Category Archives: Infectious Disease

Diet & Nutrition, Infectious Disease

Guilty Confession

Leave a comment

OK, I understand that agricultural diseases are devastating for both the farmers and people who rely on their produce to subsist, particularly in a world where food prices have increased dramatically in part due to agricultural losses from plant pathogens.  I just can't help but find the names of many agricultural diseases amusing.  The one that comes immediately to mind is banana bunchy top virus, which has recently emerged in Angola.

Agricultural disease monikers seem to always be extremely descriptive.  Imagine if some human scourges followed the same convention: "black sores ringing groin disease" (plague), "lungs full of mucous" (influenza/pneumonia), "pus dripping from urethra" (gonorrhea, chlamydia).  Maybe not so amusing...

Conservation, Infectious Disease

Elephant Deaths From Anthrax in Namibia

Leave a comment

A very sad story appeared on PROMED-mail recently about a die-off of elephants around Nakabolelwa, Namibia.  While still not completely investigated, the most likely cause seems to be anthrax.  Bad news for elephant conservation. If anthrax infection turns out truly to be the cause of mortality, then it raises all sorts of problems.  Chief among these is the possibility that people will eat meat from the carcasses, leading to almost certain infection and death if anthrax is indeed the culprit.  But even if people don't eat meat from the carcasses, scavengers might and could then spread the anthrax spores around the landscape.  Bad news for anthrax control.  Anthrax spores in the ground remain infectious for a potentially very long time -- potentially decades. One can just imagine what a control nightmare having a checkerboard of cryptic anthrax hotspots across a landscape is.

Burning the elephant carcasses, which might be done for other types of animal infections, is impractical because it would take so much fuel in this xeric region with few woodlands and chronic shortages of cooking fuel. The PROMED moderator writes:

Dealing with elephant carcasses is difficult, as one would imagine. The prescribed technique is to pile the carcass with thorn brush to discourage scavengers while the carcass decomposes. The drop in pH will kill the vegetative cells quickly in the unopened carcass. Burning takes a significant volume of wood, and it is hard to get proper ventilation of the underside of the carcass.

Wayne Getz and his collaborators have a relatively new project to study the ecology of episodic anthrax transmission around Etosha Park, Namibia.  I await the results from this project eagerly since, as far as I can tell, just about everything that comes out of his lab is great, and if not great, at least interesting.

Conservation, Infectious Disease

More Crocodile Pansteatitis

6 Comments

About a month ago, I posted on the mysterious deaths of crocodiles in the Olifants river system in Kruger National Park, South Africa.  A recent update indicates that the cause of the fatal pansteatitis outbreak is still unknown despite intensive study.  An interdisciplinary research captured 11 live crocodiles and found that seven of them were afflicted by pansteatitis.  This is a scary prevalence rate.  The media release strangely refers to these cases as "infections," but this is probably not correct as pansteatitis is typically caused by environmental poisons (e.g., rancid fat from spoiled fish).  The current theory is that the crocs are acquiring the poisoning from eating the carcasses of other afflicted crocs.  The intervention park managers are attempting now is to burn the bodies of dead crocs recovered by rangers.  So far, rangers have counted 130 crocodile carcasses in the park.

Infectious Disease, Uncategorized

Trailing Off of the Epidemic Curve?

Leave a comment

The latest CDC report on the ongoing Salmonella serotype Saintpaul suggests that we may indeed be nearing the end.  Here is the epidemic curve as of 28 July:

28 July Salmonella Epidemic Curve

While there is certainly still the possibility of more cases appearing that have not yet been reported or another introduction (see previous post), the fact that the epidemic curve has continued to trail off in two successive weeks is good news.

The epidemiological evidence continues to implicate fresh jalapeño chiles grown in México.  As of 28 July, 1307 cases have been reported since 1 April 2008. Nearly every state in the union has reported at least one case from this outbreak, as can be seen on this map:

CDC Map of Salmonella Cases 07/28/08

Again the most likely victims (at least to report illness) are 20-29 year-old adults while the least likely to report illness are 10-19 year-olds and those over 80.  Once again, I suggest that this is consistent with a vehicle consumed along with alcoholic beverages. Salsa.  Though contaminated jalapeños (or other produce) could, of course, make their way into other foods as well. The Saintpaul strain was relatively rare before this outbreak, leading CDC to suggest the following:

The previous rarity of this strain and the distribution of illnesses in all U.S. regions suggest that the implicated food is distributed throughout much of the country. Because many persons with Salmonella illness do not have a stool specimen tested, it is likely that many more illnesses have occurred than those reported. 

Let's hope that this outbreak is really coming to an end.  It would be nice if we could identify the source of the infection.  Foodborne disease is an important public health concern that probably does not receive the attention it should.  A 1999 paper by Mead and colleagues (admittedly now a bit long in the tooth) estimated that foodborne diseases cause approximately 76 million illnesses, 325,000 hospitalizations, and 5,000 deaths in the United States each year.  It is not hard to imagine that in the 10 years since this study the foodborne disease burden has increased in the U.S.  Time for another study, I'd say.

Infectious Disease

IMF Structural Adjustments Increase TB Incidence, Prevalence, and Mortality

Leave a comment

A new study has found that the structural adjustments that the International Monetary Fund requires of countries to which it loans money increase tuberculosis incidence, prevalence, and mortality.  The authors studied tuberculosis epidemiology in countries of Eastern Europe and the former Soviet Union that received IMF loans following 1989.  This result suggests that there are real health trade-offs associated with the fiscal austerity that follows an IMF loan.  This research is very welcome because it adds a reasoned empirical perspective to the often shrill debates over the relative merits of IMF policies. Harvard epidemiologist and political scientist Megan Murray and Gary King have written a companion Perspectives piece in the same issue of PLoS Medicine.  There is also a nice news story on it in The New Scientist.

Human Ecology, Infectious Disease, Statistics

More on Salmonella

Leave a comment

The first produce to positively match the Salmonella serotype Saintpaul was announced today.  A jalapeño chile, grown in México and processed at an unnamed plant in McAllen, Texas, tested positive for the strain of Salmonella that has sickened at least 1237 people since April.  This is the first time that the bug has actually shown up on a sample of fresh produce.  Perhaps it wasn't tomatoes after all, but it is a nice demonstration of confounding in epidemiological inference (tomatoes and jalapeños are commonly served together in the form of salsa, making it difficult to determine which is the actual vehicle for infection if both are implicated). Now the question is where along the production chain the contamination took place and how we can make sure that we bring an end to this outbreak.  All of the news stories and government reports on this topic can be found on the ProMedMail website.  

Conservation, Infectious Disease, Statistics

Update on Salmonellosis Saintpaul

1 Comment

The Centers for Disease Control and Prevention have just issued a new report on the ongoing outbreak of Salmonella serotype Saintpaul infection. Since April, 1237 people have been infected.  The investigation has continued to focus on raw tomatoes but also jalepeño (and serrano) chiles and cilantro.  This further supports my previous speculation, based on the age profile of the cases, that salsa consumed while drinking alcoholic beverages might be implicated in this outbreak.  Epidemiological investigations are greatly complicated when multiple vehicles that are typically consumed together are implicated.

There is an interesting caution that accompanies the epidemic curve:

Salmonellosis Saintpaul Epidemic Curve

This has to do with the fact that it can be very misleading to read too much into an epidemic curve for an ongoing outbreak. Consider the epidemic curve for the 2003 SARS outbreak in Singapore:

Singapore 2003 SARS Epidemic Curve

Now imagine we were looking at the curve as it evolved on 12 March.  We might have be tempted to say that the epidemic was coming to an end and, man, would we ever have been wrong! There are a couple of things at work here.  First, epidemics often have multiple introductions and while theory tells us that an epidemic curve will be more or less bell shaped, this is based on the assumption of a single introduction.  If you look at the SARS epidemic curve hard enough, you can see several more-or-less bell-shaped components added together.  The second issue with SARS is that there is extreme heterogeneity in transmission.  Patient #1 probably infected 21 other cases, patient #4 probably infected 62.  The great majority of others infected none.  Individuals who infect more than 10 others are what is known as "superspreaders."  There were five in the Singapore outbreak out of a total of 201 probable cases of SARS and 722 suspect cases.  Finally, there is often a delay between when people get sick and when their cases are reported.  This means that the trailing edge of the epidemic curve always looks like it's closing off its bell shape. The full case report for the Singapore outbreak can be found here. 

So, is the current Salmonellosis outbreak on the wane?  Let's hope so, but as CDC warns:

It can be difficult to say when the outbreak is over, because of the reporting delay.   The delay means that the curve for the most recent three weeks always looks like the outbreak could be ending even during an active outbreak. The full shape of the curve is only clear after the outbreak is over.

With a vehicle-borne disease, we don't have to worry about superspreaders, but the fact that we still don't know the source of the infection or the ultimate cause of the contamination is troubling.  Who knows how much contaminated (presumably) produce is lurking out there?  I, for one, will make sure to wash my produce well! 

Conservation, Infectious Disease

Pansteatitis and Questions about Affected Species

1 Comment

Here is a review of pansteatitis (and other diseases) in farm raised crocodiles (and ostriches), including a picture of the hardened yellow fat in crocodile tails.  This hardening of the fatty tissue in crocodile tails impairs their mobility and therefore their ability to hunt.  Crocs with pansteatitis therefore waste away and die of starvation.  There is no specific indication in the articles of the state of the crocs bodies.  Are they emaciated? Another posting on ProMedmail, including some details of the dam that may be a source of pollutants is here.  The moderator asks the important question: Is anything else affected?  No mention is made in any of the news articles.  What about other aquatic organisms in the Olifants River? For example, what about Cape Clawless Otters (Aonyx capensis)?

Conservation, Infectious Disease

Crocodile Die-Off in Kruger National Park

5 Comments

Crocodiles have been dying in large numbers on the Olifants River in Kruger National Park, the crown jewel of the South African Parks System.  The article rather casually states that the die-off is attributable to environmental pollutants:

There is growing consensus that the croc die-off is a result of a confluence of low level toxins, which has lead to endocrinal [sic] abnormalities (that is, hormonal changes) in croc tissues.

As the moderator for the promedmail wrote, however, it would be nice to have some specific details explaining why this consensus is apparently growing:

The article does not specify chemicals, pesticides, or heavy metals, or their amounts, yet the article boldly states, "Long term exposure to these and other toxins may well be conspiring towards the crippling condition suffered by Olifants River crocodiles." So apparently, the specifics of the chemicals, pesticides and/or heavy metals are known. It would be much more beneficial to publish what has been found and the levels of those alleged toxins, then those doing research or having experience in the area would be able to suggest a possible solution.

It certainly seems possible, particularly given the diversion of water from the Olifants River and from new mining operations in Mozambique, but it would still be nice to have some more details. One of the striking features of the dead crocs is the fact that they have hardened yellow fat deposits in their tails. The article suggests that cause of death is pansteatitis, a disease caused by excessive consumption of unstabilized polyunsaturated fatty acids (often found in rotting fish).  There is no evidence of correspondingly large fish die-off, which could complete the causal story.  How the environmental contamination story fits in with pansteatitis seems an important missing link in understanding this problem.

Cattle that eat threadleaf groundsel can die of a disease that induces hard yellow liver, providing more suggestive evidence that an environmental poison might be responsible for the croc die-off.  Maybe...? 

This is a disturbing story, the resolution of which I will follow closely.