Introduction and Spread of Dengue Virus 3, Florida, USA, May 2022-April 2023.

During May 2022-April 2023, dengue virus serotype 3 was identified among 601 travel-associated and 61 locally acquired dengue cases in Florida, USA. All 203 sequenced genomes belonged to the same genotype III lineage and revealed potential transmission chains in which most locally acquired cases occurred shortly after introduction, with little sustained transmission.

Outbreak of Locally Acquired Mosquito-Transmitted (Autochthonous) Malaria - Florida and Texas, May-July 2023.

Eight cases of locally acquired, mosquito-transmitted (i.e., autochthonous) Plasmodium vivax malaria, which has not been reported in the United States since 2003, were reported to CDC from state health departments in Florida and Texas during May 18-July 17, 2023. As of August 4, 2023, case surveillance, mosquito surveillance and control activities, and public outreach and education activities continue in both states. U.S. clinicians need to consider a malaria diagnosis in patients with unexplained fever, especially in areas where autochthonous malaria has been recently reported, although the risk for autochthonous malaria in the United States remains very low. Prompt diagnosis and treatment of malaria can prevent severe disease or death and limit ongoing transmission to local Anopheles mosquitoes and other persons. Preventing mosquito bites and controlling mosquitoes at home can prevent mosquitoborne diseases, including malaria. Before traveling internationally to areas with endemic malaria, travelers should consult with a health care provider regarding recommended malaria prevention measures, including potentially taking malaria prophylaxis. Malaria is a nationally notifiable disease; continued reporting of malaria cases to jurisdictional health departments and CDC will also help ensure robust surveillance to detect and prevent autochthonous malaria in the United States.

Vertical Transmission of Zika Virus by Florida Aedes aegypti and Ae. albopictus.

The Zika virus pandemic of 2015, with mosquitoes Aedes aegypti and Ae. albopictus as the putative vectors, prompted public health concerns and the need to improve our understanding of both the horizontal and vertical transmission of Zika virus. Local transmission is especially concerning for Florida, where these two mosquito species are abundant and widespread throughout much of the year. Here, we evaluate the relative vertical transmission and filial infection rate of progeny of Florida Ae. aegypti and Ae. albopictus following ingestion of infected blood by parental mosquitoes at either 6 or 7 log10 plaque forming units/mL of Zika virus. Florida Ae. aegypti exhibited higher rates of disseminated infection than Ae. albopictus, consistent with other studies indicating greater permissibility of Zika virus in Ae. aegypti. We observed low vertical transmission in both Ae. aegypti (1.1-3.2%) and Ae. albopictus (0-0.3%) mosquitoes, despite imbibing infected blood at titers that yielded high susceptibility to infection and modest horizontal transmission rates. Filial infection rates, testing individual mosquitoes for Ae. aegypti and Ae. albopictus, were 6-10% and 0-6.4%, respectively. Both these invasive Stegomyia mosquitoes were capable of vertically transmitting Zika virus under laboratory conditions, and approximately 5% of female progeny of Ae. aegypti were capable of transmitting Zika virus upon first bite.

Transmission of Asian Zika Lineage by Aedes aegypti and Ae. albopictus Mosquitoes in Florida.

The Asian lineage of Zika virus (ZIKV), a mosquito-borne pathogen originally from Africa, caused an epidemic into Brazil in 2015 and subsequently spread throughout the Americas. Local transmission in the U.S. is a public health concern, especially for Florida where the mosquito vectors Aedes aegypti and Ae. albopictus are widespread, abundant, and there is a high potential for virus introduction due to imported cases. Here we evaluate relative susceptibility to infection and transmission of Zika virus among geographic populations of Ae. aegypti and Ae. albopictus in Florida. Both species have been implicated as ZIKV vectors elsewhere, but both virus and vector genotype are known to influence transmission capacities and, hence, the risk of outbreaks. We test the hypothesis that Ae. aegypti and Ae. albopictus show geographic differences in midgut and salivary gland barriers that limit ZIKV transmission, using local populations of the two vector species recently colonized from three regions of Florida to compare their susceptibility to ZIKV infection, disseminated infection, and transmission potential. Susceptibility to infection was higher in Ae. aegypti (range 76-92%) than Ae. albopictus (range 47-54%). Aedes aegypti exhibited 33-44% higher susceptibility to infection than Ae. albopictus, with Ae. aegypti from Okeechobee, FL having 17% higher susceptibility to infection than Ae. aegypti from Miami, FL. Similarly, disseminated infection was higher in Ae. aegypti (range 87-89%) than Ae. albopictus (range 31-39%), although did not vary by region. Enhanced infection and disseminated infection in Ae. aegypti were associated with higher viral loads in mosquito samples than in Ae. albopictus. Transmission rates did not vary by species or region (range 26-47%). The results support the hypothesis that Ae. aegypti, but not Ae. albopictus, exhibited regional differences in midgut infection barriers. Our observation of higher vector competence for Ae. aegypti than Ae. albopictus, together with this species greater propensity to feed on humans, lends support to the notion that Ae. aegypti is regarded as the primary vector for ZIKV and public health concern in continental U.S.

Transfusion-Transmitted Cache Valley Virus Infection in a Kidney Transplant Recipient With Meningoencephalitis.

BACKGROUND: Cache Valley virus (CVV) is a mosquito-borne virus that is a rare cause of disease in humans. In the fall of 2020, a patient developed encephalitis 6 weeks following kidney transplantation and receipt of multiple blood transfusions. METHODS: After ruling out more common etiologies, metagenomic next-generation sequencing (mNGS) of cerebrospinal fluid (CSF) was performed. We reviewed the medical histories of the index kidney recipient, organ donor, and recipients of other organs from the same donor and conducted a blood traceback investigation to evaluate blood transfusion as a possible source of infection in the kidney recipient. We tested patient specimens using reverse-transcription polymerase chain reaction (RT-PCR), the plaque reduction neutralization test, cell culture, and whole-genome sequencing. RESULTS: CVV was detected in CSF from the index patient by mNGS, and this result was confirmed by RT-PCR, viral culture, and additional whole-genome sequencing. The organ donor and other organ recipients had no evidence of infection with CVV by molecular or serologic testing. Neutralizing antibodies against CVV were detected in serum from a donor of red blood cells received by the index patient immediately prior to transplant. CVV neutralizing antibodies were also detected in serum from a patient who received the co-component plasma from the same blood donation. CONCLUSIONS: Our investigation demonstrates probable CVV transmission through blood transfusion. Clinicians should consider arboviral infections in unexplained meningoencephalitis after blood transfusion or organ transplantation. The use of mNGS might facilitate detection of rare, unexpected infections, particularly in immunocompromised patients.

The Extrinsic Incubation Period of Zika Virus in Florida Mosquitoes Aedes aegypti and Ae. albopictus.

The Asian genotype of Zika virus (ZIKV) emerged in Brazil in 2015 and subsequently spread throughout the Americas. In July 2016, Florida experienced its first locally acquired ZIKV infection in the continental U.S. Concerns about health risks from ZIKV infection have increased the need to investigate the interactions between potential mosquito vectors and ZIKV. The time it takes for an arbovirus to propagate within a mosquito, and become transmissible, is the extrinsic incubation period (EIP). The EIP for potential mosquito vectors in Florida is unknown. To address this gap in the understanding of ZIKV epidemiology, Florida Aedes aegypti (L.) and Ae. albopictus (Skuse) were orally exposed to ZIKV infected blood meals and fully engorged mosquitoes were held at a constant temperature of 28 °C through the duration of the experiment. Saliva expectorates were collected from cohorts of mosquitoes and tested for the presence of ZIKV at three-day intervals over a period of 24 days to allow for an evaluation of the EIP of the emergent Asian lineage of ZIKV. High rates of infected bodies in Ae. albopictus (75-94%) and Ae. aegypti (68-86%) were observed throughout the incubation period, which did not differ by species. Higher rates of disseminated infection were observed later during the incubation period but did not differ between species. We calculated the 50% EIP to be shorter in Ae. albopictus than Ae. aegypti (16.2 and 18.2 days post infection, respectively). The competence for ZIKV observed in both species may contribute to high rates of ZIKV transmission in Florida populations.

Transmission Potential of Zika Virus by Aedes aegypti (Diptera: Culicidae) and Ae. mediovittatus (Diptera: Culicidae) Populations From Puerto Rico.

Recurrence of local transmission of Zika virus in Puerto Rico is a major public health risk to the United States, where mosquitoes Aedes aegypti (Linnaeus) and Aedes mediovittatus (Coquillett) are abundant. To determine the extent to which Ae. mediovittatus are capable of transmitting Zika virus and the influence of viremia, we evaluated infection and transmission in Ae. mediovittatus and Ae. aegypti from Puerto Rico using serial dilutions of infectious blood. Higher doses of infectious blood resulted in greater infection rates in both mosquitoes. Aedes aegypti females were up to twice as susceptible to infection than Ae. mediovittatus, indicating a more effective midgut infection barrier in the latter mosquito species. Aedes aegypti exhibited higher disseminated infection (40-95%) than Ae. mediovittatus (<5%), suggesting a substantial midgut escape barrier in Ae. mediovittatus. For Ae. aegypti, transmission rates were low over a range of doses of Zika virus ingested, suggesting substantial salivary gland barriers.

Florida Aedes aegypti (Diptera: Culicidae) and Aedes albopictus Vector Competency for Zika Virus.

Zika virus (ZIKV) first spread into Brazil in 2013 and is now present throughout the Americas. In 2016, Florida witnessed the beginnings of local ZIKV transmission. No reports of local transmission have been reported for 2018; however, travel related cases continue to be reported. Recurrence of local transmission in the United States is a major public health risk in Florida where vectors Aedes aegypti (Diptera: Culicidae, Linnaeus) and Aedes albopictus (Diptera: Culicidae, Skuse) are abundant and there is a high potential for virus reintroduction. A dose-response study was used to evaluate susceptibility and transmission potential of Florida Ae. aegypti and Ae. albopictus to ZIKV originating from Puerto Rico. Mosquitoes were orally exposed to one of three doses of ZIKV. Higher doses of infected blood resulted in overall greater infection rates in both mosquito species. Ae. aegypti and Ae. albopictus were susceptible to infection with ZIKV and revealed a significant species by dose interaction. At low doses, Ae. aegypti was significantly less susceptible to infection with ZIKV than Ae. albopictus (6.7% and 44.4%, respectively). In contrast, at high doses, Ae. aegypti was significantly more susceptible to infection than Ae. albopictus (75.8% and 53.8%, respectively). No significant differences were observed between Ae. aegypti and Ae. albopictus in disseminated infection (0-75%) and saliva infection (0-52.4%). These observations suggest greater susceptibility to infection for Ae. albopictus at lower doses likely encountered by viremic humans. However, low disseminated infection and saliva infection for Ae. albopictus, combined with catholic feeding behavior, are likely to limit transmission potential relative to Ae. aegypti.