Man and insect have come a long way, insect is beneficial to man in so many ways: It serves as source of food, pollinating agents, helps in establishing post mortem interval in homicide investigation, helps in production of silk, decomposing organic matter etc.

As beneficial as insects are to man they can have detrimental effects on man’s health depending on the circumstances therefore, this article shall focus on the detrimental effect of insects to our health.

WHAT ARE INSECTS?

Insects are animals belonging to one of the classes of arthropoda known as insecta. They are the largest groups in the animal kingdom.

Their body is divided into three(3) segment; head, thorax and abdomen.

They have six (6) legs attached to the thorax.

They usually have wings also attached to the thorax.

INSECTS AS DISEASE CARRIERS

Vectors are invertebrates or arthropods which transmit disease either through ingestion, injection or contact. Insects are among the most important vectors.

Today over 200 human diseases are being spread through insects and it other related arthropod. And these vector borne diseases impose immense health and economic burden on both individuals and nations. Every year there are more than 700,000 death from diseases such as malaria, dengue fever, schitosomiasis, human African trypanosomiasis, leishmaniasis, yellow fever,onchocerciasis (WHO 2019). With rapid climate and man-made environmental changes new disease are also becoming more prominent.

SOME DISEASES TRANSMITTED BY INSECTS

MALARIA

Vector:  Mosquitoes

Causative organism: protozoan (Plasmodium falciparum, P. vivax, P. ovale, P. malariae, P. knowlesi)

Malaria causes up to a million deaths per year and it is estimated to infect over 200 million people worldwide. Around 90% of the deaths occur in sub-Saharan Africa, especially Nigeria and the Democratic Republic of the Congo. Those at risk are the poor remote communities with few health facilities and the vulnerable group (children, pregnant women, and elderly etc.)

SYMPTOMS

Fever

Headaches

Vomiting

YELLOW FEVER

Vector: Mosquitoes

Causative organism: Virus(Flavivirus)

Yellow fever is a haemorrhagic fever cause by the virus, flavirus.

MODE OF TRANSMISSION

The mode of transmission is through the bite from an infested mosquito.

SYMPTOMS

Symptoms manifest 3-6 days after infection. It includes;

Fever

Headache

Backache

General muscle pain

Nausea and vomiting.

About 15% of cases develop into an acute, toxic phase which include jaundice due to liver damage and haemorrhagic signs — bleeding in the mouth, eyes, nose, and gastrointestinal tract giving ‘black vomit’.

ZIKA VIRUS

Vector: Mosquitoes

Causative organism: Virus(Zikas virus)

The Zika virus is a Flavivirus closely related to Yellow Fever and West Nile disease.

MODE OF TRANSMISSION

The virus is spread through bites of infected Aedes aegypti and Aedes albopictus mosquitoes, the same type of mosquito that transmit dengue, chikunguya and yellow fever. It therefore has the potential to spread anywhere these mosquitoes are present.

SYMPTOMS

Fever

Muscle pain

Headache

Skin rash

Joint pain

Conjunctivitis

AFRICAN TRYPANOSOMIASIS

Vector: Tsetse fly

Causative organism: Protozoa(Trypanosoma brucei, Trypanosomagambiense andTrypanosomarhodesiense)

Another name for Africa trypanosomiasis is sleeping sickness. The disease is only found in rural Africa affecting poor rural communities. Tsetse fly lives in woodland that is forest vegetation.

MODE OF TRANSMISSION

Both male and female feed on blood and seek a meal during daylight hours and in the process of taking a blood meal the parasite escape into the blood stream. Domestic and wild animal reservoirs play a major role in transmission of the disease.

SYMPTOMS

Fever.

Swollen lymph nodes.

Skin itching.

It can invade the brain and central nervous system causing  headaches, drowsiness, and abnormal behaviour.

It can lead to coma and death if not treated.

CHOLERA

Vector: House flies, Blow flies

Causative organism: Bacteria(vibro cholera)

Cholera is a disease that is usually associated with poor environmental sanitation, poverty and war. Caused by ingestion of faecally contaminated food and water.

MODE OF TRANSMISSION

Insects such as house fly, blow fly, flesh fly play a role in spreading the disease by carrying the bacteria from infected faeces and contaminated products around the human environment and depositing it on foods and water taken by humans.

SYMPTOMS         

watery diarrhoea.

Vomiting.

Severe dehydration.

Death if not treated.

AMOEBIC DYSENTERY

Vector: Cockroaches, Flies

Causative organism: Protozoan (Entamoeba histolytica)

Most insect serves as vectors of amoebic dysentery by mechanical transmission of the protozoa from direct contact with human faeces or contaminated products and surfaces.

MODE OF TRANSMISSION

Insects such as cockroaches, flies plays an important role in spreading the disease by carrying the bacteria from infected faeces and contaminated products around the human environment and depositing it on foods and water taken by humans.

SYMPTOMS

Bloody diarrhoea

weight loss

Fatigue

Abdominal pain

LEISHMANIASIS

Vector: Sand flies

Causative organism: Protozoa (leishmaniasis spp)

The disease occurs in many countries in the tropical and subtropical regions.WHO has estimated that 310 million people are at risk from the disease, there are 300,000 cases of visceral leishmaniasis and over 20,000 deaths per year, while 1 million cases of the cutaneous form were reported over a five-year period.

MODE OF TRANSMISSION

Leishmaniasis is spread by bites from female sandflies. The bite leaves a non-swollen red ring.

SYMPTOMS

Fever

Anaemia

SALMONELLOSIS

Vectors: House flies, Blow flies, Flesh flies, Cockroaches

Causative organism: Bacteria(Salmonella enterica)

Salmonella bacteria can be carried by flies and cockroaches that inhabit dirty environment by mechanical transmission when they come in contactwith infected faeces from humans or animals and contaminated products. Poor hygiene in vegetable and fruit harvesting, and pets, especially reptiles, baby chicks and ducklings are also sources of infection

MODE OF TRANSMISSION

The mode of transmission of salmonellosis is through injection of contaminated foods. Poor hand hygiene and poor sanitation

SYMPTOMS

Diarrhoea,

Fever,

Vomiting,

Abdominal cramps

LYMPHATIC FILARIASIS

Vector: Mosquitoes

Causative organism: Roundworm (Wuchereria bancrofti, Brugia malayi)

The adult parasitic worm only lives in the human lymph system and is spread between people by mosquito bites.

MODE OF TRANSMISSION

The disease is transmitted through bite from an infected mosquito.

SYMPTOMS

The worms can be present in the body for years without showing symptoms, slowly damaging the lymphatic system, kidneys and immune system as they produce millions of larvae over a lifetime of 6-8 years. The worst symptoms usually show in adults, more commonly in men, producing inflammation of tissue (elephantiasis) in arms, legs, genitals and the lymphatic system (lymphedema).

ONCHOCERCIASIS (RIVER BLINDNESS)

Vector: Blackfly

Causative organism: Nematode worm (Onchocerca volvulus)

River blindness affects 37 million people, mainly in 31 countries in Africa and also Central and South America. It is only a risk in remote rural areas near fast flowing streams where the blackfly breeds.

MODE OF TRANSMISSION

The parasite is transmitted when the female blackfly seek a blood meal after mating.

SYMPTOMS

Itching of the skin

Lymphadenitis (hanging groins)

Elephantiasis of the genitals

Serious visual impairment

Blindness

PREVENTION AGAINST DISEASES TRANSMITTED BY INSECTS

Since most of the diseases are not transmitted through the same means. But required an insect vector for its distribution. The general means of prevention that could help reduce the risk of infection are:

Using insect repellent.

Wearinglong sleeves shirts and trousers.

Staying in places with window and door screens.

Sleeping under an insecticide treated net (ITN)

Covering water containers and removal of stagnant water around housing areas, in buckets, flower pots and in household wastes or refuse such as tyres, cans and bottles, is an essential control measure.

Good environmental sanitation and proper hand hygiene.

For more information, check out our individual articles on these diseases.

REFERENCES
https://www.linkedin.com/company/rentokil-steritechWikipedia: www.wikipedia.com

US Centers for Disease Control: www.cdc.gov

https://www.linkedin.com/company/rentokil-steritech

WHO: www.who.int

European Centre for Disease Prevention and Control: ecdc.europa.eu

WHO. A global brief on vector-borne diseases. WHO, Geneva, 2014

WHO. Public Health Significance of Urban Pests. WHO, Copenhagen, 2008

Cases of sleeping sickness drop to lowest level in 75 years
www.who.int/trypanosomiasis_african/cases_drop_to_lowest_since_75_years

WHO. Investing to overcome the global impact of neglected tropical diseases: third WHO report on neglected diseases 2015. WHO, Geneva

WHO. Global strategy for dengue prevention and control 2012-2020. WHO. Geneva, 2012

The European Food Safety Authority
www.efsa.europa.eu

Graczyk TK, Knight R and Tamang L. Mechanical Transmission of Human Protozoan Parasites by Insects. Clin Microbiol Rev. 2005 Jan; 18(1): 128–132. doi: 10.1128/CMR.18.1.128-132.2005.