First evidence of dengue infection in domestic dogs living in different ecological settings in Thailand

An Update on the Entomology, Virology, Pathogenesis, and Epidemiology Status of West Nile and Dengue Viruses in Europe (2018-2023)

In recent decades, increases in temperature and tropical rainfall have facilitated the spread of mosquito species into temperate zones. Mosquitoes are vectors for many viruses, including West Nile virus (WNV) and dengue virus (DENV), and pose a serious threat to public health. This review covers most of the current knowledge on the mosquito species associated with the transmission of WNV and DENV and their geographical distribution and discusses the main vertebrate hosts involved in the cycles of WNV or DENV. It also describes virological and pathogenic aspects of WNV or DENV infection, including emerging concepts linking WNV and DENV to the reproductive system. Furthermore, it provides an epidemiological analysis of the human cases of WNV and DENV reported in Europe, from 1 January 2018 to 31 December 2023, with a particular focus on Italy. The first autochthonous cases of DENV infection, with the most likely vector being Aedes albopictus, have been observed in several European countries in recent years, with a high incidence in Italy in 2023. The lack of treatments and effective vaccines is a serious challenge. Currently, the primary strategy to prevent the spread of WNV and DENV infections in humans remains to limit the spread of mosquitoes.

Serological and molecular detection of dengue virus in animals: A systematic review and meta-analysis

Introduction

Dengue is a vector-borne disease, especially important in tropical and subtropical areas. The first presentation of many arboviral diseases occurred mainly in animals, including multiple Alphaviruses and Flaviviruses, such as dengue.

Objective

To determine the serological and molecular frequency of the dengue virus in animals.

Methods

A systematic literature review was carried out in five databases for the proportion of animals infected with dengue, defined by molecular and serological tests. A meta-analysis was performed using a random-effects model to calculate the pooled prevalence and 95% confidence intervals (CI). Cochran?s Q test and the I2 statistic were used to assess the heterogeneity between the two studies.

Results

The presence of dengue in bats, primates, birds, sheep, horses, cattle, pigs, rodents and buffaloes, according to serological methods, had a prevalence of 10%, 29%, 8%, 1%, 11%, 0%, 49%, 2%, 7%, respectively. According to molecular methods, the presence of dengue in bats had a seroprevalence of 6.0%.

Conclusion

The present study confirms the presence of the Dengue virus in a large group of animal species, with potential implications as possible reservoirs of this virus, raising the possibility of zoonotic transmission.

Domestic Dogs as Sentinels for West Nile Virus but not Aedes-borne Flaviviruses, Mexico

We tested 294 domestic pet dogs in Mexico for neutralizing antibodies for mosquito-borne flaviviruses. We found high (42.6%) exposure to West Nile virus in Reynosa (northern Mexico) and low (1.2%) exposure in Tuxtla Gutierrez (southern Mexico) but very limited exposure to Aedes-borne flaviviruses. Domestic dogs may be useful sentinels for West Nile virus.

Production, Transmission, Pathogenesis, and Control of Dengue Virus: A Literature-Based Undivided Perspective

Dengue remains one of the most serious and widespread mosquito-borne viral infections in human beings, with serious health problems or even death. About 50 to 100 million people are newly infected annually, with almost 2.5 billion people living at risk and resulting in 20,000 deaths. Dengue virus infection is especially transmitted through bites of Aedes mosquitos, hugely spread in tropical and subtropical environments, mostly found in urban and semiurban areas. Unfortunately, there is no particular therapeutic approach, but prevention, adequate consciousness, detection at earlier stage of viral infection, and appropriate medical care can lower the fatality rates. This review offers a comprehensive view of production, transmission, pathogenesis, and control measures of the dengue virus and its vectors.

Animals as potential reservoirs for dengue transmission: A systematic review

Dengue is a rapidly spreading mosquito-borne flavivirus infection that is prevalent in tropical and sub-tropical regions. Humans are known to be the main reservoir host maintaining the epidemic cycles of dengue but it is unclear if dengue virus is also maintained in a similar enzootic cycle. The systematic review was conducted in accordance to Cochrane's PRISMA recommendations. A search was done on PubMed, EMBASE, Scopus and Cochrane Library. Key data on animal dengue positivity was extracted and classified according to animal type and diagnostic modes. Of the 3818 articles identified, 56 articles were used in this review. A total of 16,333 animals were tested, 1817 of which were positive for dengue virus by RT-PCR or serology. Dengue positivity was detected in bats (10.1%), non-human primates (27.3%), birds (11%), bovid (4.1%), dogs (1.6%), horses (5.1%), pigs (34.1%), rodents (3.5%), marsupials (13%) and other small animals (7.3%). While majority of dengue positivity via serology suggests potential enzootic transmission, but regular dengue virus spillback cannot be excluded. With the exception of bats, acute infection among animals is limited. Further investigation on animals is critically required to better understand their role as potential reservoir in dengue transmission.

Sero-epidemiological study on Dengue fever virus in humans and camels at Upper Egypt

BACKGROUND AND AIM

Dengue fever (DF) is an important mosquito-borne viral zoonosis affecting over 100 countries worldwide and putting about 3.9 billion people at risk of infection. The disease has re-emerged in Egypt since 2011; however, there is a paucity of recent epidemiological data available. Therefore, in this study, we employed a cross-sectional study to determine DF prevalence in humans and camels in Asyut and Sohag Governorates, Egypt, during 2019.

MATERIALS AND METHODS

A total of 91 humans and a similar number of dromedary camels were utilized in this study. Sera were obtained and analyzed for the presence of specific antibodies against DF virus using enzyme-linked immunosorbent assay. Related epidemiological data affecting the disease spread in humans and camels were recorded and statistically analyzed.

RESULTS

The seroprevalence of DF in humans and camels was 12.09% and 3.3%, respectively. The disease varied significantly by the species examined as humans were found to be at a higher risk of acquiring the infection compared to camels. Nearly equal odds of exposure (odds ratio [OR]) were seen in the individuals with close contact with camels compared to those without; however, individuals exposed to mosquitoes were at approximately 3 times higher risk of infection (OR=2.95 [95% confidence interval [CI], 0.73-11.93]) compared to individuals who were not exposed to mosquitoes (OR=0.033 [95% CI, 0.084-1.37]). Interestingly, DF seropositivity in camels was significantly related to the presence or absence of symptoms within 2 weeks before sampling (p=0.02) where symptomatic animals had higher odds of exposure (OR=19.51 [95%, 0.97-392.3]) compared to asymptomatic ones (OR=0.05 [95%, 0.002-1.03]).

CONCLUSION

The current study reports the presence of specific antibodies against dengue virus (DENV) in humans residing within Asyut and Sohag Governorates, Egypt. Furthermore, it provides the first serological evidence of DENV circulation in camels which is alarming. A more comprehensive study is needed; however, this baseline investigation underscores the urgent need for increasing awareness among people residing in the area as well as application of the appropriate mosquito control measures to avoid further spread of the disease.

Robust dengue virus infection in bat cells and limited innate immune responses coupled with positive serology from bats in IndoMalaya and Australasia

Natural reservoir hosts can sustain infection of pathogens without succumbing to overt disease. Multiple bat species host a plethora of viruses, pathogenic to other mammals, without clinical symptoms. Here, we detail infection of bat primary cells, immune cells, and cell lines with Dengue virus. While antibodies and viral RNA were previously detected in wild bats, their ability to sustain infection is not conclusive. Old-world fruitbat cells can be infected, producing high titres of virus with limited cellular responses. In addition, there is minimal interferon (IFN) response in cells infected with MOIs leading to dengue production. The ability to support in vitro replication/production raises the possibility of bats as a transient host in the life cycle of dengue or similar flaviviruses. New antibody serology evidence from Asia/Pacific highlights the previous exposure and raises awareness that bats may be involved in flavivirus dynamics and infection of other hosts.

Evolution of endemic and sylvatic lineages of dengue virus

Recent disease outbreaks have raised awareness of tropical pathogens, especially mosquito-borne viruses. Dengue virus (DENV) is a widely studied mammalian pathogen transmitted by various species of mosquito in the genus Aedes, especially Aedes aegypti and Aedes albopictus. The prevailing view of the research community is that endemic viral lineages that cause epidemics of DENV in humans have emerged over time from sylvatic viral lineages, which persist in wild, non-human primates. These notions have been examined by researchers through phylogenetic analyses of the envelope gene (E) from the four serotypes of DENV (serotypes DENV-1 to DENV-4). In these previous reports, researchers used visual inspection of a phylogeny in order to assert that sylvatic lineages lead to endemic clades. In making this assertion, these researchers also reasserted the model of periodic sylvatic to endemic disease outbreaks. Since that study, there has been a significant increase in data both in terms of metadata (e.g., place and host of isolation) and genetic sequences of DENV. Here, we re-examine the model of sylvatic to endemic shifts in viral lineages through a phylogenetic tree search and character evolution study of metadata on the tree. We built a dataset of nucleotide sequences for 188 isolates of DENV that have metadata on sylvatic or endemic sampling along with three orthologous sequences from West Nile virus as the outgroup for the phylogenetic analysis. In contrast to previous research, we find that there are several shifts from endemic to sylvatic lineages as well as sylvatic to endemic lineages, indicating a much more dynamic model of evolution. We propose that a model that allows oscillation between sylvatic and endemic hosts better captures the dynamics of DENV transmission.

Viral Hemorrhagic Fevers Other than Ebola and Lassa

Viral hemorrhagic fevers represent a group of diseases caused by enveloped RNA viruses. The epidemiology is broadly variable, ranging from geographically localized to more diffuse infections. Viral hemorrhagic fevers are classified as category A bioweapon agents by the Centers for Disease Control and Prevention. Viral hemorrhagic fevers are severe febrile illnesses with hemorrhagic phenomena. Laboratory diagnosis takes place in highly specialized reference laboratories. Treatment is essentially supportive. In this article, we focus the attention on yellow fever and viral hemorrhagic fevers other than Ebola and Lassa virus diseases that have been described elsewhere in this issue.

Safety, Tumor Reduction, and Clinical Impact of Zika Virus Injection in Dogs with Advanced-Stage Brain Tumors

Malignant brain tumors are among the most aggressive cancers with poor prognosis and no effective treatment. Recently, we reported the oncolytic potential of Zika virus infecting and destroying the human central nervous system (CNS) tumors in vitro and in immunodeficient mice model. However, translating this approach to humans requires pre-clinical trials in another immunocompetent animal model. Here, we analyzed the safety of Brazilian Zika virus (ZIKV^BR) intrathecal injections in three dogs bearing spontaneous CNS tumors aiming an anti-tumoral therapy. We further assessed some aspects of the innate immune and inflammatory response that triggers the anti-tumoral response observed during the ZIKV^BR administration in vivo and in vitro. For the first time, we showed that there were no negative clinical side effects following ZIKV^BR CNS injections in dogs, confirming the safety of the procedure. Furthermore, the intrathecal ZIKV^BR injections reduced tumor size in immunocompetent dogs bearing spontaneous intracranial tumors, improved their neurological clinical symptoms significantly, and extended their survival by inducing the destruction specifically of tumor cells, sparing normal neurons, and activating an immune response. These results open new perspectives for upcoming virotherapy using ZIKV to destroy and induce an anti-tumoral immune response in CNS tumors for which there are currently no effective treatments.

Sylvatic dengue virus type 4 in Aedes aegypti and Aedes albopictus mosquitoes in an urban setting in Peninsular Malaysia

Dengue fever is endemic in Malaysia, contributing to significant economic and health burden in the country. Aedes aegypti and Ae. albopictus are the main vectors of the dengue virus (DENV), which circulates in sylvatic and human transmission cycles and has been present in Malaysia for decades. The study investigated the presence and distribution of DENV in urban localities in the Klang Valley, Peninsular Malaysia. A total of 364 Ae. aegypti and 1,025 Ae. albopictus larvae, and 10 Ae. aegypti and 42 Ae. albopictus adult mosquitoes were screened for the presence of DENV. In total, 31 (2.2%) samples were positive, of which 2 Ae. albopictus larvae were co-infected with two serotypes, one with DENV-2 and DENV-3 and the other with DENV-3 and DENV-4. Phylogenetic analysis determined that the isolates belonged to DENV-1 genotype I (1 Ae. aegypti adult), DENV-2 (1 Ae. albopictus larva), DENV-3 genotype V (3 Ae. aegypti larvae and 10 Ae. albopictus larvae) and DENV-4 genotype IV (6 Ae. aegypti larvae and 12 Ae. albopictus larvae), a sylvatic strain of DENV-4 which was most closely related with sylvatic strains isolated from arboreal mosquitoes and sentinel monkeys in Peninsular Malaysia in the 1970s. All four DENV serotypes were co-circulating throughout the study period. The detection of a sylvatic strain of DENV-4 in Ae. aegypti and Ae. albopictus mosquitoes in urban areas in Peninsular Malaysia highlights the susceptibility of these vectors to infection with sylvatic DENV. The infectivity and vector competence of these urban mosquitoes to this strain of the virus needs further investigation, as well as the possibility of the emergence of sylvatic virus into the human transmission cycle.

Identification of Host Blood Meals of Mosquitoes (Diptera: Culicidae) Collected at the Aripo Savannas Scientific Reserve in Trinidad, West Indies

Surveillance for blood-fed female mosquitoes was performed between August 2015 and February 2016 at sites along the periphery of the Aripo Savannas Environmentally Reserve (ASSR) located in northeastern Trinidad, West Indies. We collected engorged female mosquitoes representing 13 species. DNA extractions from dissected abdomens were subjected to PCR amplification with three primer pairs targeting the mitochondrial cytochrome oxidase I and cytochrome b gene sequences. High-quality sequence information and host identification were obtained for 42 specimens representing eight mosquito species with at least one primer combination. A broad range of vertebrates including humans were identified, but the majority were nonhuman mammals, both domestic and wild. Domestic dogs were the most common host and may represent potential sentinel species for monitoring local enzootic arbovirus activity in Trinidad. Culex declarator Dyer and Knab and Culex nigripalpus Theobald were the most common blood-fed mosquito species comprising 79.1% of the total number identified. These species obtained blood meals from birds, nonhuman mammals, and human hosts, and therefore pose significant risks as potential bridge vectors for epizootic arbovirus transmission in the ASSR area as well as other sylvan areas in Trinidad. These data represent the first such results for Trinidad.

The distribution of important sero-complexes of flaviviruses in Malaysia

Flaviviruses (FVs) are arthropod-borne viruses of medical and veterinary importance. Numerous species of FVs have been isolated from various host; mainly humans, animals, ticks, and mosquitoes. Certain FVs are extremely host-specific; at the same time, some FVs can infect an extensive range of species. Based on published literatures, 11 species of FVs have been detected from diverse host species in Malaysia. In humans, dengue virus and Japanese encephalitis virus have been reported since 1901 and 1942. In animals, the Batu Cave virus, Sitiawan virus, Carey Island, Tembusu virus, Duck Tembusu virus, and Japanese encephalitis viruses were isolated from various species. In mosquitoes, Japanese encephalitis virus and Kunjin virus were isolated from Culex spp., while Zika virus and Jugra virus were isolated from Aedes spp. In ticks, the Langat virus was isolated from Ixodes spp. One of the major challenges in the diagnosis of FVs is the presence of sero-complexes as a result of cross-reactivity with one or more FV species. Subsequently, the distribution of specific FVs among humans and animals in a specific population is problematic to assess and often require comprehensive and thorough analyses. Molecular assays such as quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and digital droplet RT-PCR (ddRT-PCR) have been used for the differentiation of flavivirus infections to increase the accuracy of epidemiological data for disease surveillance, monitoring, and control. In situations where sero-complexes are common in FVs, even sensitive assays such as qRT-pCR can produce false positive results. In this write up, an overview of the various FV sero-complexes reported in Malaysia to date and the challenges faced in diagnosis of FV infections are presented.