What is Different in Northeastern Brazil? Culex

Wolbachia Could Infect Vertebrates (Including Humans)

World Map Showing Where Culex are Zika Vectors and Where Wolbachia-Infected Mosquitoes are Released
Credit: World Map by Christopher Schnese on flickr (CC-by-2.0) Mosquitoes, Colors, and Text by RoseWrites

Ever since researchers in China also found Culex p. quinquefasciatus to be a Zika vector,[1] I have been trying to piece together what is different about the Culex mosquitoes in northeastern Brazil and southeastern China.

Dr. Constância F. J. Ayres alerted our public health authorities early in 2016 that Culex could also be a Zika vector.

And I believe that Aedes aegypti are also transmitting Zika.

Yet, perhaps Aedes are the genus of mosquito most responsible for the majority of milder Zika cases.

The correlation between Wolbachia-infected Aedes releases and where the most devastating Zika cases are turning up caused me to dig deeper.

What's more, every study I have uncovered about Wolbachia-infected mosquito release safety (to date) has at least one of the following conflicts of interest:

  • A grant from the University of Queensland
  • Funded by the Foundation for the National Institutes of Health through the Grand Challenges in Global Health Initiative of the Bill & Melinda Gates Foundation as part of Eliminate Dengue
  • Funded by UK Medical Research Council, Wellcome Trust

And, every study has failed to assess the risks to birds and aquatic life that feed upon Wolbachia-infected Aedes larvae.

If birds are acquiring this new source of Wolbachia (with or without the Zika virus), it is a certainty that Culex mosquitoes will be carrying it too. In 1970, Zika was found in 15 percent of birds.

Dr. Peter Hotez Talks About Zika

Published Dec. 27, 2016 CGTN America

CGTV America’s Susan Roberts spoke to Dr. Peter Hotez, Dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, about the spread of the Zika virus. 


Culex Quinquefasciatus in Brazil Possess Two Mitochondial Types - Influenced by Wolbachia?

An eye-opening study by Morais et al. 2012 called Low genetic diversity in Wolbachia-Infected Culex quinquefasciatus (Diptera: Culicidae) from Brazil and Argentina[2] revealed the following:

  • Brazilian Culex quinquefasciatus populations share identical nd4 sequences to those in North America and parts of Asia, but are from 5 to 6 percent divergent from South African populations.
  • Mitochondrial diversity may be related to Wolbachia infection.
  • Culex quinquefasciatus appears to possess two mitochondrial types in Brazil. This fact should be taken into consideration in investigations of disease distribution and in aspects of blood-hosts in those locations ... as feeding preferences may be influenced by genetic factors.
It's alarming that "among the pipiens subgroup, insecticide-resistant populations tend to be infected with higher Wolbachia densities" (Echaubard et al. 2011).[3]
In terms of physical appearance, in 2010 Morais et al. discovered that Brazilian Culex quinquefasciatus from tropical regions had wing shapes distinct from subtropical populations (also demonstrated by the use of ace-2 molecular marker).[4]

The Interplay of Wolbachia and Mitochondria

I was surprised to read passages in mainstream media that downplay Wolbachia. I even saw it written "a benign bacterium called Wolbachia". And the fact that it is present in a fair percentage of insects doesn't make it any less worrisome.

Wolbachia is far from harmless. Here are some notable points from reputable sources:

Mitochondrial Evolution Using Concatenated Alignments Networks of protein LogDet distances for an alignment of 32 proteins constructed with Neighbor-NetCredit: Phylogeny Figures on flickr (CC-by-2.0)"Though Wolbachia apparently don't infect vertebrates, it can have an impact on human health. The nematode that causes river blindness in tropical countries is able to lay eggs and reproduce in humans only thanks to the Wolbachia bacteria infecting it. Wolbachia, not the nematode itself, trigger the immune response that damages the eye."[5]

I address the similarities between lymphatic filariasis (also caused by Wolbachia) and Zika in Wolbachia-Infected Mosquitoes Might Reduce Dengue, Enhance Zika, and Cause a Million Souls to Become Sterile.

"Wolbachia can come into contact with the mammalian immune system and acquire some of the characteristics of a bacterial pathogen. Moreover, Wolbachia has an intimate relationship with many arthropod vectors of vertebrate pathogens, such that it may have an indirect, but nevertheless very important, role to play in disease transmission."[6]

"Wolbachia was seen to be associated with different mitochondria, suggesting multiple horizontal transmission events and/or transmission paternal leakage of mitochondrial and/or Wolbachia."[7]

Image: Mitochondrial evolution using concatenated alignments networks of protein LogDet distances for an alignment of 32 proteins constructed with Neighbor-Net (Bryant and Moulton 2003) by Phylogeny Figures on flickr (CC-by-2.0).

"Since Wolbachia is co-inherited with mitochondria, natural selection acting over the bacterium will also affect mitochondria. Depending on the infection context, this hitchhiking effect may increase or decrease mitochondrial genetic diversity (Keller et al., 2004, Dean et al., 2003 and Shoemaker et al., 2003)." 

"Perhaps the most fascinating aspect of the biology of Wolbachia is the variety of phenotypes they are capable of exerting upon their host. Wolbachia have been found to be anything from essential endosymbionts to parasites that effectively kill non-infective individuals.[8]

Mitochondria: Things You May Not Know 

Transmission electron microscope image of a thin section cut through an area of mammalian lung tissueCredit: By Louisa Howard [Public domain], via Wikimedia Commons

Image Credit: By Louisa Howard [Public domain], via Wikimedia Commons

If you took biology in high school, you probably recall being told mitochondria are the powerhouse of the cell. But here are some things you may not know:

Mitochondria are found in the cytoplasm of all plant and animal cells. They are thought to have originated as a result of a cell engulfing a small bacterium and then the two units living in a symbiotic relationship.[11]
Yet, scientists from Australia, Italy, and Spain found instead that "the mitochondrial ancestor most likely had a flagellum, so was able to move, and possibly acted as a parasite, rather than prey, on early eukaryotic cells."[18]
"Our results challenge the paradigm - shown in every biology textbook - that mitochondria were passive bacteria gobbled up by a primordial cell," added co-author Dr. Nathan Lo from the University of Sydney's School of Biological Sciences.[18]
Mitochondria has its own DNA. Mitochondrial DNA is only inherited through the maternal line. Any mitochondrial DNA contributed by the father is actively destroyed by programmed cell death after a sperm fuses with an egg.[11]
Certain mutations are the source of mitochondrial disease that can affect areas of high energy demand such as brain, muscles, central nervous system and the eye.[11]
And a recent dissertation by Henry, Lucas Price, M.S. titled Exploring the ecology of maternal transmission in Drosophilia-Wolbachia symbiosis[12] states:

Wolbachia do not disperse alone, but must disperse with mitochondria ... Wolbachia and mitochondria were positively correlated in common laboratory strains, suggesting that Wolbachia and mitochondria utilize the similar host elements during maternal transmission and potentially compete.[12]

But Wolbachia is Already Present in Some Culex

Phylogeny of Wolbachia based on 16S rDNA gene sequencesCredit: PLOS ONE PHYLOGENY on flickr (CC-by-2.0)It's important to note that there are taxonomic issues. There are numerous types of Wolbachia. As noted by John H. Werren:

"Some Wolbachia researchers apply the species name W. pipientis (the B-Wolbachia found in C. pipiens) to all strains, including A-Wolbachia found in highly divergent host species. This is inappropriate."[9]

Indeed, Dr. Aileen Marty, a member of  WHO's Advisory Group on Mass Gatherings, Risk Assessments, Command & Control, EID (Emerging Infectious Diseases) tried to convince me "Culex already HAVE Wolbachia.  In fact, Wolbachia helps the mosquito survive."

Wolbachia are a monophyletic group composed of at least eight different supergroups (A–H). C and D are exclusively nematode symbionts; supergroups A and B comprise the majority of [what is thought to be] arthropod infections (Glowska et al., 2015).
Image of Phylogeny of Wolbachia based on 16S rDNA gene sequences by PLOS ONE PHYLOGENY on flickr (CC-by-2.0)

Further along, Dr. Werren warned:

"... to date, Wolbachia have only been found associated with arthropod reproductive tissues, and there is no evidence that they cause disease in vertebrates. However, given the abundance of arthropod species infected with Wolbachia, this possibility cannot be ruled out."[9]

"Multiple infections also influence compatibility type. In some species, individuals harbor infections with more than one strain of Wolbachia. Double infections with A- and B-Wolbachia have been found in over 15 species."[9]

Double infections appear to create new compatibility types.

Sperm from Wolbachia-infected males has a competitive advantage relative to sperm from uninfected males. This effect could accelerate spread of the infection, according to Wade & Chang, 1995.[10]
It is unknown whether Wolbachia carry plasmids [genes carried in plasmids provide bacteria with genetic advantages, such as antibiotic resistance], but indirect evidence suggests an infectious (viral) agent of Wolbachia may exist.[9]

Wolbachia Induced Cytoplasmic Incompatibility

Unidirectional and Bidirectional Wolbachia Induced Cytoplasmic Incompatibility
Credit: By Hu.johannes (Own work) [Public domain], via Wikimedia Commons

Cytoplasmic incompatibility (CI) is a phenomenon that results in sperm and eggs being unable to form viable offspring. The effect arises from changes in the gamete cells caused by intracellular parasites like Wolbachia.


Unidirectional CI: Infected males mated with uninfected females results in early embryonic lethality. Where all other crosses are compatible.


Bidirectional CI: Infected males with Wolbachia strain I mated with females infected by Wolbachia strain II results in embryonic lethality.

Wolbachia in Humans: Why Wouldn't it Happen?

From the get-go, I naturally assumed that if Culex mosquitoes can transmit filariasis to humans, that Wolbachia (released by filarial worms) can pass through the mosquito stinger (proboscis) and into a human.

And after learning just how connected Wolbachia is to mitochondria (and possibly competes with it), I could see why Zika might be enhanced by the presence of Wolbachia in a mosquito.

Dr. Ayres stressed:  "Zika is more related to the viruses transmitted by Culex."

Dr. Hunter conceded: "If you look at the support for the phylogenetic placement of Zika, there is 99 percent support for Zika in the clade that includes West Nile and Saint Louis encephalitis viruses."

As I cited earlier, mitochondrial disease affects areas of high energy demand such as brain, muscles, central nervous system, and the eye. The Zika virus targets those areas too.

Wolbachia, carried by Drosophila melanogaster, causes widespread degeneration of tissues, including brain, retina, and muscle, culminating in early death.

Wolbachia seems to target the gonads. John Timmer wrote a fascinating article called Meet Wolbachia: the male-killing, gender-bending, gonad-eating bacteria.[13] With a title like that, I'm sure you get the gist.

According to one Zika researcher: "After returning to his home in Colorado, U.S., he experienced common symptoms of Zika virus infection and symptoms of prostatitis. Four days later, he observed signs of hematospermia [blood in his semen], and on the same day, his wife had symptoms of Zika infection."[14]

Related: Zika Shrivels Testes, Drops Testosterone, and May Cause Infertility

Our Nervous System is Not Unlike Insects

A wonderfully composed webpage by the Manchester Fly Facility reminds us:

  • Just like us, flies have to breath, digest, move, learn and coordinate in order to survive. Due to our shared evolutionary history, many of our organs have common origins and serve the same purposes, and their development, organisation and function are often regulated by the same genes.[15]
  • The functions of genes and gene networks that regulate flies turned out to be astonishingly similar to processes in mammalian development.[15]

Work on the nervous system of Drosophila has made seminal contributions to modern neurobiology (Bellen et al., 2010, Nat Rev Neurosci 11, 514ff.) and there were many more examples given.

In humans, dysfunction of the basal ganglia can cause severe mental health problems ranging from autism, schizophrenia, and psychosis, to neurodegeneration—as seen in Parkinson’s disease, motor neuron disease and dementia—as well as sleep disturbances, attention deficits, and memory impairment. When parts of the central complex are affected in fruit flies, they display similar impairments.[17]

When graduate student Diana J. Starr crossed a Wolbachia-free strain of mutant fly with a wild fly infected with Wolbachia, she found most of the resulting females fertile. The clincher was that treating these flies with the antibiotic tetracycline to kill Wolbachia made them sterile.[5]

My point: Zika in Culex with Wolbachia (possibly amplified in birds) could be responsible for the most devastating cases of Zika infections we have been told about, to date. And I suspect if Wolbachia infects people multiple times, it may have a cumulative effect.

Wolbachia and Zika may be working in tandem.

To quote notable experts about the use of Wolbachia:

"These genetic tools might not be the best strategies for the Zika virus given that at this point there seem to be multiple vectors not only at the species but also at the population level. The current genetic technologies would not be appropriately applied to such complex systems." ~ Dr. Anthony James, University of California-Irvine

Dr. Werren of the University of Rochester (cited numerous times in this article) is a world-leading authority on the Wolbachia parasite. He cautioned:

Although Wolbachia is not known to infect any vertebrates, such as humans, lateral gene transfers "have happened before in the distant past".[16]

"In our very own cells and those of nearly all plants and animals are mitochondria, special structures responsible for generating most of our cells' supply of chemical energy. These were once bacteria that lived inside cells, much like Wolbachia does today."[16]

"Like Wolbachia, mitochondria have passively exchanged DNA with their host cells. Wolbachia could follow in the path of mitochondria, eventually becoming a necessary cell component."[16]
My question: is Wolbachia the Zika virus catalyst that is causing Culex mosquitoes to become formidable Zika vectors? Because there is nothing I can find in the literature that explains why having a skeleton (being a vertebrate) would protect humans or other species from the damaging effects of Wolbachia. 
If there is competition between mitochondria and Wolbachia in human cells, I fear that our mitochondria will lose (at least, initially). And we had better hope that antibiotic resistance won't be our downfall.
Yet, the results in flies suggest that killing Wolbachia with antibiotics could cause sterility. I wonder if this is already anticipated and perhaps the desired outcome.

Reminded of Jeff Goldblum in "The Fly"?



Investigate Wolbachia Postcard by RoseWrites on Zazzle
Credit: World Map by Christopher Schnese on flickr (CC-by-2.0) Colors and Text by RoseWrites November 24th, 2016 [Postcard Available on Zazzle.com]

Important Related Articles About the Zika Virus by Me

Zika Virus: Our Tainted Blood Supply

Zika and Its Path: What Our Public Health Authorities Are Hiding

Safe Mosquito Eradication That Works: Using Coffee, Bti, Rubbing Alcohol, and a Cat

Author's note: All of my citations have a clickable link to their source. The list is found in the bibliography at the end of this page.