Monday, October 27, 2008

Mosquito classification



I have been working hard on my vector biology. To be honest, the vectors are of less interest to me than the diseases that they transmit, but I'm trying nonetheless.

A few tidbits on the classification of mosquitoes:

1. To determine the sex of a mosquito, look at the antenna. If the antenna are "plumose" (hairy), the mosquito is male. If the antenna are "pilose" (not very hairy), the mosquito is female (see diagram above)

2. To determine the genera of medically important mosquitoes, look at the palps (sensory organs just lateral to the proboscis, the stick-like organ that punctures the skin for blood meal). If it is a female mosquito with long palps, the mosquito is Anopheles. If the mosquito is female with short palps, the mosquito is Culicine.

3. To assist with genera identification: Anopheles mosquitoes rest and bite with their bottoms up (approximately 45 degree angle to the skin). If you see a mosquito biting you with it's bottom parallel to the skin, it is not likely a anopheles, and you can rest assured that you won't get malaria from that bite (although you could get Yellow Fever, Dengue, Fillariasis, West Nile virus, or another mosquito-borne arthropod virus. The diagrams of Anopheles and Culex below were downloaded from CDC's National Center for Zoonotic, Vector-Borne, and Enteric Diseases
I won't go into the details on how to identify and classify mosquito eggs, larvae and pupae, but I do know how, believe it or not.


Friday, October 24, 2008

Health and Human Rights

The Journal Health and Human Rights, published by the François-Xavier Bagnoud Center for Health and Human Rights at the Harvard School of Public Health, has recently gone online, with full text of all articles accessible for free.

In the current issue, Gavin Yamey has an essay on the importance of free and open access of the biomedical literature:

Arthur Ammann, president of the nonprofit organization, Global Strategies for HIV Prevention (http://www.globalstrategies.org), tells the following story:

I recently met a physician from southern Africa, engaged in perinatal HIV prevention, whose primary access to information was abstracts posted on the Internet. Based on a single abstract, they had altered their perinatal HIV prevention program from an effective therapy to one with lesser efficacy. Had they read the full text article they would have undoubtedly realized that the study results were based on short-term follow-up, a small pivotal group, incomplete data, and unlikely to be applicable to their country situation. Their decision to alter treatment based solely on the abstract’s conclusions may have resulted in increased perinatal HIV transmission.1

The physician in southern Africa could not afford to view the full text article due to its exorbitant cost. The full text version of a research article in a medical journal typically costs US$30 to download, while an annual subscription to a journal usually costs several hundred dollars. Hence the physician was forced to rely on abstracts alone (abstracts of some research articles are made freely available in the online database, PubMed, at www.pubmed.gov). The full text versions of most biomedical studies — an essential treasury of life-saving knowledge — are locked away behind access barriers. These access tolls bring enormous profits to the traditional corporate publishing industry, but at the same time make it impossible for many people worldwide to access the biomedical literature. The imposition of such tolls arguably violates the spirit of the Universal Declaration of Human Rights, which states that everyone has the right “to share in scientific advancement and its benefits” (Article 27, section 1).2

Tuesday, October 14, 2008

Sleeping Sickness

Trypanosoma brucei, the agent that causes sleeping sickness, is my new favorite protozoan. The African tsetse fly is the vector for both species of typanosoma: T. brucei gambiense, which causes sleeping sickness (Human African Trypanosomiasis, or HAT) in West and Central Africa, and T. brucei rhodesiense, which causes a different form of HAT in East and Southern Africa.

As I learned today, the best way to identify the tsetse fly is by the "hatchet cell" shape framed by wing veins 4 and 5 (seen upsidedown in upper wing in this pic), and by the characteristic way that resting fly holds its wings, folded over the abdomen in a "pair of closed scissors" formation. [Medical entomologists are a mad bunch, no?]

Both male and female tsetse flies inject the metacyclic trypanomastigote form of the parasite into the human host when taking a blood meal. In the peripheral blood, the trypanomastigotes multiply by binary fission, to form three different forms: the "short-stumpy" form, the "long-narrow" form, and the intermediate form. All of these forms look a bit like worms smimming in the blood stream, but of course they are single-celled organisms, not worms. What looks like the eye of a worm is actually a bit of mitochondrial DNA material called the kinetoplast. The tail of the worm is the flagellum, that ungelates for motility.

The clinical maifestations of HAT are as bizarre as the parasite morphology. The T. brucei gambiense form of the disease is much more insidioius and chronic than the T. brucei rhodesiense form, which progresses rapidly towards death. In both forms, the patient may present with a chancre or ulcer at the site of the tsetse bite. Multiple non-specific symptoms follow the bite, including: fever, fatigue, wasting, lymphadenopathy, rash, and itching. Once the parasite enters the central nervous system, the patient may get confused, then fall into the reverse sleep pattern of daytime somulence and nighttime agitation that gives the disease its nickname. If left untreated, the disease is uniformly fatal.

Like most diseases that occur only in poor countries, HAT has no decent treatment options. The only drugs available are toxic compounds that cause debilitating side effects (and 5% chance of mortality from the drug alone). All of the drugs were developed decades ago. There are few or no other options in the pipeline.

I was always taught that HAT is a rare disease, but our professor told us that it is actually prevalent and wide-spread. The 50,000 cases that are reported to WHO every year are probably at least a 12-fold underestimate. He believes that HAT and "nagana," which is the animal-version of the disease common in horses and livestock, are the reason that European colonists "gave up" on their conquest of Africa. The livestock ranches in the colonial era failed miserably due to illness of colonists and their herds, he says.

David Livingstone was onto the same idea way back in 1857, when he published a description of nagana in Missionary Travels, the narrative of his famous mid-century African expedition. Soon after, the colonists started calling the sleeping sickness syndrome "negro lethargy." They called HAT by this name until the white colonialists started getting sick too, at which time the Royal Society sent an expedition to investigate. In 1903, they identified the trypanosoma parasite in the blood and CSF of sick patients. They even managed to infect monkies with the agent, proving that typanosomes cause sleeping sickness disease.

Saturday, October 11, 2008

Friday, October 10, 2008

Refugee Camp in the Heart of the City

MSF's "Refugee Camp in the Heart of the City" exhibit, will be in California over the next couple of weeks. People who saw the exhibit last year in Manhattan and Brooklyn recommeded it for both adults and for families. It takes about an hour to tour the whole thing. Admission is free. The schedule is:

San Francisco, Little Marina Green Park
Oct 15-19

Los Angeles: Griffith Park
Oct 22-Oct 27

Santa Monica: Santa Monica Pier
Oct 31-Nov 2

San Diego: Balboa Park
Nov 6-9

Much more information at www.doctorswithoutborders.org, or by clicking on the above link.

Tuesday, October 07, 2008

World Mapper

The World Mapper Collaboration has more than 350 of these "density-equalising maps," on its website, www.worldmapper.org. Each cartogram re-sizes countries according to the variable being mapped. For example, the cartogram above left shows the relative prevalence of HIV worldwide. The map categories include: goods, services, resources, work, income, housing, education, poverty, health, disease, disaster, death, polution, violence, and many others.

Small quiz: of the maps below, which shows relative malaria deaths? Which shows military spending in 2002? Which shows electronics exports?

You can download pdf posters of all maps for teaching material. For more information on the map-making technique, see worldmapper website, or Michael T. Gastner and M. E. J. Newman (2004) Diffusion-based method for producing density equalizing maps Proc. Natl. Acad. Sci. USA 101, 7499-7504. Maps copyright 2006 SASI Group (University of Sheffield) and Mark Newman (University of Michigan).