Diptera: Significance in Medicine and Forensics

Diptera Importance

• Diptera includes flies, horseflies, mosquitoes, and are characterized by having two pairs of wings where the rear pair is smaller and fused to the legs.
• They also possess moving jaws and a pair of antennae.
• Diptera species can be beneficial or harmful to humans.
• They can transmit pathogens through their saliva when they bite.
• Some diptera can be used to determine the postmortem interval of a corpse.
• Forensic entomologists examine diptera development and presence on a corpse to determine the time of death.
• The presence of diptera at a crime scene indicates environmental conditions and temperature at the time of the crime.

Objectives

• To know the features, distribution, and medical significance of Aedes aegypti in Peru.
• To determine the forensic importance of the Calliphoridae and Sarcophagidae families, and their biology.
• To increase knowledge of the families in connection to corpse decomposition stages.
• To determine preferences of various cadaverous substrates in different conditions

Diptera of Medical Importance

• Aedes aegypti's Taxonomy
  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Diptera
  • Family: Culicidae
  • Genus: Aedes
  • Species: Aedes aegypti (Linnaeus, 1762)
  • Common Name: Dengue Mosquito

Aedes aegypti Life Cycle

• Has four metamorphic stages: egg, larva, pupa, and adult.
• Aedes aegypti eggs are deposited in freshwater containers like cups and ponds and can be found in aquatic plants.
• Eggs are white when laid and can form larvae in 12-24 hours if kept humid.
• The eggs are desiccation-resistant and can remain viable for months without water.
• The eggs hatch when submerged in water, producing a larva.
• Larvae feed on water particles and go through four stages.
• The larva turns into an inactive pupa at the end of the fourth stage.
• The larva emerges from the shell and only molts four times before pupating.
• The pupa lasts 48 to 72 hours, during which the insect does not feed, and moves towards the water's surface.
• The aquatic stage takes 7 to 10 days.
• Adult mosquitoes feed on nectar and sugars for energy.
• Females consume blood to produce eggs.
• Depending on the environment, adult mosquitoes can live for three weeks to several months.

Aedes aegypti Transmission

• Adult females must survive 10 to 14 days to be potential dengue virus vectors.

Aedes aegypti Morphology and Functions

• Aedes aegypti is small and slender, with a length of 4-7 mm.
• Males are slightly smaller than females.
• Adult mosquitoes have a unique color pattern with a grayish body and black legs and antennae.
• The legs of the females have a white band in the middle.
• Aedes aegypti has two antennae and two compound eyes, with several small eyes allowing perception of movement and light.
• The thorax of Aedes aegypti has sense hairs that allow it to detect odors and flavors.
• The thorax has two pairs of legs and two wings.
• The mouth parts include two mandibles and a proboscis, which is used to pierce victims.
• Aedes aegypti females have a pair of ovaries and a uterus, while males have a pair of testicles and a penis.

Aedes aegypti Behavior

• Females feed on human and animal blood to produce eggs, while males feed on nectar and sugar.
• Adults reproduce through mating, with the male fertilizing the female, who then lays eggs in freshwater containers.
• The life cycle begins again.
• Aedes aegypti is primarily a diurnal mosquito, found indoors in homes and buildings.
• Adult mosquitoes hide in dark places during the day and emerge at night to feed and mate.
• Adult mosquitoes can detect victims by their body heat, carbon dioxide, and other chemicals.
• Females bite people and animals to get blood to produce eggs.
• Aedes aegypti can transmit infections through its saliva, which contains proteins and chemicals that promote hemostasis.
• Diseases transmitted include dengue, West Nile fever, and Zika.
• Preventive measures include repellents, mosquito nets, protective clothing, biological control methods, and vaccination development for diseases.

Aedes aegypti Distribution

• Aedes aegypti is in South America, Mexico, the Caribbean, and parts of the United States.
• It is also in Asia, the Pacific, and Oceania.
• The mosquito can adapt to various environments and survive in both urban and rural regions.
• Ae. aegypti's geographic range may change due to environmental factors and human activity.
• The exact mortality rate is difficult to determine since mortality can vary from year to year and from region to region.
• The countries where these diseases are common and have high mortality rates include Brazil, Colombia, Indonesia, India, Philippines and Vietnam.

Aedes aegypti Distribution in Peru

• It is found mainly in the jungle and northern coast regions, up to the Lima region.
• The climate and environmental factors, such as low temperatures and low rainfall, can slow Aedes aegypti's introduction and establishment.
• Altitude can restrict Aedes aegypti, with few studies reporting its presence above 1700m.

Aedes aegypti as a Disease Vector

• Aedes aegypti is a medically important mosquito that transmits dengue, chikungunya, zika, and yellow fever.
• Aedes aegypti transmits Venezuelan equine encephalitis, Mayaro virus, and is susceptible to the West Nile virus.
• Understanding the vectorial role of Ae. aegypti is complex with explained genetic and environmental variations.

Diptera Importance in Forensic Entomology

• Forensic entomology studies the succession patterns of entomofauna associated with corpses and decomposition processes in different environments.
• Forensic entomologists study corpses in different environments and conditions.
• The study of entomofauna has expanded and can provide legal and medical information of a body, crime, and toxicological analysis.

Cadaveric Entomofauna Succession

• Necrophagous species L. sericata and C. albiceps were captured as adults.
• During the decomposition of pigs the Sarcophagidae family presence was exceptional, except for the species S. argyrostoma.
• High temperatures and cold weather affect this genus.
• Two necrophagous species, C. vicina was found in shade environments.

Calliphoridae and Sarcophagidae Families

• Calliphoridae life cycle
  • Lucilia sericata
    • Incubation - 15.3 ± .67 hours
    • First larval stage - 19.2 ± 1.48 hours
    • Second larval stage - marked by two slits in the posterior spiracles; lasts 20.4 ± 1.35 hours.
    • Third larval stage - presence of three slits in the spiracles last 51.5 ± 1.35 hours.
    • Pre-pupa and pupa stages - larvae stop feeding, enter the substrate, and emerge; 265 ± 3.53 hours until adults.
• Sarcophagidae life cycle
  • Sarconesia chlorogaster
    • Incubation - averaged 16.1 ± 0.74 hours
    • First larval stage - absence of front spiracles, one slit in the posterior spiracles. Spread and then penetrate the substrate to feed. It lasts 26.3 hours.
    • Second larval stage - presence of front spiracles, with two slits.
    • Third larval stage - showed three slits in the posterior spiracles. Larvae stopped feeding and stomachs emptied, at the end of this stage.
    • Pre-pupa and pupa stages - larvae began to retract, change color, and entered substrate.

Decomposition Stages

• Fresh state - ends when swelling is evident.
• Swollen state - putrefaction begins, abdominal swelling begins.
• Active Decomposition - tissues deteriorate by larvae, maggots.
• Advanced Decomposition/Mummification - reduction and dehydration of biomass, mummification

Sarcosaprophagous Diptera Identification

• 102 diptera poses were collected, 3 species id.
• Identifications used taxonomic identifiers.
• Species found
  • Lucilia sericata of Calliphoridae family
  • Sarcophaga sp. of Sarcophagidae family

Diptera Taxonomic Locations

• Calliphoridae Family
  • Kingdom - Animalia
  • Phylum - Arthropoda
  • Class - Insecta
  • Order - Diptera
  • Family - Calliphoridae
  • Genus - Lucilia, Species - Lucilia sericata
• Sarcophagidae
  • Kingdom - Animalia
  • Phylum - Arthropoda
  • Class - Insecta
  • Order - Diptera
  • Family - Sarcophagidae
  • Genus - Sarcophaga, Species - Sarcophaga sp.

Oviposition Abundance and Behavior

• The investigation shows that 102 poses were documented with the most collected from Lucilia sericata at 97. Whereas 3 were from Sarconesia chlorogaster.
• Oviposition site
  • Necrophagous diptera species
    • Lucilia sericata on the corpse
    • Sarcophaga sp found in the cadaver.
    • The insects showed preference for the upper thigh region mostly in both sides while L. sericata showed the preference other than on/in the nose

Humidity, Temperature and Oviposition

• Humidity was recorded at 6.0 °C to 29.0°C in the summer with 10 % - 69% humidity in Arequipa.
• When humidity went 10%, the flies went to oviposition at 41.12%.
• A consistent rate of oviposition happened for 11% of the insects. L. sericata was from range 10% -23 % of humidity where as Sarconesia chlorogaster and Sarcophaga was from the 10% to 16% range.

Conclusion

• The Ae. aegypti mosquito has a major impact since it acts as a vector for illnesses.
• Factors include anthropophilia, resistance, geographic, adaptability to urban centers and competence for diseases like dengue, yellow fever, zika, etc.
• Globalization plays role in these viruses and are quickly expanding worldwide.
• Diptera showed preference for corpse oviposition.
• The Calliphoridae and Sarcophagidae families are the most important and have species Lucilia sericata, Sarconesia chlorogaster, and Sarcophaga sp.
• Flies transmit diseases, these diptera play a significant role during criminal investigation and to ID the remains for forensics.