Plague is an acute, contagious, febrile illness transmitted to humans by the bite of an infected rat flea. The cause is the plague bacillus, a rod-shaped bacteria referred to as Yersinia pestis. Yersinia is named in honor of Alexander Yersin, who successfully isolated the bacteria in 1894 during the pandemic that began in China in the 1860s.
Y . pestis is a nonmotile, non - spore-forming, pleomorphic, gram-negative coccobacillus. The bacteria elaborate a lipopolysaccharide endotoxin, coagulase, and a fibrinolysin, which are the principal factors in the pathogenesis of this disease.
Wayson stain showing the characteristic "safety pin" appearance of Yersinia pestis, the plague bacillus. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.
Domestic and urban rats are the most important reservoirs for the plague bacillus, but field mice, cats, camels, prairie dogs, rabbits, and squirrels can be important animal reservoirs as well.
The prairie dog is a burrowing rodent of the genus Cynomys. It can harbor fleas infected with Yersinia pestis, the plague bacillus. Image courtesy of the Centers for Disease Control and Prevention (CDC), Atlanta, Ga.
The most important vector for transmission of plague is the rat flea, Xenopsylla cheopis . Ticks and human lice have been identified as possible vectors. Humans are accidental hosts in the natural cycle of this disease.
Human-to-human transmission is rare except during epidemics of pneumonic plague.
Oriental rat flea ( Xenopsylla cheopis ), the primary vector of plague, engorged with blood. Image courtesy of Centers for Disease Control and Prevention (CDC), Atlanta, Ga.
Lyme disease, or lyme borreliosis, is the tick-borne infectious disease caused by Borrelia burgdorferi and characterized by fever , headache , fatigue , depression , and a characteristic circular skin rash called erythema migrans . The disease is named after the town of Lyme , Connecticut , USA, where a number of cases were identified in 1975.
Lyme disease is classified as a zoonosis , as it is transmitted to humans from a natural reservoir among rodents by ticks that feed on both sets of hosts . Hard-bodied ticks of the genus Ixodes are the main vectors of Lyme disease.
The manifestations of Lyme disease have been divided into 3 stages: localized, disseminated, and persistent. The first 2 stages are part of the early infection, while persistent disease is considered late infection. The primary symptoms of stage 1 are erythema migrans.
Common bullseye rash pattern associated with Lyme disease
Physical exam Erythema migrans, the characteristic rash of early Lyme disease.
Because the above recommendations are not always practical, particularly for children and during the summer, and because ticks do not appear to transmit Lyme disease until they have been attached for several days, close inspection for ticks should be performed each time one has been outdoors.
The groin, axilla, and hairline should be inspected particularly well.
Malaria is a mosquito -borne infectious disease caused by plasmodium parasite . It is widespread in tropical and subtropical regions, including parts of the Americas (22 countries), Asia , and Africa . Each year, there are approximately 350–500 million cases of malaria, killing between one and three million people
Malaria is naturally transmitted by the bite of a female Anopheles mosquito .
Anopheles albimanus mosquito feeding on a human arm. This mosquito is a vector of malaria and mosquito control is a very effective way of reducing the incidence of malaria.
Epidemiology Countries which have regions where malaria is endemic as of 2003 (coloured yellow). Countries in green are free of indigenous cases of malaria in all areas. Malaria causes about 250 million cases of fever and approximately one million deaths annually. The vast majority of cases occur in children under 5 years old; pregnant women are also especially vulnerable
Epidemiology Frequency of malaria cases in 1996
Typhus is any of several similar diseases caused by Rickettsiae . The name comes from the Greek typhos (τῦφος) meaning smoky or hazy, describing the state of mind of those affected with typhus. The causative organism Rickettsia is an obligate parasite and cannot survive for long outside living cells. Typhus should not be confused with typhoid fever , as the diseases are unrelated.
Multiple diseases include the word "typhus" in their description. Types include: Etiology harvest mites on humans or rodents Orientia tsutsugamushi Scrub typhus fleas on rats Rickettsia typhi Murine typhus or "endemic typhus" lice on humans Rickettsia prowazekii Epidemic typhus Arthropod Bacterium Condition