Toxoplasmosis

A: Toxoplasmosis

B: Root causes of toxoplasmosis

Toxoplasmosis is caused by a single cell protozoan parasite called Toxoplasma gondii. It is a eukaryotic microorganism, meaning that standard bacterial treatments are ineffective against the parasite. It affects all mammals as intermediate hosts but can only complete its reproductive cycle in felines, which are the definitive hosts. It is commonly spread by contaminated meat and feces. Interestingly enough, the parasite reproduces by a very unusual method which is explained using the manipulation hypothesis. This postulates that a parasite may alter the behavior of its host for its own benefit, usually enhancing its transmission rate. Toxoplasmosis induces behavioral changes in affected rodents which then remove their innate fear of feline mammals (Berdoy M., et al 2000). This causes an increased predation of rodents by felines, thereby increasing its transmission rate to feline hosts which ultimately allows the microorganism to undergo its reproductive cycle (Which it can only do within felines). Figure 2 illustrates the life cycle

￼ C: Affected cell types/tissues/organs/systems Toxoplasmosis typically affects a wide range of organ systems due to its ability to cause a wide range of nonspecific symptoms. However, it can affect brain tissue and potentially result in psychological disorders such as schizophrenia, ADHD, OCD, and suicidal behavior. The parasite affects cells thrugh its own rapid trachyzoite division, which eventually lyses the host cell.

D: Historical background

Toxoplasmosis was first discovered in 1908 by an affected North African rodent called Ctenodactylus gundi. The first case of human toxoplasmosis was reported in 1923 as encephalomyelitis which affected an 11 month old child (Wolf et al., 1941). However, it was not until 1970 that felines were determined to be the definitive hosts while other mammals were ‘accidental’ hosts. It was also at this point that the entire life cycle of T. gondii was elucidated.

E: Common systems

In healthy individuals, early toxoplasmosis infections can cause flu-like symptoms such as swelling of the lymph nodes, sore throat, fever, and muscle pain. After initial symptoms, the disease is usually latent if the individual has a competent immune system. In immune-compromised individuals such as those living with HIV/AIDS, toxoplasmosis can cause life-threatening symptoms such as acute encephalitis.

F: Standard treatment

While there is no cure for toxoplasmosis, treatments usually involving antibiotics for those living with AIDS have shown to increase their life expectancy. The most emphasis is usually placed on preventing toxoplasmosis through properly preparing meat and maintaining good hygiene and sanitation in order to prevent transmission through infected feces.

G: Current Research

Current research revolves around targeting the bimolecular features responsible for T. gondii’’s pathogenicity. The ROP18 gene found in the parasite is thought to be responsible for 90% of its virulence considering that it encodes a kinase that inhibits important signaling pathways in the host cell (El Hajj et al., 2007). With this gene uncovered, there are much greater prospects toward finding a functionally cure for toxoplasmosis. Additionally, scientists had determined the structure of the TgMIC1 protein in the parasite which is responsible for targeting sialylated oligosaccharides in the host membrane, which the parasite must perform in order to adhere properly (Blumenschein et al., 2007). This discovery is similarly important because it has elucidated another structure with is crucial for T. gondii’s pathogenicity.

References Wolf, A., Cowen, D., & Paige, B. H. (1941). Fetal encephalomyelitis: prenatal inception of infantile toxoplasmosis. Science, 93(2423), 548-549.

El Hajj, H., Lebrun, M., Arold, S. T., Vial, H., Labesse, G., & Dubremetz, J. F. (2007). ROP18 is a rhoptry kinase controlling the intracellular proliferation of Toxoplasma gondii. PLoS pathogens, 3(2), e14.

Blumenschein, T. M., Friedrich, N., Childs, R. A., Saouros, S., Carpenter, E. P., Campanero-Rhodes, M. A., ... & Matthews, S. (2007). Atomic resolution insight into host cell recognition by Toxoplasma gondii. The EMBO journal, 26(11), 2808-2820.

Berdoy M, Webster JP, Macdonald DW Fatal attraction in Toxoplasma-infected rats: a case of parasite manipulation of its mammalian host. Proc R Soc Lond. 2000;B267:1591–4. doi: 10.1098/rspb.2000.1182.