Lecture 14 Summer.pdf

5/23/2024 Fleas Chapter 9 1 General taxonomy In the order Siphonaptera 2200 species, in 220 genera – Only a few are important to humans 94% of all fle...

5/23/2024 Fleas Chapter 9 1 General taxonomy In the order Siphonaptera 2200 species, in 220 genera – Only a few are important to humans 94% of all fleas bite mammals – The remainder feed predominantly on birds Worldwide distribution – Many species and genera have limited ranges 2 General taxonomy Most important genus (medically) is Xenopsylla Other genera may have medically important roles – Ctenocephalides may be hosts for cestodes. – One flea species (Tunga penetrans) “burrows” into people’s feet. 3 1  5/23/2024 Morphology Adults are very small, 1-6mm – Oval shaped, compressed laterally – Light to dark brown – Body is covered in small bristles and spines Lack wings, but have powerful legs – Hind legs are specialized for jumping Females: tip of the abdomen is more rounded 4 Flea morphology 5 Head Head is triangular with conspicuous eyes Club shaped antennae Mouthparts point downward – Some species have tooth like spines called genal combs 6 2  5/23/2024 Head Morphology 7 Role of blood feeding Both sexes take blood meals Saliva injected during blood feeding – Saliva has anticoagulants Blood sucked through pharynx into proventriculus (with backwards pointing spines) – These spines are thought to prevent regurgitation – The proventriculus is important for disease transmission Blood enters mid-gut for digestion 8 Flea alimentary canal 9 3  5/23/2024 Life Cycle 10 Life cycle Female deposits eggs in debris or detritus – Usually not on host animal while ovipositing – Often in habitat or dwelling where host lives (nest, burrow, etc) – Can be in the human housing as well Eggs are small (0.1 to 0.5mm), oval, yellow or white Female may lay 300-1000 eggs during her lifetime – Batches of up to 40 per day 11 Hatching Eggs hatch after 2-5 days – (depends on species, may be longer) Legless larva emerges – Pale brown, small head, distinct but similar segments Larvae are active – avoid light – Shelter in cracks and crevices, in debris or nests – Feed on organic debris – Some species need to feed of defecated blood from adult fleas Two or three larval instars 12 4  5/23/2024 Pupae and adult emergence Larval period is 2-3 weeks, may be up to 200 days Pupae have a white cocoon made of silk – Produced from the larval salivary glands Silk is sticky, picks up bits of dust, dirt, and debris After 2-3 days, larva pupates 13 Pupae and adult emergence Adults emerge as quickly as 5-14 days (variable based on environment) Stimulus required for emergence – usually a vibration of an animal moving nearby – Stimulus can also be carbon dioxide – What does this stimulus tell the flea? Normal emergence is many months – Adults can remain active INSIDE the cocoon for 4-12 months 14 Adults Can live anywhere from 10 days to 12 months Fleas avoid light, usually hide among the hair or feathers of the host (or clothing, in beds) During feeding, feces are evacuated to make room for blood meal – Presence of the flea feces (sometimes partially digested blood) can be seen in bed linens of infested houses 15 5  5/23/2024 Host specificity Most fleas have a slight preference for a specific host – Most fleas will bite other hosts when their preferred host is absent If a host dies, fleas will abandon host for a new one – Why is important medically? Some fleas can tolerate desiccation, starvation (up to 6 months) – Dog and cat fleas die after 10 days without a blood meal On the host, fleas move by crawling – They jump off of host, or jump onto to new hosts from the ground 16 Jumping Fleas can jump up to 20cm vertically or 30cm horizontally Can engage in repeat jumping without tiring out Use a molecular “spring” link trigger for jumping (not muscular jumping) 17 Medical Importance Four main reasons for medical importance – Nuisance, Plague, Murine Typhus, and Cestodes Nuisance aspect – Flea bites result in discomfort, swelling, and irritation – In US, cat fleas are the most common nuisance species (Ctenocephalides felis). – Dog fleas (Ctenocephalides canis) and human fleas (Pulex irritans) are less important – Cat fleas are actually more common on dogs than dog fleas. 18 6  5/23/2024 Medical Importance: Nuisance Fleas commonly bite people around the ankles, legs, and feet. – At night, in beds, may bite anywhere – Hypersensitivity can produce more severe reactions and allergies Infestations can develop quickly! – Long dormancy inside cocoons, waiting for an emergence stimulus – People can move into a new house, and overnight it can become infested with fleas 19 Medical Importance: Plague Bubonic plague is caused by a bacteria, Yersinia pestis Zoonotic disease – Reservoir hosts are wild animals, mostly rodents – 203 rodents and 14 lagomorphs (rabbits and hares) can harbor the bacteria Transmission cycles includes gerbils, voles, chipmunks, squirrels, etc. – Sylvatic, or enzootic cycle – rodent -> flea -> rodent Humans can get the disease when coming in contact with the wild animal hosts. – Especially dead hosts. Why? 20 Urban transmission Involves transmission between rats and fleas – Transmitted by fleas like Xenopsylla cheopis, X. astia, and X. brasiliensis. When rats live in close proximity to humans, transmission to humans is likely. – When living in close proximity, the fleas on the rats may bite humans. – Especially when rats are killed by the disease Plague can be transmitted from person to person, by the Xenopsylla fleas and Pulex irritans. – Transmission by P. irritans is probably mechanical from infected mouthparts. 21 7  5/23/2024 Other modes of transmission Contamination of soil Rubbing contaminated feces into abrasions – Contaminated feces can remain infective for up to three years Crushing fleas in mouth (bacteria come in contact with mucous membranes) Direct contact with infected individual – Pneumonic plague infects the lungs – can cough the pathogen into the air and be breathed in – Potential bio-terrorism weapon 22 23 Transmission by Fleas Bacteria are sucked up by flea during blood feeding Invade and multiply in the proventriculus. Extreme replication of bacteria may partially or completely block the proventriculus. If proventriculus is blocked, some blood may be regurgitated during feeding. This regurgitated blood is teaming with the bacterial pathogens. Blocked fleas will soon starve, but the bite more frequently trying to get a blood meal! 24 8  5/23/2024 History of the plague Current outbreaks in areas with sanitation are rare – 10-15 cases in the US every year – Worldwide, 10,000-15,000 cases per year. Antibiotics are effective treatment In the middles ages, millions of people were killed in regular outbreaks of the plague – Killed up to 60 million people in the 1300’s, up to 50% of the entire population of Europe. – Outbreak in 1300’s in China killed 1/3 of entire population – Last major outbreak in Europe was in London, 1665. – There have been continued minor outbreaks and localized outbreaks 25 26 27 9  5/23/2024 Symptoms of Plague Symptoms begin 2 to 6 days after infections. – Start with swelling on lymph glands, and pain associated with swelling. Fever, chills, headache, and extreme exhaustion follow. Bacteria then invades the bloodstream – Can infect the lungs (pneumonic form) Continued chills, fever, coughing, and possibly death 14% mortality rate if untreated. 28 Medical Importance: Murine Typhus Flea borne typhus caused by Rickettsia typhi Does not block proventriculus like plague bacteria. Transmission occurs by rubbing infected feces into abrasions or mucous membranes. – Also by release of rickettsiae from crushed fleas – Feces remain infective for up to a year 29 Transmission cycle Primarily a disease of rodents and cats Can also be transmitted by some lice and mites Xenopsylla cheopis is primary vector for transmission to humans – When a new flea bites, feces from infected fleas can contaminate the bite. Vertical transmission is possible, but no research as to how common. 30 10  5/23/2024 Transmission cycle Outbreak in 2008 in Austin, TX (53 human cases) – Most common in South and Southwest US – More common here in the RGV! Fever, headache, malaise, nausea – Most symptoms are non-specific Can increase in severity, mortality rate varies – Untreated can result in 20-60% mortality 31 32 Cestodes (Tapeworms) Tapeworms that can infect dogs, cats, and occasionally human children Gravid tapeworm proglottid (tapeworm segment) leaves animal host, dries in the air Larval fleas feed on organic material, feeds on tapeworm proglottid 33 11  5/23/2024 Cestodes (Tapeworms) Larval worms hatch in flea, enter coelom Trapped in coelom, as larval flea pupates and becomes adult Once flea is adult, host animal (dog/cat) may accidentally swallow flea while grooming, become infected with the tapeworm. – Children kissing, fondling, or being licked by pets that have crushed infected fleas in their mouth can become infected 34 35 Tunga penetrans flea Chigoe, jigger, or sand flea Does not transmit disease, but female can become imbedded in human skin Female continues to feed on blood, swells under the skin when she becomes gravid (with abdomen sticking out), and lays eggs out of the tip of the abdomen 36 12  5/23/2024 Female fleas can die when they are embedded, which can cause secondary infections. Found in Central and South America, parts of Africa, and the West Indies 37 Assassin Bugs Chapter 7 38 Research Opportunity TAMU has a joint program with UTRGV for undergraduate research Can conduct research with TAMU professor – https://entomology.tamu.edu/reeu/participating-faculty/ – Four faculty doing medical entomology research If interested, please contact me ASAP via email, and I will direct you to the application site 39 13  5/23/2024 Class evaluations Reminder – please complete class evaluations (deadline Dec 1) – I read these when considering new assignments or changes to the class Also encourage ratemyprofessor.com 40 Assassin Bugs Chapter 7 41 Taxonomy Animalia: Arthropoda: Insecta: Hemiptera: Reduviidae Order Hemiptera – “true bugs” – X-pattern on dorsal view due to crossed wings 42 14  5/23/2024 Taxonomy Many Reduviidae eat plant juices or other insects One sub family, triatominae, are blood feeders – 130 species, 15-17 genera All Triatomines species are commonly called kissing bugs or cone-nose bugs. 43 Prominent head, long antennae 5-45mm, most 20- 30 mm Many brown, black, some brightly colored 44 Geographic Distribution 45 15  5/23/2024 Morphology Proboscis is thin and straight, designed for piercing. Proboscis lies pressed against ventral surface of the head When feeding, it swings forward and downward 46 Life Cycle: Eggs Smooth or ornate shells, small constriction at operculum (egg cap) White, pearly, Small, 1.5 – pink, or yellowish 2.5mm 47 Life Cycle: Eggs Common in mud walls, thatched roof, Laid in cracks or or in animal burrows crevices in walls, and nests floors, ceilings 48 16  5/23/2024 Oviposition Females typically oviposit 1-2 eggs per day. Total number in female lifetime is between 50 and 1000. – Depends on species, life span, and number/size of blood meals – Average number of about 200-300 eggs per female. Egg generally hatch after 10-15 days. – Egg incubation can take as long as 60 days. 49 Life Cycle: Nymphs Homometabolous life cycle Nymphs emerge from eggs Newly hatched nymphs will hide for 2-3 days before feeding. Five nymph instars – Each requires a blood meal – Both sexes feed on blood. – Nymphs can ingest 6-12 times their own weight in blood. Nymphs have wing pads (undeveloped wings) in the fourth and fifth instars 50 Life Cycle: Adults The 5th instar molts to become an adult (with complete wings) Adults feed on less blood (2-4 times their own weight) but will feed every 4 to 9 days. – Ingest 300-400mg blood each time. Food competition: Hungry adults and nymphs will sometimes pierce the swollen abdomen of a engorged nymph and “steal” the blood from them. – Does not appear to harm the insect. 51 17  5/23/2024 Life Cycle: Feeding Feeding lasts 10-25 minutes, usually at night. Humans (under blankets) are bitten on exposed areas – Usually the mouth, nose, near the eyes. – Biting is usually painless, does not wake host up. 52 Life Cycle: Feeding The bugs defecate during or soon after feeding. – This is critical for disease transmission! Complete life cycle – egg to adult – can take 3-10 months. Adults can live up to 2 years. – In absence of hosts, it will take them 4-6 months to starve. 53 Habitat Found in both wet and dry areas. Many species feed on wild animals – Including armadillos, opossums, rats, mice, marsupials, squirrels, skunks, iguanas, bats, and some birds. Adults and nymph of these species often found in nests and burrows of animal hosts 54 18  5/23/2024 Habitat Some triatomines have become “domesticated” and will feed on: – Donkeys, cattle, goats, horses, pigs, cats, dogs, (many on) chickens, humans. These species often cohabitate with humans and livestock, living in the man made shelters and houses. – Associated with poverty and rural conditions – Mud, wood, and thatch are prime habitats In absence of hosts, individuals will seek out new habitats – Nymphs crawl, adults fly 55 Medical Importance Hundreds of triatomine bugs may infest houses in rural areas. Human inhabitants will receive many bites each night. – In these infested houses, humans can lose up to 2mL of blood per night, leading to anemia. Chagas disease is the primary medical concern. 56 Chagas Disease Caused by a trypanosome: Trypanosoma cruzi Trypomastigotes (life stage of the typanosome) are ingested into the midgut of the bug. – They continue development into epimastigotes the gut The epimastigotes then multiple (divide) after between 8 and 17 days. – Transform into infectious (metacyclic) trypomastigotes 57 19  5/23/2024 Chagas Disease These trypomastigotes migrate to the lumen of the hind-gut. When insect blood feeds (for 10-25 minutes), the insect excretes a liquid or semi-liquid feces. – These feces will be filled with the trypomastigotes People (or animals) get infected when they scratch the wound from the insect, and the feces are scratched into the skin/abrasion. – Can also be rubbed into mucous membranes in the mouth and eyes 58 59 Transmission 70 different triatomine species have been found to be infected naturally Only about 12 species live in close proximity to humans Vector efficiency depends on speed of feeding and defecation rate 60 20  5/23/2024 Most important species Triatoma infestans, T. dimidiata, Rhodnius prolixus, and Panstrongylus megistus – All of these spread Chagas disease Chagas is most common in Central and South America Some of these also can transmit another trypanosome, Trypanosoma rangeli, but this is a non-pathogenic species. 61 62 Transmission Zoonotic disease – the trypanosome is primarily a parasite of wild animals – These may all serve as reservoir hosts of the pathogen. The insect may also be a reservoir host Humans may also be considered a reservoir host in some areas 63 21  5/23/2024 Transmission Can also get infects by eating infected bugs or animals Infection rates are high – 25 to 50% of the triatomines in an area may be infected! – In California, 78% of Triatoma protracta are infected, but it rarely bites humans 64 Chagas disease in humans Lifelong infection – Acute and chronic phase Acute phase occurs immediately after infection – May last up to a few months – Mild swelling, fever are primary symptoms 65 Chagas disease in humans After acute phase, there is a prolonged asymptomatic phase – Lasts multiple years – May last a persons whole life! 30% of infected people develop chronic phase – Heart problems that can lead to sudden death – Dilated esophagus or colon – Dilated heart 66 22  5/23/2024 Chagas disease in humans In Latin and South America, 8-11 million people are thought to be infected. Reported cases in the US are rare – Most cases are from people who travelled and got bitten elsewhere – Due to asymptomatic phase, many people may actually be ill with the parasite – Some estimates are about 300,000 people are infected Many dog cases here in the LRGV 67 23