Clinical signs are abnormalities of structure or functions observed in the patient by the Veterinarian or Client and according to Hines (1988), they are conventionally graded as- severe, moderate or mild depending on speed and progress orHyperacute, acute, chronic.
Pathology, as viewed by Blood and Sudert (1988), is the structural and functional changes in tissues and organs, which result in a diseased condition and they categorize the pathology of Liver fluke intoAcute/Acute hepatic Liver fluke and Chronic/Chronic hepatic Liver fluke.
In the former the liver is swollen and badly damaged with the parenchyma being much more friable than normal and shows tracts of damaged tissues and capsules and many small perforations and subscapula haemorrhages.
The latter, on the other hand is characterized by the presence of leaf-like flukes in grossly enlarged and thickened bile duct, specifically within the desquamated epithelial cells and may be seen due to the blockage of the ducts with flukes and the bile ducks may protrude above the surfaces of the liver.
More About LIVER FLUKE
There is anaemia, emaciation and the hepatic parenchyma is extensively fibrous with dark brown hepatic lymphnodes. Ngategize et al. (1993),Njau and Schollens (1991) also categorized the pathology of Liver fluke into three(3) :-
(a) Lightly affected
- Here, a quarter of the organ is affected and only one bile duct is prominently enlarged on the visceral surface of the liver.
(b) Moderately affected
- Half of the organ is affected and 2 or more bile ducts are hyperplastic.
(c) Severely affected
-Almost the entire organ is involved, the liver is cirrhotic and triangular in outline as the right lobe is often atrophied.
Finally it has been reported that most of the notable pathological lesions during Liver fluke occur when immature flukes are migrating through the liver parenchyma (Rodriguez-Perez and Hillyer, 1995).
Clinical diagnosis as the identification/recognition of parasites and in relation to Liver fluke, it is a difficult task. (Mira and Ralph, 1994).
The Diagnosis is reviewed in two ways:-
(a) Coprological method
(b) ELISA Method
(a) Coprological Method.
Happich and Boray (1969) reported that the diagnosis of liver fluke infection has traditionally been made on the basis of faecal egg counts (through floatation/sedimentation, direct count andthe MC Master Method).Egg production in the liver can begin as early as 8 weeks after infection but most infections do not become portent until 11-12 weeks post infection (Jemli et al.,1992)
The other coprological method is liver examination which is carried out during post mortem. Post-mortem examination of the liver involves careful observations, palpation and incision after slaughtering and removal of the liver from the carcass. (Mira and Ralph, 1994).
The Enzyme - linked Immunosorbent Assay (ELISA) has been widely adopted in the serological studies of Liver fluke (Shahem et al; 1989; Fagbemi and Obarisiagbon, 1990).
The ELISA Method operates through an invitro reaction between antibody and antigen which are produced invivo and subsequently obtained from the blood (serum). An important question worthy of consideration is, how are the antigens and antibodies produced in the first place?
Dumenigo et al. (1999); Sanchez-Andrade et al. (2001) and Almazan et al. (2001) stated that during the migration of parasites through the Liver parenchyma (1-5 weeks after infection), the immature flukes released antigens (which stimulate the production of antibodies) which are detectable in the serum and once the flukes reach the bile ducts, antigenic release ends and its not present in serum-hence the demonstration of circulating antigens in sera definitely allows the early detection of immature flukes (Sanchez-Andrade et al. 2000).
This is in agreement with anearlier research findings by Leclipteux et al. (1998), who stated that the detection of circulating antigens is a very good way to confirm the presence of living parasites in the bile ducts.
Reports in the 21st Century shows that ELISA antibody tests, are reliable, with high sensitivity and specificity for example 95% and 98.2% respectively with f2 – antigen (Rechel et al. 2005), 98% and 96% respectively with ES antigen containing predominantly Cysteine Protease (Salimi-Bejestani et al. 2005).
Reichel et al. (2005) reported that the presence of liver flukes is not determined necessarily by a positive antibody serum result. This is because detectable antibodies may persist long after treatment or after the natural death of liver flukes. The implication of a positive result shows that the animal is, or has been infected by the parasite. In other words, antibodies detected in natural infection may or may not be related to an active infection.
This phenomenon enhances the need for a feasible test for the diagnosis of Liver fluke which is capable of detecting a current infection at the moment of sampling.
The feasible test as required above,according to Paz-Silva et al.(2003), is that when ever negative results of the sedimentation techniques are positive to the sELISA (Sandwich ELISA), it suggests that Juvenile flukes are migrating through the liver parenchyma but had not yet reached the bile ducts/gall bladder. Also, combination of direct ELISA and the coprological examination provides excellent knowledge about the real parasitic status of the animal because both tests demonstrate current Liver fluke.
Crowther (1988), stated that a key feature of the flexibility of ELISA is that more than one system can be used to measure the same thing. Some examples are cited:-
(i) Rodriguez-Perez and Hillyer (1995). Dumenigo et al.(1996). Espino et al. (1997); Abdel-Rahman et al.(1998); Sanchez- Andrade et al. (2001) Paz-Silva et al.(2002) have proved the suitability of the direct ELISA for a feasible and correct diagnosis of Liver fluke in Serum,
(ii) Institute Pourquier, Montpellier, France-Kits was used to assay sera for anti-Fasciola antibodies against the f2 - antigen using a commercially available indirect ELISA. Samples and controls were assayed in two (2) wells; one well coated with antigen, the other well not coated with antigen. Absorbance results from the uncoated (control) well were subtracted from the results obtained in the antigen -coated well. To correct for plate to-plate variation, results were expressed as the ratio of the mean absorbance values of the ‘sample’ to the mean absorbance value of the low ‘positive’ control sample (150HA units) provided with the diagnostic kit. The resultant ‘sample’ to ‘positive’ ratio (S/P) was expressed in percentage.
Dorchies (2006) also subscribes to the fact that ELISA detection of antibodies in blood is currently the most used assay with f2-antigen (Institute Pourquier, Montpellier, France) with a crude Excretary/Secretory (ES) antigen or with purified/Recombinant antigen - and that there are various methods used to produce the ES products.
One method is that freshly recovered Fasciola hepatica, from an infected animal, are incubated at various temperatures, in saline or buffer, for a set time. Hillyer (1998) is of the view that irrespective of the mode of recovery, ES products are the same.
(iii) Levieu et al. (1998) reported that a reliable, cheap, easy to use and very well adapted test for bovine Liver fluke is the indirect Haemagglutination test and because it does not necessitate a specific conjugate for each species, it is also applicable for Sheep, Horses and Man etc.
(iv) According to Dumenigo et al. (1999), a sensitive, specific and suitable method for the detection of Fasciola hepaticain serum is the Monoclonal antibody Based sandwich immunoassay (MAbsandwich ELISA) which is used in the diagnosis of active animal and human Liver fluke with Monoclonal antibody ES78 (Hybridome Laboratory, IPK).
NOTEDorchies (2006) states that even though the Ab- ELISA systems are the most frequently used and give accurate indications of farm or herd prevalence, they do not give individual current infection status. Ag-ELISA needs to be developed as a way of avoiding the drawbacks of the Ab-ELISA.