Pyrethroid treatment of cattle for tsetse control: Reducing its impact on dung fauna

Background: African trypansomiases of humans and animals can be controlled by attacking the vectors,various species of tsetse fly. Treatment of cattle with pyrethroids to kill tsetse as they feed is the most cost-effective method. However, such treatments can contaminate cattle dung, thereby killing the fauna which disperse the dung and so play an important role in soil fertility. Hence there is a need to identify cost-effective methods of treating cattle with minimal impact on dung fauna. Methodology/Principal Findings: We used dung beetles to field bioassay the levels of dung contamination following the use of spray and pour-on formulations of deltamethrin, applied to various parts of the body of cattle in Zimbabwe. Results suggested that dung was contaminated by contact with insecticide on the body surface as the cattle defecated, and by ingestion of insecticide as the cattle licked themselves. Death of dung beetles was reduced to negligible levels by using only the spray and applying it to the legs and belly or legs alone, i.e., places where most tsetse feed. Conclusion/Significance: The restricted applications suitable for minimising the impact on dung fauna have the collateral benefits of improving the economy and convenience of cattle treatments for tsetse control. The demonstration of collateral benefits is one of the surest ways of promoting environmentally friendly procedures

Concomitant transmission of human and animal trypanosomoses: Mandoul focus in Chad

Trypanosomosis is a vector-borne disease which affects both humans and animals. It is cyclically transmitted by tsetse flies and is caused by Trypanosoma sp. Although the disease is mainly endemic where its vectors are present, endemic areas where transmission of both forms of the disease coexist have seldom been studied. During our study, epidemiological and entomological surveys were carried out, followed by the analysis of collected samples by the polymerase chain reaction (PCR). Out of 13,410 persons examined, 132 sleeping sickness cases were diagnosed. After examination of 144 cattle samples by PCR, 33 were found infected by either Trypanosoma brucei (39%) or T. vivax (55%), or exhibited a co-infection (two animals). Three insect families were trapped at variable densities (Glossinidae, Stomoxyinae, and Tabanidae). Glossina fuscipes fuscipes was only caught in the southern part of the focus, and the highest apparent density per trap per day (ADT) of 0.56 was found in the gallery forest bordering the villages where the highest number of human African trypanosomosis was diagnosed. Tabanids were caught in all investigated areas but the highest ADT, i.e. 15.55, was observed in the northern part of the focus. No Stomoxys sp. was found in the prospected area located farthest from the river. The identification of trypanosomes in people and in cattle, and the presence of the cyclical vector as well as mechanical vectors, confirmed endemic human and animal trypanosomoses in the focus. Combatting vectors with a strategy common to both forms of the disease is crucial to control them sustainably

Comparison of the transmissibility of Trypanosoma congolense strains, isolated in a trypanosomiasis endemic area of eastern Zambia, by Glossina morsitans morsitans

Transmission experiments were conducted to compare the transmissibility of genetically different Trypanosoma congolense (Savannah subgroup) strains isolated from cattle in a trypanosomiasis endemic area of eastern Zambia. A total of 17 strains were compared. Three strains were extremely virulent with a short pre-patent period, high parasitaemia and a short median survival time (between 5 and 9 days) in mice. The remainder of the strains belonged to the moderate (6 strains) or low (8 strains) virulence categories with median survival times between 10 and 30 days and >30 days, respectively. Batches of 40 teneral Glossina morsitans morsitans (Diptera: Glossinidae) were offered a single bloodmeal on mice infected with one of those strains. Flies were dissected to determine their infection status 21 days later. The proportion of flies with procyclic and metacyclic infections differed significantly between trypanosome strains and were significantly higher in flies infected with extremely virulent strains (P=0.033 and P=0.016 for the differences in the procyclic infection rate of strains with moderate and low virulence, respectively and P=0.005 and P=0.019 for the differences in the metacyclic infection rate of strains with moderate and low virulence, respectively). On the other hand, moderately virulent strains had, in general, higher procyclic and metacyclic infection rates compared to low virulent strains. But the differences were not significant (P>0.05). The outcome of those experiments shows clear differences in transmissibility of trypanosome strains associated with their virulence. This observation confirms the theory for the evolution and maintenance of virulence in a parasite population and may explain the persistence of virulent trypanosome strains in a susceptible host population

Treating cattle to protect people? Impact of footbath insecticide treatment on tsetse density in Chad.

BACKGROUND: In Chad, several species of tsetse flies (Genus: Glossina) transmit African animal trypanosomoses (AAT), which represents a major obstacle to cattle rearing, and sleeping sickness, which impacts public health. After the failure of past interventions to eradicate tsetse, the government of Chad is now looking for other approaches that integrate cost-effective intervention techniques, which can be applied by the stake holders to control tsetse-transmitted trypanosomoses in a sustainable manner. The present study thus attempted to assess the efficacy of restricted application of insecticides to cattle leg extremities using footbaths for controlling Glossina m. submorsitans, G. tachinoides and G. f. fuscipes in southern Chad. METHODOLOGY/PRINCIPAL FINDINGS: Two sites were included, one close to the historical human African trypanosomiasis (HAT) focus of Moundou and the other to the active foci of Bodo and Moissala. At both sites, a treated and an untreated herd were compared. In the treatment sites, cattle were treated on a regular basis using a formulation of deltamethrin 0.005% (67 to 98 cattle were treated in one of the sites and 88 to 102 in the other one). For each herd, tsetse densities were monthly monitored using 7 biconical traps set along the river and beside the cattle pen from February to December 2009. The impact of footbath treatment on tsetse populations was strong (p < 10(-3)) with a reduction of 80% in total tsetse catches by the end of the 6-month footbath treatment. CONCLUSIONS/SIGNIFICANCE: The impact of footbath treatment as a vector control tool within an integrated strategy to manage AAT and HAT is discussed in the framework of the "One Health" concept. Like other techniques based on the treatment of cattle, this technology should be used under controlled conditions, in order to avoid the development of insecticide and acaricide resistance in tsetse and tick populations, respectively

Monthly number of treated cattle at the four study sites for the impact assessment of footbath insecticide treatment on tsetse apparent density in Chad.

<p>Points were drawn at the dates corresponding to the visits.</p

Tsetse total catches (<b>log scale</b>) at the treatment (<b>top</b>) and control (<b>bottom</b>) sites in the two regions of southern Chad.

<p>The black line represents the mean observed values; the light grey lines depict the observed values for the individual traps, and the black vertical dashed line indicates the start of footbath treatments.</p

Study sites for impact assessment of footbath insecticide treatment on tsetse apparent density in Chad.

<p>The red boxes in panels A and B show the global and specific study areas, respectively, corresponding to panels C and D. The hydrological network shown in sections B, C and D is the HydroSHEDS 15-arcsecond river network of Africa [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0067580#B49" target="_blank">49</a>].</p