The Problem
Toxoplasma gondii is a heteroxenous protozoan parasite contracted by 16 to 40% of cats in the United States, varying from state to state. Cats, both feral and domestic, are the definitive hosts for this parasite and shed the parasite in the form of oocysts through their feces, generally after consuming the tissue cysts of infected animals. Although these oocysts are usually shed for about 1 or 2 weeks, there can be millions released from a single cat. These oocysts survive the best under hot and humid conditions, sometimes living up to 18 months in soil. They can also be found in water, including drinking water, where they can survive for long periods of time and can be carried to other areas to infect more species. Toxoplasma gondii has been found to infect livestock as well as many marine mammals such as seals, otters, and cetaceans, but sea otters are the most affected by far with 54.8% infected or susceptible to the parasite. This is a significant issue as sea otters are a keystone species and are essential to the conservation of kelp forests, which shelter a vast variety of marine life. Sea otters prevent the disappearance of kelp forests by regulating the population of sea urchins, which are known to consume large amounts of kelp. It is imperative that we preserve the sea otter population for the health of the marine ecosystems along the California coast.
T. gondii is a highly common zoonoses among warm blooded mammals with many modes of transmission. These range from vertical transmission during pregnancy, to via ingestion of contaminated food or water, or due to blood or tissue transplants. There are 3 primary life states: sporozoite, tachyzoite, and bradyzoite, with cats being the definitive host. Shedding of the parasite occurs predominantly as a sporozoite, in which they are released as oocysts in their feces, and host contraction is oftentimes the result of ingesting other animals’ tissue cysts. Furthermore, the heteroxenous nature of toxoplasma and readily transmissible nature makes the issues pertaining to widespread infection more prevalent. Following infection, symptoms often include fever, diarrhea, cough, seizures, dyspnea, and death. Furthermore, in pregnant mammals, this can cause morbidity, stillbirths, and reduced reproductive rates, and can lead to numerous health conditions or death in immunocompromised animals. In humans, complications particularly those in pregnant women include fetal death, eye and nervous system diseases, as well as numerous congenital defects.
Current Treatments, Solutions, and Barriers
Despite the handful of approaches for developing treatments as well as a vaccine, there is not yet a definitive therapeutic that is considered the “gold standard” for the prevention of Toxoplasma gondii. Current attempts have included protein subunits, nucleic acids, attenuated vaccines, and nanoparticles, however the results currently are still a major obstacle, However these vary in issues from efficacy, to accessibility, to cost of development. However, the parasite is prevented via reducing zoonotic vectors and that is currently the best method to reduce human exposure caused due to three primary modes of transmission: consumption of uncooked contaminated meat, ingesting food or water contaminated by feline fecal matter, and transplantation of organs and blood transfusion. We are primarily concerned with T. Gondi being regarded as a water-borne zoonosis. Live Vaccines are primary modes for development, such as the T-263 live mutant strain, or other developments include wild type strains being genetically engineered to have transmissibility attenuated.
Our Approach
Our team has decided to use bacteriophages to impede the entry of Toxoplasma Gondii into the environment. By developing a vaccine that can be administered to cats, we believe we can prevent the sporulation of oocysts in the definitive host and reduce the spread of Toxoplasma Gondii to other species, particularly sea otters, pregnant women, and cats. Our approach uses bacteriophages to deliver the oocyst-specific antigen from the oocyst wall protein, TrOWP, into the intestine of the cat in order to trigger an immunological response and produce antibodies. Upon the formation of the antibodies that attach to the T. Gondii wall protein, the cat will be unable to shed the oocysts through its fecal matter.
To address the issue of accessibility of administration of the vaccine for both feral and domestic cats, we plan to engineer the bacteria, lactococcus or streptococcus, so that the vaccine may be orally administered through food in order to specifically deliver the phages into the small intestine of a cat. The phages will then be able to diffuse into the transcellular pathway of the epithelial cells and into the lymphatic vascular system, as they will be accepted through the mucus layer on the epithelial cells due to the high normal environmental exposure to phages mammals experience daily. The immune system will then be able to detect the antigens attached to the exterior of the phages and produce antibodies.
As cats no longer shed oocysts following antibody production, and thus the parasite no longer enters fecal matter, we are able to prevent environmental contamination due to both feral cats as well as domestic cats, preventing infection and parasite shedding.As cats no longer shed oocysts following antibody production, and thus the parasite no longer enters fecal matter, we are able to prevent environmental contamination due to both feral cats as well as domestic cats, preventing infection and parasite shedding. This will also prevent oocysts from spreading to other species, such as humans, otters, etc.
