Vector-Bourne Pathogens Flashcards
Infections through skin
-Arthropod vectors are efficient ways to introduce Pathogens
-V replicate in and are transmitted by arthropods called arboviruses but many bacteria and protozoan pathogens are transmitted by vectors
-Arthropods include: mosquitos, ticks and sandflies
Yellow Fever Vector
-mosquito-borne viral illness caused by an arbovirus of the family Flaviviridae, genus Flavivirus
-Flavivures consist of positive, single-stranded RNA genome encased in capsid which is enveloped by a lipid envelope
-Transmission is mainly by mosquitos (aedes aegypti)
Yellow fever transmission in mosquito
-virus is taken up by a female mosquito
when it feeds on the blood of an infected
person or primate.
-The virus then replicates in
stomach epithelial cells of the insect and
migrates through the mosquito blood system
to the salivary glands.
-Saliva injected into another individual upon feeding by the mosquito introduces the virus to a new host
-Three transmission cycles exist for the virus
which are interlinked
Yellow fever symptoms
-Most people infected with YF virus have minimal or no symptoms.
-Those who develop illness will present with flu-like symptoms along with nausea and vomiting after 3-6 days.
-Most people recover after a number of days.
-However approx. 12% of those that have presented with illness will, after a brief
remission of ≤48 hours progress to a very serious form the the disease which is
characterised by hemorrhagic symptoms, jaundice, and eventually shock and
multisystem organ failure.
-The case-fatality rate for severe cases is 30%–60%.
Yellow Fever Pathogenicity
-results from replication in the lymphatic system (lymph nodes) and
migration to the liver where the virus infects hepatocytes causing liver damage.
-The liver damage ultimately leads to hyperimmune activation and organ failure
-A vaccine for yellow fever was developed by Max Theiler in the 1920’s and is still in use
Flaviviruses that are transmitted by mosquitoes (excl. YF)
1) Dengue fever virus: causes haemorrhagic fever in a small proportion of
infected individuals.
2) Zika virus: Can be transmitted horizontally to the foetus, causing birth
defects including microcephaly.
3) West Nile virus: can cause encephalitis or meningitis in a small % of
infections.
Lyme disease
-An example of a tick-borne bacterial disease
-This is a disease that left untreated will become chronic and slowly progressive.
-It gets its name from Old Lyme, Connecticut where cases were first recognized.
-In the USA i caused the spirochete Borrelia burgdorferi
-it contains a linear (as opposed to a
circular) chromosome.
-Other Borrelia species are associated with this disease in Eurasia
-Mainly spread by deer tick when obtaining blood meal
Lyme disease initial symptoms
-Initial symptoms of Lyme disease include
headache, backache, chills, and fatigue.
-In 75 percent of cases, a large rash occurs at
the site of the tick bite.
Lyme disease symptoms when left untreated
- Severe headaches and neck stiffness.
- Facial palsy (loss of muscle tone or droop on one or both sides of the face).
- Arthritis with severe joint pain and swelling, particularly the knees and other large
joints. - Intermittent pain in tendons, muscles, joints, and bones.
- Heart palpitations or an irregular heartbeat.
- Episodes of dizziness or shortness of breath.
- Inflammation of the brain and spinal cord, nerve pain, shooting pains, numbness, or
tingling in the hands or feet.
why doesnt chronic lyme disease respond to antibiotics
-The chronic disease does not respond to antibiotics and is likely an autoimmune disorder.
-The bacterium may initiate inappropriate immune responses due to molecular mimicry
Plague
-Although rare now (a few hundred cases are reported annually; outbreaks occur in India,
Madagascar).
-It was responsible for approx. 50 million deaths in Europe during the middle
ages and into the 16th century.
-Only smallpox and measles have killed more among all infectious diseases
-Caused by Yersinia pestis, a gram-negative, facultatively aerobic, rod-shaped bacterium.
-Fleas are intermediate hosts and vectors that spread plague between mammalian hosts
Different effects of plague in wild rodents vis people
-In some wild rodents, sylvatic plague causes only a mild infection, but diseased animals remain a reservoir of Yersinia pestis.
-In rodents such as rats that act as disseminating hosts, as well as in humans, plague is often
fatal.
-When the domestic rodent reservoir dies off in an epidemic, infected fleas seek alternate hosts in humans which resulted in us being accidental hosts (incidental hosts)
Vector of plague
-The rat flea Xenopsylla cheopis carries cells of Yersinia pestis.
-The bacterium replicates in the flea gut
-cells of Y. pestis are transmitted to a host in a flea bite.
-The rat flea was the major vector for the pandemics of plague that ravaged medieval
Europe in the fourteenth century.
3 manifestations of plague
Bubonic
Pneumonic
Septicaemic
Bubonic plague
-so-called because of the buboes that develop
in the infected individual.
-These are masses of tender, enlarged
lymph nodes, usually in the groin or axilla, which may suppurate and drain
-accompanied by a high fever, headache, vomiting and ataxia (loss of coordination) and hemorrhaging.
-The local haemorrhages produce dark splotches on the skin and eventual
tissue necrosis, giving plague its historical name, the “Black Death”.
-Usually B is phagocytosed and transported to lymph system after infection which causes lymphadenitis
