In the past the advice has been that dog & cat poo should not be composted because of the risk of the roundworm Toxocara canis and the risk of Toxoplasma from cat faeces.
Toxocariasis in humans is relatively uncommon, with an average of 10 cases occurring each year in England, it can be serious. Evidence of human infection by T. canis in London blood donors was found to be present in 2.6% of those sampled
T. canis was found in 6.3% of soil samples from London parks and gardens (Gillespie et al., 1991) while another survey found soil samples from 66% of London parks (Lloyd S 1998).
Toxocara canis eggs from grass, soil, vegetables, other plants or compost may contaminate the hands and then be ingested. Eggs which are swallowed can hatch into larvae in humans but will not develop into adult worms. The larvae
will travel around the body – usually causing no problems but can settle in the retina where they may cause damage or blindness. Toxocariasis usually affects children who are between one and four years old. However, cases have been reported
in people of all ages. Younger children are particularly at risk because their play habits make them more likely to encounter contaminated soil. Many young children also have a habit of eating soil.
The symptoms of
toxocariasis can vary depending on where in the body the infection occurs. There are three main types:
1. Covert toxocariasis. This is the most common and mildest form of toxocariasis. Symptoms
include abdominal pain, a cough and headache.
2. Visceral larva migrans. Visceral larva migrans develops when large numbers of parasites spread through different organs of the body, such as the
lungs, liver and heart. The symptoms include fever, abdominal pain and shortness of breath.
3. Ocular larva migrans. This is the least common but potentially most serious type of toxocariasis.
The condition can develop if the larvae move into the eyes. The main symptoms are disturbed vision and irritation of the eyes. Left untreated, ocular larva migrans can result in permanent vision loss, although only one eye is usually affected. About 50 cases
of toxocara involving eye damage are reported annually. www.threerivers.gov.uk
Toxocara are survivors and can cross the placental barrier so that an infected
bitch will have infected her puppies before they are born. The parasite can remain dormant in the tissue of the bitch until she become pregnant. However recent surveys of pet dogs, which we assume are regularly wormed, have shown that only 1% of animals
are passing eggs in the faeces. Higher figures have been obtained where samples have been taken from parks in towns, but these samples are likely to include a number of stray and untreated animals (including foxes).
eggs can survive the cold or cool composting and contaminate the soil and plants on which the compost is used. It can then be transferred to the hands and be ingested by children, or by children and adults eating contaminated food.
Cat faeces may contain toxoplasmosis. In the UK 23-33% of the population are infected with toxoplasma but in most cases a person will not realise they have caught the infection. Infection
with this parasite is usually asymptomatic and does not produce any symptoms. It can cause symptoms like flu or glandular fever, sometimes including swollen lymph nodes. Once a person has had the disease they are generally thought to be protected
for life, unless they have an impaired immune system. Infection is a particular risk to pregnant women as it can cause foetal blindness, brain damage of unborn children. about 2,000 pregnant women contract toxoplasmosis in
the UK each year but most never know they have been infected as they do not experience any symptoms.
The adult parasite is carried by cats, but the eggs shed in the manure can infect humans, pigs, cows
and other mammals. The parasite can be present in meat, unpasteurised goats’ milk, cat faeces and contaminated soil or unwashed food plants carrying soil. The toxoplasma parasite can infect most birds and warm-blooded animals, including humans.
Cats become infested as a result of eating birds, mice or other raw meat. They will then pass organisms in their faeces for about 14 days.
- Toxoplasmosis cannot be caught by stroking a cat or by
simply having a cat as a pet. The infection results from contact with the infected cat faeces or ingesting anything infected with, or contaminated by, the parasite such as poorly or unwashed vegetables or fruit
Non-composting sources could include
- raw or undercooked meat and raw cured meat such as Parma ham or salami
- unpasteurised goats’ milk and dairy products made from it
- and exposure
This sounds bad but to bring the risk into perspective. It is estimated that between a third and half of the UK population
will have the infection at some point in their lives, probably without knowing it, after which they will be immune and will not become infected again. In the 60s when I was in a laboratory which was working on T.gondi only two out of the eight
or nine workers did not have antibodies.
Under normal conditions the sporulated oocysts can survive a year or more in the soil or sand (cats like to deposit samples in sand pits).
However hot composting at 60°C will reduce most pathogens to safe levels within an hour and will kill T. gondi which means that the faeces from cats who use a litter tray can be composted
provided the compostable cat litter is used together with Hot composting where 60C is maintained for a sufficient period to kill the parasite.
If you keep dogs or cats which poo in the garden the risk of
contamination already exists. In practise cat waste is more difficult than dogs faeces to deal with as it is likely to be buried in the soil rather than left sitting on the lawn or surface of the soil and there is a risk of coming into contact with it
while handling soil unless wearing gloves.
The composting/gardening risks can be controlled by taking simple precautions
- Physically remove all traces of soil and the
parasites from fruit and vegetables by thoroughly washing before eating or cooking. However, water can be a source of infection in tropical and subtropical countries where unpurified surface water is drunk and has also been
found to be a risk factor in parts of Europe. There was an outbreak of toxoplasmosis in Canada involving contamination of municipal drinking water. Untreated water that may contain Toxoplasma oocysts and contaminate fruit or
vegetables. Oocysts have been found on leafy greens so It would seem that in addition to unwashed fruit and vegetables washing with contaminated water could increase risk of infection
- Wear gloves when gardening
hands and gloves afterwards
- If taking a coffee break and eating while gardening wash your hands first.
- If pregnant or planning to become pregnant avoid gardening in areas soiled with cat faeces and cover children’s sandpits.
Simple additional control measures can be used to ensure that composting dog faeces in a wormery does not add to the risk.
- Pregnant and nursing bitches
are sources of infection they should be treated before and after whelping. Waste from these animals should not be composted
- All puppies and kittens should be assumed to be infected with worms, and they should be treated routinely
in accordance with veterinary advice.
- Treat adult dogs 3 -6 monthly to reduce the re-infection rate
- After worming wait 1 week before adding poo to your wormery.
- Do wear gloves and wash hands.
Do not use worm compost made from dog poo:
- On vegetables
or soft fruit
- As mulch on flower beds to which dogs have access or where children play.
Do not put cat faeces in a wormery
- Pregnant women should avoid contact with cat faeces.
- Garden vegetables should be washed thoroughly before eating because they may have been contaminated with cat faeces
a little dog or cat poo has been added to a cold composting system by mistake the compost should be allowed to mature and then applied to an area of flower garden away from children. Any pathogens should be have been diluted by the rest of composted
material and the turning during aeration. The pathogen count will certainly be lower than that present in an area of soil contaiminated directly by cats.