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Can Cockroaches Cause Disease?

Cockroach Biology

Cockroaches undergo incomplete metamorphosis; small wingless nymphs resembling small adults hatch from eggs and develop into winged adults. There is no pupal form. Nymphs develop quite slowly and in successive stages called instars. Each stage is completed with a moulting of their exoskeleton, which enables them to increase in size as well as revealing newly developed structures, and gradually develop wings. The exact number of moults depends on the species of cockroach. It can take anything between just a few weeks, to over a year for a cockroach complete its growth cycle, depending on species and environmental conditions. Once the cockroach has reached its final adult form it will not moult again.
There are over 4000 species of cockroach in the world, inhabiting a vast array of climates, but their basic needs are the same. Cockroach adults may survive without food for extended periods, in some cases up to a month, however like most insects they are susceptible to desiccation and generally cannot survive without moisture for more than a few days.
Male and female cockroaches may be determined by comparing the number of appendages at the tip of their abdomen. Male cockroaches have two pairs of sensory appendages (styli and cerci) at the tip of their abdomen whereas females only have one pair of cerci.
Adult females lay clusters of eggs in a case called an ootheca, which may be dropped or attached to a surface or the female carry around. Females may lay many hundreds of eggs in a lifetime. Some females mate once and are able to continually reproduce after this one insemination from a male. Males mate with females by attaching a spermatophore to her abdomen. 
american                    native
American Cockroach                                                              Native Cockroach                      


Moist, damp, dark and narrow spaces are favoured by cockroach, and they prefer to hide in very small gaps. During the day both the adults and nymphs cluster together and take shelter and in places such as; inside walls, backs of refrigerators, ovens, dishwashers, plumbing, inside crevices, in cupboards and behind mouldings and other fittings. Ideal areas include bathrooms and food preparation areas. The better a site provides for the insect to conceal itself, the more ideal it becomes as a harbourage for cockroaches.
Cockroaches also need a fairly warm temperature and moisture. If the environment is too dry then they will quickly dehydrate.  However cockroaches are in general notoriously hardy and many species can withstand higher or near freezing temperatures for a short period of time.
Cockroaches impart a foul odour where infestations are well established. Glands on their bodies discharge a malodorous pheromone, which causes aggregation of high numbers.
Cockroaches may disperse to new habitats by crawling or flying, though very often in the case of pest species they are transported around in food sources, in vehicles including ships, and in parts, appliances or fittings they have been sheltering in. They can survive months without food, and some species can survive up to 4 weeks without water. This can make infestations and the prevention of new infestations difficult to control.
cockroaches nymphs      
Cockroach Nymphs


Only a small number of the thousands of identified species play a significant role in transmission of disease to humans. These species are well adapted to life inside buildings.
The most important ones are the American Cockroach (Periplaneta americana), the German cockroach (Blatella germanica), the Oriental cockroach (Blatta orientalis) and the Smokybrown Cockroach (P. fulginosa). Our native New Zealand bush cockroaches Celatoblatta (about 16 species) normally live outdoors and are of no public health concern.
Although cockroaches are not usually associated with widespread disease outbreaks, their presence is a sign of poor sanitation procedures and they are known to carry a number of bacteria, which could give rise to serious illness in humans. They may also induce allergies and asthma symptoms in susceptible people. Cockroaches are a serious sanitary concern for humans but may also play a role in transmission of some worms and diseases to other animals when they are ingested.
Although cockroaches can bite, diseases are almost exclusively passed on through mechanical transmission whereby their bodies are contaminated with bacteria which is then transferred to other surfaces they encounter as they move about.
This may lead to wound infections, food poisoning and gastric upset. Amongst the organisms known to be carried by cockroaches are; Salmonella spp. including Salmonella typhi causing typhoid, Entamoeba histolytica causing amoebiasis, Shigella dysenteriae causing dysentery, and potentially also the poliomyelitis virus responsible for polio. Other species known to be carried are Proteus spp., Staphylococcus aureus, Staphylococcus epidermalis, Streptococcus faecali, and Escherichia coli.
Their habits and body structure enable them to potentially transmit pathogens. Cockroaches are omnivorous and will readily eat and move between food sources such as faecal matter and fresh food intended for immediate human consumption. In doing humans can become exposed to potentially dangerous pathogens through contaminated surfaces and food products. They also do not feed exclusively on one food source but will scavenge for a variety of foods.


Typhoid fever is a life-threatening illness caused by the bacterium Salmonella typhi. It is still common in the developing world, where it affects about 21.5 million persons each year. Most cases in developed countries can be attributed to infections picked up overseas.
The easiest ways to avoid typhoid are by being vaccinated and by avoiding risk food and drinks. Persons with typhoid fever usually have a sustained fever as high 39° to 40° C. They may also feel weak, or have stomach pains, headache, or loss of appetite. In some cases, patients have a rash of flat, rose-colored spots. The only way to know for sure if an illness is typhoid fever is to have samples of stool or blood tested for the presence of Salmonella Typhi. Even if your symptoms seem to be gone, you may still be carrying Salmonella Typhi. If so, the illness could return, or you could pass the disease to other people. In fact, if you work at a job where you handle food or care for small children, you may be barred legally from going back to work until a doctor has determined that you no longer carry any typhoid bacteria.


Amoebiasis is a disease caused by the parasite Entamoeba histolytica. It can affect anyone, although it is more common in people who live in tropical areas with poor sanitary conditions.
E. histolytica infection can occur when a person ingests or puts anything into their mouth which has touched faeces or been otherwise contaminated with E. histolytica, or swallows cysts of E. histolytica picked up from contaminated surfaces or fingers. Only about 10% to 20% of people who are infected with E. histolytica become sick from the infection. Symptoms usually develop within 2 to 4 weeks. The symptoms are often quite mild and can include loose faeces, stomach pain, and stomach cramping. Amoebic dysentery is a severe form of amoebiasis associated with stomach pain, bloody stools, and fever. Rarely, E. histolytica invades the liver and forms an abscess. In a small number of instances, it has been shown to spread to other parts of the body, such as the lungs or brain, but this is very uncommon.
Diagnosis of amoebiasis can be very difficult. A blood test is available but is only recommended when your health care provider thinks that your infection may have spread beyond the intestine (gut) to some other organ of your body, such as the liver. However, this blood test may not be helpful in diagnosing your current illness because the test can be positive if you have had amoebiasis in the past, even if you are no longer infected now. Several antibiotics are available to treat amoebiasis. Treatment must be prescribed by a physician. You will be treated with only one antibiotic if your E. histolytica infection has not made you sick. You probably will be treated with two antibiotics (first one and then the other) if your infection has made you sick.


Shigellosis is an infectious disease caused by a group of bacteria called Shigella. Most who are infected with Shigella develop diarrhoea, fever, and stomach cramps starting a day or two after they are exposed to the bacteria. The diarrhoea is often bloody. Shigellosis usually resolves in 5 to 7 days. A severe infection with high fever may be associated with seizures in children less than 2 years old. Some persons who are infected may have no symptoms at all, but may still pass the Shigella bacteria to others.
Appropriate antibiotic treatment kills Shigella bacteria, and may shorten the illness by a few days but some Shigella bacteria have become resistant to antibiotics.
Once someone has had shigellosis, they are not likely to get infected with that specific type again for at least several years. However, they can still get infected with other types of Shigella.
The Shigella bacteria pass from one infected person to the next. Shigella are present in the diarrheal stools of infected persons while they are sick and for up to a week or two afterwards. Most Shigella infections are the result of the bacterium passing from stools or soiled fingers of one person to the mouth of another person. This happens when basic hygiene and handwashing habits are inadequate. It is particularly likely to occur among toddlers who are not fully toilet-trained. Family members and playmates of such children are at high risk of becoming infected.
Shigella infections may be acquired from eating contaminated food. Contaminated food usually looks and smells normal. Food may become contaminated by infected food handlers who forget to wash their hands with soap after using the bathroom. Vegetables can become contaminated if they are harvested from a field with sewage in it. Flies can breed in infected faeces and then contaminate food. Shigella infections can then be acquired by drinking, swimming in, or playing with the contaminated water.
Currently, there is no vaccine to prevent shigellosis. However, the spread of Shigella from an infected person to other persons can be stopped by frequent and careful handwashing with soap.
Basic food safety precautions and disinfection of drinking water prevents shigellosis from food and water and people with shigellosis should not prepare food or drinks for others until they have been shown to no longer be carrying the Shigella bacterium, or if they have had no diarrhoea for at least 2 days. At swimming beaches, having enough bathrooms and handwashing stations with soap near the swimming area helps keep the water from becoming contaminated. Day-care centres should not provide water play area.


Polio is an infectious disease caused by a virus that lives in the throat and intestinal tract. It is most often spread through contact with the stool of an infected person and may also be spread through oral/nasal secretions
Approximately 95% of persons infected with polio will have no symptoms. About 4-8% of infected persons have minor symptoms, such as fever, fatigue, nausea, headache, flu-like symptoms, stiffness in the neck and back, and pain in the limbs, which often resolve completely. Fewer than 1% of polio cases result in permanent paralysis of the limbs (usually the legs). Of those paralyzed, 5-10% die when the paralysis strikes the respiratory muscles. The virus invades local lymphoid tissue, enters the bloodstream, and then may infect cells of the central nervous system. Replication of poliovirus in motor neurons of the anterior horn and brain stem results in cell destruction and causes the typical manifestations of poliomyelitis.
The death rate increases with increasing age.
Fewer than 1% of all polio infections result in flaccid paralysis. Paralytic symptoms generally begin 1 to 10 days after prodromal symptoms and progress for 2 to 3 days. Generally, no further paralysis occurs after the temperature returns to normal. Additional symptoms can include a loss of superficial reflexes, initially increased deep tendon reflexes and severe muscle aches and spasms in the limbs or back. The illness progresses to flaccid paralysis with diminished deep tendon reflexes, reaches a plateau without change for days to weeks, and is usually asymmetrical. Strength then begins to return. Patients do not experience sensory losses or changes in cognition. Many persons with paralytic poliomyelitis recover completely and, in most, muscle function returns to some degree. Weakness or paralysis still present 12 months after onset is usually permanent.

Cockroach Control

To protect humans from diseases associated with cockroaches, all areas likely to attract or harbour the insects should have some form of cockroach control applied. This could mean filling cracks in external walls and foundations, fixing or replacing leaking plumbing, keeping areas dry and clean, removing wastes in an efficient manner, ensuring food and human waste is not accessible by insects, setting baited traps or boards to trap or kill any cockroaches that may be present or applying an insecticide. An effective cockroach control program is essential to prevent infestations.
Cockroaches may be detected by physically searching resting sites. Looking for signs of cockroach faeces is also a good way to spot past or present cockroach activity.
Cockroaches will oftentimes be disturbed by the light and run away, making them even easier to spot.
The presence of several stages of nymph, eggs and adults in an area suggest the population has become well established. Smaller infestations can be treated with the use of traps and bait stations. They are a good option where aerosols and sprays are unable to be used such as around electrical equipment. Trapping can determine resting areas and infestation severity, monitor effectiveness of chemical controls, and detect population increases, which may then require insecticide treatment.
Several types of traps can be purchased. Most are about the size of a large matchbox, have openings at both ends, and have the inside surface covered with a very sticky adhesive and slow-release food attractant. Cockroaches detect the food odour, enter the trap, and become immobilized by the adhesive. Traps can also be made from deep glass jars with a layer of petroleum jelly on the inside to prevent escape, and either commercially available bait or a piece of fruit as an attractant. Traps should be positioned with (both) ends open and accessible to intercept cockroaches as they travel to and from harbourage and feeding areas. For maximum efficiency they should be placed in dark areas such as along bulkheads and in tight spaces. Traps should be left out for a minimum of 24 hours including an overnight period.

A suitably placed trap can catch numerous cockroach adults and/or nymphs daily. Traps are relatively inexpensive, convenient to use, disposable, and do not need to contain toxic chemicals. If two or more cockroaches are caught within a 24hour period this may signal that a pesticide control operation is required. Any live cockroaches still in traps can be killed with a 3% solution of dishwashing liquid in water.
To control a large infestation, residual or non-residual insecticides can be used.

Non-residual insecticides will need to come into direct contact with the cockroach during application to kill it. No matter what form of insecticide is used, multiple applications will be necessary as a single treatment is not likely to destroy all of the insects. How often a treatment is required will depend a little on what other control and sanitization techniques are being employed, as well as how vulnerable the area or structure is to re-infestation. Insecticides work best when applied to areas where cockroaches hide during the day or areas they regularly pass through at night to maximize the chance of exposure to the chemical. A combination of chemicals can be more effective rather than one single insecticide. The german cockroach in particular has developed resistance to a range of organophosphates, organochlorides and pyrethroids. Chemical control should always be followed up with environmental management to provide a well-rounded control program against cockroaches.

Insecticidal dusts can also be useful as they can be placed deeper into crevices and voids, and are also safe around electrical outlets where liquid sprays would not be safe to use. Dusts usually provide longer lasting residual control that sprays but are not effective in wet or damp locations. Dusts can be applied in squeeze bottles or in bulb or bellow type dusters. Where a liquid spray is to be used, it should be taken into consideration whether or not to use oil versus water based spray. Oil based sprays adhere better to smooth surfaces such glass and metal, but may damage painted surfaces, plaster or lino.
Where cockroach eradication of a site is not possible and diseases such as typhoid and polio are endemic individuals should seek immunization against these. In areas or situations where dysentery and other gastric diseases are present, good personal hygiene can help mitigate risks of further spread to the individual. Drinking bottled or thoroughly boiled water, washing all raw fruits and vegetables, and thorough cooking will also help to prevent ingestion of food contaminated with faeces or bacteria tracked around by cockroaches. 
cockroaches under fridge
Cockroach Infestation


Southern Monitoring Services Ltd is 100% Kiwi owned and operated business established in 1995. The company Directors have a strong public health background having qualified and worked in the public sectors of Environmental Health and Health Protection. 
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