Understanding the Common Parasites in Livestock

The study of parasites in animals is called parasitology and it has three major categories;

a) Helminthology- This is the study of helminths or parasitic worms.

b) Entomology- This is the study of arthropods (insects) and their relationship with humans, the environment, and other organisms.

c) Protozoology- This is the study of single-celled animals (Protozoa) or animal-like protists like motile and heterotrophic.

1. Protozoa

These are single-celled organisms, for example; Trypanosome (causes Nagana in cattle), Entamoeba (causes diarrhea in animals), and Theileria (this causes theileriosis or East coast fever).

2. Helminthes

These are worms and they are of three types.

(i). Nematodes (roundworms) for example Ascaris and Haemonchus.

(ii). Cestodes (tapeworms) for example Taenia, Echinococcus

(iii). Trematodes (flukes)  for example Fasciola, and Schistosoma.

Note: All cestodes and trematodes are flatworms.

3. Arthropods

These are divided into four;

   (i). Insects for example  Musca, Glossina (tsetse fly)

  (ii). Fleas for example Echnidinophaga.

  (iii). Lice for example Haematopinus,

  (iv). Acarines; a) Ticks for example Rhipicephalus, Boophilus. b) Mites for example Sarcoptes, and Demodex.

Relationship between Protozoa, arthropods, and helminths

1. Most protozoa are transmitted by arthropods for example;

a)    Theileria is transmitted by Rhipicephalus

b)    Trypanosomes are transmitted by Glossina.

2. Some protozoa are transmitted by helminths for example; Histomcnas is transmitted by Heterekis gallinarum.

3. Many worms are transmitted by arthropods for example;

a) Filarial worms are transmitted by insects like Musca.

b) Dirofilaria is transmitted by insects.

ORGANISM ASSOCIATIONS

1) Symbiosis

It is a permanent relationship or interaction between two specifically distinct biological organisms so dependent on each other and each benefiting from another such that life apart is impossible under natural conditions.

Examples

Some protozoa found in the digestive tract of ticks and mites help to digest blood for the production of vitamin B12.

Bacteria in the root nodules of leguminous plants can also help to fix nitrogen in the soil which is essential to legumes.

Rumen microbes in the ruminants digest cellulose.

2. Commensalism

It is the long-term interaction or association between two specifically distinct organisms where one species gains benefits from the association while the other neither benefits nor is harmed.

Example;

A protozoan(histomonas) is a parasite in the caecum of birds benefits because it’s transported from one bird to another by the Heterakis gallinarum, nematode.

Another example is a bird building a nest on a tree. The tree provides shelter and protection to the bird without affecting it or harming it.

3) Mutualism

In this association, we have two distinct organisms which both benefits from the association but it is not obligatory meaning they can live apart (mutualism differs from symbiosis) for example cattle and oxpeckers.

4) Parasitism

It is an association between two specifically distinct organisms in which one lives on or within the other to earn a living. One is the host and the other is the parasite. Some of the parasites include tapeworms, fleas, and barnacles.

There are two cases of Parasitism

  (i). Parasitosis: Here one depends on the other causing injury to it. The parasites harm their hosts causing signs and lesions of the disease.

 (ii). Pasitiasis: This is an association between two organisms where one is potentially pathogenic but does not cause signs of disease.

Note: We can have parasitosis or pasitiasis depending on the following conditions;

1.  The number of organisms in the host for example those with few parasites there is no parasitosis but pasitiasis.
2. Nutritional status of the host. If the host feeds well, then it will resist the effect of those organisms.
3. Sex of the animal (males are more resistant than females).
4. Immune status of the animal for example if the animal is routinely vaccinated, it will have antibodies to fight the parasites.
5. Stress factor. When animals are stressed, they succumb to conditions like diseases, starvation, and drought.
6. Age of the animal.

KINDS OF PARASITES

a) Obligatory parasite

It is a parasite that must live a parasitic life during all or part of its life. It must depend on another organism for survival. Examples of obligatory parasites include tapeworms and Ascaris.

b) Facultative parasite

This may be parasitic or free living at will.

Examples of facultative parasites include;  Calliphorid flies (blue or green flies) their larva can live in the living tissues of animals and this situation is called myiasis.

c) Erratic (Aberrant) parasite

It is a parasite that has wandered into an organ where it does not normally live. Examples of erratic parasites include; Schistosomes (Bilharzia) which are found in mesenteric blood vessels but their eggs may be taken to other organs in the body by blood circulation.

d) Incidental parasite

It is a parasite found in a host in which it does not ordinarily live.

 Examples of accidental parasites include; Toxocara found in dogs, rat tapeworm (hymenolepis diminuta), and Ascaris lumbricoides in sheep.

CLASSIFICATION OF PARASITES

Parasites are classified according to;

1. Number of cells.

a) Single-celled (unicellular parasites). These are composed of one cell for example Protozoa (Babesia and Theileria).

b) Multi-cellular parasites. These are composed of many cells and they include Metazoa (Helmirtks, Arthropods).

2. Location on the host.

Some parasites are found inside the animals (endoparasites) for example; tapeworms.

Some parasites are found outside the animal body (ectoparasites). These are found on the skin of the animal for example mites, fleas, and ticks.

3. The length of time spent on the host.

There are permanent parasites and others are intermittent (periodic) and these visit the hosts for a short period for example; lice, fleas, and tsetse flies.

4. Number of hosts used.

Monoxenous parasite (This uses one host to complete its life cycle) for example; Ascaris (roundworm of pigs).

Heteroxenous parasite (This uses more than one host to complete its cycle) for example all tapeworms like Taenia Saginatta.

5. Host range

There are two types of host ranges of parasites namely;

Sternoxenous parasite- A parasite that has a narrow host range for example Plasmodium species.

Euryxenous parasite- is a parasite with a wide host range. It will infest a wide range of hosts for example Trichinella will infest (Goats, rats, cattle, and pigs).

TYPES OF HOSTS

(a). Definitive (final) host

Is that organism that harbors the final stage of a parasite (or the adult stage of a parasite).

Examples of the definitive host include; Man which is the final host for Taenia saginata and the pig is the final host for metastrongylus (lungworm of pig).

(b). Intermediate host

Is the organism which harbors the larval stage of a parasite and there is always the development of this parasite in the host.

Note: There are some parasites with more than one intermediate host. The earthworm is the first intermediate host for metastrongylus and pigs are the second intermediate hosts for it.

(c). Paratenic host

This harbors the immature stage of a parasite but it acquires it accidentally and there is no development because it is always encapsulated.

Note: Paratenic host is not the normal host for a parasite and this parasite should be swallowed by a correct host to continue with development.

Examples of Paratenic hosts include; Rat is a paratenic host for Toxocara so the dog will swallow these encapsulated eggs for completion of development.

(d). Reservoir Host

 This harbors infection for other animals therefore the parasite does not have any harmful effects on the host and can only affect other animals but not the host.

(v). Prime Host: It is the host where the parasite was first found.

VECTOR

A vector is any living agent that carries and transmits an infectious pathogen to another living organism.

There are two types of vectors.

1. Biological vectors
2. Mechanical vectors

Comparison between Biological vector and Mechanical vectors.

The life cycle of vectors

This refers to the series of phases through which an individual takes from its origin as a fertilized egg up to when it can reproduce itself or when sexually mature.

There are two types of life cycles

a) Direct life cycle

This is the life cycle that is completed without the involvement of the intermediate host therefore there is the involvement of only the host (definitive/ final host) for example, Ascaris suum (large roundworm of a pig) which uses the pig to complete its life cycles.

b) Indirect life cycle

There is always an involvement of an intermediate host that is to say two or more hosts are needed to complete the life cycle for example Taenia Saginatta (cattle and man).

Other terms used here include;

Prepatent period.

This is the time between the entry of the infective stage of the parasite into the host and the demonstration of the presence of that parasite within that host by laboratory methods.

Bionomics.

Is the study of an organism and its environment. This is referring to the pre-parasitic stages.

Biotic potential.

This is the capacity of an organism to have biological success and it is related to its reproductive ability for example worms can lay very many eggs within a day. It is highly prolific or has a high biotic potential.

Infestation.

This refers to the invasion by macro-organisms.

Infection.

This refers to the invasion by micro-organisms

Entry of parasites into the host

1. Direct or indirect entry. There is contact with the infected parts and specifically mites which cause mange.
2. Ingestion of the cyst. This is found in eggs that contain parasites, or even the larva of the parasite.
3. Skin penetration for example hookworms
4. Inoculation, for example, arthropods like ticks transmit parasites into the host like theileria transmitted by rhepiciphalus through its mouth parts into the host, and several protozoa are transmitted by inoculation.
5. Prenatal infection; the parasite gains entry via the placenta.
6. Trans-mammary, parasites gain entry into the suckling animal through the milk for example Toxocarariasis (this is also a roundworm of dogs).