Luis M. Hernández-Triana

Rift Valley fever virus: A review of diagnosis and vaccination, and implications for emergence in Europe

Rift Valley fever virus (RVFV) is a mosquito-borne virus, and is the causative agent of Rift Valley fever (RVF), a zoonotic disease characterised by an increased incidence of abortion or foetal malformation in ruminants. Infection in humans can also lead to clinical manifestations that in severe cases cause encephalitis or haemorrhagic fever. The virus is endemic throughout much of the African continent. However, the emergence of RVFV in the Middle East, northern Egypt and the Comoros Archipelago has highlighted that the geographical range of RVFV may be increasing, and has led to the concern that an incursion into Europe may occur. At present, there is a limited range of veterinary vaccines available for use in endemic areas, and there is no licensed human vaccine. In this review, the methods available for diagnosis of RVFV infection, the current status of vaccine development and possible implications for RVFV emergence in Europe, are discussed.

Emergence of West Nile Virus Lineage 2 in Europe: A Review on the Introduction and Spread of a Mosquito-Borne Disease

West Nile virus (WNV) is transmitted by mosquitoes and causes fever and encephalitis in humans, equines, and occasionally wild birds. The virus was first isolated in sub-Saharan Africa where it is endemic. WNV lineage 1 has been responsible for repeated disease outbreaks in the countries of the Mediterranean basin over the past 50 years. This lineage was also introduced into North America in 1999 causing widespread human, equine, and avian mortality. WNV lineage 2, the first WNV lineage to be isolated, was believed to be restricted to sub-Saharan Africa causing a relatively mild fever in humans. However, in 2004, an investigation in Hungary of a case of encephalitis in a wild goshawk (Accipiter gentiles) resulted in the isolation of WNV lineage 2. During the summer of 2004, and in subsequent years, the virus appeared to spread locally throughout Hungary and into neighboring Austria. Subsequently, WNV lineage 2 emerged in Greece in 2010 and in Italy in 2011, involving outbreaks on the Italian mainland and Sardinia. Further spread through the Balkan countries is also suspected. Whole genome sequencing has confirmed that the virus responsible for the outbreaks in Greece and Italy was almost identical to that isolated in Hungary. However, unlike the outbreaks in Hungary, the burden of disease in Mediterranean countries has fallen upon the human population with numerous cases of West Nile fever and a relatively higher mortality rate than in previous outbreaks. The emergence of WNV lineage 2 in Europe, its over-wintering and subsequent spread over large distances illustrates the repeated threat of emerging mosquito-borne diseases. This article will review the emergence of WNV lineage 2 in Europe; consider the pathways for virus spread and the public health implications for the continent.

Babesia canis detected in dogs and associated ticks from Essex.

FOLLOWING the letter from Clive Swainsbury and others about a cluster of cases of babesiosis in dogs from Essex with no history of foreign travel ( VR , February 13, 2016, vol 178, p 172), a tick removed from one of the dogs was sent to the Animal and Plant Health Agency (APHA) to confirm its identification and investigate the presence of Babesia . Based on morphology the tick was identified as an adult male Dermacentor reticulatus , a species that has been reported from a number of locations in western Wales and the south west and south east of England, including Essex (Jameson and Medlock 2010, Medlock and others 2011, …

Japanese encephalitis virus infection, diagnosis and control in domestic animals

Japanese encephalitis virus (JEV) is a significant cause of neurological disease in humans throughout Asia causing an estimated 70,000 human cases each year with approximately 10,000 fatalities. The virus contains a positive sense RNA genome within a host-derived membrane and is classified within the family Flaviviridae. Like many flaviviruses, it is transmitted by mosquitoes, particularly those of the genus Culex in a natural cycle involving birds and some livestock species. Spill-over into domestic animals results in a spectrum of disease ranging from asymptomatic infection in some species to acute neurological signs in others. The impact of JEV infection is particularly apparent in pigs. Although infection in adult swine does not result in symptomatic disease, it is considered a significant reproductive problem causing abortion, still-birth and birth defects. Infected piglets can display fatal neurological disease. Equines are also infected, resulting in non-specific signs including pyrexia, but occasionally leading to overt neurological disease that in extreme cases can lead to death. Veterinary vaccination is available for both pigs and horses. This review of JEV disease in livestock considers the current diagnostic techniques available for detection of the virus. Options for disease control and prevention within the veterinary sector are discussed. Such measures are critical in breaking the link to zoonotic transmission into the human population where humans are dead-end hosts.

Emergence of Babesia canis in southern England

BackgroundThe United Kingdom is considered free of autochthonous transmission of canine babesiosis although cases are reported in dogs associated with recent travel abroad. During the winter months of 2015/16, a cluster of cases of disease in dogs with signs suggestive of canine babesiosis were reported in Harlow, Essex.MethodsBabesia species were detected in dog blood samples by Giemsa staining of blood smears and by pan-piroplasm PCRs. Babesia species were also detected in extracts of tick DNA using pan-piroplasm PCRs. DNA sequencing and phylogenetic analysis was used to confirm the species of Babesia present in dog blood and tick samples. Tick species were identified by PCR-sequencing based on amplification of the cytochrome c oxidase subunit one (cox1) gene. Dermacentor reticulatus ticks were sampled from field sites in England and Wales.ResultsBlood smear analysis on samples taken from some of the affected dogs confirmed the presence of a large Babesia species within erythrocytes. A tick recovered from one of these cases was identified as Dermacentor reticulatus, a species with a limited distribution in England and Wales, but a known vector of canine babesiosis in continental Europe. Babesia canis was subsequently identified in blood samples obtained from three clinical cases (all dogs) within the area and from ticks associated with these dogs. A field survey detected 17 adult D. reticulatus ticks from one area visited by the affected dogs. Fourteen of these ticks were shown to be positive for the B. canis parasite, implicating them as a potential source for babesiosis in Harlow. In order to assess whether the parasite is present in more than one tick population, D. reticulatus ticks from across England and Wales were screened for the presence of Babesia species. In addition to the Harlow site, a further five locations where D. reticulatus is present were screened for Babesia species. Babesia was not detected from most sites tested but one tick from a single location in Wales was positive for B. canis.ConclusionsInfection with B. canis was confirmed in a number of dogs in Harlow, Essex, with no history of travel outside of the country. The same pathogen was identified in field-caught D. reticulatus ticks in the same area and is considered the likely source of infection. This highlights the need for vigilance by veterinary surgeons for future outbreaks of tick-borne disease in dogs.

Enhanced West Nile virus surveillance in the North Kent marshes, UK

BackgroundAs part of efforts to more fully understand the potential risks posed by West Nile virus (WNV) and Usutu virus (USUV) in the UK, and following on from previous reports of a potential bridge vector Culex modestus for these viruses, at wetland sites in North Kent, mosquito surveillance was undertaken more widely across the Isle of Sheppey, the Hoo Peninsula and the Kent mainland.MethodsLarval surveys were conducted and Mosquito Magnet® adult traps were used to collect adult mosquitoes. Pools of female mosquitoes were tested for the presence of WNV using real-time reverse transcriptase polymerase chain reaction. A subset of samples was tested for USUV.ResultsCulex modestus was found in both the pre-imaginal and imago stage at all five locations surveyed, accounting for 90% of adult mosquitoes collected. WNV or USUV were not detected in any sample.ConclusionsAlthough no mosquitoes have been shown to be virus positive, the field survey data from this study demonstrated the dominance of an important bridge vector species for WNV in this region. Its wide geographical distribution highlights the need to update risk assessments on WNV introduction, and to maintain vigilance for WNV in the South East of England.

DNA barcoding of Neotropical black flies (Diptera: Simuliidae): Species identification and discovery of cryptic diversity in Mesoamerica.

Although correct taxonomy is paramount for disease control programs and epidemiological studies, morphology-based taxonomy of black flies is extremely difficult. In the present study, the utility of a partial sequence of the COI gene, the DNA barcoding region, for the identification of species of black flies from Mesoamerica was assessed. A total of 32 morphospecies were analyzed, one belonging to the genus Gigantodax and 31 species to the genus Simulium and six of its subgenera (Aspathia, Eusimulium, Notolepria, Psaroniocompsa, Psilopelmia, Trichodagmia). The Neighbour Joining tree (NJ) derived from the DNA barcodes grouped most specimens according to species or species groups recognized by morphotaxonomic studies. Intraspecific sequence divergences within morphologically distinct species ranged from 0.07% to 1.65%, while higher divergences (2.05%-6.13%) in species complexes suggested the presence of cryptic diversity. The existence of well-defined groups within S. callidum (Dyar & Shannon), S. quadrivittatum Loew, and S. samboni Jennings revealed the likely inclusion of cryptic species within these taxa. In addition, the suspected presence of sibling species within S. paynei Vargas and S. tarsatum Macquart was supported. DNA barcodes also showed that specimens of species that are difficult to delimit morphologically such as S. callidum, S. pseudocallidum Díaz Nájera, S. travisi Vargas, Vargas & Ramírez-Pérez, relatives of the species complexes such as S. metallicum Bellardi s.l. (e.g., S. horacioi Okazawa & Onishi, S. jobbinsi Vargas, Martínez Palacios, Díaz Nájera, and S. puigi Vargas, Martínez Palacios & Díaz Nájera), and S. virgatum Coquillett complex (e.g., S. paynei and S. tarsatum) grouped together in the NJ analysis, suggesting they represent valid species. DNA barcoding combined with a sound morphotaxonomic framework provided an effective approach for the identification of medically important black flies species in Mesoamerica and for the discovery of hidden diversity within this group.

Blood-feeding patterns of native mosquitoes and insights into their potential role as pathogen vectors in the Thames estuary region of the United Kingdom

BackgroundThe range of vertebrate hosts on which species of mosquito blood-feed is an important parameter for identifying potential vectors and in assessing the risk of incursion and establishment of vector-borne pathogens. In the United Kingdom, studies of mosquito host range have collected relatively few specimens and used techniques that could only broadly identify host species. This study conducted intensive collection and analysis of mosquitoes from a grazing marsh environment in southeast England. This site provides extensive wetland habitat for resident and migratory birds and has abundant human nuisance biting mosquitoes. The aim was to identify the blood-feeding patterns of mosquito species present at the site which could contribute to the transmission of pathogens.MethodsTwice-weekly collections of mosquitoes were made from Elmley Nature Reserve, Kent, between June and October 2014. Mosquitoes were collected using resting boxes, by aspiration from man-made structures and using a Mosquito Magnet Pro baited with 1-octen-3-ol. Blood-fed specimens were classified according to the degree of blood meal digestion using the Sella scale and vertebrate origin determined using sequencing of a fragment of the mitochondrial cytochrome C oxidase subunit I gene. Mosquitoes that were morphologically cryptic were identified to species level using multiplex PCR and sequencing methods.ResultsA total of 20,666 mosquitoes of 11 species were collected, and 2,159 (10.4%) were blood-fed (Sella scale II-VI); of these 1,341 blood-fed specimens were selected for blood meal analysis. Vertebrate origin was successfully identified in 964 specimens (72%). Collections of blood-fed individuals were dominated by Anopheles maculipennis complex (73.5%), Culiseta annulata (21.2%) and Culex pipiens form pipiens (10.4%). Nineteen vertebrate hosts comprising five mammals and 14 birds were identified as hosts for mosquitoes, including two migratory bird species. Feeding on birds by Culex modestus and Anopheles atroparvus populations in England was demonstrated.ConclusionsThis study expands the vertebrate host range of mosquitoes in the Thames estuary region of the UK. Feeding on both resident and migratory bird species by potential arbovirus vectors including Cx. pipiens f. pipiens and Cx. modestus indicates the potential for enzootic transmission of an introduced arbovirus between migratory and local bird species by native mosquito species.

Detection of Theileria orientalis in mosquito blood meals in the United Kingdom

Theileria spp. are tick-borne protozoan parasites that infect a wide range of wild and domestic animals. In this study, the utility of xenosurveillance of blood-fed specimens of Culiseta annulata for detecting the presence of piroplasms in livestock was investigated. Blood-fed mosquitoes were collected at Elmley National Nature Reserve, Kent, United Kingdom. All specimens were morphologically identified, and DNA barcoding was used to confirm the morphological identification. Both the vertebrate host species and Theileria genome was detected within the bloodmeal by real-time PCR. Sequencing was used to confirm the identity of all amplicons. In total, 105 blood-fed mosquitoes morphologically identified as Cs. annulata were collected. DNA barcoding revealed that 102 specimens were Cs. annulata (99%), while a single specimen was identified as Anopheles messeae. Two specimens could not be identified molecularly due to PCR amplification failure. Blood meal analysis revealed that Cs. annulata fed almost exclusively on cattle at the collection site (n=100). The application of a pan-piroplasm PCR detected 16 positive samples (15.2%) and sequence analysis of the amplicons demonstrated that the piroplasms present in the blood meal belonged to the Theileria orientalis group. This study demonstrates how xenosurveillance can be applied to detecting pathogens in livestock and confirms the presence of Theileria species in livestock from the United Kingdom.

Molecular approaches for blood meal analysis and species identification of mosquitoes (Insecta: Diptera: Culicidae) in rural locations in southern England, United Kingdom

Thirty-four species of Culicidae are present in the UK, of which 15 have been implicated as potential vectors of arthropod-borne viruses such as West Nile virus. Identification of mosquito feeding preferences is paramount to the understanding of vector-host-pathogen interactions which, in turn, would assist in the control of disease outbreaks. Results are presented on the application of DNA barcoding for vertebrate species identification in blood-fed female mosquitoes in rural locations. Blood-fed females (n = 134) were collected in southern England from rural sites and identified based on morphological criteria. Blood meals from 59 specimens (44%) were identified as feeding on eight hosts: European rabbit, cow, human, barn swallow, dog, great tit, magpie and blackbird. Analysis of the cytochrome c oxidase subunit I mtDNA barcoding region and the internal transcribed spacer 2 rDNA region of the specimens morphologically identified as Anopheles maculipennis s.l. revealed the presence of An. atroparvus and An. messeae. A similar analysis of specimens morphologically identified as Culex pipiens/Cx. torrentium showed all specimens to be Cx. pipiens (typical form). This study demonstrates the importance of using molecular techniques to support species-level identification in blood-fed mosquitoes to maximize the information obtained in studies investigating host feeding patterns.