Flea control - least toxic options

Indoor use of chemicals is the main source of non-occupational human exposure to pesticides. As an ongoing series in Pesticides News, this report aims to help reduce hazards from the home environment.

Every summer the Pesticides Trust [now PAN UK] information line becomes overheated with calls from concerned pet owners unsure of which flea control products to use safely on their pets and in their homes. Parasitic cat and dog fleas (Ctenocephalides felis/canis) which feed on warm blooded animals can cause pets to lose hair, scratch and bite at sensitive areas and cause owners skin irritation and allergic reactions. The veterinary medicines industry has put a vast array of insecticidal products on the market, some of which still contain organophosphates (OPs), this article offers an alternative strategy.

A female flea can lay around 25 eggs a day, which hatch into larvae in 2-12 days. In optimal conditions larvae develop into pupae in 8 -24 days but can take up to 200 days. Pupal development takes up to a year in unfavourable conditions but normally lasts 1-2 weeks. Ideal conditions are hot, rainy summers. Dryness is fatal to larvae because they cannot close their spiracles (breathing holes) to retain moisture(1). Fleas develop throughout the year and at different rates, so in the summer season infestations are likely to take hold.

Chemical control
Pesticides used to control fleas include collars, sprays, spot-ons, shampoos and powders. The main active ingredients are listed in table 1.

Table 1. Concerns about flea treatments used in UK (10, 11)
amitraz (amidine)  suspected endocrine disruptor
carbaryl (CA)  suspected endocrine disruptor; human carcinogen; cholinesterase, inhibitor; toxic to bees
coumaphos (OP)  cholinesterase inhibitor; toxic to fish
cythioate (OP)  cholinesterase inhibitor
diazinon (OP)  suspected endocrine disruptor; cholinesterase inhibitor; mild eye and skin irritant; toxic to birds; highly toxic to bees
dichlorvos (OP)  suspected endocrine disruptor; cholinesterase inhibitor; mild eye and skin irritant; moderately toxic to birds; toxic to bees and fish
fenitrothion (OP)  suspected endocrine disruptor; cholinesterase inhibitor; toxic to bees
fenthion (OP)  cholinesterase inhibitor; toxic to bees
fipronil (phenyl pyrazole)  mild eye irritant
flumethrin (SP)  
imidacloprid   toxic to bees; moderately toxic to birds
iodofenphos (OP)  cholinesterase inhibitor
lufenuron (benzoylurea)  
permethrin (SP)  suspected endocrine disruptor; mild skin and eye irritant; skin sensitizer; toxic to aquatic invertebrates and bees; highly toxic to fish
phenothrin (SP)  suspected endocrine disruptor; toxic to fish and bees
phosmet (OP)  cholinesterase inhibitor; mild skin and eye irritant; embryotoxic; teratogenic; harmful to birds and animals; toxic to fish and bees
piperonyl butoxide (synergist)  
propoxur (CA)  cholinesterase inhibitor; very toxic orally; mild eye irritant; foetotoxic; highly toxic to bees; phytotoxic to some species
pyrethrin/pyrethrum (botanical)  mild skin and eye irritant; highly toxic to fish; toxic to bees
s-methoprene   formulations can be skin sensitizers
CA = carbamates; OP = organophosphates; SP = synthetic pyrethroid.
Inerts used include: disodium edetate, polyoxy-ethylene lanoline, sulphamlamide and sodium polyborate on which there is little information available in the public domain.

Concern about the harmful effects of pesticides in flea products were heightened with press reports of veterans complaining of Gulf War Syndrome after being exposed to a combination of chemicals, including OPs during the Gulf War. OPs and carbamates are nerve poisons which kill by inhibiting the nerve enzyme cholinesterase thereby disrupting the nervous system. In February 1997, Droplix, an anti flea treatment which contains the OP diazinon, was linked with dozens of pet deaths in Britain (see PN35 pp6-7). Table 2 is a summary of incidents reported to the Appraisal Panel for Human Suspected Adverse Reactions to Veterinary Medicines in the UK(2).

Table 2. Incidents of suspected adverse reactions to veterinary products
amitraz in three separate incidents (1992-95) small children aged 2 & 3 reported to have lost consciousness after accidentally swallowing a small amount of shampoo product, in one case with bradycardia followed by hypothermia and laboured breathing. 6 other incidents include symptoms of nausea, abdominal pain, severe eye irritation, flatulent dyspepsia, and headache and vomiting
diazinon three cat owners (1994-1996) reported a variety of symptoms from diarrhoea, headache, internal trembling, nervousness, facial burning, nausea and loss of appetite, stinging eyes and breathlessness
dichlorvos & fenitrothion (1991-1995) 11 separate incidents reported, symptoms included: nausea, diarrhoea aching limbs, dizziness, rashes, flu-like symptoms, chest pain, respiratory problems, abdominal pain and vomiting, depression, anxiety and lethargy
fenthion symptoms from 9 reported cases (1994-96) include nausea, sore throat and coughing, breathlessness, sore eyes, aches and pains, burning and itching, swollen lips and eyes, and in 2 cases development of lobar pneumonia days later
permethrin after treating dog one owner had an asthmatic attack (1992), another had an itching and nettle rash on body and arms (1994)
phosmet 8 incidents (1994-1996) symptoms included burning sensation in mouth, headaches, blurred vision, dizziness, nausea, difficulty in breathing and burning sensation in chest
propoxur 2 incidents reported (1995), one with rash on hands and arms, the other with nausea, chest tightness, shortness of breath and blurred vision
pyrethrins + piperonyl butoxide pet owner reported coughing up blood for 3 days after using small animal spray product (1994). Also used paint stripper the previous day. 2 cases of itchy rashes (1994)
skin rashes were also reported in incidents concerning pyrethrum powder (1993), tetrachlorvinphos (1991), piperonyl 
butoxide + pyrethrum extract (1991)

The US Journal of Pesticides Reform 1997(3) cited research papers relating to pesticide exposure and childhood illness: In Denvor, Colorado, research has found that home pesticides may be associated with some childhood cancers(4), one study in Los Angeles found a significant increased risk of leukaemia in children whose parents used pesticides in the home and garden(5), and in Missouri childhood brain cancer was associated with use of pesticides to control household pests; flea collars on pets were identified as a risk factor(6).
The National Office of Animal Health (NOAH) and the British Pest Control Association (BPCA) both take the view that a product is safe, if used according to the label's instructions.
However in 1993 the BPCA asked: "What insecticide formulation is approved for amateur use, applied directly to the body, touched by unprotected hands, provides a source of long-term insecticide contamination of skin surface including those of children? Think twice before recommending their use."(7)
Safer chemical products that contain insect growth regulators (IGRs) act by preventing development during one of the four stages of the flea life cycle. In 1996 Your Cat readers voted Program the 'Best Flea Treatment' for cats. It is available for both cats and dogs and the active ingredient, lufenuron acts by preventing the hatching of any eggs once the flea has bitten its host. However the US Food and Drugs Administration observed the following adverse effects in cats and dogs: vomiting, depression, lethargy, diarrhoea, loss of appetite and itchy, scratchy skin(8).

Natural flea control
Knowing the size of a flea population by combing or using flea traps is very useful in controlling and minimising large flea infestations. Flea combs are designed to catch the adult flea but also catch the dried blood and flea faeces that feed larvae. Any fleas caught should be placed in a bowl of soapy water. Combing will also tell you if the controls you have in place are working effectively or need to be increased in any way. Cleaning the pet's bedding area regularly and the pet itself can drown fleas. Vacuuming areas used by pets, including skirting and soft furnishings on a regular basis is effective at picking up adult and egg stage fleas.

Herbal flea collar  
Buy a soft flea collar (untreated)  
1/2 teaspoon alcohol (Essential oils)
1 drop cedar wood oil  
1 drop lavender Mix with the contents of four
1 drop citronella garlic capsules
1 drop thyme oil  
Soak flea collar until it has absorbed sufficient mixture
(i.e. is soaked through), then dry
The effect lasts approximately one month  

In severe infestations extremities of temperature are needed such as steam-cleaning, which kills off larvae as well, although some eggs may still hatch. Vacuum cleaner bags should be burned or sealed in an airtight bag and put in the freezer prior to disposal.
Your Cat magazine recently reviewed the range of natural products available on the market in response to consumer demand for alternatives to pesticidal products(9). These include:

  • electric flea traps which work by emitting gentle heat which attracts fleas and traps them on sticky paper;
  • a wide range of cat collars containing natural ingredients such as penny-royal, citronella, eucalyptus, cedarwood, orange and sesame that work for up to 3-4 months;
  • other natural sprays, shampoos, drops, and homeopathic remedies, including diet and supplements to help boost the immune system.

The Pesticides Trust is concerned that conditions of use of domestic veterinary products together with exposure to garden and household pesticides may be leading to higher exposure levels than previously expected.
This is particularly worrying for children whose organs are still at a sensitive stage of development and are more susceptible to the effects of pesticide exposure. Their relative exposure to pesticides is higher than that of adults as they eat, drink and breathe more per pound of body weight. They can also come into contact with pesticides via toys, carpets, lawns and parks - traditional playing areas of children.

1. Common-Sense Pest Control: Least-toxic solutions for your home, garden, pets and community, Olkowski, W., Daar, S. and Olkowski, H., Taunton Press, 1991, 255-264.
2. Veterinary Products Committee Appraisal Panel 1996.
3. Journal of Pesticide Reform, 1997, 17(3):15-22.
4. Home Pesticide Use and Childhood Cancer: A Case Control Study, Leiss, J.D. and D.A. Savitz, American Journal of Public Health, 1995, 85(2): 249-252.
5. Childhood Leukaemia and Parents Occupational and home exposures, Lowengart, R.A. et. al., Journal of the National Cancer Institute, 1987, 79(1):39-46.
6. Family pesticide use in the home, garden, orchard, and yard, Davis, R.R., Brownson, R.C. and Garcia, R., Archives of Environmental Contamination and Toxicology, 1992, 22:260-266.
7. Your Cat Magazine, January 1997, 76-77.
8. Journal of Pesticide Reform, 1997, 17(3):15-22.
9. Your Cat Magazine, June 1997, 74-77.
10. Henston Small Animal Vade Mecum. Electronic Version, Business Data Systems Ltd, 1997.
11. Pesticides Trust [now PAN UK] Active Ingredient Database, 1998.

[This briefing is an extended article that first appeared in Pesticides News No.40, June 1998, p21]