Onchocerciasis transmission in Ghana: biting and parous rates of host-seeking sibling species of the Simulium damnosum complex

Background: Ghana is renowned for its sibling species diversity of the Simulium damnosum complex, vectors of Onchocerca volvulus. Detailed entomological knowledge becomes a priority as onchocerciasis control policy has shifted from morbidity reduction to elimination of infection. To date, understanding of transmission dynamics of O. volvulus has been mainly based on S. damnosum sensu stricto (s.s.) data. We aim to elucidate bionomic features of vector species of importance for onchocerciasis elimination efforts. Methods: We collected S. damnosum sensu lato from seven villages in four Ghanaian regions between 2009 and 2011, using standard vector collection, and human- and cattle-baited tents. Taxa were identified using morphological and molecular techniques. Monthly biting rates (MBR), parous rates and monthly parous biting rates (MPBR) are reported by locality, season, trapping method and hour of collection for each species. Results: S. damnosum s.s./S. sirbanum were collected at Asubende and Agborlekame, both savannah villages. A range of species was caught in the Volta region (forest-savannah mosaic) and Gyankobaa (forest), with S. squamosum or S. sanctipauli being the predominant species, respectively. In Bosomase (southern forest region) only S. sanctipauli was collected in the 2009 wet season, but in the 2010 dry season S. yahense was also caught. MBRs ranged from 714 bites/person/month at Agborlekame (100% S. damnosum s.s./S. sirbanum) to 8,586 bites/person/month at Pillar 83/Djodji (98.5% S. squamosum). MBRs were higher in the wet season. In contrast, parous rates were higher in the dry season (41.8% vs. 18.4%), resulting in higher MPBRs in the dry season. Daily host-seeking activity of S. damnosum s.s./S. sirbanum was bimodal, whilst S. squamosum and S. sanctipauli had unimodal afternoon peaks. Conclusions: The bionomic differences between sibling species of the S. damnosum complex need to be taken into account when designing entomological monitoring protocols for interventions and parameterising mathematical models for onchocerciasis control and elimination

Onchocerciasis transmission in Ghana: Persistence under different control strategies and the role of the simuliid vectors

Background: The World Health Organization (WHO) aims at eliminating onchocerciasis by 2020 in selected African countries. Current control focuses on community-directed treatment with ivermectin (CDTI). In Ghana, persistent transmission has been reported despite long-term control. We present spatial and temporal patterns of onchocerciasis transmission in relation to ivermectin treatment history. Methodology/Principal Findings: Host-seeking and ovipositing blackflies were collected from seven villages in four regions of Ghana with 3–24 years of CDTI at the time of sampling. A total of 16,443 flies was analysed for infection; 5,812 (35.3%) were dissected for parity (26.9% parous). Heads and thoraces of 12,196 flies were dissected for Onchocerca spp. and DNA from 11,122 abdomens was amplified using Onchocerca primers. A total of 463 larvae (0.03 larvae/fly) from 97 (0.6%) infected and 62 (0.4%) infective flies was recorded; 258 abdomens (2.3%) were positive for Onchocerca DNA. Infections (all were O. volvulus) were more likely to be detected in ovipositing flies. Transmission occurred, mostly in the wet season, at Gyankobaa and Bosomase, with transmission potentials of, respectively, 86 and 422 L3/person/month after 3 and 6 years of CDTI. The numbers of L3/1,000 parous flies at these villages were over 100times the WHO threshold of one L3/1,000 for transmission control. Vector species influenced transmission parameters. At Asubende, the number of L3/1,000 ovipositing flies (1.4, 95% CI = 0–4) also just exceeded the threshold despite extensive vector control and 24 years of ivermectin distribution, but there were no infective larvae in host-seeking flies. Conclusions/Significance: Despite repeated ivermectin treatment, evidence of O. volvulus transmission was documented in all seven villages and above the WHO threshold in two. Vector species influences transmission through biting and parous rates and vector competence, and should be included in transmission models. Oviposition traps could augment vector collector methods for monitoring and surveillance

Temephos resistance in <i>Simulium damnosum</i> Theobald (Diptera: Simuliidae): a comparative study between larvae and adults of the forest and savanna strains of this species complex

AbstractTemephos resistance in savanna cytospecies of Simulium damnosum Theobald s.l. and the forest cytospecies S. sanctipauli Vajime &amp; Dunbar, from West Africa is correlated with an increase in general esterase activity. Metabolism studies indicated that esterase products were the major metabolities in both forest and savanna resistant strains of S. damnosum s.l. compared to the susceptibles. In the presence of an esterase synergist, a large amount of the oxon analogue of temephos was produced by the resistant forest cytospecies S. sanctipauli. This strain is also resistant to chlorphoxim, and it is likely that the increase in oxidative activity observed is connected with the chlorphoxim rather than the temephos resistance. There was no evidence of glutathione transferase-, oxidase- or acetylcholinesterase-based temephos resistance machanisms in the savanna species of S. damnosum s.l.</jats:p

Assessment of the patency of the left portal vein during mesoportal shunting in children with extrahepatic portal hypertension

BACKGROUND: One of the most common causes of extrahepatic portal hypertension in children is portal vein thrombosis. The causes of this disease are different and, in most cases, remain unrecognized. Along with this, the mesoportal shunt (Rex shunt) proved itself and today is considered the gold standard to treat extrahepatic portal hypertension in children. The restoration of hepatopetal blood flow eliminates gastroesophageal bleeding, splenomegaly, hypersplenism, and many other complications. For the results of mesoportal shunt to be successful, several conditions must be met, one of which is the patency of the umbilical portion of the left portal vein. Despite the importance of preoperative diagnostics of the patency of this area, the most optimal instrumental research method has not yet been found.&#x0D; AIM: This literature review aims to highlight the main issues of extrahepatic portal hypertension etiopathogenesis, surgical treatment methods, and the most effective preoperative diagnostic methods to assess the patency of the left portal vein.&#x0D; RESULTS: The authors analyzed the sources of domestic and foreign literature on the etiology, pathogenesis of HSV in children, and laboratory and instrumental diagnostic methods to assess the patency of the PVI to plan the mesoportal shunting operation.&#x0D; CONCLUSIONS: Extrahepatic portal hypertension is a polyetiological disease with a possible hereditary predisposition to a thrombotic process under the influence of various triggers. The most common causes of portal vein thrombosis are omphalitis and umbilical vein catheterization in the neonatal period. Unfortunately, to date, none of the existing instrumental diagnostic methods can reliably answer the question about left portal vein patency. Due to the small number of works, the lack of a unified view on the problem of preoperative diagnosis of patients with extrahepatic portal hypertension, we could not reliably determine the specificity, sensitivity, and accuracy of each instrumental method. Therefore, we could not identify the gold standard method. Nevertheless, with further improvement of the methods for preoperative assessment of the left portal vein patency, surgeons will be more likely to predict the successful outcome of mesoportal shunting, which will generally affect the surgical treatment quality of extrahepatic portal hypertension in children.</jats:p