Toxoplasma: a potential threat to humans

Toxoplasma is protozoan parasite, belong to phylum Apicomplexa, class Sporozoasidea, Order Eucoccidiorida and family sarcocystidae.

Toxoplasma: A Potential Threat to Humans

Species that causes infection is T. gondii, Gundii is a desert rodent, in which toxoplasma was discovered by Charles Nicolle and Louis Manceaux in 1908 at Pasteur institute, Tunis. It is an intestinal coccidian and mostly infect cats. Toxoplasma is non-pathogenic to its final host but, causes tissue cyst formation in its intermediate hosts.

Intermediate hosts include ruminants, pigs, horses and human. In ruminants it causes abortion and may also have zoonotic importance. In humans if infection occurs during pregnancy, it may result in abortion or congenital disorders which primarily affect the nervous system. In cats it may act as intermediate host as well.

The life stages of parasite include Tachyzoites, Bradyzoites and cysts. Tachyzoite was the stage of parasite which was found in Gundii rodent by Nicolle and Manceaux. Tachyzoites are banana shaped. Tachyzoite can infect any cell in the body, cells including fibroblasts, reticulocytes, myocardial cells and hepatocytes. In each cell there may be up to 8-16 organisms.

The term bradyzoite was indicated by Frankel in 1973. It explains encystation in the tissues. Bradyzoites are also known as cyctozoites. Bradyzoites commonly seen in muscles, liver, lungs and brain. These tissue cysts can be differentiated from other cysts as containing organisms with subterminal nucleus periodic acid Schiff (PAS)-positive granules surrounded by an argyrophilic cyst.

Contaminated water or food by oocysts, undercooked meat, mother to fetus, organ transplant and blood transfusion are the common sources of infection. Transmission is through following routes including congenital, carnivorism and faecal-oral.

Toxoplasmosis in Humans

Wolf, Cowen and Paige were the three pathologists who identified T. gondii in an infant girl from USA in 1938. There were convulsive seizures at age of 3 days and lesions were in maculae of both eyes. She died at the age of 1 month. On postmortem there was severe encephalomyelitis and retinitis. T. gondii was found free in lesions and later rabbits were inoculated with this and they also developed the infection.

Main problem is that the people who get infected with T. gondii are not mostly aware of it. There is flu like illness with swollen lymph nodes or muscle aches with pain in acute cases. In severe toxoplasmosis if the individual is having a healthy immune system he gets infected. In ocular toxoplasmosis there is weakened eye sight, blurred eye vision, pain, tearing and redness of eyes.

The people who are most likely to be infected are the infants whose mothers got newly infected during any pregnancy stage. The people with weakened immune system, such as patients of AIDS or people who recently received some organ transplant and people with feline pets. The people with feline pets should follow the precautions to not get infected such as; The cat litter box should be changed daily. Toxoplasma doesn’t become infectious until 1-7 days after shed in the feces.

If the owner is immuno compromised or pregnant she should avoid changing the litter. You can use disposable gloves and wash your hands with soap/sanitizer and water after performing the litter removal. Keep your cats indoor. Do not let your pet hunt some wild animal. Do not adopt stray kittens. Feed your cat only with canned or dried commercial foods not raw or undercooked meat.

Preventive Measures

You can adopt several precautions to reduce the chances of getting infected by Toxoplasma gondii. Food should be cooked to safe temperatures. Most we rely on color of food as an indication of cooked or undercooked, so this parameter is not reliable. The temperature should be high enough to kill harmful pathogens like toxoplasma and many other protozoan parasites. In case of meat, according to USDA meat (whole cut & ground) should be cooked at least at 145o F.

After cooking the meat should be allowed to rest for 3-5 minutes before consumption. During this time the temperature continues to rise, then pathogenic organism is got killed by high temperature. Sea food (Oysters, mussels, clams) should also be avoided if under cooked, as a preventive measure. Fruits and vegetables should be washed thoroughly and peeled before consumption.

Avoid consumption of unpasteurized milk or other dairy products. Washing of cutting knives, dishes, utensils and hands should be washed with soapy water if got contact with raw meat. Wear gloves while gardening and handling your cat. Because contact with soil which is contaminated with cat feces, can cause transmission of pathogen. Teach your children about hygienic measures to avoid infection.

Authors: Hammad Ur Rehman Bajwa1, Muhammad Kasib Khan1, Arsalan Zafar1, Zaheer Abbas1, Muhammad Adeel Arshad2

  1. Department of parasitology
  2. Department of Animal Nutrition

University of Agriculture, Faisalabad, Pakistan

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