Fleas, rats, and plague

Fleas

• Order Siphonaptera

• 15 families

  • Most fleas of medical importance in Family Pulicidae.

• 2,500 species

• Adults are laterally compressed, wingless, ectoparasites.

Fleas undergo a _______.

Holometabolous (complete) life cycle

• Egg, larva (3 instars) pupa, adult

• Pupa spins a cocoon using bits of debris from surroundings.

Fleas have _______.

hindlegs are adapted for jumping

Adults fleas eat on blood while larvae ______.

• eat blood-rich adult excrement (“flea dirt”), other larvae, organic material in nest.

• Most are parasites of mammals.

  • Some parasitize birds (100 species)

• Some are “attached” species

  • Stick tight flea – Echidnophaga gallinacea

  • Chigoe flea – Tunga penetrans

Tunga penetrans

• Chigoe flea, sand flea

• Mated female flea becomes embedded in the skin.

  • Host skin grows over mated female.

• Gravid female grows to the size of a pea.

  • Develops several dozen eggs.

• Mature eggs and young larvae are extruded through the wound to develop on the ground

Severe infestations of the chigoe flea may lead to _______.

amputation.

• South American distribution.

Cat Flea – Ctenocephalides felis

• Adult female often lays her eggs on the host, but they roll off.

• Egg, larva, and pupa are found in the den or nest of the host animal.

• Larvae are general feeders, blood, feces, cast skins.

Life stages of Cat Flea

• Eggs

  • Fragile, hatch in 1-2 days

• Larvae

  • 11-12 days for larval development.

• Pupae

  • 7 days or extended quiescence up to 1 year.

• Adults

  • Starved conditions = 38 days

  • Fed conditions = 100-125 days

Host specificity with fleas vary ______.

by species

The cat flea is found commonly on ______.

dogs in N. America.  It is more common on dogs than the dog flea.

The dog flea is most common on ______.

dogs in the UK

• Ctenocephalides canis

Pulex irritans

the human flea, occasional problem for domestic animals such as swine.

Echidnophaga gallinacea

stick tight flea, poultry

Medical Importance of Fleas

• Irritation and discomfort to humans and land animals.

  • Reaction to bite may be severe.

  • Infestation of home may be associated with a pet.

  • Fleas in home may also be due to rodent nests.

Fleas are _______.

Intermediate hosts for dog and rodent tapeworms occasionally infesting humans.

• Double-pored dog tapeworm, Diplydium caninum.

• Vectored by cat and dog fleas.

• Eggs in feces are ingested by larval flea.

• Occurs in humans if flea is ingested, usually children.

Cat Flea pupation sites in home

carpet

• Vacuuming targets pupae

• As effective as permethrin

Traditional Insecticdes for Fleas

• Chlorpyrifos (over the counter)

• Permethrin (pest control operators)

• Malathion (evidence of resistance)

• Imidacloprid = spot on

• Advantage = fleas only

• Fipronil = spot on

• Frontline = fleas and ticks

• Selemectin = spot on for mites

• Revolution = worms, fleas, and ticks

Vectors of Murine Typhus

• Xenopsylla cheopis (Oriental rat flea)

• Nosopsyllus fasciatus (European rat flea)

• Ctenocephalides felis (cat flea)

• Echidnophaga gallinacea (stick-tight flea)

• Leptopsylla segnis (European mouse flea)

• Pulex irritans (human flea)

• Xenopsylla astia, X. brasiliensis, X. bantorum

Murine Typhus

• Caused by Rickettsia typhi (bacterium)

• Transmitted to humans via stercorarian transmission

  • Human rubs infected feces into wound

  • OR aerosolized feces

• Reservoirs:

  • Rattus rattus (roof rat)

  • Rattus norvegicus (Norway rat)

  • Opossums, raccoons, squirrels

  • Fleas found on these animals may be picked up by pets and transported into homes.

Murine Typhus is an ______.

acute infectious disease

• Transmitted from rodents to humans via rat fleas (primarily by feces but direct transmission occurs periodically).

  • 6-12 d intrinsic incubation period

  • Symptoms:  fever backache, headache, bronchitis, confusion, stupor, red eruptions on chest and limbs

Prognosis of Murine Typhus

• Victims are humans (4% mortality)

• Most severe cases associated with

  • Delayed diagnosis

  • Liver and kidney issues

  • CNS abnormalities

  • Pulmonary compromise

History of Murine Typhus

• Thousands of cases occurred in US during 1940s

• Incidence dropped to about 12/yr during 1970s

• Today, about 100 human cases reported annually in US

  • Number increasing; re-emergence in southern California and Texas (past 25 years)

• Outbreaks reported in Australia, China, Greece, Israel, Kuwait, Thailand. Recent serosurveys demonstrate high prevalence of rickettsiae in Asia and southern Europe.

Plague

• Agent:  Yersinia pestis

  • Bacterium 

• Victim:  Humans and rodents

• Vector: 

  • Fleas-Xenopsylla cheopis and many others

• Reservoir: Rodent and other small mammals

  • Roof rat (Rattus rattus)

  • Norway rat (Rattus norvegicus) 

History of Plague

• Bacterium discovered by Yersin (Swiss) and Kitasato (Japanese) in 1884 in Hong Kong.

• Simond (French) in 1898 proved that fleas were the vector.

  • Noticed that majority of patients had primary lesion (small blister containing plague bacteria); hypothesized could be related to insect bite.

Plague in the US

• Reservoirs:  many mammals

• Rodents: field mice, deer mice, pack rats, roof rat, Norway rat, cotton rat, wood rat, chipmunks, ground squirrels, tree squirrels, prairie dogs

• Rabbits: cottontails

• Carnivores: 

  • Dogs get infected, but recover (dog serology used as surveillance tool).

  • Cats get infected, but may or may not recover.

Vector of Plague

Oriental rat flea (Xenopsylla cheopis)

• Flea becomes infected after it has fed on infected rat.

• Bacteria multiply in proventriculus (part of stomach) where they form an obstruction.

• Flea becomes “blocked” so it becomes hungry.

• Repeated attempts to feed, blood is taken from victim, but cannot pass the block and mixes with bacteria.

• Infected blood regurgitated into bite wound.

• Blocked fleas may live up to 2 weeks.  Some die, but none lose the infection.

Humans acquire plague from _______.

the bite of infected fleas

• Symptoms:

• Disease develops rapidly.  Fever, headache, exhaustion, delirium 2-3 days post-infection.

• Bubo (enlarged and inflamed lymph gland) detectable by 2 days post-infection.  These appear in groin area (most common).  

• Rashes common.

Bubonic plague

Lymph nodes, especially those in groin or armpit area, are swollen and filled with plague bacteria.  The swollen lymph node is a “bubo”

Septicemic plague

Body’s defense mechanisms cannot limit the disease to the lymph glands and lymphatic vessels.  The infection invades the blood stream.  A massive blood poisoning or septicemia occurs.

Pneumonic plague

• Most dangerous type – airborne.

• Plague bacteria invade pulmonary tissue and a secondary pneumonia occurs (inflammation of lung tissue, solidification of the lung).

• At this stage, disease is transmissible as infective drops (sneezing) from the respiratory system.

• Medieval physicians wore masks to avoid infection

Plague mortality and treatment

• Bubonic plague

  • 25-50% fatality rate

• Pneumonic and Septicemic plague

  • Usually fatal

  • All people treated with antibiotics (Streptomycin, gentamycin, tetracycline, etc.)

Plague has been a important disease of ______.

humans throughout history

• Credited with the collapse of feudalism

  • Reduced human populations

• Four pandemics have been recorded

• 542 to 600: 

  • Plague of Justinian (Roman emperor)

  • Nearly worldwide scope (centered in Constantinople, Europe’s largest city during Middle Ages)

• 1346-1361: “Black Death”, 25 million lives lost worldwide (25% of the population of Europe).  Disease spread from Black Sea to Africa, Russia, Europe, China.

• 1665-1666:  “Great Plague of London”, killed 70,000 people out of 450,000 (total population)

Most recent pandemic of plague

• Began in the Chinese Province of Yunnan or Burma in the middle of the 19^th Century

• Reached Canton and Hong Kong in 1884, Calcutta and Bombay in 1896.  From these major ports, it spread to every continent.

Outbreaks of Plague was commonly depicted in _______.

European art

Plague and medicine

• Protective clothing worn by doctors (early form of

      Hazmat suit)

• Doctors used to bleed people to get rid of plague

Outbreaks of Plague globally

• Cyclic

• Flares up periodically on a global scale.  Then it retreats to endemic levels.

• 1,000-3,000 cases/yr.

• Most cases since 1990s in Africa

• Almost all cases in small towns/villages (not large towns or cities)

Plague in US

• Yersinia pestis introduced into West Coast in 1890.

• Soon spread to native rodents, especially ground squirrels.

• In Oakland, CA (1919), a man hunting ground squirrels contracted the disease and (via pneumonic plague) infected 13 people (12 died).

• 1925 Los Angeles epidemic

  • A woman contracted plague (pneumonic), infected 32 relatives/friends, all died.

  • Thought that human source of infection was domestic rats that had been infected from ground squirrels.

• Currently, most cases of rural plague occur in Rocky Mountain states

Cases of Human Plague in the US

• Average of 8 human cases/year (range 1-17 cases/year)

• Most in summer months

• 80% of cases are bubonic form

• Most cases in western US (one in IL was lab-associated): 

• Zone 1: Northern New Mexico, northern Arizona, and southern Colorado or

• Zone 2:  California, southern Oregon, and western Nevada

Plague is considered a likely candidate for ______.

bioterrorism

• 1998, production of plague vaccine discontinued.

  • Limited stores available.

Plague ecology in the US

• occurs naturally in the western US, especially Arizona, Colorado, Utah, and New Mexico

• Bacterium cycles naturally among wild rodent, ground squirrels, prairie dogs, wood rats, and rock squirrels

• Epizoonic outbreaks in the US most likely occur during cooler summers after a wetter winter

• Humans and domestic animals that are bitten from fleas on dead animals are at risk for contracting plague.

• People can also be exposed by handling skins or flesh of infected animals

• Cats can become very ill and can spread plague through air droplets while dogs are less likely to be ill