our inclusion criteria were considered for systematic review and meta-analysis.

RESULT

The study provides a global database of T. vivax, consisting of 899 records from 245 peer-reviewed articles in 41 countries. A total of 232, 6277 tests were performed on 97 different mammalian hosts, including a wide range of wild animals. Natural infections of T. vivax were recorded in 39 different African and Latin American countries and 47 mammalian host species. All the 245 articles were included into the qualitative analysis, while information from 186 cross-sectional studies was used in the quantitative analysis mainly to estimate the pooled prevalence. Pooled prevalence estimates of T. vivax in domestic buffalo, cattle, dog, dromedary camel, equine, pig, small ruminant and wild animals were 30.6%, 6.4%, 2.6%, 8.4%, 3.7%, 5.5%, 3.8% and 12.9%, respectively. Stratified according to the diagnostic method, the highest pooled prevalences were found with serological techniques in domesticated buffalo (57.6%) followed by equine (50.0%) and wild animals (49.3%).

CONCLUSION

The study provides a comprehensive dataset on the geographical distribution and host range of T. vivax and demonstrates the potential of this parasite to invade other countries out of Africa and Latin America.

Standardising visual control devices for Tsetse: East and Central African Savannah species Glossina swynnertoni, Glossina morsitans centralis and Glossina pallidipes

Background

This study focused on the savannah tsetse species Glossina swynnertoni and G. morsitans centralis, both efficient vectors of human and animal trypanosomiasis in, respectively, East and Central Africa. The aim was to develop long-lasting, practical and cost-effective visually attractive devices that induce the strongest landing responses in these two species for use as insecticide-impregnated tools in population suppression.

Methods and findings

Trials were conducted in different seasons and years in Tanzania (G. swynnertoni) and in Angola and the Democratic Republic of the Congo (DRC, G. m. centralis) to measure the performance of traps (pyramidal and epsilon) and targets of different sizes, shapes and colours, with and without chemical baits, at different population densities and under different environmental conditions. Adhesive film was used to catch flies landing on devices at the remote locations to compare tsetse-landing efficiencies. Landing rates by G. m. centralis in both Angola and the DRC were highest on blue-black 1 m² oblong and 0.5 m² square and oblong targets but were not significantly different from landings on the pyramidal trap. Landings by G. swynnertoni on 0.5 m² blue-black oblong targets were likewise not significantly lower than on equivalent 1 m² square targets. The length of target horizontal edge was closely correlated with landing rate. Blue-black 0.5 m² targets performed better than equivalents in all-blue for both G. swynnertoni and G. m. centralis, although not consistently. Baiting with chemicals increased the proportion of G. m. centralis entering pyramidal traps.

Conclusions

This study confirms earlier findings on G. swynnertoni that smaller visual targets, down to 0.5 m², would be as efficient as using 1 m² targets for population management of this species. This is also the case for G. m. centralis. An insecticide-impregnated pyramidal trap would also constitute an effective control device for G. m. centralis.

Glossina swynnertoni is restricted to open savannah in northwestern Tanzania and southwestern Kenya whereas G. morsitans centralis has a much wider distribution from western Tanzania/southern Uganda westwards through Zambia and southeast of the Democratic Republic of the Congo (DRC) to Angola. Both are savannah tsetse and are efficient vectors of human and animal trypanosomiasis. In comparison to other tsetse species, relatively little work has been done to test the efficacy of traps and targets for controlling G. swynnertoni and G. m. centralis. To determine the most visually-attractive and practical objects we conducted field tests with devices of various shapes, sizes and colours in Tanzania, DRC and Angola in different years, seasons, environmental conditions and at different population densities. The strongest landing responses were on 0.5 m² horizontal rectangular targets with respect to ground that had both black and phthalogen blue elements with fly landing rates not significantly lower than on equivalent 1 m² targets used till now for both species. The pyramidal trap proved efficient as a landing stimulus as targets of either size for G. m. centralis. Insecticide-impregnated blue-black 0.5 m² cloth targets show promise as cost-effective devices for management of G. swynnertoni and G. m. centralis populations.

The identification of Theileria bicornis in captive rhinoceros in Australia

Poaching of both black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros in Africa has increased significantly in recent years. In an effort to ensure the survival of these critically endangered species, breeding programs were established in the 1990s in Australia, where a similar climate and habitat is available. In this study we examined blood samples from two C. simum, including a 16 yr old female (Aluka) who died in captivity, and a 17 yr old asymptomatic male (Umfana). Bloods from seven healthy D. bicornis housed at the zoo were also collected. All samples were tested for the presence of piroplasms via blood smear and PCR. A generic PCR for the 18S rRNA gene of the Piroplasmida revealed the presence of piroplasm infection in both dead and asymptomatic C. simum. Subsequent sequencing of these amplicons revealed the presence of Theileria bicornis. Blood smear indicated that this organism was present at low abundance in both affected and asymptomatic individuals and was not linked to the C. simum mortality. T. bicornis was also detected in the D. bicornis population (n = 7) housed at Taronga Western Plains Zoo using PCR and blood film examination; however only animals imported from Africa (n = 1) tested T. bicornis positive, while captive-born animals bred within Australia (n = 6) tested negative suggesting that transmission within the herd was unlikely. Phylogenetic analysis of the full length T. bicornis 18S rRNA genes classified this organism outside the clade of the transforming and non-transforming Theileria with a new haplotype, H4, identified from D. bicornis. This study revealed the presence of Theileria bicornis in Australian captive populations of both C. simum and D. bicornis and a new haplotype of the parasite was identified.

The clinico-pathology and mechanisms of trypanosomosis in captive and free-living wild animals: a review

Reports on the clinico-pathology and mechanisms of trypanosomosis in free-living and captive wild animals showed that clinical disease and outbreaks occur more commonly among captive than free-living wild animals. This is because the free-living wild animals co-exist with the disease until subjected to captivity. In exceptional cases however, draught, starvation and intercurrent diseases often compromised trypanotolerance leading to overt trypanosomosis in free-living wild animals. Meanwhile, in captivity, space restriction, reduced social interactions, change in social herd structure, reduced specie-to-specie specific behaviors, altered habitat and translocation were the major stressors that precipitated the disease. The cumulative effect of these factors produced severe physiological and somatic stress leading to diminished immune response due to increased blood cortisol output from adrenal cortex. The major symptoms manifested were pyrexia, innapetence, increased respiration, anaemia, cachexia and death. At necropsy, pulmonary oedema, splenomegally, hepatomegally, lympadenopathy and atrophy of body fats were the gross changes encountered. At the ultra-structural level, the tissues manifested degenerative changes, haemorghages, necrosis and mononuclear cellular infiltrations. The mechanisms of cellular and tissue injuries were primarily associated with physical and metabolic activities of the organisms. From the foregoing, it is evident that stress is the underlying mechanism that compromises trypanotolerance in wild animals leading to severe clinico-pathological effects.

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.

Relationships between host blood factors and proteases in Glossina morsitans subspecies infected with Trypanosoma congolense

Host blood effects on Trypanosoma congolense establishment in Glossina morsitans morsitans and Glossina morsitans centralis were investigated using goat, rabbit, cow and rhinoceros blood. Meals containing goat erythrocytes facilitated infection in G.m.morsitans, whereas meals containing goat plasma facilitated infection in G.m.centralis. Goat blood effects were not observed in the presence of complementary rabbit blood components. N-acetyl-glucosamine (a midgut-lectin inhibitor) increased infection rates in some, but not all, blood manipulations. Cholesterol increased infection rates in G.m.centralis only. Both compounds together added to cow blood produced superinfection in G.m.centralis, but not in G.m.morsitans. Midgut protease levels did not differ 6 days post-infection in flies maintaining infections versus flies clearing infections. Protease levels were weakly correlated with patterns of infection, but only in G.m.morsitans. These results suggest that physiological mechanisms responsible for variation in infection rates are only superficially similar in these closely-related tsetse.

Trypanosoma simiae in the white rhinoceros (Ceratotherium simum) and the dromedary camel (Camelus dromedarius)

Trypanosoma simiae was identified as the cause of a disease outbreak in dromedary camels (Camelus dromedarius) introduced to Tsavo East National Park, confirming the susceptibility of camels to this pathogen. T. simiae was also isolated from a new host, the white rhinoceros (Ceratotherium simum) through xenodiagnosis with a susceptible tsetse species (Glossina morsitans centralis). A white rhinoceros showed some evidence of anaemia and lymphopaenia when harbouring T. simiae, but did not suffer any long-term health effects.

Detection of trypanosome infections in the saliva of tsetse flies and buffy-coat samples from antigenaemic but aparasitaemic cattle

Relatively simple protocols employing non-radioactive DNA probes have been used for the detection of African trypanosomes in the blood of mammalian hosts and the saliva of live tsetse flies. In combination with the polymerase chain reaction (PCR), the protocols revealed trypanosomes in buffy-coat samples from antigenaemic but aparasitaemic cattle and in the saliva of live, infected tsetse flies. Furthermore, the protocols were used to demonstrate concurrent natural infections of single tsetse flies with different species of African trypanosomes.

Isolation of Trypanosoma spp. from wild tsetse flies through procyclic expansion in Glossina morsitans centralis

Procyclic trypanosomes from wild tsetse flies were membrane-fed to Glossina morsitans centralis in order to develop an optimal technique for propagating field isolates. A 70% success rate was achieved in isolating Trypanosoma simiae and a variety of genotypes of T. congolense originating from G. pallidipes, G. brevipalpis and G. swynnertoni. Parasites matured into forms infective for mammals, and could be maintained by passage of gut forms to new groups of flies. In experiments with laboratory stocks, we also passaged immature gut infections of T. congolense and T. brucei from various tsetse species to G. m. centralis. The optimal technique was investigated for procyclic T. congolense through addition of various compounds to goat blood using G. m. centralis and G. m. morsitans as recipients. From these experiments, many approaches to procyclic expansion appeared possible. However, a simple and practical method based on the use of fresh goat blood for rapid feeding of G. m. centralis is recommended. Application of this technique should aid in the resolution of questions relating to the cryptic diversity of Nannomonas trypanosomes in diverse host and vector communities.

The influence of host blood on infection rates in Glossina morsitans sspp. infected with Trypanosoma congolense, T. brucei and T. simiae

Trypanosoma congolense, T. brucei and T. simiae isolated from wild-caught Glossina pallidipes were fed to laboratory-reared G. morsitans centralis and G.m. morsitans to determine the effect of host blood at the time of the infective feed on infection rates. Bloodstream forms of trypanosomes were membrane-fed to flies either neat, or mixed with blood from cows, goats, pigs, buffalo, eland, waterbuck and oryx. The use of different bloods for the infective feed resulted in differences in infection rates that were repeatable for both tsetse subspecies and most parasite stocks. Goat, and to a lesser extent, pig blood facilitated infection, producing high infection rates at low parasitaemias. Blood from cows and the wildlife species produced low infection rates, with eland blood producing the lowest. Addition of D(+)-glucosamine (an inhibitor of tsetse midgut lectin) increased infection rates in most cases. These results indicate the presence of species-specific factors in blood that affect trypanosome survival in tsetse. In certain hosts, factors actually appear to promote infection. The nature of these factors and how they might interact with midgut lectins and proteases are discussed.

Trypanosoma (Nannomonas) congolense: molecular characterization of a new genotype from Tsavo, Kenya

Trypanosoma (Nannomonas) congolense comprises morphologically identical but genetically heterogeneous parasites infective to livestock and other mammalian hosts; three different genotypes of this parasite have been described previously. Restriction enzyme fragment length polymorphisms (RFLPs) in both kinetoplast DNA minicircle and nuclear DNA sequences, and randomly amplified polymorphic deoxyribonucleic acid (RAPD) patterns have been used here to demonstrate the existence of another type of T. (N.) congolense that is genotypically distinct from those that have so far been characterized at the molecular level. A highly repetitive, tandemly arranged DNA sequence and oligonucleotide primers, for use in polymerase chain reaction (PCR) amplification are described, which can be used for specific identification of the trypanosome and its distinction from others within the Nannomonas subgenus.

Influence of d(+)-glucosamine on infection rates and parasite loads in tsetse flies (Glossina spp.) infected with Trypanosoma brucei

Teneral Glossina morsitans centralis, G. m. morsitans and G. pallidipes were infected with three different clones of Trypanosoma brucei in blood containing D(+)-glucosamine, an inhibitor of tsetse midgut lectin. On average, 5 days of D(+)-glucosamine treatment tripled infection rates, without affecting the proportion of infections that matured. Total infection rates were equal in males and females, but twice as many infections matured in males. Counts of parasites in the guts and salivary glands of 277 flies revealed order of magnitude differences among flies, with females consistently having 2-3-times as many parasites as males. Parasite numbers varied in a sex-specific manner among tsetse-clone combinations, but these differences were not correlated with similar large differences in infection rates. D(+)-glucosamine treatment had no significant effect on parasite loads.