Parasitic Flagellates and Diseases

I. Parasites: Trypanosoma, Cryptobia, Giardia and Spironucleus

Patrick Woo has always focused his research on flagellates (Figs. 1 - 3 & 7) of vertebrates and they include parasites that cause disease in humans (Fig. 2) and other animals (Figs. 3b & 7). His early research was on trypanosomes (Figs. 1 & 2), and mammalian trypanosomiasis which involved field studies in East and West Africa (Figs. 4 - 6).

Fig. 1: Trypanosoma ranarum in Rana pipiensFig. 2: Trypanosoma b. rhodesiense in Homo sapiensFig, 3a: Giardia microti in Microtus pennsylvanicusFig. 3b: Spironucleus sp. in Oncorhynchus tschawytscha

He also worked on human and small mammal Giardia spp. (Fig. 3a) after his academic appointment at U of G (profile). His program on Cryptobia (Fig. 7) and cryptobiosis (Figs. 8-10) was initiated in 1974 and it included the development of 'proof-of-concept' protectivestrategies. The program has/had continuous NSERC and otherfundings since its inception. Cryptobia salmositica (Fig. 7) has been recorded from all species of Pacific salmon (Oncorhynchus spp.) on the west coast of North America, and it is transmitted by the freshwater leech (Piscicola salmositica) in streams and rivers.
Another component of his research program is on systemic spironucleosis; outbreaks of the disease have been reported in salmonids cultured in sea cages in Canada and Norway. Large numbers of Spironucleus (Fig. 3b) are in the blood, internal organs, and ulcers on the body surface (Figs. 11-13) of infected fish. The pathogen is transmitted directly between fish.

II. Diseases: Trypanosomiasis, Cryptobiosis and Spironucleosis

(a) African Trypanosomiases [Figs. 2 & 4 - 6]

Fig. 4: Human trypanosomiasis (Trypanosoma brucei gambiense), EATRO, Uganda

Fig. 5: Haematocrit Centrifuge Technique, trypanosomiasis survey (human), SRI, Tanzania

Fig. 6: Bovine trypanosomiasis (Trypanosoma congolense), EATRO, Uganda


His first research program was on
trypanosomes and trypanosomiasis in animals and humans, and a major component of his research in Africa was on the diagnosis of trypanosomiasis. He successfully used the Haematocrit Centrifuge Technique (HCT; Woo, 1969) to detect trypanosomes in the blood and cerebral spinal fluid of patients suffering from Rhodesian and Gambian trypanosomiases. The study was conducted in the hospital attached to the East African Trypanosomiasis Research Organization (EATRO), Uganda(Woo, 1970). He then adapted HCT for use under field conditions and conducted a survey in the Lugala area, Uganda; 413 people were examined in a single day, and trypanosomes were detected in one person (with no clinical signs of the disease) and microfilariae in 17 other people (Woo, 1971). Feasibility of HCT as a field technique was confirmed in a much larger survey on human trypanosomiasis in Musoma district, Tanzania(Onyango & Woo, 1971).

"The . . . technique of Woo is the most suitable for rural hospitals" (Foulkes, 1981). It " . . . is still in use in many HAT [Human African Trypanosomiasis] control programs" in Africa (Chappuis et al, 2005), and " . . . is the test of choice . . ." (Matovu E. et al. 2012). HCT is also used to diagnose human African trypanosomiasis outside Africa (Lejon et al., 2003), for the detection of congenital Trypanosoma cruzi infection in Argentina (Moretti et al. 2005), and it is ". . . recommended for the parasitological diagnosis of acute Chagas' disease and malaria" in rural Bolivia(Fuente et al., 1985).

Woo & Kauffmann (1971) showed that HCT could also be used as a field technique to detect low virulent strains of Trypanosoma congolense in wild animals (e.g. lions); this was part of a field study to determine the epidemiology of trypanosomiasis in the Serengeti National Park. Tanzania. HCT is a rapid and sensitive technique for the detection of trypanosomes (Trypanosoma brucei brucei, T. brucei rhodesiense, T. evansi, T. congolense) under laboratory conditions (Woo & Rogers, 1974) and it is " . . . most commonly used for the diagnosis of animal trypanosomiasis . . . " (Desqquesnes & Tresse 1996). It is recommended by the‘International Office of Epizootics' (OIE 2013 - Table 1), and Moti et al. (2014) confirms that "HCT remains a robust field method as it will be more efficient than PCR to detect clinical cases that have to be treated". The technique can also be used to determine the effectiveness of chemotherapy against trypanosomiasis (e.g. Sekoni & Rekwot 2003).

The Haematocrit Centrifuge Technique is frequently used/cited in studies on trypanosomes and trypanosomiasis (e.g. in Google Scholar, Semantic Scholar), and it is sometimes also called the:
"Woo test", e.g. (i) Chappuis F et al. 2005,Options for field diagnosis of human African trypanosomiasis. Clinical Microbiol. Reviews 18: 133-146
    (ii) Desquesnes M & Tresse L1999, Sensitivity of the Woo test for detection of Trypanosoma vivax. Proceedings of First Symposium o New World Trypanosomes, pp. 76-81.
"Woo technique", e.g.(i) Quispe AP et al. 2003, Prevalencia de Trypanosoma vivax en bovinos de cuatro distritos de la provincia de Coronel Portillo, Ucayali. Rev investig. vet. Peru 14: 161-165
    (ii) Cadioli FA et al. 2012First report of Trypanosoma vivax outbreak in dairy cattle in Sao Paulo, Brazil. Rev.Bras.Parasitol.Vet. Sao Paulo 21:118-124
"Woo method", e.g. (i) Uilenberg G 1998, Chapter 3 - Diagnosis. In: A field guide for the diagnosis, treatment and prevention of African animal trypanosomosis, FAO, UN, 158 pages
    (ii) OIE 2013, Trypanosomosis (tsetse-transmitted). In: OIE Terrestrial Manual, Chapter 2.4.17: 1-11.

(b) Salmonid Cryptobiosis [Figs. 7 - 10]
Complete list of papers on
Cryptobia and cryptobiosis

Fig. 7: Cryptobia (T.) salmositica with a red cell from an anemic fishFig. 8: Bilateral exophthalmia in acute salmonid cryptobiosis
Fig. 9: Splenomegaly (6 - 8 times by volume)Fig. 10: General edema and abdominal distension with ascites
Salmonid cryptobiosis is caused by the hemoflagellate, Cryptobia salmositica (Figs. 7-10; Woo, 2003). The parasite is transmitted by leeches (Piscicola salmositica)in streams and rivers on the Pacific coast of North America; direct transmission can also occur when infected and uninfected fish are held for prolonged periods in the same tank or under certain hatchery conditions.Clinical signs include anorexia, exophthalmia (Fig.8), splenomegaly (Fig. 9), hepatomegaly, general edema and abdominal distention with ascites (Fig. 10), a microcytic and hypochromic anemia,and red cells are antiglobulin positive. Infected salmonids are susceptible to hypoxia, and their metabolism and swimming performance are reduced. Also, the lytic activities of complement in sera of infected fish are reduced, and the ability of infected fish to mount a protective response against a secondary pathogen or antigen is lowered. The anemia and anorexia in infected fish contribute to the immunodepression. Cryptobia has two proteases - the cysteine protease is a metabolic enzyme while metalloprotease (a histolytic enzyme) is the main virulent factor.

The program on cryptobiosis is a multidisciplinary study. It is on the biology of the pathogen, diagnosis of infection, pathobiology in cryptobiosis including elucidation of the disease mechanism, host immune responses, and the development of proof-of-concept strategies against the parasite and disease (Woo, 2003). Preventive strategies include exploiting innate and adaptive immunity, chemotherapy and immunochemotherapy (Woo, 2010).

Gene Sequences of Cryptobia salmositica in GENBANK
(1) Jesudhasan, P.R.R. & P.T.K. Woo (2004) Methionine adenosyltransferase gene. GENBANK No. AY603961.
(2) Jesudhasan, P.R.R. & P.T.K. Woo (2004) Major surface glycoprotein metalloproteinase gene - key gene involved in pathogensis. GENBANK No. AY632692.
(3) Jesudhasan, P.R.R. & P.T.K. Woo (2004) Cysteine proteinase gene. GENBANK No. AY713477.

(c) Salmonid Spironucleosis [Figs. 3b & 11-13]
Systemic spironucleosis is caused by Spironucleus (
Fig. 3b) - the parasite is in the blood and internal organs of salmonids. The parasite causes morbidity and mortality in fishes and there have been outbreaks of the disease in salmon cultured in sea cages - in chinook salmon on the west coast of Canada and in Atlantic salmon in Norway. Fish mortality was high and some infected chinook salmon had abdominal distensions and were anemic while infected Atlantic salmon were significantly smaller than healthy fish and they behaved'abnormally' prior to death. Little is known about the biology of the pathogen nor factors that precipitated outbreaks, and there are no preventive nor control strategies against the parasite and disease (Woo, 2006. Chapter 3. In:
Fish Diseases and Disorders, Vol. 1: Protozoan and Metazoan Infections, 2nd ed., pp. 46-114).

Fig. 11: Unilateral exophthalmiaFig. 12: Ulceration on body surfaceFig. 13: Globulated and enlarged spleen

Spironucleus barkhanus has a blood and a tissue phase in experimentally infected Atlantic salmon. It first appears in the blood about a week after infection and the parasitaemia peaks at six weeks post infection. The parasite is not detectable in the blood at about eight weeks after infection but it occurs in high numbers in the spleen, liver, eye socket, and muscles.Thirty eight out of 40 infected fish died in one experiment, and mortality was equally high (29 out of 30 infected fish) in another experiment with Atlantic salmon from three families. Clinical signs of the disease include unilateral exophthalmia (Fig. 11), skin blisters and ulcerations (Fig. 12), enlarged and globulated spleens (Fig. 13), livers with whitish/yellowish nodules, and haemorrhages in organs. The parasite can be experimentally transmitted via inoculation of infected blood or through co-habitation of infected and uninfected fish (Guo & Woo, 2004).

Sharing a joke before the 2006 Spring Convocation Ceremony
Prof. M.J. Emes, CBS Dean; Prof. P.T.K. Woo; The Hon. L.M. Alexander, Chancellor;
Prof. A.J.S. Summerlee, President & Vice Chancellor; Prof. M.M. Ferguson, DIB Chair (left to right)

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Updated: June 1, 2015