Biology 625
ANIMAL PARASITOLOGY
Fall semester lecture note outline

Updated: 04 October 1999

1. Traditionally, the highest level at which the kinetoplastids exist as a distinct group is at the order level (order: Kinetoplastida). However, some recent classifications systems raise the group to class or subphylum level.
2. Appear to have arisen distantly from euglenoids, perhaps 1 billion years ago
3. Characteristics of the kinetoplastids
   1. with mitochondrian usually containing a large mass of DNA comprised of both mini-circles and max-circles.
   2. many species with undulating membrane associated with recurved flagellum
   3. approximately 0.5% of the thymine residues have been replaced with a novel DNA "J" base (beta-D-glucosyl-hydroxymethyluracil). This base may be involved in the general repression of transcription and/or recombination of repetitive sequences
4. The kinetoplastids are divided into 2 main groups:
   1. Bodoids (you will not be tested over this taxon)
      1. 2 flagella of unequal length (1 directed anteriorly, and the other directed posteriorly)
      2. undulating membrane absent
      3. some with kinetoplastid DNA in multiple distinct bodies or dispersed throughout mitochondrian
      4. free-living or parasitic members
      5. representative genera Bodo, Cryptobia, Rhynchomonas
   2. Trypanosomatids
      1. 1-2 flagella, typically with paraxial rod (lattice of proteins) that parallels axoneme within flagellar membrane
      2. single mitochondrian, usually extending length of body (in a few, the mitochondrian is non-functional)
      3. most with kinetoplast DNA located near kinetosome
      4. all parasitic
      5. representative genrea Blastocrithidia, Crithidia, Herpetomonas, Leptomonas, Leishmania, Sauroleishmania, Trypanosoma

Family: Trypanosomatidae

1. most heteroxenous, utilizing vertebrate and non-vertebrate hosts
2. thought to have originally been parasites in the digestive tract of insect, annelids, or gastropods (many monoxenous members in this group)
3. flagellum arises from a pocket and is surrounded by an undulating membrane
4. subpellicular microtubules spiral around body just beneath the plasma membrane
5. evidence suggests that some species may have some form of sexual reproduction within the intestinal tract of the insect vector; however, this has not been well studied.
6. Pleiomorphic (varation in body shapes) at various life-cycle stages
   1. trypomastigote (kinetoplast posterior to nucelus; undulating membrane runs length of organism)
   2. epimastigote (kinetoplast anterior to nucleus; undulating membrane running a portion of the body)
   3. promastigote (kinetoplast anterior to nucleus; no undulating membrane)
   4. amastigote (kinetoplast anterior to nucelus; no free flagellum; usually spheroid or subspheroid)

Genus Trypanosoma

1. Most members heteroxenous, or at least are transmitted paratenically by vector
2. usually, trypomastigotes (sometimes epimastigotes) in vertebrate and epimastigotes in invertebrate
3. Often divided into 2 traditional groups (although evolutionarily some are quite distinct)
   1. Salivaria (or anterior station)
      1. most species develop in anterior portion of the insect gut
      2. most transmitted by bite of an insect, or appear to be derived from trypanosomes with this type of development
      3. typical life-cycle of Trypanosoma brucei in ruminants
         1. slender, medium-sized, and stumpy trypomastigotes in blood stream of vertebrate host
         2. ingested by tsetse (Glossina spp.)
         3. only stumpy forms survive; migrate to posterior portion of mid-gut
         4. divide by longitudinal binary fission for about 10 days; in process transform into slender trypomastigotes
         5. migrate to foregut and remain for 12-20 days
         6. migrate to anteriorly; get into salivary glands
         7. transform into epimastigotes; divide several times by longitudinal binary fission
         8. transform into metacyclic trypomastigotes (small and stumpy trypomastigote without free flagellum)
         9. during feeding, metacyclic trypomastigotes injected into new host
         10. once inside vertebrate, metacyclic trypomastigotes divide and the parasites gradually become slender and elongate
         11. eventually, some trypomastigotes also become short and stumpy
      4. antigenic variation
         1. some species (i.e. T. brucei, T. gambiense, T. rhodesiense, T. vivax) are capable of changing surface glycoproteins
         2. each trypanosome has 20% of its dry weight composed of a single variable surface glycoprotein (VSG)
         3. initially, 10-15 surface antigenic types on a population of metacyclic trypomastigotes inside a tsetse
         4. enter blood, and 1 emerges as dominant type (other types at very low levels)
         5. immunity eventually eliminates dominant type, and another type emerges as dominant; this process occurs indefinately
         6. in genome, about 2,000 or more different genes encoding different VSGs. Some of these change or recombine to form new VSG types
         7. VSG genes are duplicated, and the duplicate must be near a telomere to be transcribed. In most cases, only 1 VSG gene is transcribed at a given time.
      5. pathogenesis
         1. in species undergoing antigenic variation, the glycoproteins are continually shed and are toxic. Some species cause acute disease, which include anaphylactic reactions, physiological imbalance, generalized pain, swelling of lymph nodes, weakness, cramps, shock, and death within 6 months after infection. Others can become chronic, with trypomastigotes invading CNS. This can involve apathy, muscle tremors, long term neurological problems that involve paralysis and convulsions, coma, and eventually death. Sleeping sickness in animals is termed nagana.
         2. Dourine is caused by T. equiperdum and progresses from a severe venereal disease into gradual paralysis and death in equids.
      6. representative species
         1. Trypanosoma brucei (widely distributed in tropical Africa; vertebrate host ruminants,although equids, swine, etc can also be infected; vector tsetse flies; disease in animals termed nagana)
         2. Trypanosoma congolense (South Africa; infects large mammals; vectors tsetse flies)
         3. Trypanosoma equinum (South America; horses only; no kinetoplast; transmitted mechanically by biting flies; thought to be derived from T. evansi)
         4. Trypanosoma equiperdum (Africa, Asia, portions of Europe, Mexico; transmitted directly during coitus; thought to have originated from T. brucei; fatal disease termed dourine)
         5. Trypanosoma evansi (Northern Africa, Asia, Europe, Central and South America; in many species of large mammals; transmitted mechanically in mouthparts of dipterans and even vampire bats; highly pathogenic in horses, dogs, and elephants; original host thought to be camels; disease termed surra or murrina)
         6. Trypanosoma gambiense (Central and West central Africa; humans the main vertebrate host; vectors tsetse flies)
         7. Trypanosoma rhodesiense (Central and East central Africa; humans and native game animals suitable vertebrate hosts; vectors tsetse flies)
         8. Trypanosoma vivax (Tropical Africa; introduced into South America; large mammals as hosts; vectors tsetse flies in Africa and mechanically by tabanids in the Western hemisphere)
   2. Stercoraria
      1. most develop in hingut of insect
      2. most transmitted in feces of insect
      3. life-cycle of Trypanosoma cruzi
         1. Trypomastigotes in blood
         2. ingested by reduviids
         3. migrate to posterior portion of midgut
         4. divide by longitudinal binary fission as epimastigotes
         5. 8-10 days later, migrate to rectum and transform into metacyclic trypomastigotes
         6. two routes of infection
            1. during feeding, bug defecates to clear gut and parasites deposited on skin near bite; rubbed into wound by victim
            2. infected bug ingested by vertebrate
         7. binds to fibronectin receptors of phagocytic cells; engulfed, especially those of reticulo-endothelial system initially
         8. transform into amastigotes
         9. divide by binary fission, eventually destroying cell
         10. cycle continues and disseminates throughout body as new cells engulf amastigotes
         11. occasionally transformation in to trypomastigotes, which circulate in blood
         12. Chaga's disease has been found in Chilean and Peruvian mummies dated to 9,000 BP (2004, PNAS 101: 2034-2039)
      4. pathogenesis
         1. local acute inflammation at bite site (chagoma); if this occurs near eye and swelling of eyelid area, termed Romana's sign
         2. dissemination of parasites throughout body, resulting in destruction of parasitized cell
         3. gradual degeneration of tissues throughout body, the most severe of which are muscle cells which cannot be replaced
         4. edema, chills, fever, muscle pain and weakness, megaesophagus, megacolon, heart failure, death
         5. the disease manifestations of this parasite are collectively termed "Chagas' disease"
      5. representative species
         1. Trypanosoma cervi (may be cosmopolitan; in cervids; vectors tabanids; non-pathogenic)
         2. Trypanosoma cruzi (North, Central and South America; in many medium-size mammals and humans; vectors reduviids; can be fatal)
         3. Trypanosoma kansasensis (North America east of the rockies; in woodrats; vectors fleas; non-pathogenic)
         4. Trypanosoma lewisi (Cosmopolitan; in old world rats; vectors are fleas where the parasite is ingested along with the flea or its feces; non-pathogenic)
         5. Trypanosoma rangeli (Northen South America and Central America; in primates, xenarthra, and opossums; vectors reduviids; kinetoplast tiny; non-pathogenic)
         6. Trypanosoma musculi (Cosmopolitan; in old world mice; vectors are fleas; non-pathogenic)
         7. Trypanosoma peromysci (North America; in Peromyscus spp.; vectors fleas; non-pathogenic)
         8. Trypanosoma theileri (Cosmopolitan; in cattle; vectors tabanids; non-pathogenic)

Genus Leishmania

1. heteroxenous
2. amastigote (Leishman-Donovan body) in vertebrate; promastigotes in invertebrate
3. vectors sandflies
4. typical life-cycle
   1. amastigotes in tissues and fluids in dermis
   2. sandfly sucks blood and ingests amastigotes
   3. within midgut, amastigotes transform into promastigotes and divide by longitudinal binary fission
   4. move up to esophagus and amass
   5. when sandfly takes another blood meal, clogged esophagus is cleared by arthropod pumping action effectively injecting some parasites into wound
   6. promastigotes ingested by macrophages and other phagocytic cells
   7. transform into asmastigotes
   8. binary fission, destroying cell in process
5. pathogenesis
   1. each species, or complex of species, has a different pathology. Some remain in dermis, some become muco-cutaneous, whereas others become visceral
   2. erosion of tissue due to cellular destruction, not only by parasite but especially by host immune response
6. Classification of the genus Leishmania
   1. subgenus Leishmania
      1. development in sandfly in midgut and foregut (i.e. Phlebotomus spp. and Sergentomyia spp. in the Old World; Lutzomyia spp., Brumptomyia spp., and Warileya spp. in the New World)
      2. both Old World and New World species
      3. representative species in mammals (about 25 named species to date)
         1. Leishmania donovani complex (New and Old World; visceral leishmaniasis)
            1. Leishmania archibaldi (Portions of Africa; in humans, some rodents, some carnivores; visceral leishmaniasis)
            2. Leishmania chagasi (South and Central America, perhaps entering canids in North America; in canids and humans, perhaps some rats and opossum; causes severe viscercal leishmaniasis)
            3. Leishmania donovani (Portions of Africa, India, east Asia; in humans, perhaps canids, primates, equids, some rodents; visceral leishmaniasis)
            4. Leishmania infantum (India, Mediterranean region, Asia, middle east, portions of Europe; in humans, dogs, and perhaps rodents; visceral leishmaniasis)
         2. Leishmania hertigi complex (all New World)
            1. Leishmania deanei (Brazil; tree-porcupines; cutaneous)
            2. Leishmania hertigi (Panama and Costa Rica; tree porcupines; cutaneous)
         3. Leishmania mexicana complex (all New World)
            1. Leishmania amazonensis (South America; rodents, marsupials, fox; single sore cutaneous leishmaniasis)
            2. Leishmania aristidesi (Panama; rodents and marsupials; cutaneous)
            3. Leishmania enriettii (Brazil; guinea pigs only; tumor-like lesions on ears)
            4. Leishmania forattinii (Brazil; in opossum and rodents; skin lesions and have also been isolated from the liver)
            5. Leishmania garnhami (Andes; humans and opossum; cutaneous)
            6. Leishmania mexicana (North and Central America, perhaps South America; rodents and humans; deep cutaneous leishmaniasis with severe lesions on ear being common)
            7. Leishmania pifanoi (Venezuela; humans known hosts and perhaps rodents; deep cutaneous leishmaniasis)
            8. Leishmania venezuelensis (Venezuela; humans, equids, felids; single and multiple cutaneous ulcers, sometimes disseminating)
         4. Leishmania tropica complex (all Old World)
            1. Leishmania aethiopica (Ethiopia and Kenya; in hyrax, giant rat, humans; highland cutaneous leishmaniasis)
            2. Leishmania gerbili (South Mongolia; gerbils)
            3. Leishmania major (Portions of Africa, middle east, Asia, India, southern Russia; humans, rodents, mustelids, hedgehogs, rabbits; wet cutaneous lesions)
            4. Leishmania tropica (Europe, North Africa, middle East, South Russia, India; in canids and humans, perhaps some rodents; dry cutaneous lesions)
   2. subgenus Viannia
      1. development in sandfly in hindgut, followed by migration to the midgut and foregut
      2. all species Neotropical
      3. representative species all in the Leishmania braziliensis complex
         1. Leishmania braziliensis (Central and South America; in humans, rodents, canids, felids, equids; cutaneous and mucocutaneous lesions)
         2. Leishmania colombiensis (Colombia, Panama, and Venezuela; probably other regional countries; in humans, and sloths; multiple ulcerating skin lesions)
         3. Leishmania equatorensis (Nicaragua; only known from humans; cutaneous skin lesions)
         4. Leishmania guyanensis (several South American countries; in humans, xenarthra, rodents; cutaneous and sometimes multiple cutaneous ulcers)
         5. Leishmania lainsoni (Brazil; humans and rodents; single ulcer cutaneous leishmaniasis)
         6. Leishmania naiffi (Brazil and French Guyana; in humans, 9-banded armadillo; single, small cutaneous ulcers)
         7. Leishmania panamensis (Panama; in humans, xenarthra, procyonids, primates, rodents, canids; single or multiple cutaneous lesions)
         8. Leishmania peruviana (Peru; in canids; simple cutaneous leishmaniasis, often on face)
         9. Leishmania shawi (Brazil; in humans, primates, xenarthra, procyonids; normally single but sometimes multiple cutaneous lesions)
         10. Leishmania braziliensis/Leishmania guyanensis hybrids known; also Leishmania braziliensis/Leishmania peruviana hybrids

Other genera and species

1. Blastocrithidia
   1. monoxenous
   2. in insects, especially in water striders
   3. usually as epimastigotes and amastigotes in intestine
2. Crithidia
   1. monoxenous
   2. in insects; intestinal
   3. choanoflagellates and amastigotes
   4. Crithidia fasciculata in various mosquitos
3. Herpetomonas
   1. monoxenous
   2. in insects
   3. amastigotes, promastigotes, opisthomastigotes, possibly epimastigotes in some
4. Leptomonas
   1. monoxenous
   2. in a variety of invertebrates
   3. promastigotes and amastigotes
   4. Leptomonas ctenocephali in hindgut of Ctenocephalides canis
5. Phytomonas
   1. heteroxenous
   2. live in sap of plants as promastigotes
   3. promastigotes and amastigotes in intestine of insects
6. Sauroleishmania (not yet fully accepted by all researchers)
   1. heteroxenous
   2. in lizards
   3. parasites predominate as promastigotes rather than amastigotes in vertebrate host

Select references:

Ashford RW, and Bettini S. 1987. Ecology and epidemiology: old world. In, The Leishmaniasis, volume 1. Peters, W and Killick-Kendrick, R. editors. Academic Press, London. pp. 365-424.

Lainson R. 1997. On Leishmania enrietti and other enigmatic Leishmania species of the neotropics. Mem Inst Oswaldo Cruz 92: 377-387.

Lainson R, and Shaw, JJ. 1987. Evolution, classification and geographical distribution. In, The Leishmaniasis, volume 1. Peters, W and Killick-Kendrick, R. editors. Academic Press, London. pp. 1-120.

Shaw JJ, and R. Lainson. 1987. Ecology and epidemiology: New World. In, The Leishmaniasis, volume 1. Peters, W and Killick-Kendrick, R. editors. Academic Press, London. pp. 291-363.