Public service announcement

A repeat from 2011 but consider this a public service announcement.

Regardless of what you may have heard about chlamydia it's actually HPV, Human Papillomavirus Virus, that is the most common sexually transmitted infection in the US. One of the reasons for this is that in many cases the infected person has no signs or symptoms. Because of this the CDC estimate that by the age of 50 more than 80% of American women will have contracted at least one strain of genital HPV.

Whoa. Screechy noise. Backup.  By the age of 50 more than 80% of American women will have contracted at least one strain of genital HPV.

Although only a small percentage of these women will develop cervical cancer the fact that such large numbers of women are infected each year means that up to 1 million American women are diagnosed with cervical dysplasia each year. Cervical dysplasia, caused by HPV, is a precursor to cervical cancer and is painful and costly to treat. Of these 1 million cases each year about 11,000 subsequently develop cervical cancer and about 4,000 of these women will die. Every year.

So a safe and effective vaccine is going to be a great discovery right?

Widespread vaccination has the potential to reduce cervical cancer deaths around the world by as much as two-thirds, if all women were to take the vaccine and if protection turns out to be long-term. In addition, the vaccines can reduce the need for medical care, biopsies, and invasive procedures associated with the follow-up from abnormal Pap tests, thus helping to reduce health care costs and anxieties related to abnormal Pap tests and follow-up procedures.

—American National Cancer Institute

Because so many women are infected it is clear that women need to be vaccinated before they can become infected. The best way to do this is to vaccinate them before they become sexually active .

Oh oh. We used the sex word.

 

 

Wait, am I missing something here? We leave it up to private companies to develop vaccines and then we find it somehow sinister if they push for mandatory vaccinations when they develop an effective vaccine against a disease that kills thousands. Oh and did I mention that it is estimated (by the CDC) that at any one time 1% of sexually active adults have genital warts (also caused by HPV).

Don't make me post the genital wart pictures....

Bad news everyone..

 Hitting the news today is a report on a new strain of gonorrhea that is resistant to all available antibiotics.

Here's a link to the MSNBC article quoted below, but you can find hundreds of news reports on the story via google news.

For several years, public health officials have been concerned that gonorrhea, one of the most prevalent STDs in the world, might become resistant to the last widely available antibiotics used to treat it, a class of drugs called cephalosporins.  


Now, it has.

In the space of one week, infectious disease specialists have received a one-two punch of bad news that confirms those fears, including the discovery of a new, cephalosporin-resistant strain of the bacteria.

Expedited Partner Therapy

Yesterday's LA Times had an article about some new programs to help combat sexually transmitted disease.

They mainly talk about the 'I want the kit' program that supplies free in-home testing kits for three of the most commonly reported STDs, however they also mention the Get Yourself Talking, Get Yourself Tested program and the more controversial  Expedited Partner Therapy  (EPT) which allows those who test positive for certain sexually transmitted diseases to take home antibiotics for up to three partners without a health care provider first examining the partners.

Although this is not legal in all states (see the map at the CDC website) the CDC has reviewed the evidence and concludes that EPT is a useful option particularly for treatment of male partners of women with chlamydial infection or gonorrhea.

(Graphic is from inSPOT a website that allows you to send electronic postcards anonymously or from your email address to your sex partners to inform them that you have an STD).

Genital warts, Cancer and HPV

Regardless of what you may have heard about chlamydia it's actually HPV, Human Papillomavirus Virus, that is the most common sexually transmitted infection in the US. One of the reasons for this is that in many cases the infected person has no signs or symptoms. Because of this the CDC estimate that by the age of 50 more than 80% of American women will have contracted at least one strain of genital HPV.

Whoa. Screechy noise. Backup.  By the age of 50 more than 80% of American women will have contracted at least one strain of genital HPV.

Although only a small percentage of these women will develop cervical cancer the fact that such large numbers of women are infected each year means that up to 1 million American women are diagnosed with cervical dysplasia each year. Cervical dysplasia, caused by HPV, is a precursor to cervical cancer and is painful and costly to treat. Of these 1 million cases each year about 11,000 subsequently develop cervical cancer and about 4,000 of these women will die. Every year.


So a safe and effective vaccine is going to be a great discovery right?

Widespread vaccination has the potential to reduce cervical cancer deaths around the world by as much as two-thirds, if all women were to take the vaccine and if protection turns out to be long-term. In addition, the vaccines can reduce the need for medical care, biopsies, and invasive procedures associated with the follow-up from abnormal Pap tests, thus helping to reduce health care costs and anxieties related to abnormal Pap tests and follow-up procedures.

—American National Cancer Institute

Because so many women are infected it is clear that women need to be vaccinated before they can become infected. The best way to do this is to vaccinate them before they become sexually active .

Oh oh. We used the sex word.

 

 

Wait, am I missing something here? We leave it up to private companies to develop vaccines and then we find it somehow sinister if they push for mandatory vaccinations when they develop an effective vaccine against a disease that kills thousands. Oh and did I mention that it is estimated (by the CDC) that at any one time 1% of sexually active adults have genital warts (also caused by HPV).

Don't make me post the genital wart pictures....

Acquaintance Immunization

Image from inSPOT a nonprofit Internet notification service that allows you to send e-cards to your sex partners to break the bad news that they should get tested. Cards can be sent anonymously but they suggest, not unreasonably, that cards with a name are much more effective.

On a related note tell me that this isn't a good idea:

It is well established that random immunization requires immunizing a very large fraction of a computer network, or population, in order to arrest epidemics that spread upon contact between infected nodes (or individuals. Many diseases require 80%– - 100% immunization (for example, measles requires 95% of the population to be immunized). The same is correct for the Internet, where stopping computer viruses requires almost 100% immunization. On the other hand, targeted immunization of the most highly connected individuals, while effective, requires global information about the network in question, rendering it impractical in many cases. Here, we develop a mathematical model and propose an effective strategy, based on the immunization of a small fraction of random acquaintances of randomly selected nodes. In this way, the most highly connected nodes are immunized, and the process prevents epidemics with a small finite immunization threshold and without requiring speci fic knowledge of the network.

From a paper entitled 'Efficient Immunization Strategies for Computer Networks and Populations' in Physical Review Letters.

So, for example, for a sexually transmitted disease you would only need the identity of a single sexual partner from a large sample of people (unfortunately this should be a random selection from those available which may cause difficulties). You then collate this information and target your vaccination on those names that come up the most frequently (most likely the 'superspreaders' in this case). But you have identified them without constructing the whole partner network.

Because you asked.....

There are a variety of health requirements to become a permanent US resident. Having been through the process I can confirm that it is a very long, frustrating and bizarrely complicated procedure.

The medical requirements are actually one of the simplest steps.

You need to show evidence of immunization against the following diseases: Mumps; Measles; Rubella; Polio; Tetanus; Diphtheria; Pertussis; Influenza Type B and Hepatitis B
This all seems sensible and is nothing more than is recommended in the US (and required if you want to attend public school).

You also need to show you don't have Tb. As I mentioned if you have already had the Tb vaccine then the simple skin test will come back 'positive' for Tb so you have to have a chest x-ray.

Finally you need to give a blood sample that is tested for two specific diseases: AIDS and syphilis. They may also test for others but I believe they always test for AIDS and Syphilis. This also seems fairly sensible since with both diseases people can be asymptomatic for a long time whilst continuing to transmit the disease.

Even if you test positive for any of these diseases you can apply for a waiver. The most common communicable diseases for which waivers are sought are tuberculosis and AIDS. A waiver applicant with tuberculosis must agree to see a doctor immediately upon admission and make arrangements to receive private or public medical care.

An HIV+ waiver application must include evidence that 1. the danger to the public health of the United States created by his or her admission is minimal; 2. the possibility of the spread of the infection created by his or her admission to the United States is minimal; and 3. there will be no cost incurred by any level of government agency of the United States without prior consent of that agency. HIV+ applicants will also have to show the following: 1. medical treatment has been arranged in the United States; 2. the applicant is aware of the nature and severity of his or her medical condition; 3. the applicant has provided evidence of counseling; and 4. the applicant has demonstrated a knowledge of the modes of transmission of the virus.

Parasites Lost

In the third season of Futurama there is an episode called 'Parasites Lost' where Fry eats a very old egg sandwich from an interstellar truck stop and becomes infected with parasites. The parasitic worms make him smarter and stronger and cause Leela to become attracted to him. Oh and a bunch of funny stuff happens too but that isn't relevant here.

Here we have a very interesting scenario where a parasite is actually improving its host. If it improved the host's fitness we might have to reconsider whether we should call it a parasite. It is actually quite likely that many currently mutualistic (ie mutually beneficial) interactions between species began as parasitic interactions.

It is fun to speculate on how this might work in humans. Imagine a sexually transmitted disease that causes few or no symptoms but leads to an increased sexual activity in the host. There is no evidence for this in humans but there is some evidence for it in some sexually transmitted diseases of horses. Now imagine the parasite alters host hormones or pheremone levels to make them more attractive to the opposite sex. Hmmm

AIDS in Africa most prevalant in married couples

Although this was last weeks topic, I found this discovery very interesting. The article from Scientific American about the evolution of virulence implied that HIV/AIDS spread so much in certain parts of Africa because of sexual promiscuity. This article, however, contradicts that belief; it is now believed that the highest prevalence of AIDS in Kenya and Uganda is in married couples. For a long time, it has been advertised that marriage was a way to help stop the spread of HIV/AIDS, so resources were devoted to educating young, single individuals, who were thought to be most at risk for transmitting and acquiring AIDS and little was done to provide married couples with education or contraception. More information can be found in the following article: http://www.theeastafrican.co.ke/news/-/2558/527926/-/rkspnwz/-/

1 in 4 Americans

If any of you are involved with clubs, groups or organizations of any form, from sports clubs, to social groups to the Greek system then here are two events you may want to help promote and publicize.

April each year is STD awareness month to raise public awareness about the impact of sexually transmitted diseases (STDs) on the lives of Americans. The Centers for Disease Control and Prevention (CDC) estimates that there are approximately 19 million new cases of STDs each year, almost half of them among young people ages 15 to 24.

June 27 each year is National HIV testing day. The CDC estimates that 180,000 to 280,000 people nationwide are HIV-positive but are unaware of their status. HIV counseling and testing enables people with HIV to take steps to protect their own health and that of their partners, and helps people who test negative get the information they need to stay uninfected.

Routes of transmission

As we have seen some diseases, like AIDS, may have several routes of transmission. Although I didn't mention it several other diseases may also have sexual transmission as a possible, although not very likely, route of transmission.

Although those suffering from Ebola and related viruses are unlikely to be having sex whilst they are contagious some people do recover from Ebola - 10%-50% depending on the strain. Even though they have recovered from the disease they can still have virus in their semen up to seven weeks after they recovered. Recovered Ebola patients are advised to 'not have sex for 3 months or until tests show that semen is free of the virus.'

A conference presentation from 2001 documents the recovery of Lyme spirochetes by PCR in semen samples of previously diagnosed Lyme disease patients. This, of course, does not necessarily mean active infection is transmitted this way. Some documents state that there are no documented cases of sexually transmitted Lyme disease (eg the CDC here and here) whilst others strike a more cautious note:

The CDC position on sexual intra-human Borrelia burgdorferi (Bb) transmission is that it does not occur. We find no study that addresses sexual transmission of Bb among humans; conversely, we find no study supporting that it does not occur. Inferential data, however, suggest the possibility of human sexual transfer. The data come from sound veterinary studies, the finding of Bb in human semen and breast milk, and by similarity to Treponema pallidum where sexual transfer is abundantly documented. Our clinical experience strongly suggests that predictable, possibly inevitable Bb transfer between sexually active couples occurs.

From: Lyme disease': ancient engine of an unrecognized borreliosis pandemic?
W. T. Harvey, P. Salvato

[This post contains 90% recycled material]

Millions for STD prevention in stimulus package

I don't think anyone can be unaware that the House and Senate have been debating an economic stimulus package over the last few weeks. What you may not realize is that both the House and Senate versions contained substantial sums for the prevention of sexually transmitted diseases - $335 million in the House bill and $400 million in STD spending in the Senate bill.

Naturally this funding has faced criticism from Republicans who say the funding makes no sense in bill designed to get the economy back on track.

Republicans say the bill ... has become a vehicle for congressional Democrats to get approval for projects they've been unable to secure in recent years with congressional Republicans and President Bush able to foil their efforts.

Others argue that the money is desperately needed to replace jobs lost in State and local health departments due to the economic crisis.

So it is worth reminding critics of the following: Disease prevention is a job. Reinvestment in the prevention of HIV, STDs, viral hepatitis and TB — after six years of steady decreases in funding that have left our public health systems as "potholed" as any highway — will (re)create thousands of jobs, modernize and strengthen our public health infrastructure, and improve access to health care in ways that will reduce absenteeism and raise productivity at other jobs in our community.

No Glove, No Love

In Canada, antibiotic-resistant gonorrhea is increasing its threat to public health. It seems that this strain's incidence has jumped 7 fold in just four years. The scientists attribute this rise to unsafe sex. They also predict it will spread from big cities that attract visitors.



http://www.theglobeandmail.com/servlet/story/RTGAM.20090203.wlsex03/BNStory/specialScienceandHealth/home

Syphilis, Yaws and Columbus

A network path for four informative substitutions shows that New World subsp. pertenue, or yaws-causing strains, are the closest relatives of modern subsp. pallidum strains.

Syphilis, caused by a spirochete bacteria, was first reported in Europe in 1495 and there have been a number of hypothese to explain its relatively recent appearance. I briefly mentioned the possibility that the Black Death may have played a role in its emergence.

For a long time the emergence of syphilis was associated with the discovery of the New World and is sometimes cited as being the only new disease to make the journey from New World to Old World (lots of diseases made the journey the other way, and diseases like smallpox and measles decimated the New World populations). But other diseases such as Yaws, caused by the same species of bacteria, have a widespread distribution in both the New and Old World.

A paper this week in PLoS Neglected Tropical Diseases provides evidence from a phylogenetic study that suggests that while other forms of the Treponema pallidum bacterium have plagued humans since early in our evolution, it emerged as venereal syphilis only when carried back to Europe by Columbus and his crew.

Disease and culture

This week in section we will be discussing the interplay between disease and culture. We've already talked in lecture about several instances of culture/behavior impacting disease transmission. For example, boarding up windows in nineteenth century London kept the "miasma" out and the Tuberculosis bacteria in. Likewise, as mentioned today, people who like to hike around and live in rural, wooded areas in the Northeast are at greater risk for Lyme disease.

Sexually-transmitted diseases like HIV/AIDS are ripe with potential for both cultural differences in transmission and disease impacts on culture. Some reports (from research done mostly in Kenya and Uganda) have shown that circumcised men are around 50% less likely to contract HIV from heterosexual sex. In these countries, where circumcision in infancy is not the norm, the clinical trials involved circumcising adult men in a safe medical procedure. Many people may not know that in western countries, the female-to-male sexual transmission rate of HIV is very low (as shown in studies like this one). In a sense, western (American and European) females are essentially a dead-end host for HIV, since they can get the virus sexually from men but do not pass it on. Most of infected men contract HIV either by having sex with men or through intravenous drug use. On the other hand, women in Africa seem to be a more competent host, and African men contract HIV from heterosexual sex much more readily there. Though the scientific community does not yet know why, some reports suggest that this may be related to circumcision rates and concurrent STIs.

Finally, another huge source of new HIV cases in the US is from intravenous drug users (IVDUs, in the public health lingo). Australia has addressed this problem by creating needle-exchange programs that allow intravenous drug addicts to get clean needles. The US has thus far refused to adopt this strategy, which Australian National Affairs Editor Mike Steketee argues is a case of "ideology sometimes get[ting] in the way of saving lives." Is giving out clean needles as a public service antithetical to the "War on Drugs"? Does it promote drug use, or save lives? A similar ethical issue surrounds the question of whether or not to give school kids access to condoms in conjunction with sexual education. These are all direct ways in which our own culture may facilitate or inhibit disease transmission.

HPV and Cervical Cancer

I didn't have time to say much about the Human Papillomavirus vaccine but I did want to mention the issue. PBS have a very nice site from a show on the subject
You can watch the whole show at the site, or download it as an mp3 file to listen to, and also read an interview with a 'vaccine expert' that raises interesting issues and find out the basic facts about HPV and the vaccine. If you can't see what all the fuss is about take a deep breath and read some of the posted comments.

Also, over the next couple of days I will be writing the midterm and will post some sample questions here. I'll also put up a cumulative list of the terms we have covered to date (ie a subset of the larger glossary) which might be useful.

Relevant material previously on the blog:

Well, this post actually but I wanted to draw particular attention to it.
Solver for the SIR Model of the Spread of Disease
Vaccine safety
The height of reckless irresponsibility

More Sources of HIV infection

A follow up to the post below since I'm not sure I can post links in comments to posts.

Great question. The answer to this question (what percentage of people acquire HIV from sexual intercourse, through the sharing of needles, and by other means) will vary a lot depending on the time period you are asking about and the country you are asking about.

Let's look at a few examples.

According to the CDC, in 2005 the cumulative figures for the AIDS epidemic in the US were:

Male to male sexual contact - 48%
Intravenous drug use - 26%
Both Intravenous drug use and male to male sexual contact - 7%
Heterosexual sex - 17%
Other - 2%

The sample size here is almost a million people.
BUT in the year 2005 alone, the figures were:

Male to male sexual contact - 43%
Intravenous drug use - 20%
Both Intravenous drug use and male to male sexual contact - 5%
Heterosexual sex - 30%
Other - 1%

Spot the difference? Heterosexual transmission has almost doubled and now accounts for 30% of cases. The other figures have gone down accordingly.

The final example is Africa, where data is harder to come by but numerous sources suggest 80% of the HIV infections in Africa are due to heterosexual sex with mother to child (vertical) transmission accounting for most of the rest. This paper has further data on African and some other areas plus a few useful references.

Sources of HIV Infection

In my section on Thursday there was a question about what percentage of people acquire HIV from sexual intercourse, through the sharing of needles, and by other means. I was unable to find any general statistics on the subject but I did find a study conducted in Norway which examines the number of people infected by different sources from 1984 to 2006. The results of this study show that nearly fifty percent of all new cases during these period were acquired by heterosexuals through sexual intercourse, 31 percent by homosexuals through sexual intercourse, 15 percent from the use of contaminated needles, and 1 percent from both blood transfusions and from mother to child. For more specifics on this: Click Here.

Sexually transmitted Lyme Disease ?

Yesterdays post reminded me of some articles I was reading a while back about the possibility that Lyme Disease could be spread sexually. A conference presentation from 2001 documents the recovery of Lyme spirochetes by PCR in semen samples of previously diagnosed Lyme disease patients. This, of course, does not necessarily mean active infection is transmitted this way. Some documents state that there are no documented cases of sexually transmitted Lyme disease (eg the CDC here and here) whilst others strike a more cautious note:

The CDC position on sexual intra-human Borrelia burgdorferi (Bb) transmission is that it does not occur. We find no study that addresses sexual transmission of Bb among humans; conversely, we find no study supporting that it does not occur. Inferential data, however, suggest the possibility of human sexual transfer. The data come from sound veterinary studies, the finding of Bb in human semen and breast milk, and by similarity to Treponema pallidum where sexual transfer is abundantly documented. Our clinical experience strongly suggests that predictable, possibly inevitable Bb transfer between sexually active couples occurs.

From: Lyme disease': ancient engine of an unrecognized borreliosis pandemic?
W. T. Harvey, P. Salvato

Sexually transmitted Ebola ?

Because Ebola is transmitted via infected bodily fluids someone asked whether it could be sexually transmitted. I suggested this was unlikely because individuals are not infectious until they are very sick. However I was forgetting about the 10-50% of people who do recover from Ebola. Apparently even though they have recovered from the disease they can still have virus in their semen up to seven weeks after they recovered. Recovered Ebola patients are advised to 'not have sex for 3 months or until tests show that semen is free of the virus.' Another possibility is that there may be some asymptomatic carriers of Ebola. These individuals may transmit the disease sexually. I hasten to add that transmission via this route is not thought to have contributed in a significant way to any of the known outbreaks. Interesting though.

Hot off the press is a news report that Ebola may not be so hard to work with in the future after all. By removing a single gene from the virus scientists were able to stop it replicating. That's one result they might want to double check......

The Lost Children of Rockdale County

In the spring of 1996, as Atlanta prepared to host the summer Olympic Games, an outbreak of syphilis struck a group of teenagers in the prosperous bedroom community of Conyers, Georgia. When epidemiologists interviewed the victims, they were shocked by what they heard: children as young as fourteen named scores of sexual partners, others told of all-night orgies and sex parties.

I'm pretty unshockable but I found this PBS show on an outbreak of syphilis in Georgia pretty amazing. Although the show was aired in 1999, thanks to good old PBS you can access a lot of information about it at a website dedicated to the show and even read a complete transcript.

The website will also give you access to details about the actual investigation of the outbreak, the techniques used and the results. For example this paper shows the complete network visualization of the outbreak I presented in class.