Man Transmission

Man Transmission

The role of insects in Mechanical Transmission of Human Parasites

Arthropods are probably the most successful of all animals. They are found in every type of habitat and in all regions of the world. They feed on a wide variety of plant or animal material and have been known as major causes of disease for centuries.

Without the vector, the parasite life cycle would be broken and the pathogen would die. By understanding how a parasite is transmitted and the involvement of vectors in the transmission, public health personnel can better design and manage control program for a particular problem.

 

Mechanical transmission of parasites:

Transmission of etiologic agents by arthropods is a complex phenomenon, and generalizations are difficult to make. Just because an arthropod feeds on a diseased host does not ensure that it can become infected, nor does it ensure that ingested pathogens can survive and develop (1, 2). First, a distinction must be made between mechanical and biological transmission and their various modes (Table 1)

 

Table: 1 Mode of parasite transmission

 

Example

Mode of parasite transmission

 

Parasite on cockroach or fly body part

 

Flea: dog tapeworm

Mosquitoes: Plasmodium

Mechanical transmission

 

Biological transmission

 

Biological transmission:

In biological transmission, there is either multiplication or development of the parasite in the arthropod or both (3, 4)

 

 

 

Mechanical transmission:

In mechanical transmission the insects transport organisms on body parts for example, their feet, body hairs, spines, and setae that collect contamination as insect feed on dead animals or excrement.

Insect borne human diseases

Pathogen transmission

Flies have been shown to act as vectors for a number of pathogens. They are known to travel up to 20 miles (5), although more commonly for no more than two miles. Transmission of pathogens by adult flies occurs by: (1) mechanical dislodgement from their exoskeleton (eg by hair and bristles on their legs or by cushion-like structures [pulvilli] that are used for adherence to vertical surfaces), (2) faecal deposition, and (3) the regurgitation of incompletely digested food. They can carry protozoan parasites such as Cryptosporidium parvum (6), Toxoplasma gondii (7, and Sarcocystis spp. (9) on their exoskeletons and pulvilli.

 

House flies will live in the human home and lay eggs and have a new generation within two weeks. They will breed in fermenting vegetable and animal matter. They are known to have spread tuberculosis, parasitic worms, yaws, trachome and cholera. Blow flies are known as the blue bottle or the green bottle flies and carries much of the same disease-producing organisms as the house fly. There is a fly in the tropical Americas called the Dermatobia. It will infest man causing maggots to pop out of the eggs and burrow in the skin (10).

Humans have died over the years because of diseases carried by insects. The number is not small either as millions have perished from these diseases over time. Man struggles to overcome these diseases but it is a long, expensive and hard fight especially in areas of extreme poverty. Some insects infect man directly and some indirectly. Animals infested with insects are among the worse as humans ingest food from these animals and are infected with disease (11).

There are many ways that insects can transmit disease even without transferring germs. There are various mites and worms that will invade tissues. Allergies can flare from bites of bees, body lice, and bites of chiggers and ticks. Some flies will be called mechanical carries as they pick up germs by biting a diseased animal and then bite a healthy person thus contaminating them with disease. There are germs on garbage and other filth that a fly can crawl on it or walk on it and carry disease to humans. Fleas carry disease after ingest plague organisms concerned with sanitation and public health as causative agents of gastrointestinal diseases in people based on synanthropy, endophily (the preference of insects to enter buildings), communicative behaviour, and strong attraction to filth and human food (12). These species include Hermetia illuscens, Megaselia insulana, Eristalis tenax, Piophila casei, Fannia canicularis, Musca domestica, Muscina stabulans, Stomoxys calcitrans, Calliphora viscina, Calliphora vomitoria, Chryosoma putoria, Cynomyopsis cadaverina, Cochliomyia macellaria, Phaenicia cupprina, Phaenicia s

Cockroaches (Diploptera punctata) are among the most notorious pests of premises, which not only contaminate food by leaving droppings and bacteria that can cause food poisoning(13) , but also they transmit bacteria, fungi and other pathogenic microorganisms in infested areas (14, 15). Cockroaches feed indiscriminately on garbage and sewage and so have copious opportunity to disseminate human pathogens (15) .Also their nocturnal and filthy habits6 make them ideal carriers of various pathogenic microorganisms (16).

 

FILTH FLIES AND HUMAN FOOD BORNE PARASITIC DISEASE

 

 Filth flies have been, and will continue to be, a major preventive medicine issue during military exercises and operations conducted in warm weather.  Filth flies have been implicated as disease vectors, especially in refugee and prisoner of war camps.  They can also be a tremendous nuisance when they interfere with and degrade mission performance.  Fly problems may develop around field messing facilities that have inadequate screening, which can result in unsanitary conditions that make it difficult to protect food from fly-borne contamination.  Likewise, field latrines constructed without adequate fly exclusion are virtually unusable.  In mass casualty situations, such as battlefields and natural disasters, flies will breed in corpses and wounds if they are not controlled or excluded.  For these reasons, fly control is often a major responsibility of utmost importance for preventive medicine personnel (11).

 

Filth flies have been implicated in the direct and indirect mechanical transmission of a number of pathogens responsible for human diseases, especially those causing diarrheal illness.  Mechanical transmission is the transfer of pathogens from one location to another, usually passively or unintentionally.  Thus, the mechanical transmission of disease organisms is facilitated by the adult filth flies' habit of walking and  feeding on materials that tend to be contaminated, then doing the same on food to be consumed by humans. (10) 

      The common factor in the ecology of several species of filth flies is their utilization of decomposing organic materials as food sources for the adults and developmental media for their maggots (larvae). Considering that these materials are often carrion, feces and food wastes (all with associated pathogens), the potential for flies becoming contaminated can be quite high.  Filth flies have numerous hair-like structures on their legs and bodies that dramatically increase their surface area and aid in harboring pathogens.  Their deeply channeled mouthparts and hairy feet, each with sticky pads, can easily be contaminated when in contact with contaminated substrates.  Filth flies are potential mechanical vectors of disease-causing organisms because pathogens can be transferred from their contaminated bodies to our food, eyes, noses, mouths, and open wounds. (17). Filth flies are attracted to a variety of rotting organic materials and feces, but they are also attracted to human foods.  In addition to the great number of pathogens filth flies may carry on their body surfaces, they may transmit pathogens to our food in their saliva and feces.  Most filth flies have sponging mouthparts and are capable of consuming foods only in a liquid state.   Solid foods are liquefied by regurgitating the crop contents (along with any pathogens) onto the food material, allowing the vomit to liquefy the solid food.  Flies then suck the liquefied food (along with any pathogens) into their digestive tracts.  Flies further contaminate food by defecating on it while they feed.  Fecal spots are usually darker than vomit spots.  House flies can produce from 16 to 31 spots in 24 hours (most of them vomit spots) after just one feeding of milk.  From this it is easy to speculate about how many spots could be produced in a food service facility by 10, 50, or 100 flies having constant access to various food sources. (17)

      Over one hundred pathogens that cause human disease are known to contaminate filth flies; there are strong associations between filth flies and several various parasites).  However, the importance of filth flies in causing human illness through transmission of these pathogens remains undetermined.

 Myiasis

Myiasis is the invasion of tissues or organs of living humans or animals by fly larvae that may feed on the host's living or dead tissue (gangrenous or necrotic) or on food ingested by the host.  Host reactions may be asymptomatic, minor to violent or even death.  This review will concentrate on human myiasis, in which almost any exposed part of the body is at risk.  Myiasis classification may be based on the parts of the body affected, such as enteric (gastrointestinal, gastric, or intestinal), rectal, urogenital, aural (ear), ocular, cutaneous, nasopharyngeal and traumatic (wound) myiasis. 

Cockroachs as vectors of human parasites

Cockroaches have survived on the earth for more than 300 million years virtually without change. They are survivors, and will likely be with us for a few more million years. Cockroaches are basically tropical insects and will do their best to find a home that is both warm and moist. They are especially attracted to wet areas and will be found in abundance near leaking faucets or pipes, wet sponges, persistently damp corners, areas where there is frequently standing water, or areas where continual moisture is usually available, such as drains, kitchens, bathrooms and maintenance rooms with sink traps. Water and steam pipes frequently serve as migration routes from room-to- room .Also their nocturnal and filthy habits6 make them ideal carriers of various pathogenic microorganisms (18).So far numerous pathogenic bacteria, including Salmonellaspp, Shigella spp, Campylobacter spp, Pseudomonas aeruginosa and K. pneumoniae have been isolated from cockroaches4. In addition some parasites and fungi have been found in external surfaces or internal parts of body of cockroaches (19, 20) and some study have shown that exposure to cockroach antigens may play an important role in asthma-related health problems(21).

 

DUNG BEETLES AS HOSTS OF HUMAN PARASITES

Another pathogen, T. gondii, can also have serious consequences in humans, such as encephalitis, mental retardation and blindness. Even though it was shown that the chance of introduction of T. gondii by flies was estimated to be low, the authors consider fly control to be necessary to prevent transmission of T. gondii (22). Cockroaches and filth flies have been known to be transport hosts of toxoplasma gondii. Insect such as dung beetles, are one of the most important food of Norway- and roof –rats and also of field mice (23, 24) but the role of dung beetles (Onthophagusspp. ) as the carrier of coccidian oocysts is not known.  We attempted to clarify the role of dung beetles as the transport host of feline coccidian including Toxoplasma. When Isospora felis and I. rivolta oocysts are ingested by rodents, liberated sporozoites invade the tissues and develop into the ensheathed forms, which do not develop further like those of Toxoplasma gondii. The ensheathed forms remain infective for a long time in those animals until ingested by definitive hosts. In this case rodents act as a paratenic or intermediate host of feline coccidia  (25.26.27).  The paratenic or intermediate host or final host of feline coccidian including T. gondii  will have more opportunities for infection when oocyst were widely spread in the field by transport hosts such as cockroaches and filth flies (28,29,30).

 

CONCLUSIONS

Arthropods can be found on human or animals as ecto-parasites. Vectors can contaminate stored foods and transmit illness, or introduced diseases in new area.  Pet species facilitating infestations, and different risk factors related to infestation were identified.

Synanthropic insects such as flies and cockroaches can significantly contribute to the spread of food-borne parasite diseases in both developing and developed countries.

There is no need to question the necessity for fly control as flies can cause financial losses and nuisance and can spread a number of hazardous pathogens. Although the risk of pathogen transmission by a single specimen is probably limited, this is compensated by the large populations commonly found due to the rapid reproduction of flies. Finding and eliminating breeding places is an important first step in control.

The control or eradication of houseflies should be attempted, to stop intestinal-parasite transmission in the community, in addition to drug administration. Cockroaches constitute an important reservoir for infectious pathogens; therefore, control of cockroaches will substantially minimize the spread of infectious diseases in our environment.  Measures for cockroach control should be more persistent. The viability and infectivity of the ova and oocysts of parasites identified are still questionable; one would expect that high temperature in latrines and soak ways might denature these ova and oocysts of these parasites, but some of these are heat resistant, therefore, their viability and infectivity could have still been maintained. Integrated pest control programs should involve control measures for a variety of pest species including flies, cockroaches, fleas, bedbugs, ants, and rodents. Early identification of their presence is important to avoid large infestations.

 

REFERENCES

1. Bressler K, Shelton C (1993) Ear foreign-body removal: a review of 98 consecutive cases. Laryngoscope 103: 367-370

 

2. Zurek L Schal C( 2004)  Evaluation of the Germa cockroach as a vector for verotoxigenic Escherichia coli F18 in confined swine production. Vet. Microbiol 101: 263-267

 

3.Chamberlation RW, Sudia WD.Mechanism of transmission of viruses by mosquitoes. Ann.Rev. Entomol.1961; 371-390

 

4. Harwood RF, James MT: Entomology in human and Animal Health, 7th Ed. New York: Macmillan, 1979

 

5. Murvosh C M,Taggard C W1966)Ecological studies of the housefly', Annals of the Entomological Society of America. 1966(59)534–547

 

6.Graczyk TK, Cranfield M R, Fayer R, Bixler H (1999)lies (Musca domestica) as transport hosts of Cryptosporidium parvum'.American Journal of Tropical Medicine and Hygiene(61) 3:500–504

 

7. Wallace, G. ‘Experimental transmission of Toxoplasma gondii by filth-flies', American Journal of Tropical Medicine and Hygiene. 1971( 20): 411–413.

 

8. Graczyk TK, Knight R, Gilman R H, Cranfield M R (2001) ‘The role of non-biting flies in the epidemiology of human infectious diseases, Microbes and Infection ( 3): 231–235

 

9. Markus M B (1980) ‘Flies as natural transport hosts of Sarcocystis and other coccidia', Journal of Parasitology, (66): 361–362

 

10. Moon RD  (2002) Muscid Flies (Mucidae), pp. 279-301, in Mullen, G. and Durden, L. [eds], Medical and Veterinary Entomology, Academic Press, London.

11. Hogsette JA, R Farkas  (2000) Secretophagous and hematophagous higher Diptera, pp. 769-792,  In Papp, L. and Darvas, B. [eds.], Manual of Palearctic Diptera, Vol. 1 General and Applied Dipterology.  Science Herald, Budapest.

12. Thaddeus K, Ronald K, Leena T (2005) Mechanical transmission of human protozoan parasites by insects. Clin MicrobiolRev 18(1): 128–32

 

13. Pai HH, Ko YC, Chen ER (2003) Cockroaches (Periplaneta americana and Blattella germanica) as potential mechanical disseminators of Entamoeba histolytica. ActaTrop 87: 355–9

 

14. Gliniewicz A, Sawicka B, Czajka E (2003) Occurrence of insect pests in hospitals in Poland. Przegl Epidemiol 57:329–34

 

15. Gore JC, Schal C(2007) Cockroach allergen biology and mitigation in the indoor environment. Annu Rev Entomol52:439-463

 

16.  Cotton MF, Wasserman E, Pieper CH, Van Tubbergh D, Campbell G, Fang FC, Barnes J(2000) the possible role of cockroaches. J Hosp Infect 44: 13–7

17. Armed Forces Pest Management Board.  (2000) Technical Guide No. 24, Contingency Pest Management Guide.  Washington, DC

18. Thaddeus K, Ronald K, Leena  T(2005) Mechanical transmission of human protozoan parasites by insects. Clin MicrobiolRev18(1): 128–32

 

19. Thyssen PJ, Moretti T deC, Ueta MT, Ribeiro OB (2004)The role of insects (Blattodea, Diptera, and Hymenoptera) as possible mechanical vectors of helminths in the domiciliary and peridomiciliary environment. Cad Saude Publica20: 1096–102

 

20. Fotedar R, Banerjee U (1992) Nosocomial fungal infections study of the possible role of cockroaches (Blattella germanica) as vectors. Acta Trop50: 339–43

 

21. Oishi T, Morisawa Y, Yasueda H, Akiyama K, Wakiguchi H(2004) Mother and two siblings with cockroach asthma. Arerugi53: 1163–7

 

22. Kijlstra A, Meerburg B G , Mul M F(2004) Animalfriendly production systems may cause re-emergence of Toxoplasma gondii. NJAS – Wageningen Journal of Life Sciences ( 52) No 2, pp 119–132

 

23. Yabe T (1979) The relation of food habits to the ecological distribution of the Norway rat ( Rattus norvegicus) and the roof rat ( R, rattus). Jpn J Ecol 29: 235-244

 

24. Yabe T(1985) Insects as a food of Japaness house mice ( Mus molossinus) in a seed warehouse. Jpn J Sanit Zool 36: 79-81

 

25. Dubey JP, Frenkle JK(1972) Extraintestinal stages of Isospora felis and I. rivolta, ( Protozoa: Eimeriidae) in cats. J Protozool  19: 89-92

 

26. Frenkle JK , Dubet JP(1972) Rodents as vectors for feline cocccidia. Isospora felis and Isospora rivolta. J Infec Dis  1972; 125: 69-72

 

27. Wallace GD (1973) Intermediate and transport hosts in the natural history of Toxoplasma godii. Am J Trop Med Hyg 20: 456-464

 

28. Chinchilla M , Ruiz A(1976) Cockroaches as possible transport hosts of Toxoplasma gondii in Costa Rica. J Parasitol . 62: 140-142.

 

29. Wallace GD (1971) Expermintal transmission of Toxoplasma gondii by filth flies. Amm J Trop Med Hyg 20: 411-413

 

30. Wallace GD (1972) Experminatal transmission of Toxoplasma gondii by cockroaches. J Infec Dis126: 545-547

 

 

 

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