Difference between revisions of "Leishmania"

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{{OpenPagesTop}}
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{{review}}
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Causes: '''''Leishmaniasis'''''
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{{Taxobox
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{{toplink
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|name =''Leishmania spp.''             
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|linkpage =Parasites
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|kingdom =Eukaryota           
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|linktext =PARASITES
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|sub-kingdom =      
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|pagetype=Bugs
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|phylum =Euglenozoa           
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|sublink1=Protozoa
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|super-class =      
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|subtext1=PROTOZOA
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|class =Kinetoplastea             
 
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|sub-class =         
 
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|super-order =       
 
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|order =Trypanosomatida             
 
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|sub-order =         
 
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|super-family =     
 
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|family =Trypanosomatidae           
 
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|sub-family =       
 
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|genus =Leishmania             
 
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|species =''L. infantum'', ''L. donovani'', ''L.chagasi''           
 
 
}}
 
}}
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==Overview==
+
<br>
 +
==''Leishmania''==
 
[[Image:Leishmania Life Cycle.jpg|thumb|right|150px|Leishmania Life Cycle - Wikimedia Commons]]
 
[[Image:Leishmania Life Cycle.jpg|thumb|right|150px|Leishmania Life Cycle - Wikimedia Commons]]
 
[[Image:Leishmania donovani.jpg|thumb|right|150px|''Leishmania donovani'' in bone marrow cell - Dr. L.L. Moore, Jr.]]
 
[[Image:Leishmania donovani.jpg|thumb|right|150px|''Leishmania donovani'' in bone marrow cell - Dr. L.L. Moore, Jr.]]
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[[Image:Leishmania tropica.jpg|right|thumb|150px|''L. tropica'' <p> Yutaka TsutsumiWikiMedia Commons]]
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[[Image:Leishmania tropica.jpg|right|thumb|150px|''L. tropica'' - Yutaka Tsutsumi, M.D., Professor, Department of Pathology, Fujita Health University School of Medicine]]
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''Leishmania spp.'' are intracellular parasites of [[Macrophage|macrophages]] from the same family as ''[[Trypanosoma]] spp.''. These organisms parasitise human, dogs and wild animals throughout southern Europe, Africa, Asia and South America. The infection is transmitted by [[Psychodidae|sandflies]]. Infection can cause both cutaneous and visceral disease. Clinical disease cause by ''Leishmania'' is termed Leishmaniasis. Three types of ''Leishmania spp.'' are described;
+
*''Leishmania'' spp. are intracellular parasites of [[Macrophage|macrophages]]
−
# '''Hypopylaria''' - found in lizards that ingest the sandfly intermediate host. Development occurs in the hindgut of the fly.
+
 
−
# '''Peripylaria''' - found in mammals and lizards, development occurs in the fore- and hindgut of the fly.
+
*Are closely related to ''Trypanosoma'' spp.
−
# '''Suprapylaria''' - found only in mammals transmitted by the bite of a sandfly, development occurs in the fore- and midgut of the fly.
+
 
 +
*Cause diseases in humans, dogs and wild animals
 +
 
 +
*Present in southern Europe, Africa, Asia and south America
 +
 
 +
*Can cause both cutaneous and visceral diseases
 +
 
 +
'''Recognition'''
 +
*Ovoid shaped
 +
 
 +
*Possesses a rod-shaped kinetoplast
 +
 
 +
*Has a rudimentary flagellum which does not project beyond the cell margin
 +
 
 +
*After the amastigote has transformed into a promastigote inside the [[Biting Flies#Psychodidae|sand fly]], the kinetoplast is situated in the posterior of the body
  
−
==Recognition==
+
'''Life Cycle'''
−
''Leishmania spp.'' are ovoid shaped parasites containing a rod shaped 'kinetoplast'. The kinetoplast is associated with a rudimentary flagellum that does not extened beyond the cell margin. The position of the kinetoplast changes as the parasite changes between life stages. Once ingested by a sand fly the parasite takes the promastigote form and the kinetoplast moves to the posterior of the cell.
+
*Transmitted by blood sucking [[Psychodidae|sand flies]]
 +
**''Phlebotomus'' spp. in the Old World
 +
**''Lutzomyia'' spp. in the New World
  
−
==Life Cycle==
+
*The amastigote (morphological form) is found in vertebrate [[Macrophage|macrophages]]
−
The life cycle of ''Leishamania spp.'' requires transmission between mammalian (and occasionally reptile) hosts by a blood sucking fly. The [[Psychodidae|sand flies]] is the intermediate host, in the Old World the flies are of the genus ''Phlebotomus'' and in the New World they are of the genus ''Lutzomyia''.
 
  
−
The promastigote form which lacks a flagella is found in the vertebrate hosts [[Macrophage|macrophages]]. The amistgote is ingested by the sand fly whilst it feeds on the host, once ingested the ''Leishamnia'' will transform into the flagellated promastigote form in the insect gut. Replication by binary fission occurs in the insects gut followed by migration to the proboscis of the insect. The presence of ''Leishamnia'' in the insects proboscis allows inoculation of the next host on which the fly feeds with the ''Leishmania'' parasite. Crushing the sand fly on the skin of a mammal can allow percutaneous transmission.
+
*Ingested by [[Psychodidae|sand fly]] during feeding
 +
**Transforms in [[Insecta|insect]] gut
  
−
Once inside the vertebrate host the ''Leishmania'' will invade the hosts [[Macrophage|macrophages]] and having done this revert to the amastigote form.
+
*Multiplies and migrates to [[Insecta|insect]] proboscis
 +
**Inoculated during feeding
 +
**Can be transmitted percutaneously if [[Psychodidae|sand fly]] crushed on skin
  
−
==Pathogenesis==
+
*Invades [[Macrophage|macrophages]] and reverts to amastigote
−
Infection with ''Leishmania'' can produce either cutaneous or visceral disease as the infected macrophages proliferate in foci. The cutaneous form of the disease produces areas of ulceration on the pinnae of the [[Ear - Anatomy & Physiology|ears]], eyelids or on the [[Lips|lips]]. These ulcerations can also be seen between the digits of the dogs paw. This is a parasitic infection of the [[Protozoal Dermatosis|skin]]. The visceral form causes a chronic wasting condition where generalised excema can be seen. Hair is lost from around the eyes giving the animal a 'spectacled' appearance. These symptoms are accompanied by an intermittent fever and some generalized lymphadenopathy.
 
  
−
There is a very long incubation period from infection to pathology, which can take years and therefore many infected dogs either never become symptomatic or remain so for a long period of time. Even once an animal has been treated for leishmaniasis it is not uncommon for clinical symptoms to recur after a lengthy period of remission.
+
*Multiplies by binary fission
  
−
==Epidemiology==
+
'''Pathogenesis'''
−
The spread of the disease relies on the presence of the [[Psychodidae|sand fly]] as a vector. Therfore the regions in which it is found commonly are those in which conditions are suitable for the flies such as the Mediteranean coast, southern Europe as well as in central America and northern Africa. As these flies are very common in these regions, controlling their numbers has limited success, however due to control of [[Culicidae|mosquitos]] to prevent the spread of malaria, the number of sand flies has also been reduced and a reduction in the number of cases of leishmania has been noted. Although this parasite is of primary veterinary importance in dogs, large reservoirs exist in wild animals and stray dogs. This reservoir is easily accessed by the sand fly vector and compounds the issue of controlling the spread of the disease.
+
*Infection of vertebrate host
 +
**Produces foci of proliferating ''Leishmania''-infected [[Macrophage|macrophages]] in skin ('''cutaneous''') or internal organs ('''visceral''')
  
−
Although the UK is not home to any species of sand fly, leishmaniasis is being observed more frequently in the domestic dog population. This has largely been attributed to the increase in the number of animals that travel to areas of Europe and north Africa where the disease is endemic. These animals often acquire the disease whilst abroad but may not show clinical signs until they have been back in the UK for a considerable length of time. There has however been some evidence to show that close contact between dogs can spread the disease, though this method of transmission is much less common.
+
*Very long incubation period
 +
**Months to years
  
−
==Diagnosis==
+
*Many infected dogs are asymptomatic
−
Definitive diagnosis of Leishmaniasis requires combining observation of the clinical signs and the demonstration of ''Leishmania'' organisms in the animal. In the cutaneous disease this may be done by microscopic analysis of skin scrapings from the animals. For diagnosis of the visceral disease samples of joint fluid, [[Lymph Nodes - Anatomy & Physiology|lymph node]] or  [[Bone Marrow - Anatomy & Physiology|bone marrow]] biopsies may all contain macrophages that have been infected by the organisms.
 
  
−
Cytological examination of fine needle aspirates should show evidence of [[Lymph Node Abnormalities|reactive hyperplasia]] in the lymph nodes, with increased numbers of lymphoblasts and [[B cell differentiation|plasma cells]].  [[Lymph Node Abnormalities|Reactive hyperplasia]] of [[B cell differentiation|plasma cells]] is especially common in Leishmaniasis cases as it causes chronic antigen stimulation. [[B cell differentiation|Mott cells]], which are [[B cell differentiation|plasma cells]] containing vesicles of accumulated [[Immunoglobulins - Overview|immunoglobulins]] (Russell bodies)  may also be evident. They are also the result of a chronic disease process, such as Leishmaniasis.
+
*Cutaneous form
−
As mentioned above, the parasite itself can be identified cytologically within [[Macrophage|macrophages]] to confirm disease.
+
**Produces areas of ulceration on pinnae of [[Ear - Anatomy & Physiology|ears]], eyelids or on the [[Lips - Anatomy & Physiology|lips]]
  
−
==Treatment and Control==
+
*Visceral form causes chronic wasting condition
−
Control of ''Leishmania'' is difficult due to the large environmental pool and the sand flies that transmit the disease. One method is to prevent the sand flies from biting dogs by using collars impregnated with [[Ectoparasiticides|insecticides]] or repellents. These have a limited effect and do not guarantee the safety of the animal. Destruction of infected and stray dogs will decrease the pool from which sand flies may obtain the parasite but this is often morally difficult and due to the infection of wildlife does not stop spread completely.
+
**Generalised eczema
 +
***Loss of hair around eyes producing 'spectacle' effect
 +
**Intermittent fever
 +
**Generalised lymphadenopathy
  
−
Chemotherapy can be used to treat dogs with leishmaniasis; however this will not eliminate the infection completely. It may appear to resolve the infection, but it is not uncommon for clinical sign to return later in the dog's life. It is important to factor in the risks involved with chemotherapy, such as suppression of the immune system, and the expense of prolonged treatment.
+
*Long periods of remission followed by recurrence of clinical signs is not uncommon in infections
  
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{{Learning
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*Involved in [[Parasitic skin infections - Pathology#Protozoa|skin infections]]
−
|Vetstream = [https://www.vetstream.com/canis/Content/Disease/dis00998.asp Canine leishmaniosis]<br>[https://www.vetstream.com/canis/Content/Freeform/fre00654.asp PET passport travel scheme]
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|flashcards = [[Protozoa_Flashcards#Tropical_Protozoa|Tropical Protozoa Flashcards]]
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'''Epidemiology'''
−
[[Cytology Q&A 08]]
+
*Disease dependent on [[Psychodidae|sand fly]] vectors
−
|full text = [http://www.cabi.org/cabdirect/FullTextPDF/2005/20053201552.pdf ''' Canine visceral leishmaniasis.''' Gaskin, A.; Seward, R. L.; Knight, D. H.; American Heartworm Society, Batavia, USA, Recent advances in heartworm disease: Symposium 01, San Antonio, Texas, USA, 20-22 April, 2001, 2001, pp 63-65, 35 ref.]
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**E.g. Common in dogs around the Mediterranean coast, foci around southern Europe and around Madrid
−
}}
+
 
 +
*Reservoirs of infection
 +
**E.g. Wild animals such as rodents and stray dogs
 +
 
 +
*Mechanisms of transmission
 +
**[[Psychodidae|sand fly]] bite
 +
**Rarely through direct contact
 +
 
 +
*Leishmaniasis in British dogs
 +
**Susceptible to infection if exposed whilst abroad in endemic areas as have no immunity
 +
**No [[Psychodidae|sand flies]] in Britain but dogs have become infected whilst in contact with infected imported animals
 +
 
 +
'''Diagnosis'''
 +
*Demonstrate ''Leishmania'' organisms
 +
**In skin scraping or smears
 +
**In joint fluid, [[Lymph Nodes - Anatomy & Physiology|lymph node]] or [[Bone Marrow - Anatomy & Physiology|bone marrow]] biopsies
 +
 
 +
'''Treatment and Control'''
 +
*Chemotherapy
 +
**Prolonged treatment, expensive, suppresses infection
 +
**Does not cure infection
 +
 
 +
*Prevent [[Psychodidae|sand flies]] biting
 +
**Collars, sprays containing [[Ectoparasiticides|insecticide]] with repellent effect
 +
 
 +
*Destruction of infected and stray dogs
 +
**[[Psychodidae|Sand flies]] biting infected dogs may spread the disease to other dogs, humans and wildlife
 +
**There is a slight possibility of transmission to humans by direct contact
 +
 
 +
==''Trypanosoma''==
 +
[[Image:Trypanosoma.jpg|thumb|right|150px|''Trypanosoma cruzi'' - CDC/Dr. Myron G. Schultz]]
 +
[[Image:T.cruzi in monkey heart.jpg|thumb|right|150px|''T. cruzi'' in monkey heart - Dr. L.L. Moore, Jr.]]
 +
[[Image:T.cruzi Life cycle.jpg|thumb|right|150px|''T. cruzi'' Life Cycle Diagram - Wikimedia Commons]]
 +
[[Image:Triatoma infestans.jpg|thumb|right|150px|''Triatoma infestans'' the Kissing bug - WHO Wikimedia Commons]]
 +
[[Image:Chagas endemic zones 2005.jpg|thumb|right|150px|Chagas endemic zones 2005 - Wikimedia Commons]]
 +
[[Image:Ndama.jpg|thumb|right|150px|N'dama - Trypanotolerant West African Bos taurus - Wikimedia Commons]]
 +
*Protozoal parasites found in the blood and tissues of vertebrates
 +
 
 +
*Worldwide distribution
 +
 
 +
*Causes sleeping sickness in humans
 +
 
 +
*Particularly seen in sub-Saharan Africa
 +
**Affects cattle production
 +
**Causes Nagana (Wasting disease)
 +
 
 +
*Divided into two groups depending on the mode of development in the insect vector
 +
**'''Salivarian'''
 +
***Multiply in the foregut and proboscis
 +
***Transmitted via inoculation during feeding
 +
***Transmitted by [[Glossinidae|''Tsetse'' flies]]
 +
***Also known as '''anterior station development'''
 +
**'''Stercorarian'''
 +
***Multiply in the hindgut
 +
***Infective form migrates to the [[Rectum - Anatomy & Physiology|rectum]]
 +
***Transmitted via contamination of wounds with insect faeces
 +
***Also known as '''posterior station development'''
 +
 
 +
*All ''Trypansomes'' except for ''T. equiperdum'' have arthropod vectors
 +
**''T. equiperdum'' is a venereally transmitted disease
 +
 
 +
*'''Non-cyclical''' transmission can also occur
 +
**Mechanical transmission
 +
**Transferred by interrupted feeding from one host to another
 +
**Usually transmitted by [[Biting Flies|biting flies]], e.g. [[Tabanidae|''Tabanidae'']] and [[Stomoxys calcitrans|''Stomoxys'']]
 +
 
 +
'''Recognition'''
 +
*Elongated, spindle shaped protozoa
 +
 
 +
*Between 8 and 39 μm in length
 +
 
 +
*Flagellate
 +
**Flagellum runs the length of the body attached to the pellicle which forms an undulating membrane
 +
 
 +
*Kinetoplast present which contains the DNA of the single mitochondrion
 +
 
 +
'''Life Cycle'''
 +
*Undergo morphological transformations in intermediate host before becoming infective for the next host
 +
 
 +
*Blood-sucking [[Biting Flies|flies]] ingest trypanosomes whilst taking a blood meal from an infected animal
 +
**Trypanosomes multiply first in the gut of the [[Biting Flies|fly]]
 +
 
 +
*Salivarian trypanosomes are transmitted by [[Glossinidae|Tsetse flies]]
 +
**Trypanosomes pass forward to the salivary glands where they transform into the infective stage
 +
**Inoculated with saliva when [[Glossinidae|Tsetse fly]] next feeds on a host
 +
 
 +
*Stercorarian trypanosomes are transmitted by triatomid bugs, [[Tabanidae|tabanids]] and [[Biting Flies#Melophagus spp.|keds]]
 +
**Trypanosomes pass back to the rectum
 +
**Next host is infected when skin wounds are contaminated with infected [[Insecta|insect]] faeces
 +
 
 +
'''Pathogenesis'''
 +
*Salivarian
 +
**Causes wasting disease in cattle (nagana)
 +
**Sleeping sickness in humans
 +
 
 +
*Stercorarian
 +
**''T. cruzi'' most important in veterinary medicine
 +
***Occurs in South America
 +
***Infects armadillos, possums and humans
 +
***Causes Chagas' Disease
 +
**Transmitted by a triatomid (kissing) bug
 +
**Chronic infections are often fatal causing heart failure
 +
**Non-pathogenic species are transmitted by [[Tabanidae|tabanids]] and [[Melophagus spp.|keds]]
 +
***''T. theileria'' and ''T. melophagium''
 +
 
 +
*Enlarged [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] and [[Spleen - Anatomy & Physiology|spleen]]
 +
**Causes lymphoid exhaustion
 +
**Associated with plasma cell hypertrophy and hypergammaglobulinaemia
 +
***Due to an increase in [[Immunoglobulin M - WikiBlood|IgM]]
 +
**With infections of increased duration, the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]] and [[Spleen - Anatomy & Physiology|spleen]] shrink due to exhaustion of their cellular elements
 +
 
 +
*Anaemia
 +
**Red blood cells are removed from circulation ('''haemolytic''')
 +
**Is a cardinal feature of the disease
 +
 
 +
*Degeneration and inflammation of multiple organs
 +
**E.g. Skeletal muscle, myocardium and CNS
 +
 
 +
'''Clinical Signs'''
 +
*In ruminants:
 +
**Anaemia
 +
**Enlargement of the [[Lymph Nodes - Anatomy & Physiology|lymph nodes]]
 +
**Progressive loss of body condition
 +
**Fever and appetite loss occur during parasite peaks
 +
**Chronic disease usually terminates in death of the animal if untreated
 +
**Can cause abortion, infertility and decreased growth in herds
 +
 
 +
*In horses:
 +
**Acute or chronic infections of ''T. brucei''
 +
**Oedema of the limbs and genitalia
 +
 
 +
*In pigs:
 +
**''T. congolense'' infections are mild or chronic
 +
**''T. simiae'' infections are hyperacute usually leading to death from pyrexia in a few days
 +
 
 +
*In dogs and cats:
 +
**''T. brucei'' and ''T. congolese''
 +
**Acute infections
 +
**Fever, anaemia, myocarditis, corneal opacity
 +
**Occasionally neurological signs present, such as increased aggression, ataxia and convulsions
 +
 
 +
*In donkeys:
 +
**''T. brucei'' in [[Protozoal Skin Infections - Donkey|skin infections]]
 +
 
 +
'''Epidemiology'''
 +
*Vector distribution
 +
**[[Glossinidae|Tsetse flies]] found in riverine, savannah and forest habitats
 +
**Up to 20% [[Biting Flies|flies]] infected
 +
**[[Biting Flies|Flies]] infected for life
 +
 
 +
*Parasite virulence
 +
**Some parasitaemic animals survive for long periods of time
 +
***E.g. ''T. brucei'' and ''T. congolense''
 +
***Increases the opportunity for infection of [[Biting Flies|flies]]
 +
**Some trypanosomes kill their host in 1-2 weeks
 +
***E.g. ''T. vivax''
 +
***Decreases the chances of [[Biting Flies|fly]] infection
 +
**Trypanosomes avoid host immune defences by altering glycoprotein coat (surface antigen) before host [[Immunoglobulins - WikiBlood|antibody]] response
 +
***'''Antigenic variation''' can occur many times over several months causes relapsing parasitaemia
 +
 
 +
*Host response
 +
**Trypanotolerant wild animals remain parasitaemic for prolonged periods without showing clinical signs of disease
 +
***Cause lasting reservoirs of infection
 +
**Most domestic livestock are susceptible to trypanosomosis
 +
**Some local breeds of sheep, goats and cattle are trypanotolerant
 +
***E.g. ''Bos indicus''
 +
 
 +
'''Diagnosis'''
 +
*Demonstrate trypanosomes in blood
 +
**Giemsa stained smears
 +
**Fresh blood films
 +
***Motile trypanosomes
 +
**Haematocrit tube
 +
***Motile trypanosomes at the plasma/buffy coat interface
 +
 
 +
'''Control'''
 +
*[[Glossinidae|Tsetse fly]] control
 +
**Spraying and trapping
 +
 
 +
*Prophylactic drug treatment
 +
**Change drug group periodically to decrease the chances of resistance occurring
 +
**May lead to protective immunity but livestock will still be susceptible to heterologous challenges
 +
 
 +
*Barrier fences and buffer zones
 +
**Separate livestock and wild animals
 +
 
 +
*Trypanotolerant livestock
  
 +
'''Other trypanosomes'''
 +
*Mechanically transmitted by [[Biting Flies|biting flies]]
 +
**E.g. Surra affecting horses and camels in North Africa, Asia and South America
 +
**''T. equinum'' in South America
 +
**''T. evansi'' in Asia
  
−
{{review}}
+
*Venereally transmitted
 +
**E.g. Dourine
 +
***Transmitted by ''T. equiperdum''
 +
***Causes genital and abdominal oedema, emaciation and CNS signs
 +
***Affects horses and donkeys in Africa, Asia, Central and South America
  
−
{{OpenPages}}
+
*Non-pathogenic species occur in the UK
 +
**In sheep caused by ''T. melophagium''
 +
**In cattle caused by ''T. theileri''
  
−
[[Category:Tropical Protozoa]]
+
==[[Protozoa Flashcards - Wikibugs#Tropical Protozoa|Tropical Protozoa Flashcards]]==
−
[[Category:Dermatological Diseases - Dog]]
 
−
[[Category:Expert Review]]
 

Revision as of 15:24, 29 March 2010

 This article has been peer reviewed but is awaiting expert review. If you would like to help with this, please see more information about expert reviewing.


Infectious agents and parasitesWikiBugs Banner.png
PARASITES
PROTOZOA



Leishmania

Leishmania Life Cycle - Wikimedia Commons
Leishmania donovani in bone marrow cell - Dr. L.L. Moore, Jr.
L. tropica - Yutaka Tsutsumi, M.D., Professor, Department of Pathology, Fujita Health University School of Medicine
  • Leishmania spp. are intracellular parasites of macrophages
  • Are closely related to Trypanosoma spp.
  • Cause diseases in humans, dogs and wild animals
  • Present in southern Europe, Africa, Asia and south America
  • Can cause both cutaneous and visceral diseases

Recognition

  • Ovoid shaped
  • Possesses a rod-shaped kinetoplast
  • Has a rudimentary flagellum which does not project beyond the cell margin
  • After the amastigote has transformed into a promastigote inside the sand fly, the kinetoplast is situated in the posterior of the body

Life Cycle

  • Transmitted by blood sucking sand flies
    • Phlebotomus spp. in the Old World
    • Lutzomyia spp. in the New World
  • The amastigote (morphological form) is found in vertebrate macrophages
  • Multiplies and migrates to insect proboscis
    • Inoculated during feeding
    • Can be transmitted percutaneously if sand fly crushed on skin
  • Multiplies by binary fission

Pathogenesis

  • Infection of vertebrate host
    • Produces foci of proliferating Leishmania-infected macrophages in skin (cutaneous) or internal organs (visceral)
  • Very long incubation period
    • Months to years
  • Many infected dogs are asymptomatic
  • Cutaneous form
    • Produces areas of ulceration on pinnae of ears, eyelids or on the lips
  • Visceral form causes chronic wasting condition
    • Generalised eczema
      • Loss of hair around eyes producing 'spectacle' effect
    • Intermittent fever
    • Generalised lymphadenopathy
  • Long periods of remission followed by recurrence of clinical signs is not uncommon in infections

Epidemiology

  • Disease dependent on sand fly vectors
    • E.g. Common in dogs around the Mediterranean coast, foci around southern Europe and around Madrid
  • Reservoirs of infection
    • E.g. Wild animals such as rodents and stray dogs
  • Mechanisms of transmission
    • sand fly bite
    • Rarely through direct contact
  • Leishmaniasis in British dogs
    • Susceptible to infection if exposed whilst abroad in endemic areas as have no immunity
    • No sand flies in Britain but dogs have become infected whilst in contact with infected imported animals

Diagnosis

  • Demonstrate Leishmania organisms

Treatment and Control

  • Chemotherapy
    • Prolonged treatment, expensive, suppresses infection
    • Does not cure infection
  • Destruction of infected and stray dogs
    • Sand flies biting infected dogs may spread the disease to other dogs, humans and wildlife
    • There is a slight possibility of transmission to humans by direct contact

Trypanosoma

Trypanosoma cruzi - CDC/Dr. Myron G. Schultz
T. cruzi in monkey heart - Dr. L.L. Moore, Jr.
T. cruzi Life Cycle Diagram - Wikimedia Commons
Triatoma infestans the Kissing bug - WHO Wikimedia Commons
Chagas endemic zones 2005 - Wikimedia Commons
N'dama - Trypanotolerant West African Bos taurus - Wikimedia Commons
  • Protozoal parasites found in the blood and tissues of vertebrates
  • Worldwide distribution
  • Causes sleeping sickness in humans
  • Particularly seen in sub-Saharan Africa
    • Affects cattle production
    • Causes Nagana (Wasting disease)
  • Divided into two groups depending on the mode of development in the insect vector
    • Salivarian
      • Multiply in the foregut and proboscis
      • Transmitted via inoculation during feeding
      • Transmitted by Tsetse flies
      • Also known as anterior station development
    • Stercorarian
      • Multiply in the hindgut
      • Infective form migrates to the rectum
      • Transmitted via contamination of wounds with insect faeces
      • Also known as posterior station development
  • All Trypansomes except for T. equiperdum have arthropod vectors
    • T. equiperdum is a venereally transmitted disease
  • Non-cyclical transmission can also occur
    • Mechanical transmission
    • Transferred by interrupted feeding from one host to another
    • Usually transmitted by biting flies, e.g. Tabanidae and Stomoxys

Recognition

  • Elongated, spindle shaped protozoa
  • Between 8 and 39 μm in length
  • Flagellate
    • Flagellum runs the length of the body attached to the pellicle which forms an undulating membrane
  • Kinetoplast present which contains the DNA of the single mitochondrion

Life Cycle

  • Undergo morphological transformations in intermediate host before becoming infective for the next host
  • Blood-sucking flies ingest trypanosomes whilst taking a blood meal from an infected animal
    • Trypanosomes multiply first in the gut of the fly
  • Salivarian trypanosomes are transmitted by Tsetse flies
    • Trypanosomes pass forward to the salivary glands where they transform into the infective stage
    • Inoculated with saliva when Tsetse fly next feeds on a host
  • Stercorarian trypanosomes are transmitted by triatomid bugs, tabanids and keds
    • Trypanosomes pass back to the rectum
    • Next host is infected when skin wounds are contaminated with infected insect faeces

Pathogenesis

  • Salivarian
    • Causes wasting disease in cattle (nagana)
    • Sleeping sickness in humans
  • Stercorarian
    • T. cruzi most important in veterinary medicine
      • Occurs in South America
      • Infects armadillos, possums and humans
      • Causes Chagas' Disease
    • Transmitted by a triatomid (kissing) bug
    • Chronic infections are often fatal causing heart failure
    • Non-pathogenic species are transmitted by tabanids and keds
      • T. theileria and T. melophagium
  • Enlarged lymph nodes and spleen
    • Causes lymphoid exhaustion
    • Associated with plasma cell hypertrophy and hypergammaglobulinaemia
      • Due to an increase in IgM
    • With infections of increased duration, the lymph nodes and spleen shrink due to exhaustion of their cellular elements
  • Anaemia
    • Red blood cells are removed from circulation (haemolytic)
    • Is a cardinal feature of the disease
  • Degeneration and inflammation of multiple organs
    • E.g. Skeletal muscle, myocardium and CNS

Clinical Signs

  • In ruminants:
    • Anaemia
    • Enlargement of the lymph nodes
    • Progressive loss of body condition
    • Fever and appetite loss occur during parasite peaks
    • Chronic disease usually terminates in death of the animal if untreated
    • Can cause abortion, infertility and decreased growth in herds
  • In horses:
    • Acute or chronic infections of T. brucei
    • Oedema of the limbs and genitalia
  • In pigs:
    • T. congolense infections are mild or chronic
    • T. simiae infections are hyperacute usually leading to death from pyrexia in a few days
  • In dogs and cats:
    • T. brucei and T. congolese
    • Acute infections
    • Fever, anaemia, myocarditis, corneal opacity
    • Occasionally neurological signs present, such as increased aggression, ataxia and convulsions

Epidemiology

  • Vector distribution
  • Parasite virulence
    • Some parasitaemic animals survive for long periods of time
      • E.g. T. brucei and T. congolense
      • Increases the opportunity for infection of flies
    • Some trypanosomes kill their host in 1-2 weeks
      • E.g. T. vivax
      • Decreases the chances of fly infection
    • Trypanosomes avoid host immune defences by altering glycoprotein coat (surface antigen) before host antibody response
      • Antigenic variation can occur many times over several months causes relapsing parasitaemia
  • Host response
    • Trypanotolerant wild animals remain parasitaemic for prolonged periods without showing clinical signs of disease
      • Cause lasting reservoirs of infection
    • Most domestic livestock are susceptible to trypanosomosis
    • Some local breeds of sheep, goats and cattle are trypanotolerant
      • E.g. Bos indicus

Diagnosis

  • Demonstrate trypanosomes in blood
    • Giemsa stained smears
    • Fresh blood films
      • Motile trypanosomes
    • Haematocrit tube
      • Motile trypanosomes at the plasma/buffy coat interface

Control

  • Prophylactic drug treatment
    • Change drug group periodically to decrease the chances of resistance occurring
    • May lead to protective immunity but livestock will still be susceptible to heterologous challenges
  • Barrier fences and buffer zones
    • Separate livestock and wild animals
  • Trypanotolerant livestock

Other trypanosomes

  • Mechanically transmitted by biting flies
    • E.g. Surra affecting horses and camels in North Africa, Asia and South America
    • T. equinum in South America
    • T. evansi in Asia
  • Venereally transmitted
    • E.g. Dourine
      • Transmitted by T. equiperdum
      • Causes genital and abdominal oedema, emaciation and CNS signs
      • Affects horses and donkeys in Africa, Asia, Central and South America
  • Non-pathogenic species occur in the UK
    • In sheep caused by T. melophagium
    • In cattle caused by T. theileri

Tropical Protozoa Flashcards

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