[Toxoplasma gondii]

• Category: Protozoa (single-celled protozoa)
• Type of parasite: Intracellular parasite
• Life cycle:
  • With cats as the definitive host, it will parasitize the small intestinal epithelial cells of cats. After infection, the oocysts of Toxoplasma gondii will be excreted with the cat's feces and is infectious within 1-4 days.
  • Other warm-blooded animals (such as: rats, humans, etc.) are intermediate hosts, and the feces will not contain oocysts, so the feces are not infectious. Instead, it will form a tissue cyst in the body tissue, so the infected ones will still develop symptoms. 
  • Main routes of infection: Ingestion of raw meat containing tissue cysts, contact with feces containing oocysts, and accidental ingestion of food contaminated by oocysts and feces.
  • Symptoms of infection: Most cats and intermediate hosts "are not likely to have clinical symptoms" after being infected. There are a several cases of humans may have local lymph node swelling after infected. 

[Host level: Differences between final, intermediate, and abnormal]

The host of Toxoplasma cats is divided into three types: intermediate, final and abnormal intermediate:

• Intermediate host: Undergo the stage of larvae or asexual reproduction without producing oocysts.
• Definitive (Final) host: Has completed the life history, has sexual reproduction, and will produce oocysts (will appear in the feces).
• Abnormal intermediate host: Provides “space” for the growth of parasites, but is not a necessary host to complete the life history.

​[The relationship between Toxoplasma gondii and pregnant women]

• If one is infected with Toxoplasma gondii for the "first time" during pregnancy, there will be a risk of transmission of the parasite to the fetus.
• If an individual had a history of being infected before pregnancy, it indicates that the body already has antibodies against the parasites. Therefore, if that individual was infected again during pregnancy, the risk would decrease. Only if the immune system of the individual is greatly compromised then it may transmit to the fetus.  
• If infected, it may cause miscarriage, congenital malformations of the fetus, and even mental disorders.

Source of information: <弓形蟲感染症(Toxoplasmosis)>衛生福利部疾病管制署、<貓之弓形蟲感染> 國立嘉義大學獸醫學院附設動物醫院

[Cats are not the only species that can be infected by Toxoplasmosis]

Toxoplasmosis can only reproduce sexually in the intestines of cats (the definitive host), producing the next generation of infectious "oocysts". The oocysts will be excreted alongside the stool. Hence, if the infectious excrement come into contact with other types of animals, then non-cats warm-blooded animals may be infected(intermediate hosts such as humans)

<What is an oocyst>:

Oocyst is a sturdy substance that can survive in various environments and it is highly infectious as well. Even if the food contains only one oocyst, infection may still occur!

As humans and cats get closer and closer, toxoplasmosis infection has become a worldwide disease!

[Symptoms of infected cats vs other types of animals]

• Cats: Most cats have no major adverse reactions; only a small number of cats with poor immunity may have pneumonia, liver damage, but these cases are pretty rare.

Symptoms: lethargy, loss of appetite, cough, difficulty in breathing, diarrhea, jaundice, blindness, change in personality, eye diseases and other neurological symptoms

• Other warm-blooded animals: In severe cases, it may even cause systemic infection. May cause pneumonia, myocarditis, liver necrosis, meningoencephalomyelitis, chorioretinitis, lymphadenopathy and myositis.

Symptoms: fever, diarrhea, cough, dyspnea, jaundice, seizures and death, may cause abortion and stillbirth in sheep, goats and pigs, affecting their economic value.

• Human infection: Symptoms are not obvious or asymptomatic, but if a pregnant woman is infected, miscarriage may occur as aforementioned.

Source of information: <Parasites - Toxoplasmosis (Toxoplasma infection)> CDC、<弓形蟲感染症> 衛生福利部疾病管制署、<Overview of Toxoplasmosis> MSD Manual Veterinary Manual、<Toxoplasmosis> AVMA

[Life cycle of toxoplasmosis]

The infection route can be divided into: cats and non-cats

• When the definitive host of toxoplasmosis (which is cat) ingests cysts of Toxoplasma, the parasite reproduces asexually into Bradyzoites, which then produces gamenocytes for sexual reproduction. In the end, the oocytes are excreted alongside with feces as we have mentioned earlier. 

• If a non-natural host (warm-blooded animals other than cats) is infected, Toxoplasma will release sporozoites, then form asexually reproductive tachyzoites to invade various tissues, and finally slowly divide into bradyzoites. In contrast with the cats, the oocysts will not be excreted in feces. 

<Methods of infection can be divided into three categories>:

• Vertical infection: There is a possibility that the mother may infect the fetus within twelve weeks. It is a Category 4 communicable disease. 

• Infection through ingestion: If one accidentally eat raw meat containing cysts, use contaminated water, or even swallow contaminated feces, he or she may be infected. It takes 48-72 hours for the excreted oocysts to become infectious, so there is no need to panic too much. 

• Iatrogenic infection: If there is transmission of schizoids during blood transfusion or organ transplantation, the recipient may also be infected.

​[Mild to Severe Symptoms]

The symptoms of toxoplasmosis infection actually vary with the physical state of the host. The following provides an explanation according to different situations:

• Healthy individuals: For healthy people, no obvious symptoms will develop. Only when the immune system is relatively low only then there will be symptoms similar to flu developing such as swollen lymph nodes, muscle pain. However toxoplasma may cause eye diseases such as retinitis and choroiditis, leading to photophobia and eye pain.It may even lead to blindless if the symptom is too severe. 

• Immunocompromised individuals: An HIV patient that infected by Toxoplasma may have relapses as well assymptoms of confusion, headaches or seizures. 

• Pregnant women and fetuses: If the infected pregnant woman is not infected with Toxoplasma for the first time, then the pregnant women and fetuses will be protected by the existing antibodies. However, if the pregnant woman is infected for the first time, there is a chance of vertical infection to the fetus. 

The symptoms of the fetus vary according to the time of infection. By means, the earlier the fetus is infected, the more severe the symptoms will be. Symptoms include abnormal head size, impaired vision and mental retardation. Itmay lead to miscarriage in severe cases. 

Source of information: A Comparative Analysis of Coprologic Diagnostic Methods for Detection of Toxoplama gondii in Cats, NCBI、Life cycle of Toxoplasma gondii, ReaschGate、Toxoplasmosis: General FAQs, CDC、Epidemiology & Risk Factors, CDC、Toxoplasmosis DPDx, CDC、行政院衛生福利部-弓蟲感染症、藥師公會聯合會-弓形蟲感染症

Q1: What happens if a pregnant woman is infected?

A1: Generally, it is fine for a healthy person to be infected with toxoplasma, but if it is the "first" infection of a pregnant woman, due to the lack of antibody protection, toxoplasma may be transmitted to the baby through the placenta (the infection rate is about 40%).

• Infection during the first pregnancy: possible miscarriage or stillbirth
• Infection within 12 weeks of pregnancy: 20~30% of babies may have congenital Toxoplasma infection, 70~80% of babies have no symptoms but may eventually have poor eyesight, learning disabilities and mental retardation.

Therefore, if a pregnant woman is diagnosed to be infected for the first time, they should consult their obstetricians and gynecologists. If the condition permits, the pregnancy can be continued. The physiological condition of the body will be continued to be checked after it was born. Therefore, it is suggested to continue tracking the condition for at least for several months or years to provide appropriate medical care for the patient. 

Q2: Can an infected pregnant woman breastfeed her baby?

A2: Yes. If a pregnant woman has ruptured bleeding on the nipples or breast inflammation within a few weeks after an acute toxoplasma infection (while the worm is still circulating in the blood), theoretically, it is possible to transmit the parasite to the baby through breastfeeding. Yet, there is no such medical record to date.

Q3: How to prevent toxoplasma infection?

A3: There are three ways

• Avoid eating raw food. Meat must be frozen for 24 hours at -20°C, or heated or cooked at temperature above 66°C . Vegetables and raw food must be washed. In addition, do not try to test the food during the cooking process (as you may eat uncooked food).
• Do not touch cats of unknown origin. Wear gloves and wash your hands when cleaning the litter box to prevent touching and eating the oocysts in the stool.
• Do not let the cats in the house to eat uncooked things as well as not letting them outdoors to hunt. 

​

Q4: If I want to get pregnant, do I have to give up the cat at home?

A4: By following the methods and the principles mentioned above, even if the pregnant woman has a cat at home, no need to worry too much. This is because humans usually do not get infected from pet cat. Also, the infected cat will only discharge a large number of oocysts once in less than 3 weeks, and it takes 1-5 days for the oocysts to become infectious within the environment. Majority of the cats will groom before this occurs, cleaning up their poop from the body which explains why it is less likely to get infected by pet cats. 

• The risk of infection is actually very low!

Q5: What can I do if I am still worried about being infected with Toxoplasma by cats and cats at home after pregnancy?

A5: Answer: The diagnosis of human infection with Toxoplasma gondii usually involves a serology test. This test will test antibody IgG, an important substance to fight against foreign diseases. It can determine whether the person has been infected with Toxoplasma, but it is unable to distinguish the time point of infection. Besides, you can also take the cat to the animal hospital, and you can draw blood to check whether the cat is infected with toxoplasma!

<To prevent toxoplasma infection, it is very important to comply these rules>

• Do not eat raw food 
• Wear gloves and wash your hands when you may come into contact with cat feces
• Only feed the cat cooked food and keep it indoors

Source of information: <Toxoplasmosis & Pregnancy FAQs> CDC、<弓形蟲感染症 (Toxoplasmosis)>衛生福利部疾病管制署、<Should Pregnant Women Rehome Their Cats?> World Small Animal Veterinary Association

Do you remember one of the intermediate hosts of Toxoplasma we mentioned earlier was the mouse?

Turns out that a mouse infected with Toxoplasma may present interesting behaviors, making it easier to become food for the cat.

Laboratory studies have confirmed that the mice (intermediate host) infected with Toxoplasma have the following changes:

• Loss of anxiety and fear towards cats
• Rats becoming more relaxed, trusting and no longer afraid of the smell of cats
  • This makes it easier for cats to catch mice and eat raw meat containing the aforementioned "tissue cyst"
  • Thus increasing the chance of Toxoplasma infiltrating the definitive host (cat)
    • In the past, this phenomenon was called "Feline-specific attraction", which the curiosity will increase, like to explore new environments, moved in open areas, and reduced sensitivity to potential threats.
  • This shows that the impact of Toxoplasma infection on mice is comprehensive. 

[Can Toxoplasma really”bewitch” the mice?]

• Experimental method: Tracing the brain vesicles of mice infected with Toxoplasma for 10-12 weeks
  • It was discovered that the brain is full of vesicles containing Toxoplasma. Among them, the visual cortex has the most significant lesion. The greater behavioral changes occurs in the mice, the more severe the inflammation is and more vesicles within the brain.
  • The presumed cause: Toxoplasma infection causes a structure in the brain called "neurons" to induce allergic reactions consequently causing neuronal inflammation, which greatly affects the brain activity of mice. It is not the toxoplasma containing vesicles that cause the abnormality. 
  • Extension of the results: To what extent in which neuron inflammation need to achieve to affect the curiosity (abnormal behavior) of mice is still under discussion.

<The symptoms of Toxoplasma infection in humans are very different from those in mice>:

• The inflammatory response of the nervous system can cause neuronal damage, leading to neuronal degenerative diseases and the possibility of pathogenic Alzheimer’s disease. Therefore, it is recommended that more attention should be paid and do not underestimate to the health effects of human caused by the infection with Toxoplasma.

Source of Information: 

Boillat, M., Hammoudi, P. M., Dogga, S. K., Pagès, S., Goubran, M., Rodriguez, I., & Soldati-Favre, D. (2020). Neuroinflammation-associated a specific manipulation of mouse predator fear by Toxoplasma gondii. Cell Reports, 30(2). https://doi.org/10.1016/j.celrep.2019.12.019 <TOXOPLASMA INFECTION MAKES MICE MORE BRAVE>Science Connected Magazine

Toxoplasma infection target: Cats are the only definitive hosts of Toxoplasma, besides it toxoplasma is capable of infecting all warm-blooded animals including humans, domestic animals, and marine mammals as well (such as dolphins, whales, sea lions). In contrast,the parasite will not proliferate in cold-blooded animal.

Transmission route of marine mammals:

• Feline feces containing Toxoplasma oocysts enter and pollute the marine environment via ocean waves, fish or invertebrates. 
• Most marine mammals take cold-blooded animals as their staple food but the influence caused by eating alone is actually limited. 
• According to the cases of marine mammals infected with toxoplasma, these animals are regarded as sentinels of environmental pollution, which may indicate that the marine environment has been polluted. Humans may infect toxoplasma by ingesting uncooked marine mammal meat.

[Infection cases of different marine mammals]

• Sea otters: American research studies have shown that Toxoplasma can cause lesions and pathological changes in the brain, heart, thymus, muscle, and internal organs of juvenile sea otters, in severe cases, it may also lead to death. Fetus is infected through placenta, and miscarriage may occur. 
  • The positive rate of the sea otter serum antibody is related to the density of human populations (antibody positive means that they have been infected with toxoplasma), which can be inferred to be related to the number of cats raised.
• Sea lions: The autopsy report of sea lions in the United States also found that toxoplasma infection caused pathological change of the heart, lymph nodes, bladder and other organs, and even caused miscarriage.
• Hawaiian monk seals: In studies from year 2001-2015, Hawaiian monk seals, an endangered species, also had cases of infection. Among them, toxoplasma was detected in the lung, placenta, and umbilical cord in a deadbirth individual.
• Dolphins: Toxoplasma infections have been found in Amazon River Dolphins in Brazil and Maui dolphins in New Zealand.

The phenomenon of cases distributed everywhere shows that: Toxoplasma infection of marine mammals may be global!

[The invisible killer in the vast sea that came from the land]

Toxoplasma cat oocysts have a sturdy structure, being flushed down the toilet along with cat feces or cat litter, the oocysts are capable of entering the soil and sea water with ease and survive. Usually toxoplasma weakens the body of the infected marine mammals, acting as an invisible killer lurking in their bodies, until the weaken animal encounters other survival pressures or infects other diseases, it would then die easily. 

For marine mammals, once they are infected with more than one such disease, there will be an additive effect, this “cocktail-like infection” makes it more deadly to the animal. 

PS. Cocktail-like infection is like when drinking different kinds of alcohol separately, it might be tolerable, but once they mix together, the effect would be so strong!

Case: Autopsy of some sperm whales and harbor porpoises in the Northwest Pacific found that they were infected with both Toxoplasma and Neurocystis.

Sources of Information: ScienceDirect <Recent epidemiologic and clinical importance of Toxoplasma gondii infections in marine mammals: 2009–2020>, Jitender P. Dubey, Fernando H.A. Murata, Camila K. Cerqueira-Cézar, Oliver C.H. Kwok, Michael E. Grigg, Recent epidemiologic and clinical importance of Toxoplasma gondii infections in marine mammals: 2009–2020, Veterinary Parasitology, Volume 288, 2020, 109296, ISSN 0304-4017,Christopher Solomon(2013),  科學人雜誌136期 <貓殺了海豚？>

[Five Steps to Eliminate Toxoplasma]

1. Don't eat raw food 

• Meat ingredients are fully frozen in the freezer at -20°C for 24 hours, heated and cooked at a high temperature above 66°C before eating
• Wash hands, knives, cutting boards or related items that come into contact with raw meat with soap or detergent and clean water. Do not try to eat them during the cooking process as they may be still uncooked. 

2. Do not let cats to eat uncooked things, and do not let them go outside to hunt for food
3. Be careful when handling cat feces, and do not touch cats and cat feces from unknown sources

• Wear gloves before touching cats
• Wash hands with soap or detergent and clean water after cleaning or touching, this is to minimize the possibility of touching and eating toxoplasma oocysts

4. Do not allow cats to enter children's sandpits or fruit gardens to poop
5. Prevent the invasion of mice, cockroaches, and flies in addition to keeping the home environment to be clean and tidy. 

• Both humans and cats should avoid eating raw food, at the same time minimizing the chance of direct contact with cat feces!

[What should I do if I got infected?]

• There is no need to be quarantined. Most people can get better without treatment but do not forget to report to the local health authorities. 
• Investigate the source of pollution: After the case is confirmed, the Health Bureau will conduct an investigation within one week.

However, if one has more severe symptoms, need to follow the doctor's instructions to take oral medicine for treatment.

<Final reminder>: 

No vaccine is available currently, therefore self-protection is important.

Source of Information: <弓形蟲感染症防治工作手冊> 衛生福利部疾病管制署、<弓形蟲感染症Q&A>衛生福利部疾病管制署

• https://disease.nvri.gov.tw/diseshow.aspx?p=2309

• https://www.oie.int/en/disease/toxoplasmosis-t-gondii/