Parasitic Zoonoses
When a parasite that usually resides inside or on an animal’s body causes a disease in human beings, the disease caused by it is known as parasitic zoonosis. There are many types of parasites that reside in and on animals’ bodies. Pet animals like dogs and cats also have them and can become an important source of transmission of these parasites to humans if not taken good care of.
Toxocariasis
There are two species of Toxocara roundworms that cause this disease. T. canis and T. cati from dogs and cats respectively. The larvae of this parasite are responsible for causing this disease. This disease is considered to be a neglected parasitic diseases.
The clinical manifestations associated with this disease are Visceral Larva Migrans (VLM) and Ocular Larva Migrans (OLM) depending on the organs affected. Toxocara spp. are distributed worldwide because of our close association with domestic wild animals. This disease is more prevalent in low income and rural regions. Humans are usually accidental hosts, and usually, this species does not grow into adult form in humans.
Dogs and cats are the main reservoirs of this disease in developing and under-developed countries where sanitation standards are poor. This is also a trans-placental disease of animals. Urban and rural foxes can also become primary sources of transmission in certain developed countries like the UK. The prevalence of this disease is higher in young ones than adults. Soil is the main source of contamination as animals defecate in the soil thereby transmitting Toxocara eggs.
Humans usually get affected by the ingestion of eggs from the soil or food. These eggs then hatch in the small intestine and the larvae produced penetrate the intestinal walls and start to circulate leading to various clinical symptoms depending on the organ involved. It usually causes extraintestinal symptoms. The public health impact of this disease is still underestimated.
In humans-
- The clinical signs can vary depending on the organ affected.
- Fever
- Cough
- Difficulty in breathing
- Abdominal pain
- Weight loss
- Fatigue.
During ocular involvement, there can be visual impairment, strabismus, retinal detachment, retinal
mass, etc.
In animals-
- Tiredness
- Breathing difficulties
- Blurred or cloudy vision
- Rashes
- Seizures
- painful eyes
- Vomition and extreme diarrhoea can also be observed along with a pot-bellied structure.
Infection in dogs and cats is diagnosed by detecting the eggs in feces. In humans, biopsies and blood chemical analyses are performed to detect this disease along with direct microscopy of the stools. There are also various PCR based techniques available that can be used. Diagnostic imaging like CT scans, USGs can be used for the detection of various lesions.
There needs to be a proper stray animal population control programme. Deworming of household pets should be done regularly. Feces should be safely collected and hygienically disposed of. Human infections can be prevented by regularly washing hands after handling pets or contaminated areas. Parents should educate children about basic personal hygiene. Last but not the least, a pet’s living area should be cleaned at least once a week.
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