Ask a Scientist : “So What’s a Parasite Anyway?” Lecture Jim McKerrow Cont.

Ascaris

Parasites, parasites of the intestinal walls! Which is the most gross of them all? The most gross parasite title has to go to the most common of helminths, Ascaris lumbricoides.

According to the World Health Organization, Ascaris Lumbricoides infects approximately 30% of the world’s population. Infections for the most part, are in the rural areas of developing countries that use untreated human waste for fertilizer and irrigation. Without access to clean water and expensive fertilizer, farmers are left with little else to use, but human waste to grow their produce. A 2008 report in National Graphic news on the use of Human Waste cites that 200 million farmers world wide use human waste for fertilizer. The eggs from human feces used as fertilizer end up in the soil where they can stay fertilized for up to 10 years.

The eggs find their way into the human food chain via contaminated unwashed hands during food preparation, unwashed fruit and, or undercooked vegetables or fruit. When fertilized eggs are ingested, the eggs hatch in the upper intestinal tract where the larvae then penetrate the wall and move into the portal and systemic circulatory system. Once in the circulatory system, the larvae enter the lungs. In the lungs, the larvae penetrate aveoli walls and make their way up the bronchial tree to the throat. The larvae is swallowed by the host and ingested. In the lower intestines, the larvae attaches to the mucosa of the wall and feeds off the host’s partly digested food and grows to an adult. Adult Ascaris lays up to 200,000 eggs per day. The eggs are then excreted in feces. The infected feces returns to the land as fertilizer and the life-cycle of A lumbricoides repeats.

The Ascaris worm grows to approximately 30cm and about 2-4mm in diameter. The females are a little thicker and longer with their vulva making up a third of the length of the body. Gulp!

Sources:
Introduction to Microbiology, 9th Edition, Tortora, Gerard.J, Funke, Berdall R., Christine L. Case. Publisher: Pearson Benjamin Cummings. 2007 print.
Center for Disease Control – Ascariasis page
National Geographic 2008 report on use of human waste as fertilizer.
Ask a Scientist website
Dr. J. McKerrow UCSF page.

Ask a Scientist : “What is a Parasite” Featuring the Tapeworm

Tapeworm Specimen… Click the image to view the segments (proglottids) that contain testes and ovaries.

This is a continuation of the lecture on parasites by Dr. Jim McKerrow from the Department of Pathology at the University California San Francisco. Jim presented his parasites, or rather his lecture on them, at the StrEAT Park in the Mission District in San Francisco.

The diners absorbed details of the the tapeworm over their Mexican food and beer from the various food trucks in the food park. Warmed by the overhead gas lamps in the tent, we learned how we can become infected with tapeworms from eating undercooked pork or beef.

These parasitic helminths, Taenia saginata (beef Tapeworm), or Taenia solium (pork tapeworm), reside in the intestines of its definitive host by hooking their four heads (or scolex) into the walls of the intestines and absorbing nutrients intended for the host. It can reside there for up to 25 years.

The scolex of the tape worm. Note the four suckers.

This not so little flat worm reaches lengths of up to 6 meters… The strange sexual beast contains both reproductive organs. Each segment or proglottid making up the length of the worm contain ovaries and testes. There may be up to a 1000 proglottids making up the length of this flat worm. Remember; this creature is approximately 6 meters long. That’s a lot of balls. This parasite can create many more tapeworms as each mature poglottid breaks down and releases eggs which end up in feces of the definitive host.

The eggs make their way into the next host (intermediate host) when it consumes infected food from the feces, or eggs from the feces. The eggs hatch in the intestines and the larvae make their way to the liver, lungs and or, brain and develop a cyst. One cyst produces many scoleces (heads) or larvae. When these cysts are consumed by the unsuspecting human or animal, the scoleces (singl. Scolex) will embed into the intestinal wall of its host and the cycle continues.

Fettuccine anyone…? 

Additional sources:
Introduction to Microbiology, 9th Edition, Tortora, Gerard.J, Funke, Berdall R., Christine L. Case. Publisher: Pearson Benjamin Cummings. 2007 print.
CDC Taeniasis (Tapeworms)
Ask a Scientist website
Dr. Jim McKerrow page at UCSF

Ask a Scientist : “So What’s a Parasite Anyway?”

“So What’s a Parasite?” was one of a lecture series called, “Ask a Scientist”. The lectures are for “curious humans” and I for one am curious about parasites and other nasties.

I attended the lecture by Dr. Jim McKerrow from the University California San Francisco’s Department of Pathology and Laboratory Medicine on parasites that took place in a toasty warm tent heated by gas lamps at the SF StrEAT Park in the Mission, San Francisco.

Anyway, I just want to share some gross pictures and remind you how the Lord God made all these creatures great and small; very, very small. Some of these creatures are so small that they live in the guts of bugs and some organisms are so small that they burrow into the skin infecting various organs reining havoc on their host by making them extremely sick and sometimes even killing them.

As the audience drank beer and tucked into their Mexican food from the various food trucks in the StrEAT park, Jim started by introducing the dining audience to the parasite responsible for Chagas’ disease. Chagas’ disease is a protozoan that damages the cardiovascular system.The protozoa Trypanosoma cruzi grows in the gut of the bug and is transmitted by the triatomine bug via its feces. The bug bites the skin of its victim and defecates in or near the wound which subsequently irritates the person or animal who then scratches the wound rubbing the feces into the wound even more. T. cruzi makes its way into the bloodstream and hides in the muscular wall of the heart and intestines causing damage.

The parasite can be transmitted across the placenta from the infected mother to her baby. All blood for blood transfusion in the USA is tested for the T. cruzi parasite since many of them remain in the blood stream.

According to the World Health Organization, 7 to 8 million people worldwide are infected with Chagas’ Disease — many of whom are in Latin America.

More bugs to follow… Stay tuned and don’t scratch!

Additional Sources:

WHO Media centre Factsheets
Ask a Scientist website
Dr. Jim McKerrow page at UCSF