HELMINTHOLOGY Definition: Study of parasitic worms and their relationship with their hosts Helminthos[Greek word] = Worm They belong to 4 phyla 1. Nemathelminthes 2. Acanthocephala- parasitic worms armed with a spiny rostellum 3. Annelida – The only parasitic Annelids are leeches. Earthworms act as I.H. for ascarids. 4. Platyhelminthes – Flat worms. Worms usually hermaphrodites except Schistosomes

1. Nemathelminthes

Animal forms commonly called or roundworms. Are ubiquitous and are found in freshwater, marine and terrestrial environments. Most live a parasitic life though a number are free- living

Class Nematoda Occur throughout the world in all Occur in any organ or tissue of their – majority in the G.I.T. Their body is covered by a non-cellular cuticle- shed 4 times during life cycle Cuticle is modified in different worms to perform various functions. Cuticular features are used in identifying different genera and of worms. Examples: i]– Longitudinal striations, cross striations; ii] Alae = lateral expansion of cuticle

 Cervical alae,

 longitudinal alae,

 caudal alae iii] Bursa- well developed caudal alae in males= for grasping the female during copulation Worms in Order Strongylidae are Bursate Nematodes iv] Papillae= Small cuticular projections- tactile papillae Head region= Cephalic papillae Anterior region= Cervical papillae Tail region= Caudal papillae

v]Bosses = Blister-like structures on the cuticle i.e in spp

Vulva flap – Covers the ventral genital pore= Vulva opening in Haemonchus females Digestive system= Straight tube consisting of mouth, muscular oesophagus, intestines and anus posteriorly Mouth surrounded by lips= Ascarid spp, Leaf crown/ corona radiata eg Oesophagostomum spp May be expanded = Bucal capsule Within the mouth= Teeth, cutting plates, lancets, hooks for attachment and lacerating host tissue Oesophagus= Rhabditiform oesophagus= free living Filariform oesophagus= simple club shaped= parasitic

In females – Vulva occurs on ventral side anterior to anus. In Haemonchus covered by vulva flap In Males= Spicule sheath dorsal to cloaca- contains spicules= aid in maintaining patency of vulva during copulation. In spp-- Gubernaculum on dorsal wall and Telamon on ventral wall of cloaca guide the spicules. IDENTIFICATION OF NEMATODES: Done by use of:

 Cuticular modifications

 Mouth parts plus structures within (if any)

 Male reproductive system

 Female reproductive system  Size of worms -length and width

LIFE CYCLES Need to know: 1. Parasitic stage that leaves the host i.e egg or L1 2. Stage that gets into the host[infective] = in the egg or L3 3. What happens to the stage in the host 4. Final location in body of host = Predilection site Most nematodes are either: Oviparous = lay eggs, Ovoviviparous= larvae develop in the egg inutero, until they are ready to hatch; others are Viviparous = Larvae are nourished inutero by the mother then laid as – L1 Life cycle consist of egg, 4 larval stages and adult. Each separated by a moult Developing forms are symbolized as L1, L2, L3, L4, L5 L5 = immature adult and not separated by a moult from the adult. There are 5 larval stages and 4 moults. Moults of larva take place:  Within egg before hatching= Ascaris spp  During the free existence= Haemonchus spp  Within tissue of intermediate host= Spirocerca lupi  Within tissue of definitive host= Trichinella spp. L1 and L2 = free living, L3 both free living and in the host. L4 and L5 occur in parasitic environment inside the host L3= infective stage in most nematodes. L2 infective stage in Ascaris suum Those with indirect life cycle= L1,L2, L3 occur in intermediate host while L3, L4 and L5 occur in the definitive host= Natural host will harbour the adult stage. Direct and Indirect life cycles Direct= Parasite needs only one host to complete the Life Cycle Indirect= Parasite requires an Intermediate and a Definitive host. There may be more than one intermediate host. Pre- natal infection= parasites pass from mother to foetus in uterus. The direct life cycle continues in young after birth= in dog Trans-colostral infection= Infection passed through milk usually colostrum= Toxocara vitulorum in calves In most cases egg or larva is ingested by the final host or larvae may penetrate skin of their host. In indirect life cycles, L3 are either ingested when the intermediate host is eaten or may be introduced into the body of final host when the intermediate host sucks blood eg mosquitoes sucking blood from dogs introduce microfilaria of Dirofilaria immitis

BURSATE NEMATODES- Order These lay typical strongyle eggs= elliptical in shape.

Three(3) main families 1. Commonly called hook worms. Found in the small intestines of animals and are blood suckers= causing anaemia. Heavy infection cause death. Infection is by skin penetration of L3. Eggs in faeces Bunostomum plebotomum – cattle Geigeria pachyscelis – sheep and goats caninum – dog – cat – dog, cat and wild carnivores Uncinaria stenocephala – dog, cat and fox - pig

2. Family Strongylidae Found in the large intestines of animals. They cause nodule formation[=nodular worms] condemnation of the intestines Infected intestines cannot be used for suture (surgical)materials Chabertia ovina - Sheep Oesophagostomum radiatum - Cattle Oesophagostomum columbianum - “ “ Oesophagostomum dendatum – pig Oesophagostomum quadrispinulatum - pig

3. Family :Trichostrongylidae Has many genera of importance. These include: 1.Haemonchus contortus- sheep and goats Haemonchus placei – Cattle Haemonchus longistipes – Camel Gazellostrongylus lerouxi - Gazelle These are blood sucking nematodes found in the abomasum. They cause anaemia, hypoproteinaemia (bottle jaw) and death. Haemonchus contortus is the most economically important parasite of livestock(and wild ) in Kenya. Causes mortalities in kids and lambs especially weaners

2.Nematodirus spathiger- found in small intestines of sheep. Long thin worms causing diahorrea. They lay the largest strongyle eggs which are usually rugby ball-shaped.

3. Cooperia pectinata, C. punctata, C. curticei – C. yoshidai, C. hungi- Occur in small intestines of ruminants 4. Trichostrongylus axei – Found in the abomasum and small intestines of ruminants; T. colubriformis, T. vitrinus, T. probolurus = Found in the Small intestines These are small hair-like worms that cause diahorrea. 5. Ostertagia – Occurs in the small intestines of sheep in temperate regions

Non – bursate nematodes – Order 1. Family Ascaridoidea – These are large worms found in the small intestines of animals. They have 3 well developed lips and lay thick-shelled eggs. Infection is acquired by ingestion of L2 in food or earthworm which has ingested L2. Infection is severe in young with obstruction of intestines leading to stunted growth, lowered production, pot belly. Routes of infection: = per os, pre-natal, colostral or via a paratenic host. Ascaris suum - pig Toxocara vitulorum - calves Toxocara canis, T. cati, T. leonina – cats, dogs and lions Ascaridia galli - Chicken – Horse and donkey

2. Order Family Spiruridae Adults found in lumen or wall of stomach of horses and donkeys Life cycle involves an arthropod intermediate host. Important genera: Habronema muscae Habronema megastoma= intermediate host is horse fly Habronema microstoma = intermediate host is Stomoxys calcitrans

Family Thelaziidae These are found in the conjuctival sac, lacrimal ducts and digestive tracts of and . Important Genera: rhodesii- conjuctival sac in cattle Oxyspirura mansoni – Nictitating membrane of chicken and turkey Spirocerca lupi – Found in the walls of oesophagus, stomach aorta = dog and fox. Dung act as intermediate hosts. Cause tumor lesions in oesophagus which later spread to the lungs and long bones. Ascarops strongylina- stomach of pigs= Dung beetles act as intermediate hosts. - oesophagus of cattle – crop of chicken

2. Phylum: Platyhelminthes - Classes and

They are bilaterally symmetrical The body has three layers of tissues with organs and organelles No internal body cavity

CLASS: Trematoda =[ trematodes or flukes] Morphology: Dorso-ventrally flattened, unsegmented, leaf or worm like. No body cavity and organs embedded in parenchyma. Suckers or hooks attach parasites to internal organs of the host. They have a mouth, alimentary canal but some have no anus They are hermaphrodites except Schistosomes [=unisexual]. Life cycles are indirect (Order ) or direct (Order Monogenea) Monogenea= Ectoparasites of cold blooded acquatic vertebrates Digenea = Important internal parasites of domestic animals(and also man)

Order Digenea Genera and species , F. gigantica= Liver flukes of ruminants. Liver is the main organ affected. Leaf-shaped and greyish brown. Intermediate hosts are fresh water snails, Eggs are shed in faeces and hatch in water to miracidium[infective to the snail]- Then develops through these stages: Sporocyst>rediae>cercariae>metacercariae. This is the infective stage to the definitive host which encysts on water plants.

Schistosoma = Blood flukes. Have separate sexes and are found in the portal and mesenteric veins of man and animals. Males have a Gynecophoric canal for holding the female Infective stage is cercariae which penetrate intact skin to become schistosomula. Damage caused seen in the digestive, urogenital tracts bovis. S. mattheei - animals

Male and female Schistosoma spp S. japonicum, S. haematobium, s. mansoni, S. mekongi cause bilharzia in man. Important in irrigated areas. Fresh water snails are intermediate hosts

Egg of S. mansoni

Others: and Paramphistomum microbothirium Dicrocoelium-Lancet fluke. Slender and found in pancreatic ducts of ruminants Paramphistomum-Also called Rumen or Conical flukes. Found as bodies in rumen and reticulum of ruminants. These are thick fleshy cylindrical parasites. Water snails are intermediate hosts. Adults are commensals but larval stages are parasites of the small intestines where they suck blood and may cause damage Class Cestoda [Cestodes / Tape worms]

Elongate, segmented, ribbon like and flattened dorso-ventrally. Adults occur in the small intestines of their definitive hosts. They are hermaphrodites. Individual worms have a scolex (head), neck and strobila (segments / proglottids) Scolex= attachment with holdfast structures= hooks,suckers, spines, grooves. Has rostellum at apex Neck= area of strobilation Strobila= segments with male and female reproductive organs. Gravid segments are full of fully developed embryos. Eggs passed out in faeces

General Life Cycle Indirect except a few like Hymnolepis nana Involves definitive host [DH] and intermediate host[IH] Adults in the Small Intestines(SI) of DH produce eggs- faeces- ingested by IH. Larval forms in eggs- oncospheres They travel to predilection site to become metacestode Variety of metacestodes occur eg cysticercus One or more IH or paratenic hosts may be involved DH infected by ingesting IH or its tissues with infective metacestode which develops to adult tape worm in the small intestines of DH ADAPTATIONS OF TAPEWORMS Have suckers and / or hooks on their heads for attachment to the intestinal wall of their host. Have flattened bodies that offer a large surface area for absorption of food materials across the body wall. They secrete a lot of mucus and anti-enzyme substances that protect them from the digestive action of the host’s enzymes. Each worm produces millions of eggs that remain infective for long periods of time ensuring successful transmission to the next host. They can respire anaerobically and thus are able to survive the very low oxygen concentration in the host’s gut. Have intermediate hosts that enhance the efficiency of transmission from one host to another. Classification of Cestodes 11 Orders but only 2 are of Veterinary and Medical Importance. 1. – 4 suckers on scolex 2. – have sucking grooves

Order Cyclophyllidea – many families, genera and species Veterinary and Public Health importance. General Characteritics of the Order Cyclophyllidea Scolex – 4 suckers, Rostellum present with or without hooks. Larval stages (metacestodes) “bladder worms” – Various types – Cysticercus, Strobilocercus, Coenurus, Hydatid cyst –exogenous daughter cysts formed from mother cysts. Protoscolices may detach from germinal membrane – to become hydatid sand in mother cyst. Cysticercoid- solid bodied organism

Families in Order Cyclophillidea Taeniidae, Anaplocephalidae, Dilepididae, Davaineidae, Hymnolepididae and Mesocestodidae Family Taeniidae – Main characteristics Adults in Small Intestine of man and carnivores Intermediate hosts are mammals, scolex has rostellum armed (double row of hooks). In some species, gravid segments longer than wide. Larval stages are: Coenurus, Cysticercus, Strobilocercus and Hydatids and are found in tissues and organs of the Intermediate hosts. Summary of Cestodes in family Taeniidae Larval – Results from infection with any of the following species: E. granulosus (most common), E. multilocularis, E. vogeli (Central and South America) and E. oligarthrus (cat DH in Central and South America) Adults occur in the small intestines of carnivores Metacestodes – hydatid cysts in herbivores and omnivores in any organ but usually liver and lungs Morphology – adult 2 – 7 mm, 3 proglottids which are terminal and more than half length of whole worm. Scolex has 4 suckers, rostellum armed with 2 rows of circular hooks. Life cycle – eggs passed out in faeces of DH. They are ingested by IH and oncospheres are released in the small intestines - travel thru’ portal system to liver to become hydatid cysts – others to lungs In man, they affect the long bones, brain and eyes where they form fluid filled cysts which increase in size(and may become calcified). This leads to hydatid disease Two life cycles in Kenya : >Domestic cycle – dog[DH]- ruminants[IH]0 in Turkana Note: man is a dead-end host >Sylvatic cycle – wild carnivores[DH] and wild animals – Maasai land

Potential final hosts for Echinococcus Lion (Panthera leo) Wildcats (felis libyca) Jackal (canis spp) Hunting dogs (lycaon pictus) Cape foxes (vulpes chama) Spotted hyena (crocuta crocuta) Intermediate hosts Wilderbeest (Connochaetes taurinus) Cape buffalo (Snycercus caffer) Zebra (Equus burchelli) Warthog (Phachocoerus aethiopicus) Oryx (orynx gazella)

Pathogenesis and Epidemiology of Cyclophillidea Adults are harmless to carnivores Hydatid cysts cause pathological lesions and clinical signs only in man = Hydatidosis Severity depends on; >organ affected, >number of cysts in the organ, >size of cysts Effects are those of space occupying lesions such as ascites, dysponea and digestive disturbances Cysts in bone marrow – may cause fractures Incidence of disease highest in pastoral areas due to close association of man and dogs. (NB: Role of dog as a domestic maid) Dog and man share common water sources. They may be given as bride's gift during wedding Infection spreading to urban areas due to use of infected offals

Family Anoplocephalidae Main characteristics Scolex no rostellum or hooks Proglottids are wider than long with 1 or 2 sets of genital organs Eggs have three coverings: >vitelline membrane, >albuminous coat and >chitinous membrane. Are pear-shaped with a pair of hooked projections Cystic stages are cysticercoids – in mite of the family Oribatidae . Infection acquired thru’ herbage

Genus Anoplocephala Occurs worldwide in equines and there are several spp A. magna – jejunum of horses and donkeys. When in large numbers they cause catarrhal or haemorrhagic enteritis A. perfoliata – Found in large and small intestines of horses and donkeys. Localises near ileocecal orifice Causes small dark depressed ulcerative lesions. Perforations leading to peritonitis may occur Genus Paranoplocephala- P. mamillana- Small Intestine and occasionally stomach of horse

Genus Moniezia M. expansa – Small Intestine of ruminants – up to 600 cm Eggs roughly triangular with well developed pyriform apparatus M. benedeni – Occurs in cattle Cysticercoids develop in oribatid mites. Ruminants infected by ingestion of infected mite in herbage Infection common in young up to 6 months of age. Adults – experience light infections

Family Dilepididae Main characteristics Smaller than Taeniidae and Anoplocephalidae Well defined rostellum with armed suckers Segments have 1 or 2 sets of genital organs Genus Dipylidium caninum Small intestines of carnivores and man especially. Rostellum retractable and armed with 3 or 4 rows 2 sets of genital organs, ovary and vitelline glands form a mass on either side – like a bunch of grapes Mature gravid proglottids are elongate oval in shape

Family Diphyllobothriidae Main characteristics Scolex has narrow deep muscular grooves called bothria on dorsal and ventral aspects Scolex not armed One set of genital organs Eggs are operculated like those of Trematodes

Genus latum In Small Intestine of man, dog, cat, pig, 2 – 12 meters with up to 3000 segments. When fresh, its yellowish grey with dark central markings due to presence of uterus and eggs This is used for identification Life cycle Eggs in faeces of final host- coracidium(6 hooked oncosphere with ciliated embryophore). Eaten by a Crustacea – 1st Intermediate Host – Plocercoid larval stage. The crustacea is ingested by fresh water fish – 2nd IH – plerocercoid larval stage Large fish accumulate many plerocercoids Final host infected by eating raw fish In man – where cultural habits include eating of raw or lightly “pickled” fish the condition is common Pathogenicity Causes severe macrocytic, hypochromic anaemia typical of Vitamin B12 defficiency

Diagnostic Principles in Helminthology Objective= Detect helminth parasitic diseases in an individual or a flock / herd of animals. Clinical helminthosis easy to diagnose as: >There are suggestive signs/ symptoms >Eggs of helminths can be found in large numbers in faeces >At post-mortem adult worms are found at respective predilection sites / organs Diagnosis of sub-clinical infections which are most common is difficult. Diagnostic signs: Anaemia, Diahorrea, Grazing habits, Climatic / weather changes

Diagnostic Methods 1. Faecal examination – collection, preservation[to avoid eggs hatching] Examination: >Simple direct smear >Concentration methods

 Sedimentation eg Fasciola eggs

 Floatation- Modified McMaster technique eg for Strongyle eggs Bearmann’s apparatus for recovery of lung worms and infective larvae after coproculture 2. Worm counts at post mortem 3. Biochemical tests = Plasma protein and serum enzyme levels eg

Treatment: These are chemical agents / compounds used to kill helminth parasites. Two classifications: 1. Broad spectrum – against several genera of worms 2. Narrow spectrum – limited to specific genera. Alternative control methods: NOVEL/ NON CHEMICAL METHODS

 Breeding for resistance / resilience animals

 Vaccination

 Pasture management = alternative grazing

 Biological control = earthworms, fungi, dung beetles

 Nutritional supplementation = Replace lost protein

References 1. Parasitology for Veterinarians, JR Georgi and ME George: WB Saunders and Company 2. Helminths of Wildlife: N. Chowdhury and Alonso Aquirre 3. Check list of the Helminth Parasites of African Mammals: M.C. Round (CAB) 4. Helminth, Arthropods and Protozoa of Domesticated Animals: E.J.L. Soulsby