Season 3, Episode 10: Unbearable
Wes’s 12 year-old niece Molly comes to visit and shows up slightly under the weather. Wes takes her to the doctor and learns that Molly is pregnant. Although Wes and Molly’s father suspect she has been raped, Molly insists she is a virgin and is having God’s baby. Meanwhile, wild bears aren’t the only ones going crazy. Near the park where Rachel’s son was attacked by an enraged bear, a man goes crazy and tears up a restaurant. The man, a gourmand, collects foods from the forest. NorBAC investigates the possibility that he collected the wrong mushrooms as well as the possibility that a bear disease has been passed on to humans.
IS VIRGIN BIRTH POSSIBLE?
 Image provided courtesy of Shaftesbury Films. |
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An ultrasound shows Wes’s 12-year-old virgin niece is pregnant. |
What is parthenogenesis?
Parthenogenesis is a form of asexual reproduction in which a female’s egg can develop into an embryo without being fertilized by a male. This type of reproduction can occur in some plants, insects, lizards, fish and birds.
Parthenogenesis has advantages and disadvantages. One advantage to parthenogenesis is that it allows reproduction to occur when sexual reproduction is impossible; for example, if a female were isolated and unable to find a male with whom to mate. However, because only one individual’s genes are passed on to the offspring, parthenogenesis limits genetic diversity and without diversity, genetic mutations can amplify within a species.
In some species, parthenogenetic offspring are able to reproduce sexually while others only reproduce asexually or are sterile. Domesticated honeybees are a good example: within a hive, the queen bee is the only female able to mate and reproduce sexually. The other females, worker bees, cannot mate but do lay eggs that undergo parthenogenesis and become male drones, which can mate with the queen.
Can parthenogenesis occur in mammals?
In 2004, Japanese scientists used parthenogenesis to create fatherless mice, the first parthenogenetic mammals. To accomplish this feat, they took one cell from two different female mice and halved the number of chromosomes in each cell. After joining together the two half cells, they let the new whole cell develop into an adult mouse.
Parthenogenesis can occur in humans, but does not give rise to live offspring. Instead, it generates either ovarian teratomas or other growths called “complete hydatidiform moles”, depending on whether the genetic material comes from a female or a male. Ovarian teratomas are cancerous tumors whose cells contain only maternal chromosomes. Complete hydatidiform moles can form when two sperm fertilize a single egg devoid of any genetic material. The resulting cell contains only paternal chromosomes and, like the ovarian teratoma, can develop into cancer.
So ...
“Virgin birth” is possible, but not in humans.
IS IT POSSIBLE FOR DISEASES TO “JUMP” SPECIES AND SPREAD FROM ANIMALS, LIKE BEARS, TO HUMANS?
 Image provided courtesy of Shaftesbury Films. |
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Rachel visits her son Craig in the hospital as he recovers from wounds suffered in a bear attack. |
What are zoonotic diseases?
A zoonotic disease is a disease that normally infects animals but also can infect humans. Conversely, some primarily human diseases can infect animals; this is sometimes called “reverse zoonosis.”
There are more than 200 known zoonotic diseases, some of which are harmful to humans, including anthrax, avian influenza (bird flu), bubonic plague, Ebola, glanders, bovine spongiform encephalopathy (mad cow), plague, rabies, salmonellosis, SARS, and toxoplasmosis. Emerging zoonoses – diseases caused by new microorganisms and appearing in species never before infected – are of particular concern.
Zoonotic infectious agents come in all forms: bacteria, viruses, parasites, fungi and prions. They are carried most commonly by animals such as bats, cats, dogs, sheep, goats, monkeys and pigs.
Several factors can influence a disease’s ability to jump from animals to humans, including changes in the microorganisms’ genetic material, population growth of both animals and humans, shifts and movement in animal and human populations, changes in human diet and environmental factors.
What makes species jumping possible?
Consider influenza, or “the flu,” which is a particularly interesting example of a zoonotic disease. It’s believed that birds are the main animal reservoir of influenza virus, but there are forms of the virus that have adapted to living in humans, dogs, pigs and horses.
The genetic material of the influenza virus is made of ribonucleic acid (RNA) which tends to mutate more frequently than its relative, deoxyribonucleic acid (DNA). Small changes in the viral RNA genome may affect the shape of the viral proteins encoded by the virus’ genes. Differently shaped viral proteins have different abilities to bind to and infect host cells. Therefore, a slight change in viral protein shape could alter the virus enough to suddenly allow it to infect a new species.
The deadly 1918 flu pandemic, also known as the “Spanish Flu,” is thought to have jumped from birds to humans in this manner.
So ...
Yes, it is possible for diseases to “jump” species. While bear-to-human transmission is not common, there are many zoonotic diseases that can be transmitted from other animals to humans. Potential public health dangers lie in emerging diseases that have not yet been well studied. The H5N1 avian flu, for example, has killed more than 100 people worldwide since 2003 and scientists are studying the disease very carefully to determine if it will give rise to a new zoonotic pandemic.
- by Audrey M. Huang, Ph.D.
Want to read and learn more?
To learn more about mouse parthenogenesis, visit:
http://www.reproduction-online.org/cgi/content/full/128/1/1
To read more about zoonoses in wildlife, go to:
http://www.cdc.gov/ncidod/EID/13/1/6.htm
To learn more about zoonotic diseases in general, visit:
http://www.vetmed.wisc.edu/pbs/zoonoses/
