Shoo Fly, Don’t Infect Me!

Mechanical Vectors of Bacterial GI Diseases

By: Liz MeltonMarch 9th, 2012

TABLE OF CONTENTS

Common Mechanical Vectors:Cockroaches ……………………………………………………………………………………..............…… 2Musca Domestica …………………………………………………………………….……………………… 2-3Musca Sorbens ……………………………………………………………………………………………….. 3Musca Chrysoma ……………………………………………………………………………………..……… 3-4Fly Life Stages ……………………………………………………………………………….…………………4-5Mechanical Transmission Process…………………….……………...………………………………. 5-6

Mechanically Transmitted GI Diseases:Salmonella ……………………………………………………………………………………………………... 6-7Typhoid …………………………………………………………………………………………………………. 7Bacillary Dysentery (Shigellosis)……………….…………………………………………………..… 7-8

Summarized Scenarios:

Role of Cockroaches and Flies as Mechanical Vectors in Egypt …………………………. 8Role of Cockroaches as Mechanical Vectors in Thailand ………………………………...… 8Role of House Flies in Cholera Transmission in India ………………………………………. 9

Recent Research:

The housefly (Musca domestica) as a carrier of pathogenic microorganisms in a hospital environment ……………………………………………………………………………………… 9

Reduction of transmission of shigellosis by control of houseflies …………………………. 10

Political Ties and Wartime Relevance:PATH & WaterAid America …………………………………………………………………………….. 10

Armed Forces Pest Management Board TECHNICAL GUIDE NO. 30 Filth FliesSignificance, Surveillance and Control in Contingency Operations ……………………. 11

AFPMB: Disease Vector Ecology Profile for Somalia..…………………………………….11-12

References:

Reference List ..……………………………………………………………………………………………..13-

14

INTRODUCTION

Civil strife, diminished immune status, food shortages, antibiotic resistance,

and utterly unsanitary living conditions taint all settlements undergoing

humanitarian crises. Such catastrophes yield irreparable harm to innocent

bystanders, reducing everyday routine to disarray and disorganization. Refugee

camps are characterized by chaos. Internationally displaced persons are forced to

inhabit incredibly close quarters; in many cases, this equates to: defecating sans any

form of privacy, consuming meals and water of the poorest quality, and failure to

bathe in overcrowded, filthy locations. Most unsettling then, is looming potential for

rapid and virulent spread of disease via mechanical transmission: “a form of indirect

transmission in which the infectious agent does not undergo physiologic changes

inside the vector”1.

This background delineates modes of bacterial gastrointestinal disease

transmission in humanitarian crisis communities. To combat mechanical disease

transmission, this paper first distinguishes features of mechanical vectors that

supply distinct connection to areas of humanitarian crisis. Owing to feeding and

reproductive behaviors, several mechanical vectors such as cockroaches, houseflies,

filth flies, and blow flies become exceedingly prevalent in disaster zones.

Publications hailing from Egypt, Thailand, India, and Somalia provide concrete

examples of fly and cockroach infectivity in humantarian crises-esque scenarios.

Documented spread of pathogens by way of cockroaches and flies near latrines,

open-air markets, military bases, village animal pens and trash dumps, and hospitals

are also examined within this piece. Finally, a discussion of political influence and

wartime repercussions may instigate further research on intervention strategies for

control of mechanical vectors of GI bacterial disease.

Common Mechanical Vectors

Common Cockroach

Common cockroaches are typified by their 5-73mm length and dual wing

structure2. All cockroaches have a flattened appearance, and are yellowish brown in

color. What differentiates cockroaches from other beetles or land-bound insects is

their incredible agility. Moreover, they exhibit endophagic behavior, feeding on

garbage and feces indoors3. These arthropods are most active at night, scurrying in

and out of latrines and other warm, man-made structures. Often, they breed

outdoors, and opt to reside in colony form4.

Due to the fact that refugee camps have little to no shelter denying cockroach

entry into makeshift tents, and the propensity for organic waste and feces to be

proximal to sleeping individuals, it is clear how mechanical transmission is not only

possible, but probable5. Unfortunately, cockroaches are responsible for transmitting

numerous bacterial GI diseases including: many forms of diarrheal diseases, typhoid

fever, and dysentery along with a host of other viruses and diseases2.

Musca domestica (Common Housefly)

Distributed worldwide, Musca domestica, the common housefly, is marked by

its 6-7 mm length, grey color, and four dark longitudinal stripes along its thorax2. It

has been proven that high density of flies is correlated with crowded human

populations in unsanitary conditions. This habitat is a near-exact portrayal of

humanitarian crisis sites. What makes the housefly so intrinsically linked to

mechanical transmission of bacterial GI diseases in humanitarian crises is the

dependency of its life cycle on unsanitary settings4. Although house flies do not

physically lay eggs directly in latrines, landing and feeding on uncovered human and

animal excrement as well as domestic organic waste is essential to house fly

survival. What is more, houseflies are associated with the spread of infantile

diarrhea, shigellosis diarrhea, cholera, other forms of dysentery, and typhoid

fever2,6.

Musca sorbens (Filth fly)

Similar to Musca domestica, Musca sorbens, common name filth fly, is

characterized by a grey color, and usually grows to a size of 6 mm in length2. Unlike

houseflies, however, filth flies are detected by two dark stripes on the thorax, and

normally reside in tropical locations. Musca sorbens flies possess a wing-span of

around 15 mm, and, like most other flies, filth flies breed and engorge in human

feces around settlements7. Filth flies are unique in that they also feed on eye

secretions, especially those of children2. As a result, Musca sorbens is implicated in

the transmission of the eye disease trachoma. In the context of humanitarian crises,

diarrheal diseases are the most commonly transmitted pathogens from filth flies.

 Chrysomya   (Blowfly)

A compact body 10mm in length, and a shiny blue or green color set

Chrysomya, otherwise known as blow flies, apart from other flies2. Blow flies are

distributed worldwide, and also possess a strong preference for breeding in open

latrines, decomposing meat or fish, garbage, and animal excrement. Recent research

demonstrates that blow flies are most active in refugee camps, simple pit latrines,

market places, defecation holes sans lids7. Luckily, blow flies display contrasting

behavior from cockroaches, and do not enter houses. Nonetheless, Chrysomya

density rises as the number of simple pit latrines in a camp increases7—an

imminent threat to regions in the vicinity of humanitarian crises. These flies are

linked to intestinal worm eggs, diarrheal disease, and dysentery transmission.

Fly Life Stages:

Four discrete phases can be identified in fly genesis. Eggs give way to

maggots/larvae, which eventually pupate, emerging as adults within weeks3. Per

the World Health Organization, female flies seldom lay greater than 150 eggs in one

sitting, which takes place only up to five times within her lifetime8. In general, eggs

are deposited on an assortment of spots, namely: decayed, fermenting, rotting, moist

organic material of animal or vegetable origin, and heaps of animal or human feces2.

Choice of egg-laying venue is dependent on its moisture, texture, and freshness.

Following about an 8-48 hour incubation period, eggs hatch into maggot form3.

Conveniently, larvae thrive on organic matter and animal/human excrement.

Larvae are recognized by their slender, white, legless, maggot-like exterior, and

grow after burrowing far into breeding material. Reaching pupa maturity takes

anywhere from three days to as long as several weeks3. Maggot development is

contingent on temperature, fly species, and the type, quantity, and quality of food8

(high in fecal and waste-contaminated areas of humanitarian crisis). Two to ten

days subsequent to formation of a puparium, the capsule-like case containing the

fly-to-be, the adult fly emerges2. Spreading its wings, and pushing to the surface, the

body of the adult fly dries and hardens.

Adult flies can subsist for one to two months prior to death, conditional on

the species and living conditions. On account of their mouthpart design, flies only

consume food in a liquid, or readily soluble state. Solid food is wetted with saliva,

and sucked up along with water, a vital component to a fly’s livelihood. Flies cannot

exist over 48 hours without drinking water3. A fly’s diet habitually consists of: milk,

sugar, syrup, blood, meat broth, and any materials found in human settlements

ingested at least two to three times a day7.

Mechanical Transmission Process:

Fly breeding mechanisms and filthy feeding habits of cockroaches mentioned

above are precisely what make flies and cockroaches efficient mechanical vectors

and transmitters of bacterial GI diseases. Three hundred fifty fly species in twenty-

nine families have been potentially associated with the spread of food-borne

diseases4. According to Clinical Microbiology Reviews, over fifty species of

synanthropic flies have been reported to be associated with unsanitary conditions,

and are involved in dissemination of human pathogens in the environment, and

twenty-one of these species have been involved in transmission of human

gastrointestinal diseases. A fly’s configuration and flying patterns are inherently

conducive to mechanical transmission. Individual flies have been known to migrate

up to twenty miles, with unsanitary sites as targets. Sucking mouthparts, sticky

footpads, sticky substances on appendages, body and leg hair, and electrostatic

charge on exoskeletons effectively render flies “super transmitters” of disease2,4.

In particular, districts subjected to humanitarian crises are prime breeding

and feeding grounds for these infective arthropods. Waste incurred via food

preparation, handling, vending, and serving waste in public places is considered

hazardous2,7. More disturbingly, feces enhance transmission of infectious agents

much greater than that of any other substrate or medium, a major concern in

humanitarian crises. Ample animal manure and human excrement, garbage, animal

bedding, and decaying organic matter can be found scattered all over refugee camps,

and pose pending danger of mechanical disease transmission7.

Mechanically Transmitted GI Diseases

Salmonellosis:

Salmonellosis is attributed to infection with the bacteria Salmonella.

Salmonella infects the GI tract, and is frequently spread by mechanical vectors

affiliated with humanitarian crisis settings. Infecteds will present with diarrhea,

fever, and abdominal cramps 12 to 72 hours after infection. A sustained fever of

approximately 40° C, and feelings of weakness, headache, loss of appetite, or

materialization of a rash of flat, rose-colored spots are other symptoms of

Salmonellosis. Antibiotics are the suggested treatment for Salmonellosis9.

Salmonellosis persists only 4 to 7 days, though, in some individuals, severity

of diarrhea may prompt patient hospitalization. Salmonella bacteria is capable of

spreading from the GI tract to the portal system, triggering infection of other body

sites, and leading to eventual death without immediate antibiotic treatment.

Furthermore, some patients complain of joint and urination pain, as well as eye

irritation—what is deemed Reiter's syndrome. This form of the disease may

continue for months or years, bringing about chronic arthritis. Infants, the elderly,

and immuno-compromised persons are more liable to this degree of illness. All

three age/status groups are regularly observed in refugee populations, making

Salmonellosis outbreaks grave concerns in humanitarian crises7.

Typhoid fever:

Typhoid fever, caused by the bacterium Salmonella typhi is classified as a life-

threatening illness. In the developing world, this disease is fairly common, about

21.5 million persons are afflicted with typhoid fever each year10. Salmonella Typhi

lives only in humans. Infected individuals harbor bacteria in their GI tract and

bloodstream, and both silent carriers and ill persons shed bacterial residue in stool.

Fecal-oral transmission is a method of contracting typhoid fever, a logical

explanation for enormous prevalence of typhoid where handwashing and clean

water is limited7,11. Additionally, houseflies and cockroaches are known to be

wonderful mechanical vectors of typhoid fever2, and, coincidentally reside in areas

at high risk of endemicity. Typhoid fever is treated and prevented by oral

antibiotics10, which are expensive, and rarely imported in the bulk required by

humanitarian crises settings.

Bacillary Dysentery (Shigella):

As with most bacterial GI diseases, bacillary dysentery invokes bloody

diarrhea, fever, and stomach cramps a day or two after exposure to the Shigella

bacterium. Shigellosis symptoms remain for 5 to 7 days on average; in spite of this,

children younger than two years of age may experience violent seizures12. To make

matters worse, infection by the strain Shigella flexneri, causes post-infectious, and

possibly chronic, arthritis. As aforementioned, chrysomya, houseflies, and

cockroaches all mechanically transmit Shigella bacteria2. Antibiotic treatment

destroys Shigella bacteria, so ampicillin, trimethoprim/sulfamethoxazole,

ceftriaxone, or, among adults, ciprofloxacin will alleviate symptoms12. Regrettably,

Shigella bacteria have become resistant to antibiotics, requiring multiple treatments

at once—a near impossibility to administer in humanitarian crises7.

Summarized Scenarios

The role of cockroaches and flies in mechanical transmission of medical important parasites:

METHODS:

1) Surveyed residential areas in Khaldyia Village, Egypt 2009 – 2010 45 cockroaches collected in control, 178 total collected Flies from human feces also observed

2) Parasites isolated/identified from defecation areas in and around houses

RESULTS:

-Cockroaches trapped in the toilets of: houses with pit latrines: 98 parasites/ml houses with water system: 31 parasites/ml

-Pathogens isolated from external and internal surface of 98% of test cockroaches

(Adapted from: Gehad T. El-Sherbini, Eman T. El-Sherbini. The role of cockroaches and flies in mechanical transmission of medical important parasites. Journal of Entomology and Nematology. 2011;3(7):98-104.)4

The majority of cockroaches from the samutprakarn province of Thailand are carriers of parasitic organisms:

METHODS:

920 cockroaches were obtained Samutprakarn province of Thailando 18 open-air shopping markets in 5 districts

1 subdistrict of this provinceo captured during feeding time in natural habitat

wet smear and modified acid-fast bacilli staining identified parasites from the external surface or cuticle of the cockroaches

RESULTS:

-498/920 (54.1%) of the cockroaches harbored parasitic organisms**Results elucidate that markets giving refuge to cockroaches cultivate colonies that carry several pathogens activating transmission of illness such as diarrhea or bowel disorder.

(Adapted from: Pennapa Chamavit, Panupong Sahaisook, Nunthawadee Niamnuy. The majority of cockroaches from the samutprakarn province of Thailand are carriers of parasitic organisms. EXCLI Journal. 2011;(10):218-222.)5

Vector potential of houseflies (Musca domestica) in the transmission of Vibrio cholerae in India:

METHODS:

1) Small village 15 km away from Delhi city outbreak of diarrhea 2) 150 houseflies captured with sterilized nets from animal pens, yards or houses3) Collect stool samples from 50 patients within 24 hrs of illness, before anti-microbial

o all subjects of lower socioeconomic statuso all exhibiting signs of gastroenteritis

4) Samples were transferred to tubes of high pH (8.4) of alkaline peptone water suppressing commensal intestinal bacterial growth to permit uninhibited multiplication of V. cholerae

RESULTS:

-60% fly pools were positive for V. cholerae**This study bestowed convincing evidence that houseflies acted as mechanical vectors, and aided in dissemination of V. cholerae biotype El Tor.

(Adapated from: R. Fotedar. Vector potential of houseflies (Musca domestica) in the transmission of Vibrio cholerae in India. Acta Tropica. 2001;(78):31–34.)6

Recent Research:

The housefly (Musca domestica) as a carrier of pathogenic microorganisms in a hospital environment:

METHODS:

1) Collect Musca domestica from: surgical ward (All India Institute of Medical Sciences Hospital) remote residential area 5 km away as a control

2) A total of 113 flies were collected:

65 from a surgical ward (test) 48 from a residential area (comparison)

RESULTS:

-10 genera of bacteria isolated from the test group, 9 from control group-However, the load of bacteria carried by the test group of flies was significantly more.

**Evidence for houseflies acting as vectors of potentially pathogenic bacteria in a hospital environment is a frightening, and very real prospect.

(Adapted from: R. Fotedar, U. Banjeree S. Singh Shriniwas, A Verma. The housefly (Musca domestica) as a carrier of pathogenic microorganisms in a hospital environment. Journal of Hospital Infection. 1992;(20):209-215.)13

Reduction of transmission of shigellosis by control of houseflies (Musca domestica):

Prospective Crossover Intervention Study

METHODS:

1) 2 military field bases several km apart in early summer, 1988

2) Implement and track progress of intensive fly control measures at one base, keep another as control

RESULTS:

-After 11 weeks, fly counts were 64% lower on the bases exposed to fly control

-Clinic visits for diarrheal diseases dropped by 42%: 85% for shigellosis (76% for antibodies to Shigella) 57% for antibodies to enterotoxigenic Escherichia coli

**Leads one to believe that control of mechanical vectors is on the horizon, and is an achievement necessary for reducing the number of GI diseased individuals in humanitarian crises.

(Adapted from: Dani Cohen, Manfred Green, Colin Block, Raphael Slepon, Ruhama Ambar, Steven Wasserman, Myron Levine. Reduction of transmission of shigellosis by control of houseflies (Musca domestica). The Lancet. 1991;(337).)14

Political Ties and Wartime Relevance

PATH & WaterAid America:

Two leading NGOs, WaterAid America and PATH (Program for Appropriate

Technology in Health) have joined forces in order to “defeat a global killer” that

entertains little attention on our side of the continent: diarrheal disease. Both

philanthropic organizations aspire to ameliorate international living conditions

which currently foster the transmission of diarrheal diseases. With a focus

primarily on children, PATH and WaterAid will be conducting extensive research in

endemic communities on the upshot of clean water and sanitation solutions and

dispensation of adequate resources. Thus, surveillance carried out by NGOs akin to

WaterAid and PATH may be an alternative route for testing exploratory mechanical

vector control strategies in humanitarian crisis locations.

(Adapted from: (May, 2009). Defeating a Global Killer: The Need for Action on Diarrheal Disease. www.who.int/entity/pmnch/events/2009/InvitationDDevent.pdf. [Flyer]. February 13, 2012.)15

Armed Forces Pest Management Board TECHNICAL GUIDE NO. 30 Filth Flies: Significance, Surveillance and Control in Contingency Operations: 

Historically, arthropods have plagued military operations whether it be as a

result of physical distress induced by spread of infection, or simply by sustained,

non-stop pestering base-side. Evidenced by journals dating back to World War I,

Colonel J.C.G. Ledingham of the Royal Army Medical Corps, Mesopotamian

Expeditionary Force found a strong correlation between fly density and the

incidence of dysentery. World War II battles, especially that of El Alamein in North

Africa, bore extreme troops loss to to dysentery presumably from flies as well.

Farther down the historical line, flies were proven a “monumental nuisance”

throughout the Vietnam War, with testimonies regarding one mess hall in which fly

infestation was so heavy it was difficult to eat without ingesting one or two.

The Persian Gulf War of 1991 posed parallel problems, and fly infestation

finally began to be established as a chief issue in humanitarian relief operations.

Somalian relief forces encountered brutally insufficient sanitation, and detailed vast

fly infestations within military bases, and refugee shelters. Realizing that a blend of

deficient sanitation, and growing livestock populations (inevitably initiating a

greater garbage and excrement load), was a recipe for fly and cockroach influx, the

Armed Forces Pest Management launched the creation of Disease Vector Ecology

Profiles, and technical guides to narrow the risk of mechanical transmission of

disease in wartime and humanitarian crises.

(Adapted from: Armed Forces Pest Management Board TECHNICAL GUIDE NO. 30 Filth Flies: Significance, Surveillance and Control in Contingency OperationsPublished and Distributed by Armed Forces Pest Management Board Information Services Division Forest Glen Section/Walter Reed Army Medical Center, Washington, DC 20307-5001, Office of the Deputy Under Secretary of Defense (Installations and Environment))7

Armed Forces Pest Management Board: Disease Vector Ecology Profile for Somalia:

Disease Vector Ecology Profiles (DVEPs) single out relevant vector-borne and

other militarily significant diseases in countries with an emphasis on: “essential

epidemiology, vector bionomics, behavior, and pesticide resistance”. A Somalian

example on “Fly-Associated Diseases: ENTERIC DISEASES” highlights agents of

disease, vector transmission, and vector bionomics. Generally, profiles are

constructed as compilations of contemporary research on both vector

characteristics and control measures. DVEPs are constantly evolving owing to swift

Third World urban development, civil strife, ecological change, and invariable

growth in the number of countries tormented by humanitarian crisis.

(Adapted from: (15, September, 1993). Disclosure. Armed Forces Pest Management Board: Disease Vector Ecology Profile for Somalia, 4th Ed. Armed Forces Pest Management Board. Retrieved from: file:///C|/Inetpub/wwwroot/AFPMB/pubs/dveps/somalia.htm.)11

Reference List1. Centers for Disease Control and Prevention: Public Health Foundation. Glossary of Epidemiology Terms. Glossary. http://www.cdc.gov/excite/library/glossary.htm#T. April 25, 2007. February 13, 2012.

2. Keiding J. The housefly—biology and control. Training and information guide (advanced level). Geneva, World Health Organization, 1986 (unpublished document WHO/VBC/ 86.937; available on request from Division of Control of Tropical Diseases, World Health Organization, 1211 Geneva 27, Switzerland).

AND Ch. 2, Adapted from: Birley, 1991; Thomson, 1995; Sabatinelli, 1996; Chavasse and Yap, 1997; Rozendaal, 1997

3. Thaddeus K. Graczyk, Ronald Knight, Leena Tamang. Mechanical Transmission of Human Protozoan Parasites by Insects. Clin. Microbiol. Rev. 2005;18(1):128.

4. Gehad T. El-Sherbini, Eman T. El-Sherbini. The role of cockroaches and flies in mechanical transmission of medical important parasites. Journal of Entomology and Nematology. 2011;3(7):98-104.

5. Pennapa Chamavit, Panupong Sahaisook, Nunthawadee Niamnuy. The majority of cockroaches from the samutprakarn province of Thailand are carriers of parasitic organisms. EXCLI Journal. 2011;(10):218-222.

6. R. Fotedar. Vector potential of houseflies (Musca domestica) in the transmission of Vibrio cholerae in India. Acta Tropica. 2001;(78):31–34.

7. Armed Forces Pest Management Board TECHNICAL GUIDE NO. 30 Filth FliesSignificance, Surveillance and Control in Contingency OperationsPublished and Distributed by Armed Forces Pest Management Board Information Services Division Forest Glen Section/Walter Reed Army Medical Center, Washington, DC 20307-5001, Office of the Deputy Under Secretary of Defense (Installations and Environment)

8. Orin S. Levine, Myron M. Levine. Houseflies (Musca domestica) as Mechanical Vectors of Shigellosis Reviews of Infectious Diseases. 1991;13(4):688-696.

9. Centers for Disease Control and Prevention. Salmonella. What is Salmonellosis? September 27, 2010. http://www.cdc.gov/salmonella/general/. February 13, 2012.

10. Centers for Disease Control and Prevention. National Center for Emerging and Zoonotic Infectious Diseases. Typhoid Fever. October 5, 2010. http://www.cdc.gov/nczved/divisions/dfbmd/diseases/typhoid_fever/. February 13, 2012.

11. (15, September, 1993). Disclosure. Armed Forces Pest Management Board: Disease Vector Ecology Profile for Somalia, 4th Ed. Armed Forces Pest Management Board. Retreived from: file:///C|/Inetpub/wwwroot/AFPMB/pubs/dveps/somalia.htm.

12. Centers for Disease Control and Prevention. National Center for Emerging and Zoonotic Infectious Diseases. Shigellosis. November 16, 2009. http://www.cdc.gov/nczved/divisions/dfbmd/diseases/shigellosis/. February 13, 2012.

13. R. Fotedar, U. Banjeree S. Singh Shriniwas, A Verma. The housefly (Musca domestica) as a carrier of pathogenic microorganisms in a hospital environment. Journal of Hospital Infection. 1992;(20):209-215. 14. Dani Cohen, Manfred Green, Colin Block, Raphael Slepon, Ruhama Ambar, Steven Wasserman, Myron Levine. Reduction of transmission of shigellosis by control of houseflies (Musca domestica). The Lancet. 1991;(337).

15. (May, 2009). Defeating a Global Killer: The Need for Action on Diarrheal Disease. www.who.int/entity/pmnch/events/2009/InvitationDDevent.pdf. [Flyer]. February 13, 2012.