zoonoses and communicable diseases common to ... - PAHO/WHO

PROTOTHECOSIS 349organs affected. Weakness and weight loss were observed in all cases of dissemination(Kaplan, 1978).Approximately one-half of the cases in dogs are caused by P. wickerhamii and theother half by P. zopfii (Dillberger et al., 1988). Other animal species in which protothecosishas been diagnosed are Atlantic salmon and cats. In salmon, P. salmoniscauses a disseminated and fatal disease (Gentles and Bond, 1977). The clinical manifestationof protothecosis in cats more closely resembles the cutaneous disease inhumans and does not tend to disseminate as it does in dogs. The infection in cats iscaused by P. wickerhamii (Dillberger et al., 1988).Source of Infection and Mode of Transmission: Prototheca spp. and greenalgae are saprophytes found in nature, primarily in stagnant or slow-moving waters.Humans acquire the infection, possibly through skin lesions, when they come intocontact with contaminated water or other habitats of these agents. The profusion ofthese agents in the environment, as well as the few cases described in humans, indicatethat they are not very virulent and that lowered host resistance is required forthem to act as pathogens. In fact, five of nine patients with cutaneous or subcutaneousprotothecosis had a preexisting or intercurrent disease. Similarly, seven ofeight patients with the olecranon bursitis form had previously sustained a trauma tothe elbow (Kaplan, 1978). Cattle contract mastitis caused by P. zopfii in the environmentitself; the portal is probably the teat. P. zopfii is abundant in dairies, in cowfeces as well as in drinking troughs, feed, and mud. A study conducted on variousdairy cows, some with mastitis caused by Prototheca and others without any historyof the disease, isolated the agent (94% P. zopfii and 6% P. wickerhamii) in 48(25.3%) of 190 samples (Anderson and Walker, 1988). Little is known of the predisposingconditions in dogs, which almost always manifest systemic protothecosis.In cattle, the retropharyngeal and mandibular lymph nodes affected by green algaeindicate that the infection is possibly contracted by ingestion of contaminated water.The few cases described in cattle and sheep suggest that these species are not verysusceptible to green algal infection.Diagnosis: Special stains such as Gomori, Gridley, and PAS (periodic acid-Schiff) applied to histological sections from affected tissues permit detection ofPrototheca in all developmental stages. To determine the species, cultures or theimmunofluorescence test with species-specific reagents must be used. The immunofluorescencetechnique can be used for cultures as well as for histological sectionsstained with hematoxylin-eosin, but not for those stained with the methods mentionedabove.Control: Treatment of underlying conditions or diseases in humans.BibliographyAnderson, K.L., R.L. Walker. Sources of Prototheca spp. in a dairy herd environment. J AmVet Med Assoc 193:553–556, 1988.Dillberger, J.E., B. Homer, D. Daubert, N.H. Altman. Protothecosis in two cats. J Am VetMed Assoc 192:1557–1559, 1988.Gentles, J.C., P.M. Bond. Protothecosis of Atlantic salmon. Sabouraudia 15:133–139, 1977.