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The results of a recent study have shown that some areas of Mexico are experiencing 'vertical transmission' by mosquitoes of Zika virus.
This is not good news, as this type of mode of transmission of the virus could continue to spread Zika in Mexico for years.
This study published July 16, 2019 by the Centers for Disease Control and Prevention (CDC) of the United States revealed the natural vertical transmission of wild Ae. Aegypti mosquito populations in the municipality of Jojutla, Morelos State, Mexico.
In this new study, the researchers demonstrated the natural vertical transmission of the Zika virus by detecting viral RNA and isolating the infectious Zika virus from larvae hatched from eggs harvested in the field.
The researchers reported that Zika virus RNA was detected in 17 larval pools and obtained the complete genome of the virus by Next Generation Sequencing (NGS).
In 2016, the incidence of locally contracted Zika virus infections in humans increased in Morelos, Mexico, with 269 cases reported at the end of the year.
And, vertical transmission rates of Zika virus in the wild Ae. Aegypti populations were estimated by calculating maximum incremental reactivity (MIR).
The highest MIR (6.95), calculated from egg larvae collected in November 2016, contrasts with the MIR of eggs larvae collected in June 2016 (2.6).
This MIR trend could be correlated with the increase in the number of cases of Zika virus in humans reported in November, while in June, no human cases were reported.
The absence of reported human cases of Zika virus in June may be the result of asymptomatic cases, or cases clinically misdiagnosed as dengue virus infections, or both.
It is possible that vertical transmission contributes to the number of infected mosquitoes, which in turn are capable of transmitting the Zika virus to a larger number of humans.
However, the relative importance of vertical transmission for the maintenance and spread of the virus can not be elucidated, with the data available to date, said these researchers.
Transmission of the mosquito virus
Horizontal transmission is considered the most common mode of transmission of arbovirus between mosquitoes and their vertebrate hosts, including humans.
On the other hand, the maintenance of the dengue virus in the environment during the interepidemic periods is due to the "vertical" transmission of the virus by infected adult mosquitoes to their offspring for 7 successive generations.
The two mechanisms together are considered essential for the survival of viral pathogens in their habitats, preventing their extinction under harsh environmental conditions or in populations where the presence of sensitive mammalian hosts is low.
However, the evidence from this study is insufficient to confirm that vertical transmission is the main mechanism for Zika virus maintenance in wild Aedes mosquitoes.
Additional studies have also demonstrated the presence of infectious Zika virus in offspring of artificially infected Ae. aegypti and Ae. albopictus, suggesting that vertical transmission may occur in laboratory-reared mosquitoes.
Symptoms of Zika virus
Zika virus is an arthropod-borne (arbovirus), single-stranded, enveloped positive-sense RNA that belongs to the genus Flavivirus, family Flaviviridae.
Zika virus is closely related to other viruses of medical importance, such as dengue virus, West Nile virus and yellow fever.
Many people infected with Zika virus have no symptoms or only mild symptoms. The most common symptoms of Zika are fever, rashes and a headache.
The Zika virus has attracted the attention of specialists in recent years due to its rapid spread in the Pacific and the Americas in 2015, as well as severe neurological manifestations badociated with Zika virus infections, such as neonatal microcephaly and Guillain-Barré syndrome.
The CDC says that you should consult a health care provider if you develop symptoms and are living or have recently stayed in an area where the risk of zika is high.
Zika Virus News
As of July 16, 2019, the CDC and the states of Florida (26), California (21), Utah (1) and Nebraska (1) had reported 49 cases of Zika related to trips this year.
In addition, the US territory of Puerto Rico confirmed 22 cases of Zika in 2019. These new cases were contracted during the allegedly local transmission and transmitted by a mosquito in 2019.
This new research was funded by the CONACyT 183448, CONACyT 233977 and CONACyT 269826 grants. No conflicts of interest were disclosed.
Author Affiliations: Autonomous University of Mexico City, Mexico City, Mexico (Mr. Izquierdo-Suzán, S. Zárate, Mr. Yocupicio-Monroy); Instituto Politécnico Nacional, Mexico City (J. Torres-Flores); National Center for Crime Prevention and Control, Mexico City (Correa-Morales, C. González-Acosta); Instituto Nacional de Enfermedades Respiratorias, Mexico City (E.E. Sevilla-Reyes); Instituto Mexicano del Seguro Social, Mexico City (R. Lira); Institute of Security and Social Services of State Treatment, Mexico City (S.L. Alcaraz-Estrada).
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