Knowledge and use of prevention measures for chikungunya virus among visitors to Virgin Islands National Park

By: Helen Beilinson

Reprinted with permission from Open Science DB. Open Science DB is a centralized database of scientific research. It is led by graduate students from Northwestern University and scientists from leading research universities/institutes contribute summaries of research papers to the database. Each summary is reviewed to ensure accuracy and accessibility. 

 

Pretravel health research— not something people typically think about when they’re packing their flip flops and sunscreen for a sunny vacation in the tropics. Unfortunately, mosquitos love the warm temperatures just as much as humans do. Without the knowledge of proper mosquito bite prevention strategies, vacationers are put at risk for catching viruses carried by mosquitos.
 
Chikungunya is caused by Chikungunya Virus that is transmitted to human by mosquitoes. Chikungunya outbreaks have been observed in countries in Africa, Asia, Europe, and the Indian and Pacific Oceans. But Chikungunya spread to Americas in 2013, and by the end of 2014, about 1 million suspected and confirmed cases of Chikungunya were reported across 43 countries in the Americas. Infected people start feeling symptoms about a week after being infected by a Chikungunya-carrying mosquito, the most common of which are a high fever and joint pain. Although most patients start feeling better within a week, many experience prolonged joint pain up to several months. There is no vaccine against Chikungunya, so the best way to prevent infection is making sure that people are educated about the virus and instilling mosquito bite prevention practices. However, there is no information regarding how many travelers are aware of Chikungunya and prevention methods.  
 
To answer this question, the Center for Disease Control and Prevention (CDC) investigated what percentage of travelers to the U.S. Virgin Islands are aware of mosquito-borne diseases (Chikungunya and other viruses) and mosquito bite prevention measures. Visitors to Virgin Islands National Park on St. John were asked to complete a questionnaire addressing knowledge related to mosquito-spread diseases and prevention measures .446 of 783 travelers completed the survey.
 
According to the survey results, more than half of respondents were unaware of Chikungunya virus. Moreover, the majority responded that they had not been wearing clothing treated with an insect repellent or long-sleeve shirts/pants, or using bed nets for the past three days.
 
Overall, this survey showed that most visitors arrive the U.S. Virgin Islands without adequate pre-travel research and knowledge about mosquito safety. As the number of international travelers increases each year, this survey data strongly emphasizes the urgent need for developing creative ways to encourage pre-travel health research among travelers. 

The Other Sputnik: The First Known Virophage

By: Helen Beilinson

For every organism on earth, there are a multitude of viruses that can infect it. Every. Single. Organism. There are viruses that infect everything from bacteria to fish to humans, and anything in between. I’m going to tell you about one of my personal favorite viruses, Sputnik.

But first, let me introduce our host, the amoeba. Amoebae are single celled organisms, more closely resembling our cells than those of bacteria. Unlike humans, they don’t have an extensive immune system that protects them from harmful pathogens in their environment. Their main mechanism of protection is ‘eating’ things in their environment and breaking them down, in a process called ‘phagocytosis’. Although this defense works great often enough, there is not much the amoeba can do to protect itself once it’s infected with a virus.

One such virus is the Mamavirus. Mamavirus is a HUGE virus at around 750 nm in diameter. This may seem small, but that’s about half the size of the bacterium E. coli and it’s almost eight times as large as the infamous influenza virus. You can even see it under a regular light microscope, the kind of microscope used in many high school science labs, compared to most other smaller viruses that you need a high powered microscope to see them. It was first found almost seven years ago living inside amoeba in a cooling tower. Mamavirus lives and replicates in the cytoplasm of amoeba, where it sets up a “replication factory” that takes over the cell. This replication factory is where the virus replicates its DNA genome and makes the proteins necessary to build the outer shell in which it keeps its genome. Once Mamavirus replicates to a high degree, the viruses break down the amoeba cell, a process called ‘lysis’, to be released. As I’m sure is clear, this isn’t a great fate for the amoeba who has little defense against the virus once it starts replicating. That’s where Sputnik comes in.

Sputnik is a very small DNA virus, only about 50 nm in size, about fifteen times smaller than Mamavirus. It became fairly famous after its discovery as the first known virophage, a virus that infects viruses. That’s right—Sputnik is a virus that infects viruses. In fact, it infects Mamaviruses. Although Sputnik can infect amoeba on its own, it’s not that great at replicating by itself. However, when the amoeba is also infected with Mamavirus, Sputnik replicates like crazy. It takes over Mamavirus’ replication factory, which is a perfect little nook for the smaller virus to replicate. Although it might sound kind of unpleasant to be infected with two viruses at once, it’s actually a benefit for the amoeba. By hijacking the Mamavirus’ machinery, Sputnik reduces the ability for the big virus to replicate and make proper virions (or virus particles). It can reduce the Mamavirus load up to 70% and decreases amoeba lysis by threefold. Turns out the old proverb “the enemy of my enemy is my friend” really is the case with the amoeba and Sputnik.

Since the discovery of Sputnik, many more virophages have been discovered, which predominantly attack the large viruses that infect amoeba and zooplankton (a marine microorganism). Virophages have increased our knowledge of the deep complexity of the microbial world. As these critters are essentially brand new to our understanding, there is still a lot to learn about how they influence our ecosystems. There has been an ongoing battle amongst scientists about whether or not viruses are living things. Without getting too much into the details of things, the major point of contention is whether we can consider something living if it has to live within another organism’s cells to replicate. Maybe we need to reconsider whether we should classify viruses are living organisms or not. If they can also be infected with viruses, just like us and our pets and the bacteria that live in our guts—why can’t they be alive?

Viral infections and the microbiota

By: Helen Beilinson

Take home points:

1)    The microbiota can influence viral infections—exacerbating disease or preventing disease—so we need to be mindful of how we take antibiotics during viral infection

2)    Antibiotic treatment during flu infection can exacerbate disease

3)    Antibiotic treatment during other viral infections could prevent viruses from taking advantage of immunosuppressive properties of microbiota

 The microbiota—two words that have been splattered across scientific papers, the evening news, and “yogurt for women” packages. The multitude of bacterium that live within and on us constitutes, essentially, another organ that plays a role in many aspects of development and maintenance of the larger organism. It has been long appreciated that the microbiota plays a beneficial role in a host’s metabolism. However, only recently it has been shown that the microbiota is a significant player in the host’s immune system. In fact, it has a huge influence on how we interact with external pathogens and on the pathogenesis (the development of disease) of these pathogens. The predominantly bacterial microbiota live mostly at mucosal surfaces of the host (such as the gastrointestinal tract, genital mucosa, and upper airways), as well as on the skin. Interestingly, viruses are predominantly spread through routes where they would interact with the aforementioned microbiota. Thus, it is highly probable that the microbiota and viral pathogens interact and influence each other in some way. In fact, it has been documented that the microbiota can either obstruct or advance infections of various viral pathogens (or have no effect).

In mouse studies, it has been shown that eliminating the microbiota, either through antibiotics treatment (treatments against bacteria) or by raising mice germ-free (meaning that they have never been colonized with any bacteria), is very detrimental during influenza infection. Mice have more viral particles, higher mortality rates, and more degeneration and death of their lung tissue without their proper bacterial population. The mechanism of microbiota-dependent protection currently is unknown. This trend is incredibly important to study for its implications in human health. Flu infection changes the landscape of our lungs, making it easier for bacteria to infect the lungs. One such bacterium is Streptococcus pneumoniae, a causative agent of pneumonia. The most fatal cases of influenza are due to such secondary bacterial infections. Increases in mortality due to co-infection have been confirmed in mouse models. When patients enter the hospital with bacterial pneumonia, they are placed on antibiotics. This could potentially exacerbate flu disease by eliminating the beneficial bacteria of the patient’s microbiota, leading to death. Unfortunately, there have not yet been studies to show that antibiotic treatment causes patients to fare worse in co-infection situations.

In theory, our immune systems are activated once they sense an invader via certain molecular patterns that are unique to the invaders. For all intents and purposes, however, the molecular patterns decorating pathogenic bacteria are the same as those decorating the bacteria composing our microbiota. Although one of the current mysteries of the microbiota is why our immune system doesn’t eliminate it, it is known that these commensal organisms possess immunosuppressive properties. For example, a molecule that decorates the surface of particular bacteria is called lipopolysaccharide (LPS). There are various forms of LPS, some forms are immunostimulatory, while others, such as those expressed by the microbiota, are immunosuppressive. It has been shown that there are viruses that take advantage of the immunosuppressive properties of commensal LPS to dampen the responses of the host, allowing for active viral replication. Thus, although depletion of a host’s microbiota may be detrimental in flu infection, in cases where the microbiota aids viral replication and disease progression, antibiotics may be a source of treatment.

Studies in mice utilizing two different retroviruses (the family of viruses to which HIV belongs) have shown that these viruses require the presence of the microbiota to be present to flourish. By binding to LPS of the gut bacteria, the viral particles stimulate immunosuppressive pathways, allowing the virus to replicate without the host attempting to eliminate it. These studies were done in mice with murine viruses, so the question remains: Do human viruses interact similarly with LPS? Potentially.

It has been shown that HIV virions can directly bind to LPS molecules. It has also been shown that the presence of LPS during HIV infection (in a series of experiments in cells, not full organisms) decreases the “activated” state of antiviral immune cells, called plasmacytoid dendritic cells, preventing them from potently attacking infected cells. LPS is recognized by Toll-like receptor 4 (TLR4) in our immune system. In an unknown fashion, different LPS variants stimulate TLR4 to produce either a pro- or anti-inflammatory state, which is defined by immune signaling molecules called cytokines. An HIV protein, Tat, has been shown to stimulate the same immunosuppressive pathway as the mouse viruses by interacting with TLR4. This study did not show whether or not LPS was present in the experiments shown (LPS is a pesky molecule that is incredibly difficult to eliminate in a lab setting). Either way, it points to interesting evidence that HIV, as the mouse retroviruses, has possibly evolved the ability to take advantage of the immunosuppressive properties of the microbiota to allow for its replication. Thus, antibiotic treatment could be a potential treatment for HIV replication by decreasing the amount of commensal-expressed LPS that the virus may take advantage of to evade the immune system.

Living predominantly in areas that are directly exposed to the elements and invading pathogens, our microbiota may hold essential information regarding how our body battles infection and either wins or loses. The modulation of our live-in bugs will certainly be a future step in medicine in aiding the treatment of various infections, including those of viral pathogens. So next time you have a viral infection, be sure to ask your doctor whether it is safe for you to take antibiotics—or whether it could possibly help your immune system eliminate the infection.

It is important to note that neither the flu nor the HIV findings have been confirmed in humans, particularly the HIV studies. The intricacies of the microbiota, and particularly the details of how it interacts with intruding viruses, are still very enigmatic. Presented here are very brief summaries of very few papers on this topic, these should not be taken as medical advice.

Is the human immune system driving HIV to become less virulent?

By: Zuri Sullivan

Humans are extremely diverse. We have different skin colors, different hair colors, different personalities, different body types…in almost every characteristic, no two people are exactly the same. One of the ways in which we are most diverse, and one of the most important ways that we are diverse, is our HLA type, which stands for human leukocyte antigen. The HLA locus is actually the most polymorphic, or variable, set of genes in the human genome. Currently, the number of alleles, or types, of the two HLA classes is 9,232 for HLA class I, and 3,010 for HLA class II. Compare that to the number of skin, hair, or eye colors that exist in our species, and you can appreciate how diverse our HLA type is. From an evolutionary standpoint, this high level of diversity in our HLA alleles is crucial for the survival of our species, as HLA alleles can affect what kinds of infections or autoimmune disease we’re susceptible to. Thus, by selecting for a high level of diversity at the HLA locus, evolution has safeguarded our species against being wiped out by any one pathogen, because we each have a differential susceptibility to different pathogens.

One such pathogen is the human immunodeficiency virus (HIV), which is the leading cause of death from an infectious agent worldwide.  And indeed, there are certain HLA alleles that confer protection against HIV. In particular, two alleles, HLA-B57 and HLA-B58, are strongly associated with HIV elite control, the phenomenon by which some individuals get infected with the virus but never progress to AIDS, even in the absence of anti-HIV drugs. The presence of these protective alleles really illustrates the evolutionary utility of HLA diversity—in the absence of modern medicine, these people would likely be the only ones to survive HIV infection.

Evolution is a two way street, however, and just as viruses exert evolutionary pressure on our immune system, our immune system exerts evolutionary pressure on viruses, including HIV. That’s the subject of a paper recently published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), in which researchers from Oxford University showed that in areas with an extremely high burden of HIV, protective HLA alleles may be driving the virus to become less virulent.

What would be the advantage to the virus of becoming less virulent? In the case of viruses that kill their hosts quickly, such as Ebola, being less virulent would likely help the virus to spread. In order to infect other individuals, viruses need their host to be alive, and ideally walking around and contacting other individuals that can get infected. If a virus causes debilitating disease soon after infection, its host is less able to spread the infection to other individuals. So extremely virulent viruses, like Ebola, are actually bad for us (the host) and bad for the virus. This is why some of the most successful viruses, like rhinovirus (the cause of the common host) and influenza virus (the cause of the flu) don’t make most people extremely sick, and have managed to stick around in the population for centuries.

Another reason why a virus would become less virulent is that virulence could be a trade off for another advantage. Often when pathogens acquire mutations that allow them to resist certain evolutionary pressures, such as antibiotics or the immune system, these mutations have a fitness cost to the pathogen. But, the relative benefit of evading the immune system or antibiotics outweighs the cost of a moderate decrease in fitness. This is the hypothesis raised by Payne, et al in their PNAS paper.

They compared Botswana and South Africa, two countries with an extremely high burden of HIV, but an overall higher seroprevalence (infections per capita) in Botswana. First, they found that HIV-infected people had relatively lower viral loads than those in South Africa, suggesting that circulating viruses in Botwswana may have overall lower replicating capacity than viruses in South Africa. When they directly tested the replicative capacity of viruses isolated from 64 infected individuals in Botswana and 16 in South Africa, they confirmed that viruses from the cohort of Botswanans had lower replicative capacity. To look at whether protective HLA alleles may be playing a role in this differential viral replicative capacity, they next looked at viral mutations known to confer resistance to HLA-B57 and HLA-B58. Their results seemed consistent with their hypothesis—viruses from the Botswana cohort had a greater proportion of resistance mutations to HLA-B57 and 58 than those from the South Africa cohort. Finally, they compared a South African cohort from the early 2000s to one from 2012-13, and found that the frequency of mutations that allow HIV to escape protective HLA alleles had increased during this period, further supporting the idea that the virus is evolving resistance to these protective alleles over time.

One caveat to the findings in this study is that they were unable to find a correlation between viral replicative capacity and HLA-driven mutations. This suggests that this evolutionary relationship is more complex than was captured by their experiments, and that other factors, such as HLA diversity and antiretroviral therapy coverage, are likely important. However, other studies in South Africa have found viral replicative capacity to be correlated with the accumulation of HLA-driven mutations, supporting the overall idea that the mutations to evade the immune system come at a cost to viral fitness.

These results echo a longstanding phenomenon in the study of HIV and its close relative, siminan immunodeficiency virus (SIV), which infects non-human primates. While HIV infection in humans results in mortality rate close to 100% when untreated, many primate species, such as the African green monkey, can be infected with SIV without any apparent effect on their health. This points to the importance of host-pathogen co-evolution in disease susceptibility. HIV has infected the human population for less than a century, while SIV has been around for tens of millennia. Over that amount of time, both virus and host have evolved to resist each other without overtly killing each other. While it’s unlikely that we will see any HIV-driven evolutionary pressure on our on biology in our lifetime, it is clear our biology has placed significant pressure on the virus in its short history.