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Vector-Borne Diseases

Selected Insect-borne diseases
Selected Arachnid-borne diseases
Selected Zoonoses

 Selected Insect-borne diseases  

Since vector-borne disease include both insects (especially mosquitoes) and arachnids (ticks and mites), it is more appropriate to collectively refer to these diseases as arthropod borne diseases (sometimes abbreviated as arbo -- for example, an arbovirus is an arthropod borne virus). Among the true insect-borne diseases, we begin this section with a disease spread by the black fly, and then survey the wide range of mosquito borne diseases.

   1. Onchocerciasis (river blindness)

      Agent:		Onchocerca volvulus (nematode, or roundworm)

      Reservoir:        	Mostly humans

      Transmission:     Bite of infected female black fly (genus Similium), biological vector 

      Symptoms:         Chronic, nonfatal (incubation 1 year or more), intense itching, impaired vision

A. mosquito-borne                                                   
 
   2. Human Malarias                                                     

      Agent:            	A parasitic protozoan in the Plasmodium genus                                      

      Reservoir:        	Mostly humans and infected mosquitoes                      

      Transmission:     Anopheles mosquitoes                     

      Symptoms:         Fever, chills, sweats, CNS effects (headache, delirium, coma)          


   3. Filariasis                         

      Agent:            	Wuchereria or Brugia genus (nematodes, or roundworms) 

      Reservoir:        	Humans                                             

      Transmission:     Mosquitoes (Aedes, Anopheles, or Culex) The mosquito carries the microscopic larval stage of the worm

      Symptoms:         Asymptomatic; fever, asthma, elephantiasis in chronic cases (enlarged limbs) 
 

   4. Yellow Fever:     One of the few immunizations required for travel in endemic areas

      Agent:            	Yellow fever virus (a flavivirus)               

      Reservoir:        	Humans (sometimes monkeys) and mosquitoes       

      Transmission:     Aedes species mosquitoes

      Symptoms:         Sudden onset of fever, jaundice, headache, backache, vomiting, diarrhea


   5. Dengue Fever (also called breakbone fever)                                           

      Agent:            	Dengue virus                                    

      Reservoir:        	Human, infected mosquitoes                      

      Transmission:     Aedes species mosquitoes                                

      Symptoms:         Headache, joint and muscle pain, rash, with low case fatality rate           


   6. Arthropod-born viral encephalitis                                  

      Agents:           	Eastern equine encephalitis, Western equine encephalitis, California encephalitis, West Nile virus, etc.                   

      Reservoir:        	Unknown for most agents (possibly birds, rodents, bats, reptiles) found in more temperate areas (e.g., North America)

      Transmission:     Culex species mosquitoes, possibly Aedes and others  

      Symptoms:         Often asymptomatic, inflammation of brain, spinal cord, meninges, headache, fever, convulsions, paralysis, coma

Selected Arachnid-borne diseases                                                                                      

A. Tick-borne             
                                                                    
 
 1.  Rocky mountain spotted fever                                      
                                                                   
      Agent:                Rickettsia rickettsii

      Reservoir:            Dogs, rodents, other animals

      Transmission:     Bite of infected ticks (various species), tick must be attached 4-6 hours

      Symptoms:         Maculopapular rash (bumpy spots), fever, headache, malaise, chills, rash, death
                                                                               
  2. Tularemia: Discovered in Tulare County, California

      Agent:                Francisella tularensis (related to plague bacteria)

      Reservoir:            Wild animals (rabbits, muskrats, squirrels), this disease is sometimes known as "rabbit fever"

      Transmission:      Bite of deer flies or wood ticks, handling or ingestion of infected animals

      Symptoms:         Typically: swollen lymph nodes, gastroenteritis, untreated, it can be fatal    
                                                                     

  3. Colorado tick fever
                                                                    
      Agent:                Colorado tick fever virus                      

      Reservoir:            Small animals (squirrels, chipmunks, porcupine)

      Transmission:     Infected ticks:  Dermacentor andersoni

      Symptoms:         Similar to Dengue fever (joint and muscle pain)                      
                                                                      

  4. Q fever                                                           
                                                                        
      Agent:                Coxiella burneti (rickettsia)                  

      Reservoir:            Ticks, various wild and domestic animals       

      Transmission:     Raw milk from infected cows, or direct contact 

      Symptoms:         Typically: chills, headache                    
                                                                      

  5. Relapsing fever
 
      Agent:                Borrelia recurrentis (spirochete)              

      Reservoir:            Louse-borne: human 
                                Tick-borne: rodents       

      Transmission:     Lice or tick bites                             

      Symptoms:         Gets its name from a fever that disappears and reappears, fever also 
                                                                    
B. Mite-borne                                             
                                                                   
   6. Scrub typhus (also known as mite-borne typhus)
                                                                      
      Agent:                Rickettsia tsutsugamushi

      Reservoir:            Infected larval mites (chiggers), wild rodents            

      Transmission:     Mite bites                                     

      Symptoms:         Skin ulcer at site of bite, maculopapular rash, headache 
                                                                        
   7. Scabies  (sarcoptic itch, acariases)                              

      Agent:                Sarcoptes scabiei (a mite)                     

      Reservoir:            Humans                                         

      Transmission:     Skin to skin, mites can burrow into skin in < 3 minutes  

      Symptoms:         Itching, lesions 


Selected Zoonoses

1. Zoonoses:        diseases and infections transmitted between vertebrate animals and humans

2. Plague:

   Agent:           	Yersinia pestis                                

   Reservoir:       	Wild rodents and infected fleas (especially squirrels)               

   Transmission:    	Bubonic plague is spread by flea bite (especially Xenopsylla cheopis)
		Pneumonic plague is spread person to person (respiratory route)       

   Symptoms:        	Swollen lymph nodes, fever, pneumonia 


3. Murine typhus fever (also called endemic typhus or flea-borne typhus):

   Agent:           	Mainly Rickettsia typhi                         

   Reservoir:       	Rodents, fleas                       

   Transmission:    	Bite or feces of rat flea (Xenopsylla cheopis)  

   Symptoms:        	Headache, chills, fever with low case fatality rate                         

4. Leptospirosis: 

   Agent:           	Leptospira interrogans (a spirochete)                                 

   Reservoir:       	Farm animals and pets; usually rats and other rodents                  

   Transmission:    	Contact of skin with water, soil or vegetation contamination by urine 

   Symptoms:        	May be asymptomatic, fever, headache, chills, malaise, vomiting     

5. Psittacosis: found worldwide but very often unrecognized 

   Agent:           	Chlamydia psittaci

   Reservoir:       	Birds (pigeons, parrots, parakeets, turkeys, ducks)                           

   Transmission:    	Airborne (inhaling dried droppings), person to person is rare, incubation 4-15 days (usually about 10 days)

   Symptoms:        	Varies (fever, headache, chills, sometimes cough)  

6. Rabies:   

   Agent:           	Rabies virus                    

   Reservoir:       	1. skunks           2. bats and raccoons       
                    	3. foxes              4. dogs, cats, cattle 

   Transmission:    	Mainly animal bites, or licks on wounds; rarely: scratches, airborne, person to person 

   Symptoms:        Incubation period: 2-8 weeks; fever, paralysis; untreated, almost always fatal